Document And Entity Information - shares	9 Months Ended
Document And Entity Information - shares	Sep. 30, 2017	Oct. 31, 2017
Document Information [Line Items]
Entity Registrant Name	Great Plains Energy Inc
Entity Central Index Key	0001143068
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		215,661,646
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2017

Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Current Assets
Cash and cash equivalents	$ 1,097.9	$ 1,293.1
Time deposit	0.0	1,000.0
Receivables, net	186.4	166.0
Accounts receivable pledged as collateral	195.0	172.4
Fuel inventories, at average cost	89.2	108.8
Materials and supplies, at average cost	171.9	162.2
Deferred refueling outage costs	10.2	22.3
Refundable income taxes	1.4	0.0
Interest rate derivative instruments	77.4	79.3
Prepaid expenses and other assets	31.5	55.4
Total	1,860.9	3,059.5
Utility Plant, at Original Cost
Electric	13,552.9	13,597.7
Less - accumulated depreciation	5,149.5	5,106.9
Net utility plant in service	8,403.4	8,490.8
Construction work in progress	415.0	403.9
Plant to be retired, net	146.3	0.0
Nuclear fuel, net of amortization of $196.2 and $172.1	64.9	62.0
Total	9,029.6	8,956.7
Investments and Other Assets
Nuclear decommissioning trust fund	247.5	222.9
Regulatory assets	1,005.5	1,048.0
Goodwill	169.0	169.0
Other	116.4	113.9
Total	1,538.4	1,553.8
Total	12,428.9	13,570.0
Current Liabilities
Collateralized note payable	195.0	172.4
Commercial paper	247.9	334.8
Current maturities of long-term debt	351.1	382.1
Accounts payable	196.8	323.7
Accrued taxes	127.0	33.3
Accrued interest	57.4	50.8
Accrued compensation and benefits	51.9	52.1
Pension and post-retirement liability	3.0	3.0
Other	62.2	32.6
Total	1,292.3	1,384.8
Deferred Credits and Other Liabilities
Deferred income taxes	1,422.6	1,329.7
Deferred tax credits	125.1	126.2
Asset retirement obligations	258.5	316.0
Pension and post-retirement liability	495.3	488.3
Regulatory liabilities	310.5	309.9
Other	90.1	87.9
Total	2,702.1	2,658.0
Shareholders' equity
Common stock	4,231.1	4,217.0
Preference Stock	0.0	836.2
Retained earnings	897.6	1,119.2
Treasury stock - 136,952 and 128,087 shares, at cost	(4.0)	(3.8)
Accumulated other comprehensive loss	(2.2)	(6.6)
Total shareholders' equity	5,122.5	6,162.0
Long-term debt (Note 11)	3,312.0	3,365.2
Total	8,434.5	9,527.2
Commitments and Contingencies (Note 13)
Total	12,428.9	13,570.0
Kansas City Power and Light Company [Member]
Current Assets
Cash and cash equivalents	4.6	4.5
Receivables, net	143.8	139.1
Related party receivables	82.1	67.2
Accounts receivable pledged as collateral	130.0	110.0
Fuel inventories, at average cost	62.1	72.9
Materials and supplies, at average cost	126.1	118.9
Deferred refueling outage costs	10.2	22.3
Refundable income taxes	0.0	12.7
Prepaid expenses and other assets	26.9	27.9
Total	585.8	575.5
Utility Plant, at Original Cost
Electric	10,120.8	9,925.1
Less - accumulated depreciation	4,012.7	3,858.4
Net utility plant in service	6,108.1	6,066.7
Construction work in progress	310.8	300.4
Nuclear fuel, net of amortization of $196.2 and $172.1	64.9	62.0
Total	6,483.8	6,429.1
Investments and Other Assets
Nuclear decommissioning trust fund	247.5	222.9
Regulatory assets	761.4	801.8
Other	39.1	29.1
Total	1,048.0	1,053.8
Total	8,117.6	8,058.4
Current Liabilities
Collateralized note payable	130.0	110.0
Commercial paper	72.0	132.9
Current maturities of long-term debt	350.0	281.0
Accounts payable	154.1	231.6
Accrued taxes	137.2	27.0
Accrued interest	40.5	32.4
Accrued compensation and benefits	51.9	52.1
Pension and post-retirement liability	1.6	1.6
Other	44.0	11.4
Total	981.3	880.0
Deferred Credits and Other Liabilities
Deferred income taxes	1,266.4	1,228.3
Deferred tax credits	122.0	122.8
Asset retirement obligations	228.7	278.0
Pension and post-retirement liability	473.1	465.8
Regulatory liabilities	201.6	187.4
Other	72.3	70.6
Total	2,364.1	2,352.9
Shareholders' equity
Common stock	1,563.1	1,563.1
Retained earnings	977.8	982.6
Accumulated other comprehensive loss	(0.4)	(4.2)
Total shareholders' equity	2,540.5	2,541.5
Long-term debt (Note 11)	2,231.7	2,284.0
Total	4,772.2	4,825.5
Commitments and Contingencies (Note 13)
Total	$ 8,117.6	$ 8,058.4

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Utility Plant, at Original Cost
Nuclear fuel, amortization	$ 196.2	$ 172.1
Shareholder's equity
Common stock - shares authorized (in shares)	600,000,000	600,000,000
Common stock-shares issued (in shares)	215,798,848	215,479,105
Treasury stock- shares (in shares)	136,952	128,087
Series B Preferred Stock [Member]
Shareholder's equity
Preferred Stock, Shares Issued	0	862,500
Preferred Stock, Dividend Rate, Percentage	7.00%	7.00%
Preferred Stock, Liquidation Preference Per Share	$ 1,000.00	$ 1,000.00
No Par Preference Stock [Member]
Shareholder's equity
Preference stock, Shares Authorized	11,000,000	11,000,000
Kansas City Power and Light Company [Member]
Utility Plant, at Original Cost
Nuclear fuel, amortization	$ 196.2	$ 172.1
Shareholder's equity
Common stock - shares authorized (in shares)	1,000.0	1,000.0
Common stock-shares issued (in shares)	1.0	1.0

Consolidated Statements of Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Operating Revenues
Electric revenues	$ 857.2	$ 856.8	$ 2,110.5	$ 2,099.7
Operating Expenses
Fuel and purchased power	180.0	184.1	464.0	462.2
Transmission	29.1	23.8	80.4	64.5
Utility operating and maintenance expenses	187.9	193.3	555.0	553.1
Costs to achieve the anticipated merger with Westar Energy, Inc.	(2.4)	14.4	24.4	19.4
Depreciation and amortization	92.7	86.4	277.7	256.9
General taxes	63.5	63.7	176.1	174.5
Other	0.5	9.2	3.1	15.0
Total	551.3	574.9	1,580.7	1,545.6
Operating income	305.9	281.9	529.8	554.1
Other Income and Expenses
Non-operating income	8.1	4.3	27.6	9.7
Non-operating expenses	(20.3)	(3.0)	(27.9)	(10.7)
Loss on Series B Preferred Stock dividend make-whole provisions [Note 12]	(67.7)	0.0	(124.8)	0.0
Loss on extinguishment of debt [Note 11]	(82.8)	0.0	(82.8)	0.0
Total	(162.7)	1.3	(207.9)	(1.0)
Interest charges	(30.9)	(67.6)	(242.8)	(251.7)
Income before income tax expense and income from equity investments	112.3	215.6	79.1	301.4
Income tax expense	(102.3)	(82.7)	(87.2)	(111.5)
Income from equity investments, net of income taxes	0.5	0.7	2.0	2.1
Net income (loss)	10.5	133.6	(6.1)	192.0
Preferred stock dividend requirements and redemption premium	7.1	0.9	37.3	1.7
Earnings (loss) available for common shareholders	$ 3.4	$ 132.7	$ (43.4)	$ 190.3
Average number of basic common shares outstanding	215.6	154.6	215.5	154.5
Average number of diluted common shares outstanding	215.7	154.9	215.5	154.9
Basic and diluted earnings (loss) per common share	$ 0.02	$ 0.86	$ (0.20)	$ 1.23
Cash dividends per common share	$ 0.275	$ 0.2625	$ 0.825	$ 0.7875
Comprehensive Income
Net income (loss)	$ 10.5	$ 133.6	$ (6.1)	$ 192.0
Other comprehensive income
Reclassification to expenses, net of tax	1.3	1.3	4.1	4.1
Derivative hedging activity, net of tax	1.3	1.3	4.1	4.1
Amortization of net losses included in net periodic benefit costs, net of tax	0.1	0.2	0.3	0.4
Change in unrecognized pension expense, net of tax	0.1	0.2	0.3	0.4
Total other comprehensive income	1.4	1.5	4.4	4.5
Comprehensive income (loss)	11.9	135.1	(1.7)	196.5
Kansas City Power and Light Company [Member]
Operating Revenues
Electric revenues	595.7	597.6	1,474.3	1,474.1
Operating Expenses
Fuel and purchased power	124.1	118.5	314.4	298.7
Transmission	19.8	14.5	52.9	44.8
Utility operating and maintenance expenses	125.6	131.9	374.2	379.6
Costs to achieve the anticipated merger with Westar Energy, Inc.	(1.5)	0.0	10.3	0.0
Depreciation and amortization	66.3	61.9	199.9	184.1
General taxes	51.4	51.0	140.2	136.9
Other	0.1	0.6	0.5	2.3
Total	385.8	378.4	1,092.4	1,046.4
Operating income	209.9	219.2	381.9	427.7
Other Income and Expenses
Non-operating income	2.7	3.6	6.9	7.5
Non-operating expenses	(2.0)	(1.9)	(6.4)	(5.6)
Total	0.7	1.7	0.5	1.9
Interest charges	(34.3)	(34.7)	(105.5)	(104.9)
Income before income tax expense and income from equity investments	176.3	186.2	276.9	324.7
Income tax expense	(62.2)	(68.5)	(99.0)	(116.5)
Net income (loss)	114.1	117.7	177.9	208.2
Comprehensive Income
Net income (loss)	114.1	117.7	177.9	208.2
Other comprehensive income
Reclassification to expenses, net of tax	1.2	1.2	3.8	4.0
Derivative hedging activity, net of tax	1.2	1.2	3.8	4.0
Total other comprehensive income	1.2	1.2	3.8	4.0
Comprehensive income (loss)	$ 115.3	$ 118.9	$ 181.7	$ 212.2

Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash Flows from Operating Activities
Net income (loss)	$ (6.1)	$ 192.0
Adjustments to reconcile income (loss) to net cash from operating activities:
Depreciation and amortization	277.7	256.9
Amortization of:
Nuclear fuel	24.1	22.4
Other	55.2	52.4
Deferred income taxes, net	89.7	109.9
Investment tax credit amortization	(1.1)	(1.1)
Income from equity investments, net of income taxes	(2.0)	(2.1)
Fair value impacts of interest rate swaps	1.9	78.8
Loss on Series B Preferred Stock dividend make-whole provisions (Note 12)	124.8	0.0
Loss on extinguishment of debt (Note 11)	82.8	0.0
Other operating activities (Note 3)	2.7	(24.4)
Net cash from operating activities	649.7	684.8
Cash Flows from Investing Activities
Utility capital expenditures	(392.5)	(435.3)
Allowance for borrowed funds used during construction	(5.1)	(4.7)
Purchases of nuclear decommissioning trust investments	(23.8)	(23.7)
Proceeds from nuclear decommissioning trust investments	21.3	21.2
Proceeds from time deposit	1,000.0	0.0
Other investing activities	(30.7)	(48.7)
Net cash from investing activities	569.2	(491.2)
Cash Flows from Financing Activities
Issuance of common stock	2.9	2.4
Issuance of long-term debt	4,591.1	0.0
Issuance fees	(38.3)	(68.7)
Repayment of long-term debt, including redemption premium	(4,725.1)	(1.1)
Net change in short-term borrowings	(86.9)	27.1
Net change in collateralized short-term borrowings	22.6	15.0
Dividends paid	(212.7)	(122.5)
Redemption of preferred stock	(963.4)	(40.1)
Purchase of treasury stock	(4.1)	(4.9)
Other financing activities	(0.2)	(0.1)
Net cash from financing activities	(1,414.1)	(192.9)
Net Change in Cash and Cash Equivalents	(195.2)	0.7
Cash and Cash Equivalents at Beginning of Year	1,293.1	11.3
Cash and Cash Equivalents at End of Period	1,097.9	12.0
Kansas City Power and Light Company [Member]
Cash Flows from Operating Activities
Net income (loss)	177.9	208.2
Adjustments to reconcile income (loss) to net cash from operating activities:
Depreciation and amortization	199.9	184.1
Amortization of:
Nuclear fuel	24.1	22.4
Other	23.4	25.6
Deferred income taxes, net	33.4	74.0
Investment tax credit amortization	(0.8)	(0.8)
Other operating activities (Note 3)	68.7	74.7
Net cash from operating activities	526.6	588.2
Cash Flows from Investing Activities
Utility capital expenditures	(295.1)	(286.1)
Allowance for borrowed funds used during construction	(4.2)	(3.8)
Purchases of nuclear decommissioning trust investments	(23.8)	(23.7)
Proceeds from nuclear decommissioning trust investments	21.3	21.2
Net money pool lending	0.0	(11.1)
Other investing activities	(17.0)	(23.8)
Net cash from investing activities	(318.8)	(327.3)
Cash Flows from Financing Activities
Issuance of long-term debt	299.2	0.0
Issuance fees	(3.0)	(0.2)
Repayment of long-term debt, including redemption premium	(281.0)	0.0
Net change in short-term borrowings	(60.9)	(180.3)
Net change in collateralized short-term borrowings	20.0	0.0
Dividends paid	(182.0)	(77.0)
Net cash from financing activities	(207.7)	(257.5)
Net Change in Cash and Cash Equivalents	0.1	3.4
Cash and Cash Equivalents at Beginning of Year	4.5	2.3
Cash and Cash Equivalents at End of Period	$ 4.6	$ 5.7

Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Kansas City Power and Light Company [Member]	Common Stock [Member]	Common Stock [Member] Kansas City Power and Light Company [Member]	Preferred Stock [Member] Cumulative Preferred Stock [Member]	Preferred Stock [Member] Preference Stock [Member]	Retained Earnings [Member]	Retained Earnings [Member] Kansas City Power and Light Company [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Other Comprehensive Income (Loss) [Member] Kansas City Power and Light Company [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of adoption of ASU 2016-09 (Note 1)								$ 0.0
Beginning balance at Dec. 31, 2015			$ 2,646.7	$ 1,563.1	$ 39.0	$ 0.0	$ 1,024.4	879.6	$ (2.6)	$ (12.0)	$ (9.6)
Beginning balance (in shares) at Dec. 31, 2015			154,504,900	1	390,000	0
Beginning balance, treasury stock (in shares) at Dec. 31, 2015									(101,229)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock			$ 12.5
Issuance of stock (in shares)			420,207
Equity compensation expense, net of forfeitures			$ 3.1
Redemption of preferred stock					$ (39.0)	$ 0.0
Redemption of preferred stock (in shares)					(390,000)	0
Unearned Compensation [Abstract]
Issuance of restricted common stock			(2.8)
Forfeiture of restricted common stock			0.0
Compensation expense recognized			2.0
Other			0.2
Net income (loss)	$ 192.0	$ 208.2					192.0	208.2
Redemption premium on preferred stock							(0.6)
Dividends:
Common stock ($0.825 and $0.7875 per share)							(121.8)	(77.0)
Preferred stock - at required rates							(0.7)
Performance shares							(0.6)
Treasury shares acquired									$ (4.1)
Treasury shares acquired (in shares)									(136,562)
Treasury shares reissued									$ 2.9
Treasury shares reissued (in shares)									109,695
Derivative hedging activity, net of tax	4.1	4.0								4.1	4.0
Change in unrecognized pension expense, net of tax	0.4									0.4
Ending balance at Sep. 30, 2016	3,743.1	2,568.3	$ 2,661.7	$ 1,563.1	$ 0.0	$ 0.0	1,092.7	1,010.8	$ (3.8)	(7.5)	(5.6)
Ending balance, treasury stock (in shares) at Sep. 30, 2016									(128,096)
Ending balance (in shares) at Sep. 30, 2016			154,925,107	1	0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of adoption of ASU 2016-09 (Note 1)								(0.7)
Beginning balance at Dec. 31, 2016	$ 6,162.0	2,541.5	$ 4,217.0	$ 1,563.1	$ 0.0	$ 836.2	1,119.2	982.6	$ (3.8)	(6.6)	(4.2)
Beginning balance (in shares) at Dec. 31, 2016			215,479,105	1	0	862,500
Beginning balance, treasury stock (in shares) at Dec. 31, 2016	(128,087)								(128,087)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock			$ 11.6
Issuance of stock (in shares)			319,743
Equity compensation expense, net of forfeitures			$ 4.0
Redemption of preferred stock					$ 0.0	$ (836.2)
Redemption of preferred stock (in shares)					0	(862,500)
Unearned Compensation [Abstract]
Issuance of restricted common stock			(2.3)
Forfeiture of restricted common stock			0.6
Compensation expense recognized			1.7
Other			(1.5)
Net income (loss)	$ (6.1)	177.9					(6.1)	177.9
Redemption premium on preferred stock							(2.4)
Dividends:
Common stock ($0.825 and $0.7875 per share)							(177.8)	(182.0)
Preferred stock - at required rates							(34.9)
Performance shares							(0.4)
Treasury shares acquired									$ (4.2)
Treasury shares acquired (in shares)									(145,301)
Treasury shares reissued									$ 4.0
Treasury shares reissued (in shares)									136,436
Derivative hedging activity, net of tax	4.1	3.8								4.1	3.8
Change in unrecognized pension expense, net of tax	0.3									0.3
Ending balance at Sep. 30, 2017	$ 5,122.5	$ 2,540.5	$ 4,231.1	$ 1,563.1	$ 0.0	$ 0.0	$ 897.6	$ 977.8	$ (4.0)	$ (2.2)	$ (0.4)
Ending balance, treasury stock (in shares) at Sep. 30, 2017	(136,952)								(136,952)
Ending balance (in shares) at Sep. 30, 2017			215,798,848	1	0	0

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2017

Accounting Policies [Abstract]

Summary of Significant Accounting Policies [Text Block]

1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Organization

Great Plains Energy, a Missouri corporation incorporated in 2001, is a public utility holding company and does not own or operate any significant assets other than the stock of its subsidiaries and cash and cash equivalents. Great Plains Energy's wholly owned direct subsidiaries with significant operations are as follows:


•	KCP&L is an integrated, regulated electric utility that provides electricity to customers primarily in the states of Missouri and Kansas. KCP&L has one active wholly owned subsidiary, Kansas City Power & Light Receivables Company (KCP&L Receivables Company).

•

KCP&L Greater Missouri Operations Company (GMO) is an integrated, regulated electric utility that provides electricity to customers in the state of Missouri. GMO also provides regulated steam service to certain customers in the St. Joseph, Missouri area. GMO has two active wholly owned subsidiaries, GMO Receivables Company and MPS Merchant Services, Inc. (MPS Merchant). MPS Merchant has certain long-term natural gas contracts remaining from its former non-regulated trading operations.

Great Plains Energy also wholly owns GPE Transmission Holding Company, LLC (GPETHC). GPETHC owns 13.5% of Transource Energy, LLC (Transource) with the remaining 86.5% owned by AEP Transmission Holding Company, LLC (AEPTHC), a subsidiary of American Electric Power Company, Inc. GPETHC accounts for its investment in Transource under the equity method. Transource is focused on the development of competitive electric transmission projects.

Each of Great Plains Energy's and KCP&L's consolidated financial statements includes the accounts of their subsidiaries. Intercompany transactions have been eliminated.

Great Plains Energy's sole reportable business segment is electric utility. See Note 19 for additional information.

Basic and Diluted Earnings (Loss) per Common Share Calculation

To determine basic earnings (loss) per common share (EPS), preferred stock dividend requirements and redemption premium are deducted from net income (loss) before dividing by the average number of common shares outstanding. To determine diluted EPS, preferred stock dividend requirements and redemption premium are deducted from net income (loss) before dividing by the diluted average number of common shares outstanding. The effect of dilutive securities assumes the issuance of common shares applicable to performance shares and restricted stock calculated using the treasury stock method.

The following table reconciles Great Plains Energy's basic and diluted EPS.



	Three Months Ended September 30				Year to Date September 30
	2017		2016		2017			2016
Income (loss)	(millions, except per share amounts)
Net income (loss)	$	10.5	$	133.6	$	(6.1	)	$	192.0
Less: preferred stock dividend requirements and redemption premium	7.1		0.9		37.3			1.7
Earnings (loss) available for common shareholders	$	3.4	$	132.7	$	(43.4	)	$	190.3
Common Shares Outstanding
Average number of common shares outstanding	215.6		154.6		215.5			154.5
Add: effect of dilutive securities	0.1		0.3		—			0.4
Diluted average number of common shares outstanding	215.7		154.9		215.5			154.9
Basic and diluted EPS	$	0.02	$	0.86	$	(0.20	)	$	1.23

There were no anti-dilutive shares excluded from the computation of diluted EPS for the three months ended September 30, 2017 and 2016 or for year to date September 30, 2016. Anti-dilutive shares excluded from the computation of diluted EPS for year to date September 30, 2017 were 53,079 performance shares and 136,970 restricted stock shares.

Dividends Declared

In October 2017, Great Plains Energy's Board of Directors (Great Plains Energy Board) declared a quarterly dividend of $0.275 per share on Great Plains Energy's common stock. The common dividend is payable December 20, 2017, to shareholders of record as of November 29, 2017.

In October 2017, KCP&L's Board of Directors declared a cash dividend payable to Great Plains Energy of $30.0 million payable on December 19, 2017.

New Accounting Standards

In March 2017, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2017-07, Compensation-Retirement Benefits, which requires an employer to disaggregate the service cost component from the other components of net benefit cost. The service cost component is to be reported in the same line item or items as other compensation costs arising from services rendered by the pertinent employees during the period. The non-service cost components are to be reported separately from service costs and outside of a subtotal of income from operations. The amendments in this update allow only the service cost component to be eligible for capitalization as part of utility plant. The non-service cost components that are no longer eligible for capitalization as part of utility plant will be recorded as a regulatory asset. The new guidance is to be applied retrospectively for the presentation of service cost and non-service cost components in the income statement and prospectively for the capitalization of the service cost component. The Companies plan to adopt ASU No. 2017-07 on January 1, 2018, and do not expect it to have a material impact on their consolidated financial statements as the impacts of adoption will be limited to changes in the classification of non-service cost.

