Evergy Metro 10-Q 4 May 17 2017 Q1 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	3 Months Ended
	Mar. 31, 2017	Apr. 30, 2017
Document Information [Line Items]
Entity Registrant Name	Great Plains Energy Inc
Entity Central Index Key	1,143,068
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		215,605,456
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q1
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2017

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Current Assets
Cash and cash equivalents	$ 6,552.3	$ 1,293.1
Time deposit	0	1,000
Receivables, net	110.4	166
Accounts receivable pledged as collateral	172.2	172.4
Fuel inventories, at average cost	107	108.8
Materials and supplies, at average cost	166.4	162.2
Deferred refueling outage costs	18.3	22.3
Interest rate derivative instruments	91.4	79.3
Prepaid expenses and other assets	40.6	55.4
Total	7,258.6	3,059.5
Utility Plant, at Original Cost
Electric	13,712.9	13,597.7
Less - accumulated depreciation	5,165.2	5,106.9
Net utility plant in service	8,547.7	8,490.8
Construction work in progress	370.9	403.9
Nuclear fuel, net of amortization of $180.1 and $172.1	54.9	62
Total	8,973.5	8,956.7
Investments and Other Assets
Nuclear decommissioning trust fund	232.5	222.9
Regulatory assets	1,046.4	1,048
Goodwill	169	169
Other	117.5	113.9
Total	1,565.4	1,553.8
Total	17,797.5	13,570
Current Liabilities
Collateralized note payable	172.2	172.4
Commercial paper	454.7	334.8
Current maturities of long-term debt	732.1	382.1
Accounts payable	177.7	323.7
Accrued taxes	69.6	33.3
Accrued interest	77.3	50.8
Accrued compensation and benefits	44.1	52.1
Pension and post-retirement liability	3	3
Other	85.5	32.6
Total	1,816.2	1,384.8
Deferred Credits and Other Liabilities
Deferred income taxes	1,322.7	1,329.7
Deferred tax credits	125.8	126.2
Asset retirement obligations	282.6	316
Pension and post-retirement liability	483.9	488.3
Regulatory liabilities	313.6	309.9
Other	88.8	87.9
Total	2,617.4	2,658
Shareholders' equity
Common stock	4,225.5	4,217
Preference Stock	836.2	836.2
Retained earnings	1,035.2	1,119.2
Treasury stock - 129,122 and 128,087 shares, at cost	(3.8)	(3.8)
Accumulated other comprehensive loss	(5.1)	(6.6)
Total shareholders' equity	6,088	6,162
Long-term debt (Note 10)	7,275.9	3,365.2
Total	13,363.9	9,527.2
Commitments and Contingencies (Note 11)
Total	17,797.5	13,570
Kansas City Power and Light Company [Member]
Current Assets
Cash and cash equivalents	2.1	4.5
Receivables, net	99	139.1
Related party receivables	69.1	67.2
Accounts receivable pledged as collateral	110	110
Fuel inventories, at average cost	73.4	72.9
Materials and supplies, at average cost	122	118.9
Deferred refueling outage costs	18.3	22.3
Refundable income taxes	2.3	12.7
Prepaid expenses and other assets	27.9	27.9
Total	524.1	575.5
Utility Plant, at Original Cost
Electric	10,009.1	9,925.1
Less - accumulated depreciation	3,898.4	3,858.4
Net utility plant in service	6,110.7	6,066.7
Construction work in progress	271.3	300.4
Nuclear fuel, net of amortization of $180.1 and $172.1	54.9	62
Total	6,436.9	6,429.1
Investments and Other Assets
Nuclear decommissioning trust fund	232.5	222.9
Regulatory assets	799.6	801.8
Other	29.5	29.1
Total	1,061.6	1,053.8
Total	8,022.6	8,058.4
Current Liabilities
Collateralized note payable	110	110
Commercial paper	195.3	132.9
Current maturities of long-term debt	631	281
Accounts payable	136.3	231.6
Accrued taxes	52.3	27
Accrued interest	42.5	32.4
Accrued compensation and benefits	44.1	52.1
Pension and post-retirement liability	1.6	1.6
Other	42	11.4
Total	1,255.1	880
Deferred Credits and Other Liabilities
Deferred income taxes	1,237.4	1,228.3
Deferred tax credits	122.5	122.8
Asset retirement obligations	246.5	278
Pension and post-retirement liability	461.5	465.8
Regulatory liabilities	194.5	187.4
Other	71.3	70.6
Total	2,333.7	2,352.9
Shareholders' equity
Common stock	1,563.1	1,563.1
Retained earnings	939.1	982.6
Accumulated other comprehensive loss	(2.9)	(4.2)
Total shareholders' equity	2,499.3	2,541.5
Long-term debt (Note 10)	1,934.5	2,284
Total	4,433.8	4,825.5
Commitments and Contingencies (Note 11)
Total	$ 8,022.6	$ 8,058.4