In March 2016, the FASB issued ASU No. 2016-09, Compensation-Stock Compensation, which is intended to simplify several areas of accounting for share-based compensation arrangements, including the income tax impact, classification on the statement of cash flows and forfeitures. The Companies adopted ASU No. 2016-09 on January 1, 2017. The cumulative effect from the adoption of ASU No. 2016-09 was insignificant to Great Plains Energy's consolidated financial statements and resulted in a reduction to retained earnings of $0.7 million for KCP&L. The Companies have elected to adopt the cash flow presentation of the excess tax benefits as an operating activity prospectively and no prior periods have been adjusted.

In February 2016, the FASB issued ASU No. 2016-02, Leases, which requires an entity that is a lessee to record a right-of-use asset and a lease liability for lease payments on the balance sheet for all leases with terms longer than 12 months. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. The new guidance is effective for interim and annual periods beginning after December 15, 2018, with early adoption permitted, and is required to be applied using a modified retrospective approach. Great Plains Energy and KCP&L plan to adopt the new guidance on January 1, 2019. The Companies expect that the new guidance will affect the balance sheet by increasing the assets and liabilities recorded related to operating leases and continue to evaluate the effect that ASU No. 2016-02 will have on their income statement, statement of cash flows and related disclosures.

In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers, which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. The ASU will replace most existing revenue recognition guidance in Generally Accepted Accounting Principles (GAAP) when it becomes effective. In August 2015, the FASB issued ASU No. 2015-14, deferring the effective date of ASU No. 2014-09 one year, from January 1, 2017, to January 1, 2018. The Companies plan to adopt ASU No. 2014-09 on January 1, 2018. The standard permits the use of either the full retrospective or modified retrospective transition method. The Companies plan to apply the guidance using the modified retrospective transition method. The Companies have completed a review of their revenue arrangements and do not expect the standard to have a material impact on the amount or timing of revenue recognition within their consolidated financial statements. Great Plains Energy and KCP&L continue to evaluate the disclosure requirements and internal control impacts of the new standard on their consolidated financial statements and will finalize these evaluations by the end of 2017.

Anticipated Merger with Westar Energy, Inc.

9 Months Ended

Sep. 30, 2017

Anticipated Merger with Westar Energy, Inc. [Abstract]

Anticipated Buiness Combination Disclosure [Text Block]

2. ANTICIPATED MERGER WITH WESTAR ENERGY, INC.

On May 29, 2016, Great Plains Energy entered into an Agreement and Plan of Merger (Original Merger Agreement) by and among Great Plains Energy, Westar Energy, Inc. (Westar), and, from and after its accession to the Original Merger Agreement, GP Star, Inc., a Kansas corporation and wholly owned subsidiary of Great Plains Energy (GP Star). Pursuant to the Original Merger Agreement, Great Plains Energy would have acquired Westar for (i) $51.00 in cash and (ii) a number of shares of Great Plains Energy common stock, equal to an exchange ratio for each share of Westar common stock issued and outstanding immediately prior to the effective time of the merger, with Westar becoming a wholly owned subsidiary of Great Plains Energy. The acquisition was subject to various shareholder and regulatory approvals, including from The State Corporation Commission of the State of Kansas (KCC), the Public Service Commission of the State of Missouri (MPSC), and The Federal Energy Regulatory Commission (FERC).

On April 19, 2017, KCC issued an order denying Great Plains Energy's, KCP&L's and Westar's joint application for approval of the acquisition of Westar by Great Plains Energy citing concerns with the purchase price, Great Plains Energy's capital structure, quantifiable and demonstrable customer benefits and staffing levels in Westar's service territory, among other items.

On July 9, 2017, Great Plains Energy entered into an Amended and Restated Agreement and Plan of Merger (Amended Merger Agreement) by and among Great Plains Energy, Westar, Monarch Energy Holding, Inc., a Missouri corporation (Holdco), and King Energy, Inc., a Kansas corporation and wholly owned subsidiary of Holdco (Merger Sub). Pursuant to the Amended Merger Agreement, subject to the satisfaction or waiver of certain conditions, Great Plains Energy will merge with and into Holdco, with Holdco surviving such merger, and Merger Sub will merge with and into Westar, with Westar surviving such merger. Pursuant to the Amended Merger Agreement, at closing each outstanding share of Great Plains Energy's and Westar's common stock will be converted into the right to receive 0.5981 and 1.0, respectively, of validly issued, fully paid and nonassessable shares of common stock, no par value, of Holdco. Following the mergers, Holdco, with a new name that has yet to be established, will be the parent of Great Plains Energy's direct subsidiaries, including KCP&L, and Westar.

The anticipated merger with Westar has been structured as a merger of equals in a tax-free exchange of shares that involves no premium paid or received with respect to either Great Plains Energy or Westar. Following the completion of the anticipated merger, Westar shareholders will own approximately 52.5 percent and Great Plains Energy shareholders will own approximately 47.5 percent of the combined company.

Regulatory and Shareholder Approvals

Great Plains Energy's anticipated merger with Westar was unanimously approved by the Great Plains Energy Board and Westar's Board of Directors (Westar Board). The anticipated merger remains subject to the approval of Great Plains Energy's and Westar's shareholders; regulatory approvals from KCC, the MPSC, the Nuclear Regulatory Commission (NRC), FERC, The Federal Communications Commission (FCC); Hart-Scott-Rodino (HSR) antitrust review; as well as other customary conditions.

KCC Approval

In August 2017, Great Plains Energy, KCP&L and Westar filed a joint application with KCC for approval of the anticipated merger with Westar. Under applicable Kansas regulations, KCC has 300 days following the filing to rule on the transaction. A decision from KCC on this joint application is expected in the first half of 2018.

MPSC Approval

In August 2017, Great Plains Energy, KCP&L, GMO and Westar filed a joint application with the MPSC for approval of the anticipated merger with Westar. An evidentiary hearing in the case is expected to occur in March 2018. While there is not a statutory deadline for an MPSC ruling on the joint application, a decision from the MPSC is expected in the first half of 2018.

Other Approvals

In September 2017, Great Plains Energy and Westar filed applications with FERC and the NRC for approval of the merger. In October 2017, the Securities and Exchange Commission (SEC) declared effective a registration statement on Form S-4 of Holdco including a joint proxy statement of Great Plains Energy and Westar that will be used in connection with Great Plains Energy's and Westar's special shareholder meetings on November 21, 2017, and the registration of shares of Holdco common stock to be issued to Great Plains Energy's and Westar's shareholders at the closing of the anticipated merger.

Termination Fees

The Amended Merger Agreement provides that in connection with a termination of the agreement under specified circumstances relating to a failure to obtain regulatory approvals by July 9, 2018 (which date may be extended to January 9, 2019), a final and nonappealable order enjoining the consummation of the anticipated merger in connection with regulatory approvals or failure by Great Plains Energy to comply with its obligations under the Amended Merger Agreement to consummate the closing of the anticipated merger once all of the conditions have been satisfied, Great Plains Energy may be required to pay Westar a termination fee of $190 million. In addition, in the event that the Amended Merger Agreement is terminated by Westar under certain circumstances to enter into a definitive acquisition agreement with respect to a superior proposal or by Great Plains Energy as a result of the Westar Board changing its recommendation of the anticipated merger prior to the Westar shareholder approval having been obtained, Westar may be required to pay Great Plains Energy a termination fee of $190 million. Similarly, in the event that the Amended Merger Agreement is terminated by Great Plains Energy under certain circumstances to enter into a definitive acquisition agreement with respect to a superior proposal or by Westar as a result of the Great Plains Energy Board changing its recommendation of the anticipated merger prior to the Great Plains Energy shareholder approval having been obtained, Great Plains Energy may be required to pay Westar a termination fee of $190 million. Additionally, if the Amended Merger Agreement is terminated by either Great Plains Energy or Westar as a result of Great Plains Energy's shareholders not approving the Amended Merger Agreement, Great Plains Energy may be required to pay Westar a termination fee of $80 million.

Shareholder Lawsuits

Following the announcement of the Original Merger Agreement in May 2016, two putative class action complaints (which were consolidated and superseded by a consolidated complaint) were filed in the District Court of Shawnee County, Kansas. On October 20, 2017, the lead plaintiff in that consolidated putative class action filed an amended class action petition. The amended petition names as defendants Westar, the Westar Board, Great Plains Energy, Holdco and Merger Sub. The amended petition challenges the proposed merger and alleges breaches of fiduciary duties against the Westar Board in connection with the proposed merger, including the duty of candor, and that Westar, Great Plains Energy, Holdco and Merger Sub aided and abetted such breaches of fiduciary duties.

On September 21, 2017, a putative class action lawsuit was filed in the United States District Court for the District of Kansas. The federal class action complaint names as defendants Westar, the Westar Board, Great Plains Energy, Holdco and Merger Sub. The complaint challenges the merger and alleges violations of section 14(a) of the Securities Exchange Act of 1934, as amended (“Exchange Act”) against all of the defendants and violations of section 20(a) of the Exchange Act against the Westar Board.

On October 6, 2017, a putative class action lawsuit was filed in the United States District Court for the District of Kansas. The federal class action complaint names as defendants Westar, the Westar Board, Great Plains Energy, Holdco and Merger Sub. The complaint challenges the proposed merger and alleges violations of section 14(a) of the Exchange Act against Westar and the Westar Board and violations of section 20(a) of the Exchange Act against the Westar Board, Great Plains Energy, Holdco and Merger Sub.

On October 13, 2017, a putative class action lawsuit was filed in the United States District Court for the Western District of Missouri, Western Division. The federal class action complaint names as defendants Great Plains Energy and the Great Plains Energy Board. The complaint challenges the proposed merger and alleges violations of section 14(a) of the Exchange Act against all of the defendants and violations of section 20(a) of the Exchange Act against the Great Plains Energy Board.

On October 18, 2017, a putative derivative complaint was filed in Shawnee County, Kansas. This putative derivative action names as defendants the Westar Board, Great Plains Energy, Holdco and Merger Sub, with Westar named as a nominal defendant. The complaint challenges the proposed merger and alleges that the Westar Board determined to forego a $380 million break-up fee allegedly payable to Westar associated with the Original Merger Agreement, breached their fiduciary duties to Westar shareholders in connection with the proposed merger, and that Great Plains Energy, Holdco and Merger Sub aided and abetted such breaches of fiduciary duties.

Great Plains Energy does not believe these suits will impact the completion of the anticipated merger with Westar and they are not expected to have a material impact on Great Plains Energy's consolidated financial statements. While Great Plains Energy believes that dismissal of these lawsuits is warranted, the outcome of any litigation is inherently uncertain.

Redemption of Acquisition Financing

In order to fund the cash portion of the acquisition under the Original Merger Agreement, Great Plains Energy completed registered public offerings of 60.5 million shares of common stock for total net proceeds of $1.55 billion and 17.3 million depositary shares each representing a 1/20th interest in a share of 7.00% Series B Mandatory Convertible Preferred Stock (Series B Preferred Stock) for total net proceeds of $836.2 million in October 2016 and issued, at a discount, $4.3 billion of unsecured senior notes in March 2017. Great Plains Energy also entered into a stock purchase agreement with OCM Credit Portfolio LP (OMERS), pursuant to which Great Plains Energy would issue and sell to OMERS 750,000 shares of preferred stock of Great Plains Energy designated as 7.25% Mandatory Convertible Preferred Stock, Series A (Series A Preferred Stock), without par value, for an aggregate purchase price equal to $750 million at the closing of the acquisition.

In addition to the financings discussed above, Great Plains Energy also entered into a senior unsecured bridge term loan facility in connection with the Original Merger Agreement in an aggregate principal amount of $8.017 billion (which was subsequently reduced to $864.5 million as a result of the completed financings noted above) to support the anticipated transaction and provide flexibility for the timing of long-term financing.

As a result of the Amended Merger Agreement, the following occurred with regards to Great Plains Energy's acquisition financing arrangements:


•	In July 2017, Great Plains Energy redeemed its $4.3 billion of unsecured senior notes at a redemption price of 101% of the aggregate principle amount, plus accrued and unpaid interest. See Note 11 for additional information;


•	In August 2017, Great Plains Energy redeemed its Series B Preferred Stock at a redemption price that was equal to a make-whole formula set forth in the terms of the Series B Preferred Stock. See Note 12 for additional information;


•	In July 2017, Great Plains Energy and OMERS terminated their stock purchase agreement for $750 million of Series A Preferred Stock. As a result of this termination, Great Plains Energy recorded $15 million of previously deferred offering fees to non-operating expenses in the third quarter of 2017; and


•	In July 2017, Great Plains Energy terminated its $864.5 million unsecured bridge term loan facility.

Under the Amended Merger Agreement, Great Plains Energy is required to have not less than $1.25 billion in cash and cash equivalents on its balance sheet at the closing of the anticipated merger with Westar. It is expected that this excess cash will be returned to shareholders of the combined company through the repurchase of common stock in a series of transactions over time after the closing of the anticipated merger.

Supplemental Cash Flow Information

9 Months Ended

Sep. 30, 2017

Supplemental Cash Flow Elements [Abstract]

Cash Flow, Supplemental Disclosures [Text Block]

3. SUPPLEMENTAL CASH FLOW INFORMATION



Great Plains Energy Other Operating Activities
Year to Date September 30	2017			2016
Cash flows affected by changes in:	(millions)
Receivables	$	(20.4	)	$	(45.9	)
Accounts receivable pledged as collateral	(22.6		)	(15.0		)
Fuel inventories	19.6			19.8
Materials and supplies	(9.7		)	(5.3		)
Accounts payable	(125.7		)	(119.8		)
Accrued taxes	92.4			97.2
Accrued interest	6.6			16.7
Deferred refueling outage costs	12.1			7.5
Pension and post-retirement benefit obligations	52.0			53.2
Allowance for equity funds used during construction	(3.4		)	(4.3		)
Fuel recovery mechanisms	(10.1		)	(16.8		)
Other	11.9			(11.7		)
Total other operating activities	$	2.7		$	(24.4	)
Cash paid during the period:
Interest	$	198.7		$	130.2
Income taxes	$	0.1		$	0.2
Non-cash investing activities:
Liabilities accrued for capital expenditures	$	31.2		$	30.7



KCP&L Other Operating Activities
Year to Date September 30	2017			2016
Cash flows affected by changes in:	(millions)
Receivables	$	(19.5	)	$	(53.5	)
Accounts receivable pledged as collateral	(20.0		)	—
Fuel inventories	10.8			12.7
Materials and supplies	(7.2		)	(3.8		)
Accounts payable	(75.1		)	(80.3		)
Accrued taxes	122.7			179.3
Accrued interest	8.1			8.9
Deferred refueling outage costs	12.1			7.5
Pension and post-retirement benefit obligations	48.6			53.7
Allowance for equity funds used during construction	(3.4		)	(4.0		)
Fuel recovery mechanisms	7.6			(31.0		)
Other	(16.0		)	(14.8		)
Total other operating activities	$	68.7		$	74.7
Cash paid during the period:
Interest	$	88.6		$	86.7
Income taxes	$	4.9		$	—
Non-cash investing activities:
Liabilities accrued for capital expenditures	$	24.7		$	25.7

Receivables

9 Months Ended

Sep. 30, 2017

Receivables [Abstract]

Loans Notes Trade And Other Receivables Disclosure And Transfers And Servicing Of Financial Asset [Text Block]

4. RECEIVABLES

Great Plains Energy's and KCP&L's receivables are detailed in the following table.



	September 30				December 31
		2017				2016
Great Plains Energy		(millions)
Customer accounts receivable - billed		$	25.0			$	26.2
Customer accounts receivable - unbilled		114.9				79.1
Allowance for doubtful accounts - customer accounts receivable		(5.4		)		(4.0		)
Other receivables		51.9				64.7
Total		$	186.4			$	166.0
KCP&L
Customer accounts receivable - billed		$	24.4			$	25.5
Customer accounts receivable - unbilled		80.0				63.7
Allowance for doubtful accounts - customer accounts receivable		(2.8		)		(1.8		)
Other receivables		42.2				51.7
Total		$	143.8			$	139.1

Great Plains Energy's and KCP&L's other receivables at September 30, 2017, and December 31, 2016, consisted primarily of receivables from partners in jointly owned electric utility plants and wholesale sales receivables.

Sale of Accounts Receivable – KCP&L and GMO

KCP&L and GMO sell all of their retail electric accounts receivable to their wholly owned subsidiaries, KCP&L Receivables Company and GMO Receivables Company, respectively, which in turn sell an undivided percentage ownership interest in the accounts receivable to Victory Receivables Corporation, an independent outside investor. Each of KCP&L Receivables Company's and GMO Receivables Company's sale of the undivided percentage ownership interest in accounts receivable to Victory Receivables Corporation is accounted for as a secured borrowing with accounts receivable pledged as collateral and a corresponding short-term collateralized note payable recognized on the balance sheets. At September 30, 2017, and December 31, 2016, Great Plains Energy's accounts receivable pledged as collateral and the corresponding short-term collateralized note payable were $195.0 million and $172.4 million, respectively. At September 30, 2017, and December 31, 2016, KCP&L's accounts receivable pledged as collateral and the corresponding short-term collateralized note payable were $130.0 million and $110.0 million, respectively. In September 2017, KCP&L and GMO amended their respective receivable sale agreements with Victory Receivables Corporation to extend the termination date to September 2018 and to allow for $130 million in aggregate outstanding principal amount of borrowings at any time for KCP&L and $50 million in aggregate outstanding principal amount of borrowings from mid-November through mid-June and then $65 million from mid-June through mid-November for GMO.

Nuclear Plant

9 Months Ended

Sep. 30, 2017

Nuclear Plant [Abstract]

Nuclear Plant

5. NUCLEAR PLANT

KCP&L owns 47% of Wolf Creek Generating Station (Wolf Creek), its only nuclear generating unit. Wolf Creek is located in Coffey County, Kansas, just northeast of Burlington, Kansas. Wolf Creek's operating license expires in 2045. Wolf Creek is regulated by the NRC with respect to licensing, operations and safety-related requirements.

Spent Nuclear Fuel and High-Level Radioactive Waste

Under the Nuclear Waste Policy Act of 1982, the Department of Energy (DOE) is responsible for the permanent disposal of spent nuclear fuel. Wolf Creek historically paid the DOE a quarterly fee of one-tenth of a cent for each kWh of net nuclear generation delivered and sold for the future disposal of spent nuclear fuel. In May 2014, this fee was set to zero.

In 2010, the DOE filed a motion with the NRC to withdraw its then pending application to the NRC to construct a national repository for the disposal of spent nuclear fuel and high-level radioactive waste at Yucca Mountain, Nevada. An NRC board denied the DOE's motion to withdraw its application. In 2011, the NRC announced that it was evenly divided on whether to take affirmative action to overturn or uphold the board's decision and ordered the licensing board, consistent with budgetary limitations, to close out its work on the DOE's application. In August 2013, a federal court of appeals ruled that the NRC must resume its review of the DOE's application to the extent of appropriated funds. With the available funds, the NRC was able to complete its technical review of the Yucca Mountain application but was not able to resume the licensing hearing.

Wolf Creek is currently evaluating alternatives for expanding its existing on-site spent nuclear fuel storage to provide additional capacity prior to 2025. Management cannot predict when, or if, an off-site storage site or alternative disposal site will be available to receive Wolf Creek's spent nuclear fuel and will continue to monitor this activity.

Low-Level Radioactive Waste

Wolf Creek disposes of most of its low-level radioactive waste (Class A waste) at an existing third-party repository in Utah. Management expects that the site located in Utah will remain available to Wolf Creek for disposal of its Class A waste. Wolf Creek has contracted with a waste processor that will process, take title and dispose in another state most of the remainder of Wolf Creek's low-level radioactive waste (Classes B and C waste, which is higher in radioactivity but much lower in volume). Should on-site waste storage be needed in the future, Wolf Creek has current storage capacity on site for about four years' generation of Classes B and C waste and believes it will be able to expand that storage capacity as needed if it becomes necessary to do so.

Nuclear Plant Decommissioning Costs

The MPSC and KCC require KCP&L and the other owners of Wolf Creek to submit an updated decommissioning cost study every three years and to propose funding levels. The most recent study was submitted to the MPSC and KCC in September 2017 and is the basis for the current cost of decommissioning estimates in the following table. Funding levels included in KCP&L retail rates have not changed.



		KCC			MPSC
	(millions)
Current cost of decommissioning (in 2017 dollars)
Total Station		$	813.7		$	813.7
KCP&L's 47% Share		382.5			382.5

Future cost of decommissioning (in 2045-2053 dollars) ^(a)
Total Station		$	1,982.4		$	2,137.8
KCP&L's 47% Share		931.7			1,004.8

Annual escalation factor		2.91		%	3.16		%
Annual return on trust assets ^(b)		5.64		%	5.46		%

^(a)Total future cost over an eight year decommissioning period

^(b)The 5.64% KCC rate of return is through 2029 and then systematically decreases through 2053 to 0.32%. The 5.46% MPSC rate of return is through 2027 and then systematically decreases through 2053 to 2.22%. The KCC and MPSC rates of return systematically decrease based on the assumption that the fund's investment mix will become increasingly conservative as the decommissioning period approaches.

Nuclear Decommissioning Trust Fund

The following table summarizes the change in Great Plains Energy's and KCP&L's nuclear decommissioning trust fund.



	September 30			December 31
	2017			2016
Decommissioning Trust		(millions)
Beginning balance January 1		$	222.9		$	200.7
Contributions		2.5			3.3
Earned income, net of fees		3.1			4.1
Net realized gains		0.5			0.3
Net unrealized gains		18.5			14.5
Ending balance		$	247.5		$	222.9

The nuclear decommissioning trust is reported at fair value on the balance sheets and is invested in assets as detailed in the following table.



	September 30, 2017												December 31, 2016
	Cost Basis		Unrealized Gains			Unrealized Losses				Fair Value			Cost Basis			Unrealized Gains			Unrealized Losses				Fair Value
	(millions)
Equity securities	$	95.8		$	79.2		$	(0.8	)		$	174.2		$	93.3		$	62.1		$	(1.5	)		$	153.9
Debt securities	67.3			2.7			(0.2		)		69.8			63.4			2.3			(0.5		)		65.2
Other	3.5			—			—				3.5			3.8			—			—				3.8
Total	$	166.6		$	81.9		$	(1.0	)		$	247.5		$	160.5		$	64.4		$	(2.0	)		$	222.9

The weighted average maturity of debt securities held by the trust at September 30, 2017, was approximately 9 years. The costs of securities sold are determined on the basis of specific identification. The following table summarizes the realized gains and losses from the sale of securities in the nuclear decommissioning trust fund.



	Three Months Ended September 30						Year to Date September 30
	2017			2016			2017			2016
	(millions)
Realized gains	$	0.7		$	0.6		$	1.1		$	1.5
Realized losses	(0.5		)	(0.3		)	(0.6		)	(1.3		)

Regulatory Matters	9 Months Ended
Regulatory Matters	Sep. 30, 2017
Regulated Operations [Abstract]
Regulatory Matters	6. REGULATORY MATTERS KCP&L Kansas 2016 Abbreviated Rate Case Proceedings In November 2016, KCP&L filed an abbreviated application with KCC to request a decrease to its retail revenues of $2.8 million, reflecting the true-up to actuals of construction and environmental upgrade costs at the La Cygne Station and Wolf Creek capital addition costs and the removal of certain regulatory asset and liability amortizations. The previously approved return on equity and rate-making ratio for KCP&L was not addressed in this case. In April 2017, KCP&L, KCC staff and the Citizens' Utility Ratepayer Board filed a joint motion to approve a unanimous settlement agreement with KCC that requested a decrease in retail revenues of $3.6 million. In June 2017, KCC issued an order approving the unanimous settlement agreement. The rates established by the order took effect on June 28, 2017. KCP&L Missouri 2016 Rate Case Proceedings In July 2016, KCP&L filed an application with the MPSC to request an increase to its retail revenues of $62.9 million, with a return on equity of 9.9% and a rate-making equity ratio of 49.88%. The request reflects increases in infrastructure investment costs, costs for regional transmission lines, property tax costs and costs to comply with environmental and cybersecurity mandates. KCP&L also requested an additional $27.2 million increase associated with rebasing fuel and purchased power expense. In May 2017, the MPSC issued an order for KCP&L authorizing an increase in annual revenues of $32.5 million, a return on equity of 9.5% and a rate-making equity ratio of approximately 49.2%. The rates established by the order took effect on June 8, 2017.

Goodwill	9 Months Ended
Goodwill	Sep. 30, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets [Text Block]	7. GOODWILL Accounting rules require goodwill to be tested for impairment annually and when an event occurs indicating the possibility that an impairment exists. The annual impairment test for the $169.0 million of GMO acquisition goodwill was conducted on September 1, 2017. The goodwill impairment test consists of comparing the fair value of a reporting unit to its carrying amount, including goodwill, to identify potential impairment. In the event that the carrying amount exceeds the fair value of the reporting unit, an impairment loss is recognized for the difference between the carrying amount of the reporting unit and its fair value. Great Plains Energy's regulated electric utility operations are considered one reporting unit for assessment of impairment, as they are included within the same operating segment and have similar economic characteristics. The determination of fair value of the reporting unit consisted of two valuation techniques: an income approach consisting of a discounted cash flow analysis and a market approach consisting of a determination of reporting unit invested capital using market multiples derived from the historical revenue; earnings before interest, income taxes, depreciation and amortization; net utility asset values and market prices of stock of peer companies. The results of the two techniques were evaluated and weighted to determine a point within the range that management considered representative of fair value for the reporting unit. Fair value of the reporting unit exceeded the carrying amount, including goodwill; therefore, there was no impairment of goodwill.

- Definition

The entire disclosure for the aggregate amount of goodwill and a description of intangible assets, which may include (a) for amortizable intangible assets (also referred to as finite-lived intangible assets), the carrying amount, the amount of any significant residual value, and the weighted-average amortization period, (b) for intangible assets not subject to amortization (also referred to as indefinite-lived intangible assets), the carrying amount, and (c) the amount of research and development assets acquired and written off in the period, including the line item in the income statement in which the amounts written off are aggregated, if not readily apparent from the income statement. Also discloses (a) for amortizable intangibles assets in total and by major class, the gross carrying amount and accumulated amortization, the total amortization expense for the period, and the estimated aggregate amortization expense for each of the five succeeding fiscal years, (b) for intangible assets not subject to amortization the carrying amount in total and by major class, and (c) for goodwill, in total and for each reportable segment, the changes in the carrying amount of goodwill during the period (including the aggregate amount of goodwill acquired, the aggregate amount of impairment losses recognized, and the amount of goodwill included in the gain (loss) on disposal of a reporting unit). If any part of goodwill has not been allocated to a reportable segment, discloses the unallocated amount and the reasons for not allocating. For each impairment loss recognized related to an intangible asset (excluding goodwill), discloses: (a) a description of the impaired intangible asset and the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method for determining fair value, (c) the caption in the income statement or the statement of activities in which the impairment loss is aggregated, and (d) the segment in which the impaired intangible asset is reported. For each goodwill impairment loss recognized, discloses: (a) a description of the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method of determining the fair value of the associated reporting unit, and (c) if a recognized impairment loss is an estimate not finalized and the reasons why the estimate is not final. May also disclose the nature and amount of any significant adjustments made to a previous estimate of an impairment loss.

+ References + Details

Pension Plans and Other Employee Benefits

9 Months Ended

Sep. 30, 2017

Compensation and Retirement Disclosure [Abstract]

Pension Plans and Other Employee Benefits

8. PENSION PLANS AND OTHER EMPLOYEE BENEFITS

Great Plains Energy maintains defined benefit pension plans for the majority of KCP&L's and GMO's active and inactive employees, including officers, and its 47% ownership share of Wolf Creek Nuclear Operating Corporation (WCNOC) defined benefit plans. For the majority of employees, pension benefits under these plans reflect the employees' compensation, years of service and age at retirement. Effective in 2014, the non-union plan was closed to future employees. Great Plains Energy also provides certain post-retirement health care and life insurance benefits for substantially all retired employees of KCP&L, GMO and its 47% ownership share of WCNOC.

KCP&L and GMO record pension and post-retirement expense in accordance with rate orders from the MPSC and KCC that allow the difference between pension and post-retirement costs under GAAP and costs for ratemaking to be recognized as a regulatory asset or liability. This difference between financial and regulatory accounting methods is due to timing and will be eliminated over the life of the plans.

The following tables provide Great Plains Energy's components of net periodic benefit costs prior to the effects of capitalization and sharing with joint owners of power plants.



	Pension Benefits						Other Benefits
Three Months Ended September 30	2017			2016			2017			2016
Components of net periodic benefit costs	(millions)
Service cost	$	11.0		$	10.5		$	0.5		$	0.7
Interest cost	13.4			13.2			1.4			1.5
Expected return on plan assets	(12.8		)	(12.3		)	(0.7		)	(0.8		)
Prior service cost	0.2			0.2			—			0.3
Recognized net actuarial (gain)/loss	12.4			13.0			(0.1		)	(0.3		)
Net periodic benefit costs before regulatory adjustment	24.2			24.6			1.1			1.4
Regulatory adjustment	(0.2		)	(1.1		)	0.1			1.4
Net periodic benefit costs	$	24.0		$	23.5		$	1.2		$	2.8

	Pension Benefits						Other Benefits
Year to Date September 30	2017			2016			2017			2016
Components of net periodic benefit costs	(millions)
Service cost	$	33.0		$	31.5		$	1.5		$	2.0
Interest cost	40.2			39.7			4.1			4.6
Expected return on plan assets	(38.4		)	(36.9		)	(2.0		)	(2.3		)
Prior service cost	0.6			0.5			—			0.9
Recognized net actuarial (gain)/loss	37.2			38.9			(0.3		)	(1.1		)
Net periodic benefit costs before regulatory adjustment	72.6			73.7			3.3			4.1
Regulatory adjustment	2.3			(3.1		)	1.9			4.4
Net periodic benefit costs	$	74.9		$	70.6		$	5.2		$	8.5

Year to date September 30, 2017, Great Plains Energy contributed $28.0 million to the pension plans and expects to contribute an additional $51.6 million in 2017 to satisfy the Employee Retirement Income Security Act of 1974, as amended (ERISA) funding requirements and the MPSC and KCC rate orders, the majority of which is expected to be paid by KCP&L. Also in 2017, Great Plains Energy expects to make contributions of $4.1 million to the post-retirement benefit plans, the majority of which is expected to be paid by KCP&L.

Equity Compensation

9 Months Ended

Sep. 30, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Equity Compensation

9. EQUITY COMPENSATION

Great Plains Energy's Long-Term Incentive Plan is an equity compensation plan approved by Great Plains Energy's shareholders. The Long-Term Incentive Plan permits the grant of restricted stock, restricted stock units, bonus shares, stock options, stock appreciation rights, director shares, director deferred share units, performance shares and other stock-based awards to directors, officers and other employees of Great Plains Energy and KCP&L. Forfeiture rates are based on historical forfeitures and future expectations and are reevaluated annually.

The following table summarizes Great Plains Energy's and KCP&L's equity compensation expense and the associated income tax benefit.



	Three Months Ended September 30					Year to Date September 30
	Three Months Ended September 30					Year to Date September 30
		2017		2016		2017		2016
Great Plains Energy		(millions)
Equity compensation expense		$	1.8	$	0.4	$	4.4	$	3.9
Income tax benefit		0.6		—		1.7		1.3
KCP&L
Equity compensation expense		$	1.2	$	0.2	$	2.9	$	2.5
Income tax benefit		0.4		—		1.2		0.8

Performance Shares

Performance share activity year to date September 30, 2017, is summarized in the following table.



	Performance Shares			Grant Date Fair Value*
Beginning balance January 1, 2017		625,100			$	28.13
Granted		236,433			31.26
Earned		(212,992	)		28.48
Forfeited		(97,036	)		29.24
Ending balance September 30, 2017		551,505			29.12

* weighted-average

At September 30, 2017, the remaining weighted-average contractual term was 1.4 years. There were no shares granted for the three months ended September 30, 2017, and 2016, respectively. The weighted-average grant-date fair value of shares granted was $31.26 and $31.41 year to date September 30, 2017, and 2016, respectively. At September 30, 2017, there was $7.5 million of total unrecognized compensation expense, net of forfeiture rates, related to performance shares granted under the Long-Term Incentive Plan, which will be recognized over the remaining weighted-average contractual term. The total fair value of performance shares earned and paid was $6.1 million and $7.4 million year to date September 30, 2017, and 2016, respectively.

The fair value of performance share awards is estimated using the market value of the Company's stock at the valuation date and a Monte Carlo simulation technique that incorporates assumptions for inputs of expected volatilities, dividend yield and risk-free rates. Expected volatility is based on daily stock price change during a historical period commensurate with the remaining term of the performance period of the grant. The risk-free rate is based upon the rate at the time of the evaluation for zero-coupon government bonds with a maturity consistent with the remaining performance period of the grant. The dividend yield is based on the most recent dividends paid and the actual closing stock price on the valuation date. For shares granted in 2017, inputs for expected volatility, dividend yield and risk-free rates were 18%, 3.80% and 1.58%, respectively.

Restricted Stock

Restricted stock activity year to date September 30, 2017, is summarized in the following table.



	Nonvested Restricted Stock			Grant Date Fair Value*
Beginning balance January 1, 2017		249,672			$	27.20
Granted and issued		78,840			28.60
Vested		(109,813	)		27.48
Forfeited		(22,521	)		27.26
Ending balance September 30, 2017		196,178			27.81

* weighted-average

At September 30, 2017, the remaining weighted-average contractual term was 1.4 years. There were no shares granted for the three months ended September 30, 2017, and 2016, respectively. The weighted-average grant-date fair value of shares granted was $28.60 and $29.41 year to date September 30, 2017, and 2016, respectively. At September 30, 2017, there was $2.5 million of total unrecognized compensation expense, net of forfeiture rates, related to nonvested restricted stock granted under the Long-Term Incentive Plan, which will be recognized over the remaining weighted-average contractual term. Total fair value of shares vested was $0.2 million and $3.0 million for the three months ended and year to date September 30, 2017, respectively. Total fair value of shares vested was $0.1 million and $1.7 million for the three months ended and year to date September 30, 2016.

- Definition

The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details.

+ References + Details

Short-term Borrowings and Short-term Bank Lines of Credit	9 Months Ended
	Sep. 30, 2017
Short-term Borrowings and Short-term Bank Lines of Credit [Abstract]
Short-term Borrowings and Short-term Bank Lines of Credit [Text Block]	10. SHORT-TERM BORROWINGS AND SHORT-TERM BANK LINES OF CREDIT Great Plains Energy's $200 Million Revolving Credit Facility Great Plains Energy's $200 million revolving credit facility with a group of banks expires in October 2019. The facility's terms permit transfers of unused commitments between this facility and the KCP&L and GMO facilities discussed below, with the total amount of the facility not exceeding $400 million at any one time. A default by Great Plains Energy or any of its significant subsidiaries on other indebtedness totaling more than $50.0 million is a default under the facility. Under the terms of this facility, Great Plains Energy is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times. At September 30, 2017, Great Plains Energy was in compliance with this covenant. At September 30, 2017, and December 31, 2016, Great Plains Energy had no outstanding cash borrowings and had issued $1.0 million in letters of credit under the credit facility. KCP&L's $600 Million Revolving Credit Facility and Commercial Paper KCP&L's $600 million revolving credit facility with a group of banks provides support for its issuance of commercial paper and other general corporate purposes and expires in October 2019. Great Plains Energy and KCP&L may transfer up to $200 million of unused commitments between Great Plains Energy's and KCP&L's facilities. A default by KCP&L on other indebtedness totaling more than $50.0 million is a default under the facility. Under the terms of this facility, KCP&L is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times. At September 30, 2017, KCP&L was in compliance with this covenant. At September 30, 2017, KCP&L had $72.0 million of commercial paper outstanding at a weighted-average interest rate of 1.37%, had issued letters of credit totaling $2.7 million and had no outstanding cash borrowings under the credit facility. At December 31, 2016, KCP&L had $132.9 million of commercial paper outstanding at a weighted-average interest rate of 0.98%, had issued letters of credit totaling $2.8 million and had no outstanding cash borrowings under the credit facility. GMO's $450 Million Revolving Credit Facility and Commercial Paper GMO's $450 million revolving credit facility with a group of banks provides support for its issuance of commercial paper and other general corporate purposes and expires in October 2019. Great Plains Energy and GMO may transfer up to $200 million of unused commitments between Great Plains Energy's and GMO's facilities. A default by GMO or any of its significant subsidiaries on other indebtedness totaling more than $50.0 million is a default under the facility. Under the terms of this facility, GMO is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times. At September 30, 2017, GMO was in compliance with this covenant. At September 30, 2017, GMO had $175.9 million of commercial paper outstanding at a weighted-average interest rate of 1.41%, had issued letters of credit totaling $2.0 million and had no outstanding cash borrowings under the credit facility. At December 31, 2016, GMO had $201.9 million of commercial paper outstanding at a weighted-average interest rate of 1.02%, had issued letters of credit totaling $1.9 million and had no outstanding cash borrowings under the credit facility. Great Plains Energy's $864.5 Million Term Loan Facility In connection with the Original Merger Agreement, Great Plains Energy entered into a commitment letter for a 364-day senior unsecured bridge term loan facility, originally for an aggregate principal amount of $8.017 billion to support the anticipated transaction and provide flexibility for the timing of long-term financing. Following Great Plains Energy's completed acquisition financings, the aggregate principal amount of the facility was subsequently reduced to $864.5 million and the expiration date of the facility was extended to November 30, 2017. The remaining commitment of $864.5 million was terminated in July 2017 in connection with the Amended Merger Agreement.

Long-Term Debt

9 Months Ended

Sep. 30, 2017

Debt Disclosure [Abstract]

Long-Term Debt

11. LONG-TERM DEBT

Great Plains Energy's and KCP&L's long-term debt is detailed in the following table.



		September 30				December 31
	Year Due	2017				2016
KCP&L			(millions)
General Mortgage Bonds
2.95% EIRR bonds	2023		$	79.5			$	110.5
7.15% Series 2009A (8.59% rate)^(a)	2019		400.0				400.0
Senior Notes
5.85% Series (5.72% rate)^(a)			—				250.0
6.375% Series (7.49% rate)^(a)	2018		350.0				350.0
3.15% Series	2023		300.0				300.0
3.65% Series	2025		350.0				350.0
6.05% Series (5.78% rate)^(a)	2035		250.0				250.0
5.30% Series	2041		400.0				400.0
4.20% Series	2047		300.0				—
EIRR Bonds
0.889% Series 2007A and 2007B^(b)	2035		146.5				146.5
2.875% Series 2008	2038		23.4				23.4
Current maturities			(350.0		)		(281.0		)
Unamortized discount and debt issuance costs			(17.7		)		(15.4		)
Total KCP&L excluding current maturities^(c)			2,231.7				2,284.0
Other Great Plains Energy
GMO First Mortgage Bonds 9.44% Series	2018-2021		4.6				5.7
GMO Senior Notes
8.27% Series	2021		80.9				80.9
3.49% Series A	2025		125.0				125.0
4.06% Series B	2033		75.0				75.0
4.74% Series C	2043		150.0				150.0
GMO Medium Term Notes
7.33% Series	2023		3.0				3.0
7.17% Series	2023		7.0				7.0
Great Plains Energy Senior Notes
6.875% Series (7.33% rate)^(a)			—				100.0
4.85% Series	2021		350.0				350.0
5.292% Series	2022		287.5				287.5
Current maturities			(1.1		)		(101.1		)
Unamortized discount and premium, net and debt issuance costs			(1.6		)		(1.8		)
Total Great Plains Energy excluding current maturities^(c)			$	3,312.0			$	3,365.2


^(a)	Rate after amortizing gains/losses recognized in other comprehensive income (OCI) on settlements of interest rate hedging instruments


^(b)	Variable rate


^(c)	At September 30, 2017, and December 31, 2016, does not include $50.0 million and $21.9 million of secured Series 2005 Environmental Improvement Revenue Refunding (EIRR) bonds because the bonds were repurchased in September 2015 and are held by KCP&L

Great Plains Energy Senior Notes

In March 2017, Great Plains Energy issued, at a discount, the following series of unsecured senior notes in order to fund the majority of the cash portion of the acquisition of Westar under the Original Merger Agreement:


•	$750.0 million of 2.50% Notes, maturing in 2020;


•	$1,150.0 million of 3.15% Notes, maturing in 2022;


•	$1,400.0 million of 3.90% Notes, maturing in 2027; and


•	$1,000.0 million of 4.85% Notes, maturing in 2047.

In July 2017, as a result of the Amended Merger Agreement, Great Plains Energy determined in its reasonable judgment that the acquisition of Westar would not close prior to November 30, 2017 and exercised its special optional redemption right to redeem each series of the senior notes issued in March 2017. The redemption price was equal to 101% of the principle amount of the senior notes, including accrued and unpaid interest, for a total redemption cost of $4,400.1 million. As a result of the redemption, Great Plains Energy recorded a loss on extinguishment of debt of $82.8 million in July 2017.

Great Plains Energy repaid its $100.0 million of 6.875% unsecured Senior Notes at maturity in September 2017.

KCP&L Senior Notes

In June 2017, KCP&L issued, at a discount, $300.0 million of 4.20% unsecured Senior Notes, maturing in 2047. KCP&L also repaid its $250.0 million of 5.85% unsecured Senior Notes at maturity in June 2017.

KCP&L General Mortgage Bonds

KCP&L repaid its $31.0 million secured Series 1992 EIRR bonds at maturity in July 2017.

Preferred Stock	9 Months Ended
Preferred Stock	Sep. 30, 2017
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred Stock [Text Block]	12. PREFERRED STOCK Series A Mandatory Convertible Preferred Stock On May 29, 2016, Great Plains Energy entered into a stock purchase agreement with OMERS, pursuant to which Great Plains Energy will issue and sell to OMERS 750,000 shares of Series A Preferred Stock, for an aggregate purchase price equal to $750 million at the closing of the Original Merger Agreement. In July 2017, as a result of the Amended Merger Agreement, Great Plains Energy and OMERS terminated their stock purchase agreement for the Series A Preferred Stock. As a result of this termination, Great Plains Energy recorded $15 million of previously deferred offering fees to non-operating expenses in the third quarter of 2017. Series B Mandatory Convertible Preferred Stock Great Plains Energy's Series B Preferred Stock contained an acquisition termination redemption option whereby in the event that the Original Merger Agreement was terminated or if Great Plains Energy determined in its reasonable judgment that the acquisition of Westar would not close or if the acquisition of Westar had not closed by November 30, 2017, then Great Plains Energy could at its sole option (but was not required to) redeem all of the Series B Preferred Stock. If exercised, the redemption price would be equal to either: (a) $1,000 per share plus accumulated and unpaid dividends up to the redemption date; or (b) if the average price of Great Plains Energy's common stock exceeded a certain threshold amount, then a repurchase price that is equal to a make-whole formula. The Series B Preferred Stock also contained a fundamental change conversion option whereby upon the occurrence of certain events deemed to be a fundamental change, including an acquisition, liquidation, or delisting of Great Plains Energy common stock, holders of the Series B Preferred Stock could: (a) convert their existing shares into shares of Great Plains Energy common stock; and (b) receive a dividend make-whole payment. As a result of the Amended Merger Agreement, Great Plains Energy determined in its reasonable judgment that the acquisition of Westar would not close and exercised its acquisition termination redemption option and redeemed the Series B Preferred Stock in August 2017. The Series B Preferred Stock was redeemed at a redemption price that was equal to a make-whole formula set forth in the terms of the Series B Preferred Stock. The total cost of the redemption was $963.4 million. Great Plains Energy made the entire redemption payment in cash. The dividend make-whole provisions within both the acquisition termination redemption and fundamental change conversion options discussed above represented embedded derivatives that in accordance with GAAP, were accounted for on a combined basis separately from the Series B Preferred Stock and reported at fair value. The fair value of the Series B Preferred Stock dividend make-whole provisions at inception and December 31, 2016 was insignificant. As part of the $963.4 million redemption of the Series B Preferred Stock, the Series B Preferred Stock dividend make-whole provisions liability was settled in August 2017. For the three months ended and year to date September 30, 2017, Great Plains Energy recognized a loss of $67.7 million and $124.8 million, respectively, for the settlement of these provisions, which is recorded within loss on Series B Preferred Stock dividend make-whole provisions on the consolidated statements of comprehensive income (loss). Great Plains Energy also recognized a redemption premium of $2.4 million in connection with the redemption of the Series B Preferred Stock for the three months ended and year to date September 30, 2017. This premium is represented as the difference between the redemption cost of $963.4 million and the $836.2 million carrying value of the Series B Preferred Stock, less the $124.8 million paid to settle the Series B Preferred Stock dividend make-whole provisions. The redemption premium is recorded as a reduction to earnings (loss) available for common shareholders and is recorded within preferred stock dividend requirements and redemption premium on the consolidated statements of comprehensive income (loss).

Commitments and Contingencies

9 Months Ended

Sep. 30, 2017

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

13. COMMITMENTS AND CONTINGENCIES

Environmental Matters

Great Plains Energy and KCP&L are subject to extensive federal, state and local environmental laws, regulations and permit requirements relating to air and water quality, waste management and disposal, natural resources and health and safety. In addition to imposing continuing compliance obligations and remediation costs, these laws, regulations and permits authorize the imposition of substantial penalties for noncompliance, including fines, injunctive relief and other sanctions. The cost of complying with current and future environmental requirements is expected to be material to Great Plains Energy and KCP&L. Failure to comply with environmental requirements or to timely recover environmental costs through rates could have a material effect on Great Plains Energy's and KCP&L's results of operations, financial position and cash flows.

Great Plains Energy's and KCP&L's current estimates of capital expenditures (exclusive of Allowance for Funds Used During Construction (AFUDC) and property taxes) over the next four years to comply with environmental regulations are in the following table. The total cost of compliance with any existing, proposed or future laws and regulations may be significantly different from these cost estimates provided.



	2017		2018		2019		2020
	(millions)
Great Plains Energy	$	36.3	$	16.6	$	9.2	$	13.7
KCP&L	34.9		16.5		7.9		13.0

The Companies expect to seek recovery of the costs associated with environmental requirements through rate increases; however, there can be no assurance that such rate increases would be granted. The Companies may be subject to materially adverse rate treatment in response to competitive, economic, political, legislative or regulatory factors and/or public perception of the Companies' environmental reputation.

The following discussion groups environmental and certain associated matters into the broad categories of air and climate change, water, solid waste and remediation.

Clean Air Act and Climate Change Overview

The Clean Air Act Amendments of 1990 (Clean Air Act) and associated regulations enacted by the Environmental Protection Agency (EPA) form a comprehensive program to preserve and enhance air quality. States are required to establish regulations and programs to address all requirements of the Clean Air Act and have the flexibility to enact more stringent requirements. All of Great Plains Energy's and KCP&L's generating facilities, and certain of their other facilities, are subject to the Clean Air Act.

Climate Change

The Companies' current generation capacity is primarily coal-fired and is estimated to produce about one ton of carbon dioxide (CO₂) per MWh, or approximately 19 million tons and 15 million tons per year for Great Plains Energy and KCP&L, respectively. The Companies are subject to existing greenhouse gas reporting regulations and certain greenhouse gas requirements. Federal or state legislation concerning the reduction of emissions of greenhouse gases, including CO₂, could be enacted in the future. At the international level, the Paris Agreement was adopted in December 2015 by nearly 200 countries and became effective in November 2016. The Paris Agreement does not result in any new, legally binding obligations on the United States to meet a particular greenhouse gas emissions target, but establishes a framework for international cooperation on climate change. In June 2017, United States President Donald Trump announced the United States would withdraw from the Paris Agreement. Under the rules of the Paris Agreement, the earliest any country can withdraw is November 2020. Other international agreements legally binding on the United States may be reached in the future. Greenhouse gas legislation has the potential of having significant financial and operational impacts on Great Plains Energy and KCP&L; however, the ultimate financial and operational consequences to Great Plains Energy and KCP&L cannot be determined until such legislation is passed. In the absence of new Congressional mandates, the EPA is proceeding with the regulation of greenhouse gases under the existing Clean Air Act.

In August 2015, the EPA finalized CO₂ emission standards for new, modified and reconstructed affected fossil-fuel-fired electric utility generating units. The standards would not apply to Great Plains Energy's and KCP&L's existing units unless the units were modified or reconstructed in the future. Also in August 2015, the EPA finalized its Clean Power Plan which sets CO₂ emission performance rates for existing affected fossil-fuel-fired electric generating units. Nationwide, by 2030, the EPA projects the Clean Power Plan would achieve CO₂ emission reductions from the power sector of approximately 32% from CO₂ emission levels in 2005.

In February 2016, the U.S. Supreme Court granted a stay of the Clean Power Plan putting the rule on hold pending review in the United States Court of Appeals for the District of Columbia Circuit and any subsequent review by the U.S. Supreme Court if such review is sought. In October 2017, the EPA proposed to repeal the Clean Power Plan on the basis that it exceeded the EPA’s statutory authority. The EPA has not yet determined if it will propose a new rule to replace the Clean Power Plan and if so, what form that rule would take and when it will do so. Compliance with the Clean Power Plan or any replacement rule has the potential of having significant financial and operational impacts on Great Plains Energy and KCP&L; however, the ultimate financial and operational consequences to Great Plains Energy and KCP&L cannot be determined until the outcome of the EPA's proposal to repeal the Clean Power Plan and pending litigation is known.

Clean Water Act

The Clean Water Act and associated regulations enacted by the EPA form a comprehensive program to restore and preserve water quality. Like the Clean Air Act, states are required to establish regulations and programs to address all requirements of the Clean Water Act, and have the flexibility to enact more stringent requirements. All of Great Plains Energy's and KCP&L's generating facilities, and certain of their other facilities, are subject to the Clean Water Act.

In May 2014, the EPA finalized regulations pursuant to Section 316(b) of the Clean Water Act regarding cooling water intake structures pursuant to a court approved settlement. KCP&L generation facilities with cooling water intake structures are subject to the best technology available standards based on studies completed to comply with such standards. The rule provides flexibility to work with the states to develop the best technology available to minimize aquatic species impacted by being pinned against intake screens (impingement) or drawn into cooling water systems (entrainment). Estimated costs to comply with Section 316(b) of the Clean Water Act are included in the estimated capital expenditures table above.

KCP&L holds a permit from the Missouri Department of Natural Resources (MDNR) covering water discharge from its Hawthorn Station. The permit authorizes KCP&L to, among other things, withdraw water from the Missouri River for cooling purposes and return the heated water to the Missouri River. KCP&L has applied for a renewal of this permit and the EPA has submitted an interim objection letter regarding the allowable amount of heat that can be contained in the returned water. Until this matter is resolved, KCP&L continues to operate under its current permit. Great Plains Energy and KCP&L cannot predict the outcome of this matter; however, while less significant outcomes are possible, this matter may require a reduction in generation, installation of cooling towers or other technology to cool the water, or both, any of which could have a significant impact on Great Plains Energy's and KCP&L's results of operations, financial position and cash flows.

In September 2015, the EPA finalized a revision of the technology-based effluent limitations guidelines and standards regulation to make the existing controls on discharges from steam electric power plants more stringent. The final rule sets the first federal limits on the levels of toxic metals in wastewater that can be discharged from power plants. The new requirements for existing power plants would be phased in between 2018 and 2023. The final rule establishes new or additional requirements for wastewaters associated with the following processes and byproducts at certain KCP&L and GMO stations: flue gas desulfurization, fly ash, bottom ash, flue gas mercury control, and combustion residual leachate from landfills and surface impoundments. In September 2017, the EPA announced it intends to conduct a rulemaking to potentially revise certain effluent limitations and standards for existing sources required by the rule. The EPA is postponing the earliest compliance dates for flue gas desulfurization and bottom ash transport waste water in the rule for a period of two years. Estimated capital costs to comply with the final rule are included in the estimated capital expenditures table above.

Solid Waste

Solid and hazardous waste generation, storage, transportation, treatment and disposal are regulated at the federal and state levels under various laws and regulations. In December 2014, the EPA finalized regulations to regulate coal combustion residuals (CCRs) under the Resource Conservation and Recovery Act (RCRA) subtitle D to address the risks from the disposal of CCRs generated from the combustion of coal at electric generating facilities. The Companies use coal in generating electricity and dispose of the CCRs in both on-site facilities and facilities owned by third parties. KCP&L's Iatan, La Cygne, and Montrose Stations and GMO's Sibley Station have on-site facilities affected by the rule. The rule requires periodic assessments; groundwater monitoring; location restrictions; design and operating requirements; recordkeeping and notifications; and closure, among other requirements, for CCR units. The rule was promulgated in the Federal Register on April 17, 2015, and became effective six months after promulgation with various obligations effective at specified times within the rule. Estimated capital costs to comply with the CCR rule are included in the estimated capital expenditures table above. Certain requirements of the rule would require Great Plains Energy or KCP&L to expedite or incur additional capital expenditures in the future.

Great Plains Energy and KCP&L have asset retirement obligations (AROs) on their balance sheets for closure and post-closure of ponds and landfills containing CCRs. Certain requirements of the rule could in the future require further evaluation of the expected method of compliance and refinement of assumptions underlying the cost estimates for closure and post-closure. Great Plains Energy's and KCP&L's AROs could increase from the amounts presently recorded.

Remediation

Certain federal and state laws, including the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), hold current and previous owners or operators of contaminated facilities and persons who arranged for the disposal or treatment of hazardous substances liable for the cost of investigation and cleanup. CERCLA and other laws also authorize the EPA and other agencies to issue orders compelling potentially responsible parties to clean up sites that are determined to present an actual or potential threat to human health or the environment. GMO retains some environmental liability for several operations and investments it no longer owns. In addition, GMO also owns, or has acquired liabilities from companies that once owned or operated, former manufactured gas plant (MGP) sites, which are subject to the supervision of the EPA and various state environmental agencies.

At September 30, 2017, and December 31, 2016, KCP&L had $0.3 million accrued for environmental remediation expenses, which covers ground water monitoring at a former MGP site. The amount accrued was established on an undiscounted basis and KCP&L does not currently have an estimated time frame over which the accrued amount may be paid.

In addition to the $0.3 million accrual above, at September 30, 2017, and December 31, 2016, Great Plains Energy had $1.4 million accrued for the future investigation and remediation of certain additional GMO identified MGP sites and retained liabilities. This estimate was based upon review of the potential costs associated with conducting investigative and remedial actions at identified sites, as well as the likelihood of whether such actions will be necessary. This estimate could change materially after further investigation, and could also be affected by the actions of environmental agencies and the financial viability of other potentially responsible parties; however, given the uncertainty of these items the possible loss or range of loss in excess of the amount accrued is not estimable.

GMO has pursued recovery of remediation costs from insurance carriers and other potentially responsible parties. As a result of a settlement with an insurance carrier, approximately $1.5 million in insurance proceeds less an annual deductible is available to GMO to recover qualified MGP remediation expenses. GMO would seek recovery of additional remediation costs and expenses through rate increases; however, there can be no assurance that such rate increases would be granted.

Legal Proceedings	9 Months Ended
Legal Proceedings	Sep. 30, 2017
Legal Proceedings [Abstract]
Contingencies Disclosure [Text Block]	14. LEGAL PROCEEDINGS GMO Western Energy Crisis In response to complaints of excessive prices in the California energy markets, FERC issued an order in July 2001 requiring net sellers of power in the California markets from October 2, 2000, through June 20, 2001, at prices above a FERC-determined competitive market clearing price, to make refunds to net purchasers of power in the California market during that time period. MPS Merchant was a net purchaser of power during the refund period. In November 2014, FERC issued an order finding that MPS Merchant engaged in tariff violations during the periods prior to October 2, 2000 (the Summer Period) and ordered refunds in the form of disgorgement of certain revenues. In November 2015 and February 2016, FERC issued additional orders regarding the refunds MPS Merchant owed. In October 2016, MPS Merchant reached a settlement agreement, which was subsequently revised in February 2017, with certain California utilities and governmental agencies that would settle all issues in the case in exchange for $7.5 million of cash consideration as well as MPS Merchant's interest in additional funds it was entitled to during the refund period discussed above. In September 2017, the settlement agreement was approved by FERC and the settlement payment was made by MPS Merchant in October 2017. In accordance with the terms of the settlement agreement, the $7.5 million of cash consideration accrued interest at the FERC interest rate beginning on January 1, 2017, until the date of the payment of the settlement. At September 30, 2017, and December 31, 2016, Great Plains Energy had accrued for the cash consideration and any applicable interest pursuant to the settlement agreement.

- Definition

The entire disclosure for loss and gain contingencies. Describes any existing condition, situation, or set of circumstances involving uncertainty as of the balance sheet date (or prior to issuance of the financial statements) as to a probable or reasonably possible loss incurred by an entity that will ultimately be resolved when one or more future events occur or fail to occur, and typically discloses the amount of loss recorded or a range of possible loss, or an assertion that no reasonable estimate can be made.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Publisher FASB
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-Publisher FASB
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+ Details

Related Party Transactions and Relationships

9 Months Ended

Sep. 30, 2017

15. RELATED PARTY TRANSACTIONS AND RELATIONSHIPS

KCP&L employees manage GMO's business and operate its facilities at cost, including GMO's 18% ownership interest in KCP&L's Iatan Nos. 1 and 2. The operating expenses and capital costs billed from KCP&L to GMO were $49.2 million and $145.0 million, respectively, for the three months ended and year to date September 30, 2017. These costs totaled $48.9 million and $143.8 million, respectively, for the three months ended and year to date September 30, 2016.

KCP&L and GMO are also authorized to participate in the Great Plains Energy money pool, an internal financing arrangement in which funds may be lent on a short-term basis to KCP&L and GMO from Great Plains Energy and between KCP&L and GMO. At September 30, 2017, and December 31, 2016, KCP&L had no outstanding receivables or payables under the money pool.

The following table summarizes KCP&L's related party net receivables.



	September 30		December 31
	2017			2016
	(millions)
Net receivable from GMO	$	55.1		$	64.6
Net receivable from Great Plains Energy	27.0			2.6

Fair Value Measurements

9 Months Ended

Sep. 30, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements

16. FAIR VALUE MEASUREMENTS

GAAP defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. GAAP establishes a fair value hierarchy, which prioritizes the inputs to valuation techniques used to measure fair value into three broad categories, giving the highest priority to quoted prices in active markets for identical assets or liabilities and lowest priority to unobservable inputs. A definition of the various levels, as well as discussion of the various measurements within the levels, is as follows:

Level 1 – Unadjusted quoted prices for identical assets or liabilities in active markets that Great Plains Energy and KCP&L have access to at the measurement date.

Level 2 – Market-based inputs for assets or liabilities that are observable (either directly or indirectly) or inputs that are not observable but are corroborated by market data.

Level 3 – Unobservable inputs, reflecting Great Plains Energy's and KCP&L's own assumptions about the assumptions market participants would use in pricing the asset or liability.

Great Plains Energy and KCP&L record cash and cash equivalents and short-term borrowings on the balance sheet at cost, which approximates fair value due to the short-term nature of these instruments.

Interest Rate Derivatives

In June 2016, Great Plains Energy entered into four interest rate swaps, with a total notional amount of $4.4 billion, to hedge against interest rate fluctuations on future issuances of long-term debt expected to be issued to finance a portion of the cash consideration for the acquisition of Westar under the Original Merger Agreement. The interest rate swaps were designated as economic hedges (non-hedging derivatives). Settlement of the interest rate swaps was contingent on the consummation of the acquisition of Westar. In July 2017, the interest rate swap agreements were amended to make them contingent on the consummation of the anticipated merger with Westar under the Amended Merger Agreement by November 30, 2018.

In March 2017, in connection with Great Plains Energy's $4.3 billion senior note issuance, the settlement value of the interest rate swaps to Great Plains Energy of $140.6 million was fixed. Cash settlement of the $140.6 million is contingent on the consummation of the anticipated merger with Westar by November 30, 2018. The fair value of the interest rate swaps recorded on Great Plains Energy's balance sheets reflects a contingency factor that management believes is representative of what a market participant would use in valuing these instruments in order to account for the contingent nature of the cash settlement of the interest rate swaps. The contingency factor was 0.45 and 0.35 at September 30, 2017, and December 31, 2016, respectively. At September 30, 2017, and December 31, 2016, the fair value of the interest rate swaps was $77.4 million and $79.3 million, respectively, and was recorded on the consolidated balance sheets in interest rate derivative instruments. For the three months ended and year to date September 30, 2017, Great Plains Energy recognized a $28.2 million gain and a $1.9 million loss, respectively, in interest charges for the change in fair value. For the three months ended and year to date September 30, 2016, Great Plains Energy recognized losses of $1.8 million and $78.8 million, respectively, in interest charges for the change in fair value.

Fair Value of Long-Term Debt

Great Plains Energy and KCP&L record long-term debt on the balance sheet at amortized cost. The fair value of long-term debt is measured as a Level 2 liability and is based on quoted market prices, with the incremental borrowing rate for similar debt used to determine fair value if quoted market prices are not available. At September 30, 2017, the book value and fair value of Great Plains Energy's long-term debt, including current maturities, were $3.7 billion and $3.9 billion, respectively. At December 31, 2016, the book value and fair value of Great Plains Energy's long-term debt, including current maturities, were $3.8 billion and $4.0 billion, respectively. At September 30, 2017, the book value and fair value of KCP&L's long-term debt, including current maturities, were $2.6 billion and $2.8 billion, respectively. At December 31, 2016, the book value and fair value of KCP&L's long-term debt, including current maturities, were $2.6 billion and $2.7 billion, respectively.

Supplemental Executive Retirement Plan

At September 30, 2017, and December 31, 2016, GMO's Supplemental Executive Retirement Plan rabbi trusts included $15.0 million and $16.0 million, respectively, of fixed income funds valued at net asset value per share (or its equivalent) that are not categorized in the fair value hierarchy. The fixed income fund invests primarily in intermediate and long-term debt securities, can be redeemed immediately and is not subject to any restrictions on redemptions.

The following tables include Great Plains Energy's and KCP&L's balances of financial assets and liabilities measured at fair value on a recurring basis.



Description	September 30 2017			Level 1		Level 2			Level 3
KCP&L		(millions)
Assets
Nuclear decommissioning trust ^(a)
Equity securities		$	174.2	$	174.2		$	—		$	—
Debt securities
U.S. Treasury		33.6		33.6			—			—
U.S. Agency		0.4		—			0.4			—
State and local obligations		2.5		—			2.5			—
Corporate bonds		33.2		—			33.2			—
Foreign governments		0.1		—			0.1			—
Cash equivalents		2.9		2.9			—			—
Other		0.6		0.6			—			—
Total nuclear decommissioning trust		247.5		211.3			36.2			—
Self-insured health plan trust ^(b)
Equity securities		0.4		0.4			—			—
Debt securities		2.8		0.4			2.4			—
Cash and cash equivalents		8.1		8.1			—			—
Total self-insured health plan trust		11.3		8.9			2.4			—
Total		$	258.8	$	220.2		$	38.6		$	—
Other Great Plains Energy
Assets
Interest rate derivative instruments ^(c)		$	77.4	$	—		$	—		$	77.4
Total		$	77.4	$	—		$	—		$	77.4
Great Plains Energy
Assets
Nuclear decommissioning trust ^(a)		$	247.5	$	211.3		$	36.2		$	—
Self-insured health plan trust ^(b)		11.3		8.9			2.4			—
Interest rate derivative instruments ^(c)		77.4		—			—			77.4
Total		$	336.2	$	220.2		$	38.6		$	77.4



Description	December 31 2016			Level 1			Level 2			Level 3
KCP&L		(millions)
Assets
Nuclear decommissioning trust ^(a)
Equity securities		$	153.9		$	153.9		$	—		$	—
Debt securities
U.S. Treasury		27.8			27.8			—			—
U.S. Agency		1.7			—			1.7			—
State and local obligations		3.2			—			3.2			—
Corporate bonds		32.4			—			32.4			—
Foreign governments		0.1			—			0.1			—
Cash equivalents		3.8			3.8			—			—
Total nuclear decommissioning trust		222.9			185.5			37.4			—
Self-insured health plan trust ^(b)
Equity securities		0.9			0.9			—			—
Debt securities		4.8			0.1			4.7			—
Cash and cash equivalents		5.6			5.6			—			—
Total self-insured health plan trust		11.3			6.6			4.7			—
Total		$	234.2		$	192.1		$	42.1		$	—
Other Great Plains Energy
Assets
Interest rate derivative instruments ^(c)		$	79.3		$	—		$	—		$	79.3
Total		$	79.3		$	—		$	—		$	79.3
Great Plains Energy
Assets
Nuclear decommissioning trust ^(a)		$	222.9		$	185.5		$	37.4		$	—
Self-insured health plan trust ^(b)		11.3			6.6			4.7			—
Interest rate derivative instruments ^(c)		79.3			—			—			79.3
Total		$	313.5		$	192.1		$	42.1		$	79.3


^(a)	Fair value is based on quoted market prices of the investments held by the fund and/or valuation models.


^(b)	Fair value is based on quoted market prices of the investments held by the trust. Debt securities classified as Level 1 are comprised of U.S. Treasury securities. Debt securities classified as Level 2 are comprised of corporate bonds, U.S. Agency, state and local obligations, and other asset-backed securities.

^(c)

At September 30, 2017, the fair value of interest rate derivative instruments is based on the settlement value of $140.6 million discounted by a contingency factor of 0.45 that management believes is representative of what a market participant would use in valuing these instruments in order to account for the contingent nature of the cash settlement of these instruments. At December 31, 2016, the fair value of interest rate derivative instruments is determined by calculating the net present value of expected payments and receipts under the interest rate swaps using observable market inputs including interest rates and London Interbank Offered Rate (LIBOR) swap rates discounted by a contingency factor of 0.35. A decrease in the contingency factor would result in a higher fair value measurement. The contingency factor will increase in response to facts and circumstances that in the view of a market participant, would increase the likelihood that the merger with Westar is not consummated. Because of the unobservable nature of the contingency factor, the interest rate derivatives have been classified as Level 3.

The following tables reconcile the beginning and ending balances for all Level 3 assets and liabilities measured at fair value on a recurring basis.



Great Plains Energy
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
	Derivative Instruments
	2017			2016
	(millions)
Net liability at July 1	$	(7.9	)	$	(77.0	)
Total realized/unrealized gains (losses):
included in interest charges	28.2			(1.8		)
included in loss on Series B Preferred Stock dividend make-whole provisions	(67.7		)	—
Settlements	124.8			—
Net asset (liability) at September 30	$	77.4		$	(78.8	)
Total unrealized gains (losses) relating to assets and liabilities still on the consolidated balance sheet at September 30:
included in interest charges	$	28.2		$	(1.8	)

Great Plains Energy
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
	Derivative Instruments
	2017			2016
	(millions)
Net asset at January 1	$	79.3		$	—
Total realized/unrealized losses:
included in interest charges	(1.9		)	(78.8		)
included in loss on Series B Preferred Stock dividend make-whole provisions	(124.8		)	—
Settlements	124.8			—
Net asset (liability) at September 30	$	77.4		$	(78.8	)
Total unrealized losses relating to assets and liabilities still on the consolidated balance sheet at September 30:
included in interest charges	$	(1.9	)	$	(78.8	)

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Accumulated Other Comprehensive Income (Loss)

9 Months Ended

Sep. 30, 2017

Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]

Accumulated Other Comprehensive Income (Loss) [Text Block]

17. ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)

The following tables reflect the change in the balances of each component of accumulated other comprehensive loss for Great Plains Energy and KCP&L.



Great Plains Energy
	Gains and Losses on Cash Flow Hedges^(a)				Defined Benefit Pension Items^(a)				Total^(a)
	(millions)
Year to Date September 30, 2017
Beginning balance January 1		$	(4.5	)		$	(2.1	)	$	(6.6	)
Amounts reclassified from accumulated other comprehensive loss		4.1				0.3			4.4
Net current period other comprehensive income		4.1				0.3			4.4
Ending balance September 30		$	(0.4	)		$	(1.8	)	$	(2.2	)
Year to Date September 30, 2016
Beginning balance January 1		$	(10.1	)		$	(1.9	)	$	(12.0	)
Amounts reclassified from accumulated other comprehensive loss		4.1				0.4			4.5
Net current period other comprehensive income		4.1				0.4			4.5
Ending balance September 30		$	(6.0	)		$	(1.5	)	$	(7.5	)

^(a) Net of tax



KCP&L
	Gains and Losses on Cash Flow Hedges^(a)
	(millions)
Year to Date September 30, 2017
Beginning balance January 1		$	(4.2	)
Amounts reclassified from accumulated other comprehensive loss		3.8
Net current period other comprehensive income		3.8
Ending balance September 30		$	(0.4	)
Year to Date September 30, 2016
Beginning balance January 1		$	(9.6	)
Amounts reclassified from accumulated other comprehensive loss		4.0
Net current period other comprehensive income		4.0
Ending balance September 30		$	(5.6	)

^(a) Net of tax

The following tables reflect the effect on certain line items of net income from amounts reclassified out of each component of accumulated other comprehensive loss for Great Plains Energy and KCP&L.



Great Plains Energy
Details about Accumulated Other Comprehensive Loss Components	Amount Reclassified from Accumulated Other Comprehensive Loss						Affected Line Item in the Income Statement
Three Months Ended September 30	2017			2016
	(millions)
Gains and (losses) on cash flow hedges (effective portion)
Interest rate contracts	$	(2.1	)	$	(2.3	)	Interest charges
	(2.1		)	(2.3		)	Income before income tax expense and income from equity investments
	0.8			1.0			Income tax benefit
	$	(1.3	)	$	(1.3	)	Net income (loss)
Amortization of defined benefit pension items
Net losses included in net periodic benefit costs	$	(0.2	)	$	(0.2	)	Utility operating and maintenance expenses
	(0.2		)	(0.2		)	Income before income tax expense and income from equity investments
	0.1			—			Income tax benefit
	$	(0.1	)	$	(0.2	)	Net income (loss)

Total reclassifications, net of tax	$	(1.4	)	$	(1.5	)	Net income (loss)

Great Plains Energy
Details about Accumulated Other Comprehensive Loss Components	Amount Reclassified from Accumulated Other Comprehensive Loss						Affected Line Item in the Income Statement
Year to Date September 30	2017			2016
	(millions)
Gains and (losses) on cash flow hedges (effective portion)
Interest rate contracts	$	(6.7	)	$	(6.9	)	Interest charges
	(6.7		)	(6.9		)	Income before income tax expense and income from equity investments
	2.6			2.8			Income tax benefit
	$	(4.1	)	$	(4.1	)	Net income (loss)
Amortization of defined benefit pension items
Net losses included in net periodic benefit costs	$	(0.6	)	$	(0.6	)	Utility operating and maintenance expenses
	(0.6		)	(0.6		)	Income before income tax expense and income from equity investments
	0.3			0.2			Income tax benefit
	$	(0.3	)	$	(0.4	)	Net income (loss)

Total reclassifications, net of tax	$	(4.4	)	$	(4.5	)	Net income (loss)



KCP&L
Details about Accumulated Other Comprehensive Loss Components	Amount Reclassified from Accumulated Other Comprehensive Loss						Affected Line Item in the Income Statement
Three Months Ended September 30	2017			2016
	(millions)
Gains and (losses) on cash flow hedges (effective portion)
Interest rate contracts	$	(1.9	)	$	(2.2	)	Interest charges
	(1.9		)	(2.2		)	Income before income tax expense
	0.7			1.0			Income tax benefit
Total reclassifications, net of tax	$	(1.2	)	$	(1.2	)	Net income

KCP&L
Details about Accumulated Other Comprehensive Loss Components	Amount Reclassified from Accumulated Other Comprehensive Loss						Affected Line Item in the Income Statement
Year to Date September 30	2017			2016
	(millions)
Gains and (losses) on cash flow hedges (effective portion)
Interest rate contracts	$	(6.3	)	$	(6.6	)	Interest charges
	(6.3		)	(6.6		)	Income before income tax expense
	2.5			2.6			Income tax benefit
Total reclassifications, net of tax	$	(3.8	)	$	(4.0	)	Net income

- Definition

The entire disclosure for comprehensive income, which includes, but is not limited to, 1) the amount of income tax expense or benefit allocated to each component of other comprehensive income, including reclassification adjustments, 2) the reclassification adjustments for each classification of other comprehensive income and 3) the ending accumulated balances for each component of comprehensive income.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=6522872

+ Details

Taxes

9 Months Ended

Sep. 30, 2017

Income Tax Disclosure [Abstract]

Income Tax Disclosure [Text Block]

18. TAXES

Components of income tax expense are detailed in the following tables.



	Three Months Ended September 30						Year to Date September 30
Great Plains Energy	2017			2016			2017			2016
Current income taxes	(millions)
Federal	$	(1.1	)	$	—		$	(1.1	)	$	(0.1	)
State	(0.3		)	—			(0.3		)	0.3
Total	(1.4		)	—			(1.4		)	0.2
Deferred income taxes
Federal	86.6			70.1			74.7			91.5
State	17.5			13.0			15.0			18.4
Total	104.1			83.1			89.7			109.9
Investment tax credit
Deferral	—			—			—			2.5
Amortization	(0.4		)	(0.4		)	(1.1		)	(1.1		)
Total	(0.4		)	(0.4		)	(1.1		)	1.4
Income tax expense	$	102.3		$	82.7		$	87.2		$	111.5



	Three Months Ended September 30						Year to Date September 30
KCP&L	2017			2016			2017			2016
Current income taxes	(millions)
Federal	$	41.8		$	35.4		$	56.2		$	36.6
State	7.6			6.4			10.2			6.7
Total	49.4			41.8			66.4			43.3
Deferred income taxes
Federal	10.3			22.5			27.2			61.5
State	2.8			4.5			6.2			12.5
Total	13.1			27.0			33.4			74.0
Investment tax credit amortization	(0.3		)	(0.3		)	(0.8		)	(0.8		)
Income tax expense	$	62.2		$	68.5		$	99.0		$	116.5

Effective Income Tax Rates

Effective income tax rates reflected in the financial statements and the reasons for their differences from the statutory federal rates are detailed in the following tables.



	Three Months Ended September 30				Year to Date September 30
Great Plains Energy	2017		2016		2017		2016
Federal statutory income tax rate	35.0	%	35.0	%	35.0	%	35.0	%
Differences between book and tax depreciation not normalized	(0.6	)	(0.3	)	(0.9	)	(0.2	)
Amortization of investment tax credits	(1.5	)	(0.2	)	(1.9	)	(0.4	)
Federal income tax credits	(7.8	)	(1.1	)	(10.0	)	(2.7	)
State income taxes	9.8		3.9		11.5		4.0
Transaction-related costs	54.1		1.0		70.8		1.0
Valuation allowance	1.7		—		2.4		—
Other	(0.1	)	(0.1	)	0.5		—
Effective income tax rate	90.6	%	38.2	%	107.4	%	36.7	%



	Three Months Ended September 30				Year to Date September 30
KCP&L	2017		2016		2017		2016
Federal statutory income tax rate	35.0	%	35.0	%	35.0	%	35.0	%
Differences between book and tax depreciation not normalized	(0.6	)	(0.5	)	(0.5	)	(0.3	)
Amortization of investment tax credits	(0.4	)	(0.1	)	(0.4	)	(0.2	)
Federal income tax credits	(3.1	)	(1.2	)	(2.6	)	(2.3	)
State income taxes	3.8		3.8		3.8		3.8
Valuation allowance	0.7		—		0.4		—
Other	(0.1	)	(0.2	)	0.1		(0.1	)
Effective income tax rate	35.3	%	36.8	%	35.8	%	35.9	%

The increase in Great Plains Energy's effective income tax rate for the three months ended and year to date September 30, 2017, compared to the same periods in 2016, is primarily driven by significant transaction-related costs incurred in connection with the anticipated merger with Westar and the previous plan to acquire Westar that are not deductible for tax purposes.

Segments and Related Information

9 Months Ended

Sep. 30, 2017

Segment Reporting [Abstract]

Segments and Related Information

19. SEGMENTS AND RELATED INFORMATION

Great Plains Energy has one reportable segment based on its method of internal reporting, which segregates reportable segments based on products and services, management responsibility and regulation. The one reportable business segment is electric utility, consisting of KCP&L, GMO's regulated utility operations and GMO Receivables Company. Other includes GMO activity other than its regulated utility operations, GPETHC and unallocated corporate charges including certain costs to achieve the anticipated merger with Westar. The summary of significant accounting policies applies to the reportable segment. Segment performance is evaluated based on net income (loss).

The following tables reflect summarized financial information concerning Great Plains Energy's reportable segment.



Three Months Ended September 30, 2017	Electric Utility				Other				Eliminations			Great Plains Energy
		(millions)
Operating revenues		$	857.2			$	—			$	—		$	857.2
Depreciation and amortization		(92.7		)		—				—			(92.7		)
Interest (charges) income		(49.1		)		10.1				8.1			(30.9		)
Income tax expense		(92.7		)		(9.6		)		—			(102.3		)
Net income (loss)		162.9				(152.4		)		—			10.5

Year to Date September 30, 2017	Electric Utility				Other				Eliminations			Great Plains Energy
		(millions)
Operating revenues		$	2,110.5			$	—			$	—		$	2,110.5
Depreciation and amortization		(277.7		)		—				—			(277.7		)
Interest (charges) income		(149.3		)		(117.6		)		24.1			(242.8		)
Income tax (expense) benefit		(142.6		)		55.4				—			(87.2		)
Net income (loss)		247.4				(253.5		)		—			(6.1		)

Three Months Ended September 30, 2016	Electric Utility				Other				Eliminations			Great Plains Energy
		(millions)
Operating revenues		$	856.8			$	—			$	—		$	856.8
Depreciation and amortization		(86.4		)		—				—			(86.4		)
Interest (charges) income		(49.3		)		(26.4		)		8.1			(67.6		)
Income tax (expense) benefit		(95.9		)		13.2				—			(82.7		)
Net income (loss)		161.1				(27.5		)		—			133.6

Year to Date September 30, 2016	Electric Utility				Other				Eliminations			Great Plains Energy
		(millions)
Operating revenues		$	2,099.7			$	—			$	—		$	2,099.7
Depreciation and amortization		(256.9		)		—				—			(256.9		)
Interest (charges) income		(147.4		)		(128.4		)		24.1			(251.7		)
Income tax (expense) benefit		(160.2		)		48.7				—			(111.5		)
Net income (loss)		278.4				(86.4		)		—			192.0



	Electric Utility			Other			Eliminations				Great Plains Energy
September 30, 2017		(millions)
Assets		$	11,586.7		$	1,244.0		$	(401.8	)		$	12,428.9
Capital expenditures ^(a)		392.5			—			—				392.5
December 31, 2016
Assets		$	11,444.2		$	2,461.3		$	(335.5	)		$	13,570.0
Capital expenditures ^(a)		609.4			—			—				609.4

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8981-108599

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e9038-108599

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8971-108599

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8595-108599

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8380-108599

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8933-108599

Reference 7: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 26
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8844-108599

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8984-108599

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 40
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e9031-108599

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e9054-108599

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8538-108599

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Paragraph 29
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8864-108599

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 31
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8924-108599

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8906-108599

+ Details

Plant to be Retired, Net	9 Months Ended
Plant to be Retired, Net	Sep. 30, 2017
Plant to be Retired, Net [Abstract]
Plant to be Retired, Net Disclosure	20. PLANT TO BE RETIRED, NET When Great Plains Energy and KCP&L retire utility plant, the original cost, net of salvage, is charged to accumulated depreciation. However, when it becomes probable an asset will be retired significantly in advance of its original expected useful life and in the near term, the cost of the asset and related accumulated depreciation is recognized as a separate asset as a probable abandonment. If the asset is still in service, the net amount is classified as plant to be retired, net on the consolidated balance sheets. If the asset is no longer in service, the net amount is classified in regulatory assets on the consolidated balance sheets. Great Plains Energy and KCP&L must also assess the probability of full recovery of the remaining net book value of the abandonment. The net book value that may be retained as an asset on the balance sheet for the abandonment is dependent upon amounts that may be recovered through regulated rates, including any return. An impairment charge, if any, would equal the difference between the remaining net book value of the asset and the present value of the future revenues expected from the asset. In June 2017, Great Plains Energy and KCP&L announced the expected retirement of certain older generating units, including GMO's Sibley No. 3 Unit, over the next several years. As of September 30, 2017, Great Plains Energy has determined that Sibley No. 3 Unit meets the criteria to be considered probable of abandonment and has classified its remaining net book value of $146.3 million within plant to be retired, net on its consolidated balance sheet. The Company is currently allowed a full recovery of and a full return on Sibley No. 3 Unit in rates and has concluded that no impairment is required as of September 30, 2017.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2017

Accounting Policies [Abstract]

Organization [Policy Text Block]

Organization


•	KCP&L is an integrated, regulated electric utility that provides electricity to customers primarily in the states of Missouri and Kansas. KCP&L has one active wholly owned subsidiary, Kansas City Power & Light Receivables Company (KCP&L Receivables Company).

•

Each of Great Plains Energy's and KCP&L's consolidated financial statements includes the accounts of their subsidiaries. Intercompany transactions have been eliminated.

Great Plains Energy's sole reportable business segment is electric utility. See Note 19 for additional information.

Basic and Diluted Earnings per Common Share Calculation [Policy Text Block]

Basic and Diluted Earnings (Loss) per Common Share Calculation

New Accounting Pronouncements, Policy [Policy Text Block]

New Accounting Standards

Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2017

Accounting Policies [Abstract]

Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]

The following table reconciles Great Plains Energy's basic and diluted EPS.



	Three Months Ended September 30				Year to Date September 30
	2017		2016		2017			2016
Income (loss)	(millions, except per share amounts)
Net income (loss)	$	10.5	$	133.6	$	(6.1	)	$	192.0
Less: preferred stock dividend requirements and redemption premium	7.1		0.9		37.3			1.7
Earnings (loss) available for common shareholders	$	3.4	$	132.7	$	(43.4	)	$	190.3
Common Shares Outstanding
Average number of common shares outstanding	215.6		154.6		215.5			154.5
Add: effect of dilutive securities	0.1		0.3		—			0.4
Diluted average number of common shares outstanding	215.7		154.9		215.5			154.9
Basic and diluted EPS	$	0.02	$	0.86	$	(0.20	)	$	1.23

Supplemental Cash Flow Information (Tables)

9 Months Ended

Sep. 30, 2017

Supplemental Cash Flow Elements [Abstract]

Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]



Great Plains Energy Other Operating Activities
Year to Date September 30	2017			2016
Cash flows affected by changes in:	(millions)
Receivables	$	(20.4	)	$	(45.9	)
Accounts receivable pledged as collateral	(22.6		)	(15.0		)
Fuel inventories	19.6			19.8
Materials and supplies	(9.7		)	(5.3		)
Accounts payable	(125.7		)	(119.8		)
Accrued taxes	92.4			97.2
Accrued interest	6.6			16.7
Deferred refueling outage costs	12.1			7.5
Pension and post-retirement benefit obligations	52.0			53.2
Allowance for equity funds used during construction	(3.4		)	(4.3		)
Fuel recovery mechanisms	(10.1		)	(16.8		)
Other	11.9			(11.7		)
Total other operating activities	$	2.7		$	(24.4	)
Cash paid during the period:
Interest	$	198.7		$	130.2
Income taxes	$	0.1		$	0.2
Non-cash investing activities:
Liabilities accrued for capital expenditures	$	31.2		$	30.7



KCP&L Other Operating Activities
Year to Date September 30	2017			2016
Cash flows affected by changes in:	(millions)
Receivables	$	(19.5	)	$	(53.5	)
Accounts receivable pledged as collateral	(20.0		)	—
Fuel inventories	10.8			12.7
Materials and supplies	(7.2		)	(3.8		)
Accounts payable	(75.1		)	(80.3		)
Accrued taxes	122.7			179.3
Accrued interest	8.1			8.9
Deferred refueling outage costs	12.1			7.5
Pension and post-retirement benefit obligations	48.6			53.7
Allowance for equity funds used during construction	(3.4		)	(4.0		)
Fuel recovery mechanisms	7.6			(31.0		)
Other	(16.0		)	(14.8		)
Total other operating activities	$	68.7		$	74.7
Cash paid during the period:
Interest	$	88.6		$	86.7
Income taxes	$	4.9		$	—
Non-cash investing activities:
Liabilities accrued for capital expenditures	$	24.7		$	25.7

Receivables (Tables)

9 Months Ended

Sep. 30, 2017

Receivables [Abstract]

Schedule of receivables [Table Text Block]

Great Plains Energy's and KCP&L's receivables are detailed in the following table.



	September 30				December 31
		2017				2016
Great Plains Energy		(millions)
Customer accounts receivable - billed		$	25.0			$	26.2
Customer accounts receivable - unbilled		114.9				79.1
Allowance for doubtful accounts - customer accounts receivable		(5.4		)		(4.0		)
Other receivables		51.9				64.7
Total		$	186.4			$	166.0
KCP&L
Customer accounts receivable - billed		$	24.4			$	25.5
Customer accounts receivable - unbilled		80.0				63.7
Allowance for doubtful accounts - customer accounts receivable		(2.8		)		(1.8		)
Other receivables		42.2				51.7
Total		$	143.8			$	139.1

Nuclear Plant (Tables)

9 Months Ended

Sep. 30, 2017

Nuclear Plant [Abstract]

Changes in nuclear decommissioning trust fund

The following table summarizes the change in Great Plains Energy's and KCP&L's nuclear decommissioning trust fund.



	September 30			December 31
	2017			2016
Decommissioning Trust		(millions)
Beginning balance January 1		$	222.9		$	200.7
Contributions		2.5			3.3
Earned income, net of fees		3.1			4.1
Net realized gains		0.5			0.3
Net unrealized gains		18.5			14.5
Ending balance		$	247.5		$	222.9

Detail of assets held in nuclear decommissioning trust fund

The nuclear decommissioning trust is reported at fair value on the balance sheets and is invested in assets as detailed in the following table.



	September 30, 2017												December 31, 2016
	Cost Basis		Unrealized Gains			Unrealized Losses				Fair Value			Cost Basis			Unrealized Gains			Unrealized Losses				Fair Value
	(millions)
Equity securities	$	95.8		$	79.2		$	(0.8	)		$	174.2		$	93.3		$	62.1		$	(1.5	)		$	153.9
Debt securities	67.3			2.7			(0.2		)		69.8			63.4			2.3			(0.5		)		65.2
Other	3.5			—			—				3.5			3.8			—			—				3.8
Total	$	166.6		$	81.9		$	(1.0	)		$	247.5		$	160.5		$	64.4		$	(2.0	)		$	222.9

Gains and losses from the sale of securities by the nuclear decommissioning trust fund

The following table summarizes the realized gains and losses from the sale of securities in the nuclear decommissioning trust fund.



	Three Months Ended September 30						Year to Date September 30
	2017			2016			2017			2016
	(millions)
Realized gains	$	0.7		$	0.6		$	1.1		$	1.5
Realized losses	(0.5		)	(0.3		)	(0.6		)	(1.3		)

Nuclear plant decommissioning costs [Table Text Block]



		KCC			MPSC
	(millions)
Current cost of decommissioning (in 2017 dollars)
Total Station		$	813.7		$	813.7
KCP&L's 47% Share		382.5			382.5

Future cost of decommissioning (in 2045-2053 dollars) ^(a)
Total Station		$	1,982.4		$	2,137.8
KCP&L's 47% Share		931.7			1,004.8

Annual escalation factor		2.91		%	3.16		%
Annual return on trust assets ^(b)		5.64		%	5.46		%

^(a)Total future cost over an eight year decommissioning period

Pension Plans and Other Employee Benefits (Tables)

9 Months Ended

Sep. 30, 2017

Defined Benefit Plan Disclosure [Line Items]

Schedule of Net Benefit Costs [Table Text Block]

The following tables provide Great Plains Energy's components of net periodic benefit costs prior to the effects of capitalization and sharing with joint owners of power plants.



	Pension Benefits						Other Benefits
Three Months Ended September 30	2017			2016			2017			2016
Components of net periodic benefit costs	(millions)
Service cost	$	11.0		$	10.5		$	0.5		$	0.7
Interest cost	13.4			13.2			1.4			1.5
Expected return on plan assets	(12.8		)	(12.3		)	(0.7		)	(0.8		)
Prior service cost	0.2			0.2			—			0.3
Recognized net actuarial (gain)/loss	12.4			13.0			(0.1		)	(0.3		)
Net periodic benefit costs before regulatory adjustment	24.2			24.6			1.1			1.4
Regulatory adjustment	(0.2		)	(1.1		)	0.1			1.4
Net periodic benefit costs	$	24.0		$	23.5		$	1.2		$	2.8

	Pension Benefits						Other Benefits
Year to Date September 30	2017			2016			2017			2016
Components of net periodic benefit costs	(millions)
Service cost	$	33.0		$	31.5		$	1.5		$	2.0
Interest cost	40.2			39.7			4.1			4.6
Expected return on plan assets	(38.4		)	(36.9		)	(2.0		)	(2.3		)
Prior service cost	0.6			0.5			—			0.9
Recognized net actuarial (gain)/loss	37.2			38.9			(0.3		)	(1.1		)
Net periodic benefit costs before regulatory adjustment	72.6			73.7			3.3			4.1
Regulatory adjustment	2.3			(3.1		)	1.9			4.4
Net periodic benefit costs	$	74.9		$	70.6		$	5.2		$	8.5

Equity Compensation (Tables)

9 Months Ended

Sep. 30, 2017

Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]

Equity compensation expense and associated income tax benefits



	Three Months Ended September 30					Year to Date September 30
	Three Months Ended September 30					Year to Date September 30
		2017		2016		2017		2016
Great Plains Energy		(millions)
Equity compensation expense		$	1.8	$	0.4	$	4.4	$	3.9
Income tax benefit		0.6		—		1.7		1.3
KCP&L
Equity compensation expense		$	1.2	$	0.2	$	2.9	$	2.5
Income tax benefit		0.4		—		1.2		0.8

Performance share activity



	Performance Shares			Grant Date Fair Value*
Beginning balance January 1, 2017		625,100			$	28.13
Granted		236,433			31.26
Earned		(212,992	)		28.48
Forfeited		(97,036	)		29.24
Ending balance September 30, 2017		551,505			29.12

Restricted stock activity



	Nonvested Restricted Stock			Grant Date Fair Value*
Beginning balance January 1, 2017		249,672			$	27.20
Granted and issued		78,840			28.60
Vested		(109,813	)		27.48
Forfeited		(22,521	)		27.26
Ending balance September 30, 2017		196,178			27.81

Long-Term Debt (Tables)

9 Months Ended

Sep. 30, 2017

Debt Disclosure [Abstract]

Schedule of Debt [Table Text Block]

Great Plains Energy's and KCP&L's long-term debt is detailed in the following table.



		September 30				December 31
	Year Due	2017				2016
KCP&L			(millions)
General Mortgage Bonds
2.95% EIRR bonds	2023		$	79.5			$	110.5
7.15% Series 2009A (8.59% rate)^(a)	2019		400.0				400.0
Senior Notes
5.85% Series (5.72% rate)^(a)			—				250.0
6.375% Series (7.49% rate)^(a)	2018		350.0				350.0
3.15% Series	2023		300.0				300.0
3.65% Series	2025		350.0				350.0
6.05% Series (5.78% rate)^(a)	2035		250.0				250.0
5.30% Series	2041		400.0				400.0
4.20% Series	2047		300.0				—
EIRR Bonds
0.889% Series 2007A and 2007B^(b)	2035		146.5				146.5
2.875% Series 2008	2038		23.4				23.4
Current maturities			(350.0		)		(281.0		)
Unamortized discount and debt issuance costs			(17.7		)		(15.4		)
Total KCP&L excluding current maturities^(c)			2,231.7				2,284.0
Other Great Plains Energy
GMO First Mortgage Bonds 9.44% Series	2018-2021		4.6				5.7
GMO Senior Notes
8.27% Series	2021		80.9				80.9
3.49% Series A	2025		125.0				125.0
4.06% Series B	2033		75.0				75.0
4.74% Series C	2043		150.0				150.0
GMO Medium Term Notes
7.33% Series	2023		3.0				3.0
7.17% Series	2023		7.0				7.0
Great Plains Energy Senior Notes
6.875% Series (7.33% rate)^(a)			—				100.0
4.85% Series	2021		350.0				350.0
5.292% Series	2022		287.5				287.5
Current maturities			(1.1		)		(101.1		)
Unamortized discount and premium, net and debt issuance costs			(1.6		)		(1.8		)
Total Great Plains Energy excluding current maturities^(c)			$	3,312.0			$	3,365.2


^(a)	Rate after amortizing gains/losses recognized in other comprehensive income (OCI) on settlements of interest rate hedging instruments


^(b)	Variable rate


^(c)	At September 30, 2017, and December 31, 2016, does not include $50.0 million and $21.9 million of secured Series 2005 Environmental Improvement Revenue Refunding (EIRR) bonds because the bonds were repurchased in September 2015 and are held by KCP&L

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2017

Fair Value Disclosures [Abstract]

Fair value of assets and liabilities

The following tables include Great Plains Energy's and KCP&L's balances of financial assets and liabilities measured at fair value on a recurring basis.



Description	September 30 2017			Level 1		Level 2			Level 3
KCP&L		(millions)
Assets
Nuclear decommissioning trust ^(a)
Equity securities		$	174.2	$	174.2		$	—		$	—
Debt securities
U.S. Treasury		33.6		33.6			—			—
U.S. Agency		0.4		—			0.4			—
State and local obligations		2.5		—			2.5			—
Corporate bonds		33.2		—			33.2			—
Foreign governments		0.1		—			0.1			—
Cash equivalents		2.9		2.9			—			—
Other		0.6		0.6			—			—
Total nuclear decommissioning trust		247.5		211.3			36.2			—
Self-insured health plan trust ^(b)
Equity securities		0.4		0.4			—			—
Debt securities		2.8		0.4			2.4			—
Cash and cash equivalents		8.1		8.1			—			—
Total self-insured health plan trust		11.3		8.9			2.4			—
Total		$	258.8	$	220.2		$	38.6		$	—
Other Great Plains Energy
Assets
Interest rate derivative instruments ^(c)		$	77.4	$	—		$	—		$	77.4
Total		$	77.4	$	—		$	—		$	77.4
Great Plains Energy
Assets
Nuclear decommissioning trust ^(a)		$	247.5	$	211.3		$	36.2		$	—
Self-insured health plan trust ^(b)		11.3		8.9			2.4			—
Interest rate derivative instruments ^(c)		77.4		—			—			77.4
Total		$	336.2	$	220.2		$	38.6		$	77.4



Description	December 31 2016			Level 1			Level 2			Level 3
KCP&L		(millions)
Assets
Nuclear decommissioning trust ^(a)
Equity securities		$	153.9		$	153.9		$	—		$	—
Debt securities
U.S. Treasury		27.8			27.8			—			—
U.S. Agency		1.7			—			1.7			—
State and local obligations		3.2			—			3.2			—
Corporate bonds		32.4			—			32.4			—
Foreign governments		0.1			—			0.1			—
Cash equivalents		3.8			3.8			—			—
Total nuclear decommissioning trust		222.9			185.5			37.4			—
Self-insured health plan trust ^(b)
Equity securities		0.9			0.9			—			—
Debt securities		4.8			0.1			4.7			—
Cash and cash equivalents		5.6			5.6			—			—
Total self-insured health plan trust		11.3			6.6			4.7			—
Total		$	234.2		$	192.1		$	42.1		$	—
Other Great Plains Energy
Assets
Interest rate derivative instruments ^(c)		$	79.3		$	—		$	—		$	79.3
Total		$	79.3		$	—		$	—		$	79.3
Great Plains Energy
Assets
Nuclear decommissioning trust ^(a)		$	222.9		$	185.5		$	37.4		$	—
Self-insured health plan trust ^(b)		11.3			6.6			4.7			—
Interest rate derivative instruments ^(c)		79.3			—			—			79.3
Total		$	313.5		$	192.1		$	42.1		$	79.3


^(a)	Fair value is based on quoted market prices of the investments held by the fund and/or valuation models.


^(b)	Fair value is based on quoted market prices of the investments held by the trust. Debt securities classified as Level 1 are comprised of U.S. Treasury securities. Debt securities classified as Level 2 are comprised of corporate bonds, U.S. Agency, state and local obligations, and other asset-backed securities.

^(c)

Unobservable inputs reconciliation

The following tables reconcile the beginning and ending balances for all Level 3 assets and liabilities measured at fair value on a recurring basis.



Great Plains Energy
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
	Derivative Instruments
	2017			2016
	(millions)
Net liability at July 1	$	(7.9	)	$	(77.0	)
Total realized/unrealized gains (losses):
included in interest charges	28.2			(1.8		)
included in loss on Series B Preferred Stock dividend make-whole provisions	(67.7		)	—
Settlements	124.8			—
Net asset (liability) at September 30	$	77.4		$	(78.8	)
Total unrealized gains (losses) relating to assets and liabilities still on the consolidated balance sheet at September 30:
included in interest charges	$	28.2		$	(1.8	)

Great Plains Energy
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
	Derivative Instruments
	2017			2016
	(millions)
Net asset at January 1	$	79.3		$	—
Total realized/unrealized losses:
included in interest charges	(1.9		)	(78.8		)
included in loss on Series B Preferred Stock dividend make-whole provisions	(124.8		)	—
Settlements	124.8			—
Net asset (liability) at September 30	$	77.4		$	(78.8	)
Total unrealized losses relating to assets and liabilities still on the consolidated balance sheet at September 30:
included in interest charges	$	(1.9	)	$	(78.8	)

Accumulated Other Comprehensive Income (Loss) (Tables)

9 Months Ended

Sep. 30, 2017

Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]

Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]

The following tables reflect the change in the balances of each component of accumulated other comprehensive loss for Great Plains Energy and KCP&L.



Great Plains Energy
	Gains and Losses on Cash Flow Hedges^(a)				Defined Benefit Pension Items^(a)				Total^(a)
	(millions)
Year to Date September 30, 2017
Beginning balance January 1		$	(4.5	)		$	(2.1	)	$	(6.6	)
Amounts reclassified from accumulated other comprehensive loss		4.1				0.3			4.4
Net current period other comprehensive income		4.1				0.3			4.4
Ending balance September 30		$	(0.4	)		$	(1.8	)	$	(2.2	)
Year to Date September 30, 2016
Beginning balance January 1		$	(10.1	)		$	(1.9	)	$	(12.0	)
Amounts reclassified from accumulated other comprehensive loss		4.1				0.4			4.5
Net current period other comprehensive income		4.1				0.4			4.5
Ending balance September 30		$	(6.0	)		$	(1.5	)	$	(7.5	)

^(a) Net of tax



KCP&L
	Gains and Losses on Cash Flow Hedges^(a)
	(millions)
Year to Date September 30, 2017
Beginning balance January 1		$	(4.2	)
Amounts reclassified from accumulated other comprehensive loss		3.8
Net current period other comprehensive income		3.8
Ending balance September 30		$	(0.4	)
Year to Date September 30, 2016
Beginning balance January 1		$	(9.6	)
Amounts reclassified from accumulated other comprehensive loss		4.0
Net current period other comprehensive income		4.0
Ending balance September 30		$	(5.6	)

^(a) Net of tax

Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]

The following tables reflect the effect on certain line items of net income from amounts reclassified out of each component of accumulated other comprehensive loss for Great Plains Energy and KCP&L.



Great Plains Energy
Details about Accumulated Other Comprehensive Loss Components	Amount Reclassified from Accumulated Other Comprehensive Loss						Affected Line Item in the Income Statement
Three Months Ended September 30	2017			2016
	(millions)
Gains and (losses) on cash flow hedges (effective portion)
Interest rate contracts	$	(2.1	)	$	(2.3	)	Interest charges
	(2.1		)	(2.3		)	Income before income tax expense and income from equity investments
	0.8			1.0			Income tax benefit
	$	(1.3	)	$	(1.3	)	Net income (loss)
Amortization of defined benefit pension items
Net losses included in net periodic benefit costs	$	(0.2	)	$	(0.2	)	Utility operating and maintenance expenses
	(0.2		)	(0.2		)	Income before income tax expense and income from equity investments
	0.1			—			Income tax benefit
	$	(0.1	)	$	(0.2	)	Net income (loss)

Total reclassifications, net of tax	$	(1.4	)	$	(1.5	)	Net income (loss)

Great Plains Energy
Details about Accumulated Other Comprehensive Loss Components	Amount Reclassified from Accumulated Other Comprehensive Loss						Affected Line Item in the Income Statement
Year to Date September 30	2017			2016
	(millions)
Gains and (losses) on cash flow hedges (effective portion)
Interest rate contracts	$	(6.7	)	$	(6.9	)	Interest charges
	(6.7		)	(6.9		)	Income before income tax expense and income from equity investments
	2.6			2.8			Income tax benefit
	$	(4.1	)	$	(4.1	)	Net income (loss)
Amortization of defined benefit pension items
Net losses included in net periodic benefit costs	$	(0.6	)	$	(0.6	)	Utility operating and maintenance expenses
	(0.6		)	(0.6		)	Income before income tax expense and income from equity investments
	0.3			0.2			Income tax benefit
	$	(0.3	)	$	(0.4	)	Net income (loss)

Total reclassifications, net of tax	$	(4.4	)	$	(4.5	)	Net income (loss)



KCP&L
Details about Accumulated Other Comprehensive Loss Components	Amount Reclassified from Accumulated Other Comprehensive Loss						Affected Line Item in the Income Statement
Three Months Ended September 30	2017			2016
	(millions)
Gains and (losses) on cash flow hedges (effective portion)
Interest rate contracts	$	(1.9	)	$	(2.2	)	Interest charges
	(1.9		)	(2.2		)	Income before income tax expense
	0.7			1.0			Income tax benefit
Total reclassifications, net of tax	$	(1.2	)	$	(1.2	)	Net income

KCP&L
Details about Accumulated Other Comprehensive Loss Components	Amount Reclassified from Accumulated Other Comprehensive Loss						Affected Line Item in the Income Statement
Year to Date September 30	2017			2016
	(millions)
Gains and (losses) on cash flow hedges (effective portion)
Interest rate contracts	$	(6.3	)	$	(6.6	)	Interest charges
	(6.3		)	(6.6		)	Income before income tax expense
	2.5			2.6			Income tax benefit
Total reclassifications, net of tax	$	(3.8	)	$	(4.0	)	Net income

Taxes (Tables)

9 Months Ended

Sep. 30, 2017

Income Tax Disclosure [Abstract]

Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]

Components of income tax expense are detailed in the following tables.



	Three Months Ended September 30						Year to Date September 30
Great Plains Energy	2017			2016			2017			2016
Current income taxes	(millions)
Federal	$	(1.1	)	$	—		$	(1.1	)	$	(0.1	)
State	(0.3		)	—			(0.3		)	0.3
Total	(1.4		)	—			(1.4		)	0.2
Deferred income taxes
Federal	86.6			70.1			74.7			91.5
State	17.5			13.0			15.0			18.4
Total	104.1			83.1			89.7			109.9
Investment tax credit
Deferral	—			—			—			2.5
Amortization	(0.4		)	(0.4		)	(1.1		)	(1.1		)
Total	(0.4		)	(0.4		)	(1.1		)	1.4
Income tax expense	$	102.3		$	82.7		$	87.2		$	111.5



	Three Months Ended September 30						Year to Date September 30
KCP&L	2017			2016			2017			2016
Current income taxes	(millions)
Federal	$	41.8		$	35.4		$	56.2		$	36.6
State	7.6			6.4			10.2			6.7
Total	49.4			41.8			66.4			43.3
Deferred income taxes
Federal	10.3			22.5			27.2			61.5
State	2.8			4.5			6.2			12.5
Total	13.1			27.0			33.4			74.0
Investment tax credit amortization	(0.3		)	(0.3		)	(0.8		)	(0.8		)
Income tax expense	$	62.2		$	68.5		$	99.0		$	116.5

Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]

Effective Income Tax Rates

Effective income tax rates reflected in the financial statements and the reasons for their differences from the statutory federal rates are detailed in the following tables.



	Three Months Ended September 30				Year to Date September 30
Great Plains Energy	2017		2016		2017		2016
Federal statutory income tax rate	35.0	%	35.0	%	35.0	%	35.0	%
Differences between book and tax depreciation not normalized	(0.6	)	(0.3	)	(0.9	)	(0.2	)
Amortization of investment tax credits	(1.5	)	(0.2	)	(1.9	)	(0.4	)
Federal income tax credits	(7.8	)	(1.1	)	(10.0	)	(2.7	)
State income taxes	9.8		3.9		11.5		4.0
Transaction-related costs	54.1		1.0		70.8		1.0
Valuation allowance	1.7		—		2.4		—
Other	(0.1	)	(0.1	)	0.5		—
Effective income tax rate	90.6	%	38.2	%	107.4	%	36.7	%



	Three Months Ended September 30				Year to Date September 30
KCP&L	2017		2016		2017		2016
Federal statutory income tax rate	35.0	%	35.0	%	35.0	%	35.0	%
Differences between book and tax depreciation not normalized	(0.6	)	(0.5	)	(0.5	)	(0.3	)
Amortization of investment tax credits	(0.4	)	(0.1	)	(0.4	)	(0.2	)
Federal income tax credits	(3.1	)	(1.2	)	(2.6	)	(2.3	)
State income taxes	3.8		3.8		3.8		3.8
Valuation allowance	0.7		—		0.4		—
Other	(0.1	)	(0.2	)	0.1		(0.1	)
Effective income tax rate	35.3	%	36.8	%	35.8	%	35.9	%

Segments and Related Information (Tables)

9 Months Ended

Sep. 30, 2017

Segment Reporting [Abstract]

Segment Financial Information [Table Text Block]

The following tables reflect summarized financial information concerning Great Plains Energy's reportable segment.



Three Months Ended September 30, 2017	Electric Utility				Other				Eliminations			Great Plains Energy
		(millions)
Operating revenues		$	857.2			$	—			$	—		$	857.2
Depreciation and amortization		(92.7		)		—				—			(92.7		)
Interest (charges) income		(49.1		)		10.1				8.1			(30.9		)
Income tax expense		(92.7		)		(9.6		)		—			(102.3		)
Net income (loss)		162.9				(152.4		)		—			10.5

Year to Date September 30, 2017	Electric Utility				Other				Eliminations			Great Plains Energy
		(millions)
Operating revenues		$	2,110.5			$	—			$	—		$	2,110.5
Depreciation and amortization		(277.7		)		—				—			(277.7		)
Interest (charges) income		(149.3		)		(117.6		)		24.1			(242.8		)
Income tax (expense) benefit		(142.6		)		55.4				—			(87.2		)
Net income (loss)		247.4				(253.5		)		—			(6.1		)

Three Months Ended September 30, 2016	Electric Utility				Other				Eliminations			Great Plains Energy
		(millions)
Operating revenues		$	856.8			$	—			$	—		$	856.8
Depreciation and amortization		(86.4		)		—				—			(86.4		)
Interest (charges) income		(49.3		)		(26.4		)		8.1			(67.6		)
Income tax (expense) benefit		(95.9		)		13.2				—			(82.7		)
Net income (loss)		161.1				(27.5		)		—			133.6

Year to Date September 30, 2016	Electric Utility				Other				Eliminations			Great Plains Energy
		(millions)
Operating revenues		$	2,099.7			$	—			$	—		$	2,099.7
Depreciation and amortization		(256.9		)		—				—			(256.9		)
Interest (charges) income		(147.4		)		(128.4		)		24.1			(251.7		)
Income tax (expense) benefit		(160.2		)		48.7				—			(111.5		)
Net income (loss)		278.4				(86.4		)		—			192.0



	Electric Utility			Other			Eliminations				Great Plains Energy
September 30, 2017		(millions)
Assets		$	11,586.7		$	1,244.0		$	(401.8	)		$	12,428.9
Capital expenditures ^(a)		392.5			—			—				392.5
December 31, 2016
Assets		$	11,444.2		$	2,461.3		$	(335.5	)		$	13,570.0
Capital expenditures ^(a)		609.4			—			—				609.4

Summary of Significant Accounting Policies Equity Method Investment (Details) - Transource Energy, LLC [Member]	9 Months Ended
	Sep. 30, 2017 Rate
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Description of Principal Activities	Transource is focused on the development of competitive electric transmission projects.
GPE Transmission Holding Company, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	13.50%
AEP Transmission Holding Company, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage of Majority Owner	86.50%

Summary of Significant Accounting Policies Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income [Abstract]
Net income (loss)	$ 10.5	$ 133.6	$ (6.1)	$ 192.0
Less: preferred stock dividend requirements and redemption premium	7.1	0.9	37.3	1.7
Earnings (loss) available for common shareholders	$ 3.4	$ 132.7	$ (43.4)	$ 190.3
Common Shares Outstanding [Abstract]
Average number of common shares outstanding (in shares)	215.6	154.6	215.5	154.5
Add: effect of dilutive securities (in shares)	0.1	0.3	0.0	0.4
Diluted average number of common shares outstanding (in shares)	215.7	154.9	215.5	154.9
Earnings Per Share [Abstract]
Basic and Diluted EPS	$ 0.02	$ 0.86	$ (0.20)	$ 1.23
Series B Preferred Stock [Member]
Preferred Stock, Dividend Rate, Percentage			7.00%		7.00%

Summary of Significant Accounting Policies Antidilutive Securities (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0	0		0
Performance Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount			53,079
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount			136,970

Summary of Significant Accounting Policies Summary of Significant Accounting Policies New Accounting Pronouncements (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Subsidiaries [Member] \| Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of ASU 2016-09 (Note 1)	$ 0.7	$ 0.0

Summary of Significant Accounting Policies Subsequent Events (Details) - Subsequent Event [Member]	1 Months Ended
	Oct. 31, 2017 $ / shares
Kansas City Power and Light Company [Member]
Dividends Declared [Abstract]
Dividends Payable, Amount Per Share	$ 30,000,000
Dividends Payable, Date to be Paid	Dec. 19, 2017
Dividends Payable, Date Declared, Month and Year	2017-10
Common Stock [Member]
Dividends Declared [Abstract]
Dividends Payable, Amount Per Share	$ 0.275
Dividends Payable, Date to be Paid	Dec. 20, 2017
Dividends Payable, Date of Record	Nov. 29, 2017
Dividends Payable, Date Declared, Month and Year	2017-10

Anticipated Merger with Westar Energy, Inc. (Details) $ / shares in Units, $ in Millions			1 Months Ended			9 Months Ended		12 Months Ended
	Jul. 09, 2017 USD ($) Rate	May 29, 2016 USD ($) $ / shares shares	Jul. 31, 2017 USD ($) Rate	Mar. 31, 2017 USD ($)	Oct. 31, 2016 USD ($) shares	Sep. 30, 2017 USD ($) Rate shares	Sep. 30, 2016 USD ($) shares	Dec. 31, 2016 Rate
Anticipated Merger With Westar Energy, Inc. [Line Items]
Cash consideration to be transferred (per share) \| $ / shares		$ 51.00
Issuance of long-term debt						$ 4,591.1	$ 0.0
Minimum Required Cash Balance at Closing of Anticipated Merger with Westar						$ 1,250.0
Unsecured Debt [Member] \| GPE 4.3 Billion Senior Notes [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Debt Instrument, Mandatory Redemption Price, Percentage \| Rate						101.00%
Debt Instrument, Redemption Price, Percentage \| Rate			101.00%
Great Plains Energy [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Holdco Common Stock Conversion Ratio \| Rate	0.5981
Merger Termination Fee Regulatory Approvals	$ 190.0
Merger Termination Fee Great Plains Energy Termination	190.0
Merger Termination Fee Great Plains Energy Shareholder	$ 80.0
Ownership in Holdco - Percentage \| Rate	47.50%
Merger Termination Fee Original Merger Agreement						$ 380.0
Great Plains Energy [Member] \| GPE 4.3 Billion Senior Notes [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Long-term Debt, Gross				$ 4,300.0
Great Plains Energy [Member] \| Unsecured Debt [Member] \| GPE 4.3 Billion Senior Notes [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Issuance of long-term debt				$ 4,300.0
Long-term Debt, Gross			$ 4,300.0
Westar Energy Inc [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Holdco Common Stock Conversion Ratio \| Rate	1.0
Merger Termination Fee Westar Termination	$ 190.0
Ownership in Holdco - Percentage \| Rate	52.50%
Bridge Loan [Member] \| Great Plains Energy [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Amount of bridge facility						8,017.0
Amount of bridge facility, as amended			864.5			$ 864.5
7.25% Mandatory Convertible Preferred Stock, Series A [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Preferred Shares To Be Issued, Stock Purchase Agreement, Series A Preferred Stock \| shares		750,000				750,000
Preferred Stock, Dividend Rate, Percentage \| Rate						7.25%
Preferred Stock, Purchase Agreement, Proceeds		$ 750.0	750.0			$ 750.0
Previously deferred offering costs written off			$ 15.0
Depositary Shares [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Stock Issued During Period, Shares, New Issues \| shares					17,300,000
Net Proceeds from Issuance of Depositary Shares					$ 836.2
Series B Preferred Stock [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Preferred Stock, Dividend Rate, Percentage \| Rate						7.00%		7.00%
Common Stock [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Stock Issued During Period, Shares, New Issues \| shares					60,500,000	319,743	420,207
Net Proceeds from Issuance of Common Stock					$ 1,550.0

Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows affected by changes in:
Receivables	$ (20.4)	$ (45.9)
Accounts receivable pledged as collateral	(22.6)	(15.0)
Fuel inventories	19.6	19.8
Materials and supplies	(9.7)	(5.3)
Accounts payable	(125.7)	(119.8)
Accrued taxes	92.4	97.2
Accrued interest	6.6	16.7
Deferred refueling outage costs	12.1	7.5
Pension and post-retirement benefit obligations	52.0	53.2
Allowance for equity funds used during construction	(3.4)	(4.3)
Fuel recovery mechanisms	(10.1)	(16.8)
Other	11.9	(11.7)
Total other operating activities	2.7	(24.4)
Cash paid during the period:
Interest	198.7	130.2
Income taxes	0.1	0.2
Non-cash investing activities:
Liabilities accrued for capital expenditures	31.2	30.7
Kansas City Power and Light Company [Member]
Cash flows affected by changes in:
Receivables	(19.5)	(53.5)
Accounts receivable pledged as collateral	(20.0)	0.0
Fuel inventories	10.8	12.7
Materials and supplies	(7.2)	(3.8)
Accounts payable	(75.1)	(80.3)
Accrued taxes	122.7	179.3
Accrued interest	8.1	8.9
Deferred refueling outage costs	12.1	7.5
Pension and post-retirement benefit obligations	48.6	53.7
Allowance for equity funds used during construction	(3.4)	(4.0)
Fuel recovery mechanisms	7.6	(31.0)
Other	(16.0)	(14.8)
Total other operating activities	68.7	74.7
Cash paid during the period:
Interest	88.6	86.7
Income taxes	4.9	0.0
Non-cash investing activities:
Liabilities accrued for capital expenditures	$ 24.7	$ 25.7

Receivables Accounts, Notes, and Financing (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other receivables	$ 51.9	$ 64.7
Total	186.4	166.0
Kansas City Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other receivables	42.2	51.7
Total	143.8	139.1
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts	(5.4)	(4.0)
Trade Accounts Receivable [Member] \| Kansas City Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts	(2.8)	(1.8)
Trade Accounts Receivable [Member] \| Billed Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	25.0	26.2
Trade Accounts Receivable [Member] \| Billed Revenues [Member] \| Kansas City Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	24.4	25.5
Trade Accounts Receivable [Member] \| Unbilled Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	114.9	79.1
Trade Accounts Receivable [Member] \| Unbilled Revenues [Member] \| Kansas City Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	$ 80.0	$ 63.7

Receivables Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Sale Of Accounts Receivable - KCPL and GMO
Accounts receivable pledged as collateral	$ 195.0	$ 172.4
Collateralized note payable	195.0	172.4
Kansas City Power and Light Company [Member]
Sale Of Accounts Receivable - KCPL and GMO
Accounts receivable pledged as collateral	130.0	110.0
Collateralized note payable	130.0	$ 110.0
Maximum amount of outstanding principal under receivables agreement	130.0
KCPL Greater Missouri Operations [Member]
Sale Of Accounts Receivable - KCPL and GMO
Maximum amount of outstanding principal under receivables agreement from mid-November to mid-June	50.0
Maximum amount of outstanding principal under receivables agreement from mid-June to mid-November	$ 65.0

Nuclear Plant (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Nuclear Plant (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Investments in decommissioning trust fund [Line Items]
Cost Basis	$ 166.6		$ 166.6		$ 160.5
Unrealized Gains	81.9		81.9		64.4
Unrealized Losses	(1.0)		(1.0)		(2.0)
Fair Value	247.5		$ 247.5		222.9	$ 200.7
Weighted average maturity of debt securities (in years)			9 years
Realized gains	0.7	$ 0.6	$ 1.1	$ 1.5
Realized losses	(0.5)	$ (0.3)	(0.6)	$ (1.3)
Equity Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	95.8		95.8		93.3
Unrealized Gains	79.2		79.2		62.1
Unrealized Losses	(0.8)		(0.8)		(1.5)
Fair Value	174.2		174.2		153.9
Debt Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	67.3		67.3		63.4
Unrealized Gains	2.7		2.7		2.3
Unrealized Losses	(0.2)		(0.2)		(0.5)
Fair Value	69.8		69.8		65.2
Other Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	3.5		3.5		3.8
Fair Value	$ 3.5		$ 3.5		$ 3.8

Nuclear Plant Decommissioning Trust (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2017	Sep. 30, 2017
Nuclear decommissioning trust fund [Roll Forward]
Beginning balance January 1	$ 222.9	$ 200.7
Contributions	2.5	3.3
Earned income, net of fees	3.1	4.1
Net realized gains	0.5	0.3
Net unrealized gains	18.5	14.5
Ending balance	$ 247.5	222.9
Wolf Creek [Member] \| Missouri Public Service Commission [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Current Cost of Decommissioning (in 2017 Dollars)			$ 813.7
Future cost of decommissioning (in 2045 through 2053 dollars)			2,137.8
Annual Escalation Factor	3.16%
Annual return on trust assets through 2027	5.46%
Annual return on trusts assets in 2053	2.22%
Wolf Creek [Member] \| Kansas Corporation Commission [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Current Cost of Decommissioning (in 2017 Dollars)			813.7
Future cost of decommissioning (in 2045 through 2053 dollars)			1,982.4
Annual Escalation Factor	2.91%
Annual return on trust assets through 2029	5.64%
Annual return on trusts assets in 2053	0.32%
Kansas City Power and Light Company [Member]
Nuclear decommissioning trust fund [Roll Forward]
Beginning balance January 1	$ 222.9	200.7
Contributions	2.5	3.3
Earned income, net of fees	3.1	4.1
Net realized gains	0.5	0.3
Net unrealized gains	18.5	14.5
Ending balance	$ 247.5	$ 222.9
Kansas City Power and Light Company [Member] \| Wolf Creek [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	47.00%			47.00%
Kansas City Power and Light Company [Member] \| Wolf Creek [Member] \| Missouri Public Service Commission [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Current Cost of Decommissioning (in 2017 Dollars)			382.5
Future cost of decommissioning (in 2045 through 2053 dollars)			1,004.8
Kansas City Power and Light Company [Member] \| Wolf Creek [Member] \| Kansas Corporation Commission [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Current Cost of Decommissioning (in 2017 Dollars)			382.5
Future cost of decommissioning (in 2045 through 2053 dollars)			$ 931.7

Regulatory Matters (Details) - Kansas City Power and Light Company [Member] - USD ($) $ in Millions	1 Months Ended
	May 31, 2017	Apr. 30, 2017	Nov. 30, 2016	Jul. 31, 2016
Missouri Public Service Commission [Member]
Regulatory Proceedings [Line Items]
Annual revenue increase, requested, portion related to rebasing fuel and purchased power expense				$ 27.2
Annual revenue increase, requested, not including rebasing fuel and purchased power expense				$ 62.9
Return on equity, requested (in hundredths)				9.90%
Rate-making equity ratio, requested (in hundredths)				49.88%
Annual revenue increase (decrease), approved	$ 32.5
Return on equity, approved (in hundredths)	9.50%
Ratemaking equity ratio, approved (in hundredths)	49.20%
Kansas Corporation Commission [Member]
Regulatory Proceedings [Line Items]
Annual revenue decrease, requested			$ 2.8
Public Utilities, KCPL and Commission Staff Recommended Rate Decrease, Amount		$ 3.6

Goodwill (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Goodwill [Line Items]
Goodwill	$ 169.0	$ 169.0

Pension Plans and Other Employee Benefits (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Contributions by Employer			$ 28.0
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year			51.6
Components of net periodic benefit costs [Abstract]
Service cost	$ 11.0	$ 10.5	33.0	$ 31.5
Interest cost	13.4	13.2	40.2	39.7
Expected return on plan assets	(12.8)	(12.3)	(38.4)	(36.9)
Prior service cost	0.2	0.2	0.6	0.5
Recognized net actuarial (gain)/loss	12.4	13.0	37.2	38.9
Net periodic benefit costs before regulatory adjustment	24.2	24.6	72.6	73.7
Regulatory adjustment	(0.2)	(1.1)	2.3	(3.1)
Net periodic benefit costs	24.0	23.5	74.9	70.6
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year			4.1
Components of net periodic benefit costs [Abstract]
Service cost	0.5	0.7	1.5	2.0
Interest cost	1.4	1.5	4.1	4.6
Expected return on plan assets	(0.7)	(0.8)	(2.0)	(2.3)
Prior service cost	0.0	0.3	0.0	0.9
Recognized net actuarial (gain)/loss	(0.1)	(0.3)	(0.3)	(1.1)
Net periodic benefit costs before regulatory adjustment	1.1	1.4	3.3	4.1
Regulatory adjustment	0.1	1.4	1.9	4.4
Net periodic benefit costs	$ 1.2	$ 2.8	$ 5.2	$ 8.5
Wolf Creek [Member] \| Kansas City Power and Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	47.00%		47.00%		47.00%

Equity Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation expense	$ 1.8	$ 0.4	$ 4.4	$ 3.9
Income tax benefit	$ 0.6	$ 0.0	$ 1.7	$ 1.3
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility (in hundredths)			18.00%
Expected dividend yield (in hundredths)			3.80%
Risk-free interest rate (in hundredths)			1.58%
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares)			625,100
Granted (in shares)	0	0	236,433
Earned (in shares)			(212,992)
Forfeited (in shares)			(97,036)
Ending balance (in shares)	551,505		551,505
Weighted average beginning balance (in dollars per share)			$ 28.13
Weighted average granted (in dollars per share)			31.26	$ 31.41
Weighted average earned (in dollars per share)			28.48
Weighted average forfeited (in dollars per share)			29.24
Weighted average ending balance (in dollars per share)	$ 29.12		$ 29.12
Total unrecognized compensation expense	$ 7.5		$ 7.5
Remaining weighted-average contractual term (in years)			1 year 5 months
Fair value of performance shares earned and paid			$ 6.1	$ 7.4
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares)			249,672
Granted (in shares)	0	0	78,840
Vested (in shares)			(109,813)
Forfeited (in shares)			(22,521)
Ending balance (in shares)	196,178		196,178
Weighted average beginning balance (in dollars per share)			$ 27.20
Weighted average granted (in dollars per share)			28.60	$ 29.41
Weighted average vested (in dollars per share)			27.48
Weighted average forfeited (in dollars per share)			27.26
Weighted average ending balance (in dollars per share)	$ 27.81		$ 27.81
Total unrecognized compensation expense	$ 2.5		$ 2.5
Total fair value of shares vested	0.2	$ 0.1	$ 3.0	$ 1.7
Remaining weighted-average contractual term (in years)			1 year 5 months
Kansas City Power and Light Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation expense	1.2	0.2	$ 2.9	2.5
Income tax benefit	$ 0.4	$ 0.0	$ 1.2	$ 0.8

Short-term Borrowings and Short-term Bank Lines of Credit (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Jul. 31, 2017	Dec. 31, 2016
Short-term Debt [Line Items]
Commercial paper outstanding	$ 247.9		$ 334.8
Great Plains Energy [Member] \| Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 200.0
Credit facility expiration date	Oct. 31, 2019
Maximum borrowing capacity with transfer of unused commitments	$ 400.0
Line of Credit Facility, Covenant Terms	A default by Great Plains Energy or any of its significant subsidiaries on other indebtedness totaling more than $50.0 million is a default under the facility. Under the terms of this facility, Great Plains Energy is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times.
Line of Credit Facility, Covenant Compliance	in compliance
Amount of outstanding cash borrowings	$ 0.0		0.0
Amount of letters of credit outstanding	1.0		1.0
Great Plains Energy [Member] \| Bridge Loan [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	8,017.0
Amount of bridge facility, as amended	864.5	$ 864.5
Kansas City Power and Light Company [Member]
Short-term Debt [Line Items]
Commercial paper outstanding	$ 72.0		$ 132.9
Weighted-average interest rate from outstanding borrowings	1.37%		0.98%
Kansas City Power and Light Company [Member] \| Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 600.0
Credit facility expiration date	Oct. 31, 2019
Maximum transfer of unused commitments	$ 200.0
Line of Credit Facility, Covenant Terms	A default by KCP&L on other indebtedness totaling more than $50.0 million is a default under the facility. Under the terms of this facility, KCP&L is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times.
Line of Credit Facility, Covenant Compliance	in compliance
Amount of outstanding cash borrowings	$ 0.0		$ 0.0
Amount of letters of credit outstanding	2.7		2.8
KCPL Greater Missouri Operations [Member]
Short-term Debt [Line Items]
Commercial paper outstanding	$ 175.9		$ 201.9
Weighted-average interest rate from outstanding borrowings	1.41%		1.02%
KCPL Greater Missouri Operations [Member] \| Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 450.0
Credit facility expiration date	Oct. 31, 2019
Maximum transfer of unused commitments	$ 200.0
Line of Credit Facility, Covenant Terms	A default by GMO or any of its significant subsidiaries on other indebtedness totaling more than $50.0 million is a default under the facility. Under the terms of this facility, GMO is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times.
Line of Credit Facility, Covenant Compliance	in compliance
Amount of outstanding cash borrowings	$ 0.0		$ 0.0
Amount of letters of credit outstanding	$ 2.0		$ 1.9

Long-Term Debt (Details) - USD ($) $ in Millions	1 Months Ended				3 Months Ended		9 Months Ended
Long-Term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2017	Jul. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Current maturities									$ (351.1)		$ (382.1)
Long-term debt excluding current maturities									3,312.0		3,365.2
GMO Senior Notes [Abstract]
Loss on extinguishment of debt					$ 82.8	$ 0.0	$ 82.8	$ 0.0
Unsecured Debt [Member] \| GPE 4.3 Billion Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Mandatory Redemption Price, Percentage							101.00%
Kansas City Power and Light Company [Member]
Debt Instrument [Line Items]
Current maturities									(350.0)		(281.0)
Unamortized discount and premium, net and debt issuance costs									(17.7)		(15.4)
Long-term debt excluding current maturities									2,231.7		2,284.0
Kansas City Power and Light Company [Member] \| Secured Debt [Member] \| General Mortgage bonds Series 2009A due 2019 [Member]
Debt Instrument [Line Items]
Principal outstanding									400.0		400.0
Debt Instrument, Maturity Date							Dec. 31, 2019
Interest rates (in hundredths)										7.15%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)										8.59%
Kansas City Power and Light Company [Member] \| Secured Debt [Member] \| General Mortgage bonds EIRR series 2005 [Member]
Debt Instrument [Line Items]
EIRR bonds repurchased and held									50.0		50.0
Kansas City Power and Light Company [Member] \| Secured Debt [Member] \| General Mortgage Bonds EIRR Due 2023 [Member]
Debt Instrument [Line Items]
Principal outstanding									79.5		110.5
EIRR bonds repurchased and held									21.9		21.9
Debt Instrument, Maturity Date							Dec. 31, 2023
Interest rates (in hundredths)										2.95%
Kansas City Power and Light Company [Member] \| Secured Debt [Member] \| General Mortgage Bonds EIRR Due 2017 [Member]
Debt Instrument [Line Items]
Repayments of Long-Term Debt		$ 31.0
Kansas City Power and Light Company [Member] \| Senior Notes [Member] \| Senior notes due 2017 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding									0.0		250.0
Interest rates (in hundredths)			5.85%							5.85%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)										5.72%
Repayments of Long-Term Debt			$ 250.0
Kansas City Power and Light Company [Member] \| Senior Notes [Member] \| Senior notes due 2018 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding									350.0		350.0
Debt Instrument, Maturity Date							Dec. 31, 2018
Interest rates (in hundredths)										6.375%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)										7.49%
Kansas City Power and Light Company [Member] \| Senior Notes [Member] \| Senior Notes due 2023 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding									300.0		300.0
Debt Instrument, Maturity Date							Dec. 31, 2023
Interest rates (in hundredths)										3.15%
Kansas City Power and Light Company [Member] \| Senior Notes [Member] \| Senior Notes due 2025 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding									350.0		350.0
Debt Instrument, Maturity Date							Dec. 31, 2025
Interest rates (in hundredths)										3.65%
Kansas City Power and Light Company [Member] \| Senior Notes [Member] \| Senior notes due 2035 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding									250.0		250.0
Debt Instrument, Maturity Date							Dec. 31, 2035
Interest rates (in hundredths)										6.05%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)										5.78%
Kansas City Power and Light Company [Member] \| Senior Notes [Member] \| Senior Notes Due 2041 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding									400.0		400.0
Debt Instrument, Maturity Date							Dec. 31, 2041
Interest rates (in hundredths)										5.30%
Kansas City Power and Light Company [Member] \| Senior Notes [Member] \| Senior Notes Due 2047 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding			$ 300.0						300.0		0.0
Debt Instrument, Maturity Date			Dec. 31, 2047				Dec. 31, 2047
Interest rates (in hundredths)			4.20%							4.20%
Kansas City Power and Light Company [Member] \| Unsecured Debt [Member] \| EIRR Bonds Series 2007A and 2007B due 2035 [Member]
Debt Instrument [Line Items]
Principal outstanding									146.5		146.5
Debt Instrument, Maturity Date							Dec. 31, 2035
Variable rate (in hundredths)										0.889%
Kansas City Power and Light Company [Member] \| Unsecured Debt [Member] \| EIRR bonds 2.875 percent Series 2008 [Member]
Debt Instrument [Line Items]
Principal outstanding									23.4		23.4
Debt Instrument, Maturity Date							Dec. 31, 2038
Interest rates (in hundredths)										2.875%
KCPL Greater Missouri Operations [Member] \| Secured Debt [Member] \| First Mortgage Bonds due through 2021 [Member]
Debt Instrument [Line Items]
Principal outstanding									4.6		5.7
Debt Instrument Maturity Date Range End							Dec. 31, 2021
Debt Instrument Maturity Date Range Start							Dec. 31, 2018
Interest rates (in hundredths)										9.44%
KCPL Greater Missouri Operations [Member] \| Senior Notes [Member] \| Senior notes 8.27 percent series due 2021 [Member]
Debt Instrument [Line Items]
Principal outstanding									80.9		80.9
Debt Instrument, Maturity Date							Dec. 31, 2021
Interest rates (in hundredths)										8.27%
KCPL Greater Missouri Operations [Member] \| Senior Notes [Member] \| Senior Notes Series A due 2025 [Member]
Debt Instrument [Line Items]
Principal outstanding									125.0		125.0
Debt Instrument, Maturity Date							Dec. 31, 2025
Interest rates (in hundredths)										3.49%
KCPL Greater Missouri Operations [Member] \| Senior Notes [Member] \| Senior Notes Series B due 2033 [Member]
Debt Instrument [Line Items]
Principal outstanding									75.0		75.0
Debt Instrument, Maturity Date							Dec. 31, 2033
Interest rates (in hundredths)										4.06%
KCPL Greater Missouri Operations [Member] \| Senior Notes [Member] \| Senior Notes Series C due 2043 [Member]
Debt Instrument [Line Items]
Principal outstanding									150.0		150.0
Debt Instrument, Maturity Date							Dec. 31, 2043
Interest rates (in hundredths)										4.74%
KCPL Greater Missouri Operations [Member] \| Medium-term Notes [Member] \| Medium term notes 7.33 percent series due 2023 [Member]
Debt Instrument [Line Items]
Principal outstanding									3.0		3.0
Debt Instrument, Maturity Date							Dec. 31, 2023
Interest rates (in hundredths)										7.33%
KCPL Greater Missouri Operations [Member] \| Medium-term Notes [Member] \| Medium term notes 7.17 percent series due 2023 [Member]
Debt Instrument [Line Items]
Principal outstanding									7.0		7.0
Debt Instrument, Maturity Date							Dec. 31, 2023
Interest rates (in hundredths)										7.17%
Great Plains Energy [Member] \| GPE 4.3 Billion Senior Notes [Member]
Debt Instrument [Line Items]
Principal outstanding				$ 4,300.0
Great Plains Energy [Member] \| Senior Notes [Member] \| Senior notes due 2017 [Member]
Debt Instrument [Line Items]
Principal outstanding									0.0		100.0
Interest rates (in hundredths)	6.875%				6.875%		6.875%			6.875%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)										7.33%
Repayments of Long-Term Debt	$ 100.0
Great Plains Energy [Member] \| Senior Notes [Member] \| Senior Notes Due 2020 [Member]
Debt Instrument [Line Items]
Principal outstanding				$ 750.0
Debt Instrument, Maturity Date				Dec. 31, 2020
Interest rates (in hundredths)				2.50%
Great Plains Energy [Member] \| Senior Notes [Member] \| Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Principal outstanding									350.0		350.0
Debt Instrument, Maturity Date							Dec. 31, 2021
Interest rates (in hundredths)										4.85%
Great Plains Energy [Member] \| Senior Notes [Member] \| Senior Notes 5.292 Percent Series Due 2022 [Member]
Debt Instrument [Line Items]
Principal outstanding									287.5		287.5
Debt Instrument, Maturity Date							Dec. 31, 2022
Interest rates (in hundredths)										5.292%
Great Plains Energy [Member] \| Senior Notes [Member] \| Senior Notes 3.15 Percent Series Due 2022 [Member]
Debt Instrument [Line Items]
Principal outstanding				$ 1,150.0
Debt Instrument, Maturity Date				Dec. 31, 2022
Interest rates (in hundredths)				3.15%
Great Plains Energy [Member] \| Senior Notes [Member] \| Senior Notes Due 2027 [Member]
Debt Instrument [Line Items]
Principal outstanding				$ 1,400.0
Debt Instrument, Maturity Date				Dec. 31, 2027
Interest rates (in hundredths)				3.90%
Great Plains Energy [Member] \| Senior Notes [Member] \| Senior Notes Due 2047 [Member]
Debt Instrument [Line Items]
Principal outstanding				$ 1,000.0
Debt Instrument, Maturity Date				Dec. 31, 2047
Interest rates (in hundredths)				4.85%
Great Plains Energy [Member] \| Senior Notes [Member] \| GPE 4.3 Billion Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed		101.00%
GMO Senior Notes [Abstract]
Total Redemption Cost		$ 4,400.1
Loss on extinguishment of debt		82.8
Great Plains Energy [Member] \| Unsecured Debt [Member] \| GPE 4.3 Billion Senior Notes [Member]
Debt Instrument [Line Items]
Principal outstanding		$ 4,300.0
Other Consolidated Entities [Member]
Debt Instrument [Line Items]
Current maturities									(1.1)		(101.1)
Unamortized discount and premium, net and debt issuance costs									$ (1.6)		$ (1.8)

Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended		3 Months Ended		9 Months Ended
	May 29, 2016	Jul. 31, 2017	Oct. 31, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Mandatory Convertible Preferred Stock [Abstract]
Loss on Series B Preferred Stock dividend make-whole provisions				$ 67.7	$ 0.0	$ 124.8	$ 0.0
Payments for Repurchase of Redeemable Preferred Stock						963.4	$ 40.1
Preferred Stock, Value, Issued				$ 0.0		0.0		$ 836.2
7.25% Mandatory Convertible Preferred Stock, Series A [Member]
Class of Stock [Line Items]
Preferred Stock, Purchase Agreement, Proceeds	$ 750.0	$ 750.0				$ 750.0
Mandatory Convertible Preferred Stock [Abstract]
Preferred Shares To Be Issued, Stock Purchase Agreement, Series A Preferred Stock	750,000					750,000
Previously deferred offering costs written off		$ 15.0
Series B Preferred Stock [Member]
Mandatory Convertible Preferred Stock [Abstract]
Preferred Stock, Liquidation Preference Per Share				$ 1,000.00		$ 1,000.00		$ 1,000.00
Loss on Series B Preferred Stock dividend make-whole provisions				$ 67.7		$ 124.8
Preferred Stock Redemption Premium				2.4		2.4
Payments for Repurchase of Redeemable Preferred Stock						963.4
Preferred Stock, Value, Issued				$ 836.2		$ 836.2
Depositary Shares [Member]
Mandatory Convertible Preferred Stock [Abstract]
Stock Issued During Period, Shares, New Issues			17,300,000

Commitments and Contingencies Environmental Matters (Details) T in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($) T	Dec. 31, 2016 USD ($)
Estimated Environmental Capital Expenditures [Abstract]
Estimate Of Environmental Capital Expenditures Current	$ 36.3
Estimate Of Environmental Capital Expenditures In Two Years	16.6
Estimate Of Environmental Capital Expenditures In Three Years	9.2
Estimate Of Environmental Capital Expenditures In Four Years	$ 13.7
Climate Change [Abstract]
CO2 produced per year (in millions of tons) \| T	19
EPA nationwide CO2 emission reductions by 2030	32.00%
Remediation [Abstract]
Accrued environmental remediation expenses	$ 1.4	$ 1.4
Kansas City Power and Light Company [Member]
Estimated Environmental Capital Expenditures [Abstract]
Estimate Of Environmental Capital Expenditures Current	34.9
Estimate Of Environmental Capital Expenditures In Two Years	16.5
Estimate Of Environmental Capital Expenditures In Three Years	7.9
Estimate Of Environmental Capital Expenditures In Four Years	$ 13.0
Climate Change [Abstract]
CO2 produced per year (in millions of tons) \| T	15
Remediation [Abstract]
Accrued environmental remediation expenses	$ 0.3	$ 0.3
KCPL Greater Missouri Operations [Member]
Remediation [Abstract]
Estimated amount of insurance proceeds available to cover qualified remediation expenses	$ 1.5

Related Party Transactions and Relationships (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Kansas City Power and Light Company [Member] \| Money Pool [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	$ 0.0		$ 0.0		$ 0.0
Kansas City Power and Light Company [Member] \| KCPL Greater Missouri Operations [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	55.1		55.1		64.6
Kansas City Power and Light Company [Member] \| KCPL Greater Missouri Operations [Member] \| Operating Expenses and Capital Costs Billed [Member]
Related Party Transaction [Line Items]
Operating expenses and capital costs billed from KCPL to GMO	49.2	$ 48.9	145.0	$ 143.8
Kansas City Power and Light Company [Member] \| Great Plains Energy [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	$ 27.0		$ 27.0		$ 2.6
Iatan No 1 And 2 [Member] \| KCPL Greater Missouri Operations [Member]
Related Party Transaction [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	18.00%		18.00%

Fair Value Measurements Level 3 (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Loss on Series B Preferred Stock dividend make-whole provisions	$ (67.7)	$ 0.0	$ (124.8)	$ 0.0
Derivative Financial Instruments, Assets [Member] \| Fair Value, Inputs, Level 3 [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance net asset (liability)	(7.9)	(77.0)	79.3	0.0
Net asset (liability) at September 30	77.4	(78.8)	77.4	(78.8)
Derivative Financial Instruments, Assets [Member] \| Fair Value, Inputs, Level 3 [Member] \| Fair Value, Measurements, Recurring [Member] \| Interest Charges [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	28.2	(1.8)	(1.9)	(78.8)
Total unrealized gains (losses) relating to assets and liabilities still on the consolidated balance sheet at September 30:	28.2	(1.8)	(1.9)	(78.8)
Derivative Financial Instruments, Liabilities [Member] \| Fair Value, Inputs, Level 3 [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Settlements	124.8	0.0	124.8	0.0
Derivative Financial Instruments, Liabilities [Member] \| Fair Value, Inputs, Level 3 [Member] \| Fair Value, Measurements, Recurring [Member] \| Loss On Series B Preferred Stock Dividend Make-Whole Provisions [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	$ (67.7)	$ 0.0	$ (124.8)	$ 0.0

Fair Value Measurements Fair Value Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)
Fair value of financial instruments [Abstract]
Derivatives, Interest Rate Swaps, Finalized Settlement Value	$ 140.6		$ 140.6
Great Plains Energy [Member]
Fair value of financial instruments [Abstract]
Notional Contract Amount							$ 4,400.0
Derivatives, Interest Rate Swaps, Finalized Settlement Value					$ 140.6
KCPL Greater Missouri Operations [Member]
SERP rabbi trust [Abstract]
Alternative Investments, Fair Value Disclosure	15.0		15.0			$ 16.0
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair value of financial instruments [Abstract]
Long-term Debt	3,700.0		3,700.0			3,800.0
Carrying (Reported) Amount, Fair Value Disclosure [Member] \| Kansas City Power and Light Company [Member]
Fair value of financial instruments [Abstract]
Long-term Debt	2,600.0		2,600.0			2,600.0
GPE 4.3 Billion Senior Notes [Member] \| Great Plains Energy [Member]
Fair value of financial instruments [Abstract]
Long-term Debt, Gross					$ 4,300.0
Fair Value, Inputs, Level 2 [Member] \| Estimate of Fair Value Measurement [Member]
Fair value of financial instruments [Abstract]
Long-term debt fair value	3,900.0		3,900.0			4,000.0
Fair Value, Inputs, Level 2 [Member] \| Estimate of Fair Value Measurement [Member] \| Kansas City Power and Light Company [Member]
Fair value of financial instruments [Abstract]
Long-term debt fair value	$ 2,800.0		$ 2,800.0			$ 2,700.0
Interest Rate Contract [Member]
Fair value of financial instruments [Abstract]
Fair Value Inputs, Contingency Factor, Interest Rate Derivative	0.45		0.45			0.35
Derivative Asset, Fair Value, Gross Asset	$ 77.4		$ 77.4			$ 79.3
Interest Rate Contract [Member] \| Interest Expense [Member]
Fair value of financial instruments [Abstract]
Derivative, Gain (Loss) on Derivative, Net	$ 28.2	$ (1.8)	$ (1.9)	$ (78.8)

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ (6.6)	$ (12.0)
Amounts reclassified from accumulated other comprehensive loss			4.4	4.5
Net current period other comprehensive income	$ 1.4	$ 1.5	4.4	4.5
Ending balance	(2.2)	(7.5)	(2.2)	(7.5)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(4.5)	(10.1)
Amounts reclassified from accumulated other comprehensive loss			4.1	4.1
Net current period other comprehensive income			4.1	4.1
Ending balance	(0.4)	(6.0)	(0.4)	(6.0)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(2.1)	(1.9)
Amounts reclassified from accumulated other comprehensive loss			0.3	0.4
Net current period other comprehensive income			0.3	0.4
Ending balance	(1.8)	(1.5)	(1.8)	(1.5)
Kansas City Power and Light Company [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(4.2)
Net current period other comprehensive income	1.2	1.2	3.8	4.0
Ending balance	(0.4)		(0.4)
Kansas City Power and Light Company [Member] \| Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(4.2)	(9.6)
Amounts reclassified from accumulated other comprehensive loss			3.8	4.0
Net current period other comprehensive income			3.8	4.0
Ending balance	$ (0.4)	$ (5.6)	$ (0.4)	$ (5.6)

Accumulated Other Comprehensive Income (Loss) Reclassification (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges	$ (30.9)	$ (67.6)	$ (242.8)	$ (251.7)
Utility operating and maintenance expenses	(187.9)	(193.3)	(555.0)	(553.1)
Income (loss) before income tax (expense) benefit and income from equity investments	112.3	215.6	79.1	301.4
Income tax (expense) benefit	(102.3)	(82.7)	(87.2)	(111.5)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)	(1.4)	(1.5)	(4.4)	(4.5)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] \| Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income tax (expense) benefit and income from equity investments	(2.1)	(2.3)	(6.7)	(6.9)
Income tax (expense) benefit	0.8	1.0	2.6	2.8
Net income (loss)	(1.3)	(1.3)	(4.1)	(4.1)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] \| Reclassification out of Accumulated Other Comprehensive Income [Member] \| Interest Rate Contract [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges	(2.1)	(2.3)	(6.7)	(6.9)
Accumulated Defined Benefit Plans Adjustment [Member] \| Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Utility operating and maintenance expenses	(0.2)	(0.2)	(0.6)	(0.6)
Income (loss) before income tax (expense) benefit and income from equity investments	(0.2)	(0.2)	(0.6)	(0.6)
Income tax (expense) benefit	0.1	0.0	0.3	0.2
Net income (loss)	(0.1)	(0.2)	(0.3)	(0.4)
Kansas City Power and Light Company [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges	(34.3)	(34.7)	(105.5)	(104.9)
Utility operating and maintenance expenses	(125.6)	(131.9)	(374.2)	(379.6)
Income (loss) before income tax (expense) benefit and income from equity investments	176.3	186.2	276.9	324.7
Income tax (expense) benefit	(62.2)	(68.5)	(99.0)	(116.5)
Kansas City Power and Light Company [Member] \| Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] \| Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income tax (expense) benefit and income from equity investments	(1.9)	(2.2)	(6.3)	(6.6)
Income tax (expense) benefit	0.7	1.0	2.5	2.6
Net income (loss)	(1.2)	(1.2)	(3.8)	(4.0)
Kansas City Power and Light Company [Member] \| Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] \| Reclassification out of Accumulated Other Comprehensive Income [Member] \| Interest Rate Contract [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges	$ (1.9)	$ (2.2)	$ (6.3)	$ (6.6)

Income Tax Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Income Tax Expense (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Current income taxes
Federal	$ (1.1)	$ 0.0	$ (1.1)	$ (0.1)
State	(0.3)	0.0	(0.3)	0.3
Total	(1.4)	0.0	(1.4)	0.2
Deferred income taxes
Federal	86.6	70.1	74.7	91.5
State	17.5	13.0	15.0	18.4
Total	104.1	83.1	89.7	109.9
Investment tax credit
Deferral	0.0	0.0	0.0	2.5
Amortization	(0.4)	(0.4)	(1.1)	(1.1)
Total	(0.4)	(0.4)	(1.1)	1.4
Income tax expense	$ 102.3	$ 82.7	$ 87.2	$ 111.5
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax (in hundredths)	35.00%	35.00%	35.00%	35.00%
Differences between book and tax depreciation not normalized (in hundredths)	(0.60%)	(0.30%)	(0.90%)	(0.20%)
Amortization of investments tax credits (in hundredths)	(1.50%)	(0.20%)	(1.90%)	(0.40%)
Federal income tax credits (in hundredths)	(7.80%)	(1.10%)	(10.00%)	(2.70%)
State income taxes (in hundredths)	9.80%	3.90%	11.50%	4.00%
Transaction costs (in hundredths)	54.10%	1.00%	70.80%	1.00%
Valuation allowance	1.70%	0.00%	2.40%	0.00%
Other (in hundredths)	(0.10%)	(0.10%)	0.50%	0.00%
Effective income tax rate (in hundredths)	90.60%	38.20%	107.40%	36.70%
Kansas City Power and Light Company [Member]
Current income taxes
Federal	$ 41.8	$ 35.4	$ 56.2	$ 36.6
State	7.6	6.4	10.2	6.7
Total	49.4	41.8	66.4	43.3
Deferred income taxes
Federal	10.3	22.5	27.2	61.5
State	2.8	4.5	6.2	12.5
Total	13.1	27.0	33.4	74.0
Investment tax credit
Amortization	(0.3)	(0.3)	(0.8)	(0.8)
Income tax expense	$ 62.2	$ 68.5	$ 99.0	$ 116.5
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax (in hundredths)	35.00%	35.00%	35.00%	35.00%
Differences between book and tax depreciation not normalized (in hundredths)	(0.60%)	(0.50%)	(0.50%)	(0.30%)
Amortization of investments tax credits (in hundredths)	(0.40%)	(0.10%)	(0.40%)	(0.20%)
Federal income tax credits (in hundredths)	(3.10%)	(1.20%)	(2.60%)	(2.30%)
State income taxes (in hundredths)	3.80%	3.80%	3.80%	3.80%
Valuation allowance	0.70%	0.00%	0.40%	0.00%
Other (in hundredths)	(0.10%)	(0.20%)	0.10%	(0.10%)
Effective income tax rate (in hundredths)	35.30%	36.80%	35.80%	35.90%

Segments and Related Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Operating revenues	$ 857.2	$ 856.8	$ 2,110.5	$ 2,099.7
Depreciation and amortization	(92.7)	(86.4)	(277.7)	(256.9)
Interest charges	(30.9)	(67.6)	(242.8)	(251.7)
Income tax expense	(102.3)	(82.7)	(87.2)	(111.5)
Net income (loss)	10.5	133.6	(6.1)	192.0
Assets	12,428.9		12,428.9		$ 13,570.0
Capital expenditures			392.5	435.3	609.4
Operating Segments [Member] \| Electric Utility Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	857.2	856.8	2,110.5	2,099.7
Depreciation and amortization	(92.7)	(86.4)	(277.7)	(256.9)
Interest charges	(49.1)	(49.3)	(149.3)	(147.4)
Income tax expense	(92.7)	(95.9)	(142.6)	(160.2)
Net income (loss)	162.9	161.1	247.4	278.4
Assets	11,586.7		11,586.7		11,444.2
Capital expenditures			392.5		609.4
Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	0.0	0.0	0.0	0.0
Depreciation and amortization	0.0	0.0	0.0	0.0
Interest charges	10.1	(26.4)	(117.6)	(128.4)
Income tax expense	(9.6)	13.2	55.4	48.7
Net income (loss)	(152.4)	(27.5)	(253.5)	(86.4)
Assets	1,244.0		1,244.0		2,461.3
Capital expenditures			0.0		0.0
Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	0.0	0.0	0.0	0.0
Depreciation and amortization	0.0	0.0	0.0	0.0
Interest charges	8.1	8.1	24.1	24.1
Income tax expense	0.0	0.0	0.0	0.0
Net income (loss)	0.0	$ 0.0	0.0	$ 0.0
Assets	$ (401.8)		(401.8)		(335.5)
Capital expenditures			$ 0.0		$ 0.0

Legal Proceedings Loss Contingencies (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	Oct. 31, 2016	Sep. 30, 2017
MPS Merchant Services, Inc. [Member] \| GMO Western Energy Crisis [Member]
Loss Contingencies [Line Items]
Litigation Settlement, Amount	$ 7.5	$ 7.5

Fair Value Measurements (Details) $ in Millions	Sep. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Assets [Abstract]
Derivatives, Interest Rate Swaps, Finalized Settlement Value	$ 140.6
Interest Rate Contract [Member]
Assets [Abstract]
Derivative instruments, assets	$ 77.4		$ 79.3
Fair Value Inputs, Contingency Factor, Interest Rate Derivative	0.45		0.35
Great Plains Energy [Member]
Assets [Abstract]
Derivatives, Interest Rate Swaps, Finalized Settlement Value		$ 140.6
Fair Value, Measurements, Recurring [Member]
Assets [Abstract]
Derivative instruments, assets	$ 77.4		$ 79.3
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	247.5		222.9
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	11.3		11.3
Total assets	336.2		313.5
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Derivative instruments, assets	0.0		0.0
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	211.3		185.5
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	8.9		6.6
Total assets	220.2		192.1
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Derivative instruments, assets	0.0		0.0
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	36.2		37.4
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	2.4		4.7
Total assets	38.6		42.1
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Derivative instruments, assets	77.4		79.3
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0		0.0
Total assets	77.4		79.3
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	247.5		222.9
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	11.3		11.3
Total assets	258.8		234.2
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Equity Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	174.2		153.9
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.4		0.9
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Debt Securities [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	2.8		4.8
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	33.6		27.8
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| US Government Corporations and Agencies Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.4		1.7
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| US States and Political Subdivisions Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	2.5		3.2
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Corporate Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	33.2		32.4
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Foreign Government Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.1		0.1
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Cash Equivalents [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	2.9		3.8
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Cash and Cash Equivalents [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	8.1		5.6
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Other Trust Assets [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.6
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 1 [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	211.3		185.5
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	8.9		6.6
Total assets	220.2		192.1
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 1 [Member] \| Equity Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	174.2		153.9
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.4		0.9
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 1 [Member] \| Debt Securities [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.4		0.1
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 1 [Member] \| US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	33.6		27.8
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 1 [Member] \| US Government Corporations and Agencies Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 1 [Member] \| US States and Political Subdivisions Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 1 [Member] \| Corporate Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 1 [Member] \| Foreign Government Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 1 [Member] \| Cash Equivalents [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	2.9		3.8
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 1 [Member] \| Cash and Cash Equivalents [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	8.1		5.6
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 1 [Member] \| Other Trust Assets [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.6
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 2 [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	36.2		37.4
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	2.4		4.7
Total assets	38.6		42.1
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 2 [Member] \| Equity Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 2 [Member] \| Debt Securities [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	2.4		4.7
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 2 [Member] \| US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 2 [Member] \| US Government Corporations and Agencies Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.4		1.7
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 2 [Member] \| US States and Political Subdivisions Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	2.5		3.2
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 2 [Member] \| Corporate Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	33.2		32.4
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 2 [Member] \| Foreign Government Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.1		0.1
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 2 [Member] \| Cash Equivalents [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 2 [Member] \| Cash and Cash Equivalents [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 2 [Member] \| Other Trust Assets [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 3 [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0		0.0
Total assets	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 3 [Member] \| Equity Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 3 [Member] \| Debt Securities [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 3 [Member] \| US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 3 [Member] \| US Government Corporations and Agencies Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 3 [Member] \| US States and Political Subdivisions Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 3 [Member] \| Corporate Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 3 [Member] \| Foreign Government Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 3 [Member] \| Cash Equivalents [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 3 [Member] \| Cash and Cash Equivalents [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Kansas City Power and Light Company [Member] \| Fair Value, Inputs, Level 3 [Member] \| Other Trust Assets [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0
Fair Value, Measurements, Recurring [Member] \| Other Consolidated Entities [Member]
Self-insured health plan trust [Abstract]
Total assets	77.4		79.3
Fair Value, Measurements, Recurring [Member] \| Other Consolidated Entities [Member] \| Interest Rate Contract [Member]
Assets [Abstract]
Derivative instruments, assets	77.4		$ 79.3
Derivatives, Interest Rate Swaps, Finalized Settlement Value	$ 140.6
Fair Value Inputs, Contingency Factor, Interest Rate Derivative	0.45		0.35
Fair Value, Measurements, Recurring [Member] \| Other Consolidated Entities [Member] \| Fair Value, Inputs, Level 1 [Member]
Self-insured health plan trust [Abstract]
Total assets	$ 0.0		$ 0.0
Fair Value, Measurements, Recurring [Member] \| Other Consolidated Entities [Member] \| Fair Value, Inputs, Level 1 [Member] \| Interest Rate Contract [Member]
Assets [Abstract]
Derivative instruments, assets	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Other Consolidated Entities [Member] \| Fair Value, Inputs, Level 2 [Member]
Self-insured health plan trust [Abstract]
Total assets	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Other Consolidated Entities [Member] \| Fair Value, Inputs, Level 2 [Member] \| Interest Rate Contract [Member]
Assets [Abstract]
Derivative instruments, assets	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Other Consolidated Entities [Member] \| Fair Value, Inputs, Level 3 [Member]
Self-insured health plan trust [Abstract]
Total assets	77.4		79.3
Fair Value, Measurements, Recurring [Member] \| Other Consolidated Entities [Member] \| Fair Value, Inputs, Level 3 [Member] \| Interest Rate Contract [Member]
Assets [Abstract]
Derivative instruments, assets	$ 77.4		$ 79.3

Plant to be Retired, Net (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Schedule of Plant to be Retired, Net [Line Items]
Plant to be Retired, Net	$ 146.3	$ 0.0