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Utility Plant, at Original Cost
Nuclear fuel, amortization	$ 180.1	$ 172.1
Shareholder's equity
Common stock - shares authorized (in shares)	600,000,000	600,000,000
Common stock-shares issued (in shares)	215,728,275	215,479,105
Treasury stock- shares (in shares)	129,122	128,087
Series B Preferred Stock [Member]
Shareholder's equity
Preferred Stock, Shares Issued	862,500	862,500
Preferred Stock, Dividend Rate, Percentage	7.00%	7.00%
Preferred Stock, Liquidation Preference Per Share	$ 1,000	$ 1,000
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	$ 180.1	$ 172.1
Shareholder's equity
Common stock - shares authorized (in shares)	1,000	1,000
Common stock-shares issued (in shares)	1	1

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating Revenues
Electric revenues	$ 570.7	$ 572.1
Operating Expenses
Fuel and purchased power	126.5	135.6
Transmission	23.1	23.5
Utility operating and maintenance expenses	185.4	179.4
Costs to achieve the anticipated acquisition of Westar Energy, Inc.	39.4	0
Depreciation and amortization	90.3	85.2
General taxes	57.1	56.3
Other	1.5	2.2
Total	523.3	482.2
Operating income	47.4	89.9
Non-operating income	6.6	2.1
Non-operating expenses	(3.7)	(3.4)
Interest charges	(66.6)	(51.2)
Income (loss) before income tax (expense) benefit and income from equity investments	(16.3)	37.4
Income tax (expense) benefit	5.8	(11.7)
Income from equity investments, net of income taxes	0.9	0.7
Net income (loss)	(9.6)	26.4
Preferred stock dividend requirements	15.1	0.4
Earnings (loss) available for common shareholders	$ (24.7)	$ 26
Average number of basic common shares outstanding	215.3	154.4
Average number of diluted common shares outstanding	215.3	155
Basic and diluted earnings (loss) per common share	$ (0.11)	$ 0.17
Cash dividends per common share	$ 0.275	$ 0.2625
Comprehensive Income
Net income (loss)	$ (9.6)	$ 26.4
Other comprehensive income
Reclassification to expenses, net of tax	1.4	1.4
Derivative hedging activity, net of tax	1.4	1.4
Amortization of net losses included in net periodic benefit costs, net of tax	0.1	0.1
Change in unrecognized pension expense, net of tax	0.1	0.1
Total other comprehensive income	1.5	1.5
Comprehensive income (loss)	(8.1)	27.9
Kansas City Power and Light Company [Member]
Operating Revenues
Electric revenues	395.9	400.9
Operating Expenses
Fuel and purchased power	78.9	86.3
Transmission	14.3	15.4
Utility operating and maintenance expenses	126.4	123.7
Costs to achieve the anticipated acquisition of Westar Energy, Inc.	7.9	0
Depreciation and amortization	65.3	61.1
General taxes	44.6	43.6
Other	0.3	0.2
Total	337.7	330.3
Operating income	58.2	70.6
Non-operating income	2.5	1.3
Non-operating expenses	(2.1)	(1.3)
Interest charges	(35.6)	(35.3)
Income (loss) before income tax (expense) benefit and income from equity investments	23	35.3
Income tax (expense) benefit	(8.8)	(10.7)
Net income (loss)	14.2	24.6
Comprehensive Income
Net income (loss)	14.2	24.6
Other comprehensive income
Reclassification to expenses, net of tax	1.3	1.4
Derivative hedging activity, net of tax	1.3	1.4
Total other comprehensive income	1.3	1.4
Comprehensive income (loss)	$ 15.5	$ 26

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash Flows from Operating Activities
Net income (loss)	$ (9.6)	$ 26.4
Adjustments to reconcile income to net cash from operating activities:
Depreciation and amortization	90.3	85.2
Amortization of:
Nuclear fuel	8	8.3
Other	24.9	12.8
Deferred income taxes, net	(5.6)	12
Investment tax credit amortization	(0.4)	(0.4)
Income from equity investments, net of income taxes	(0.9)	(0.7)
Fair value impact of interest rate swaps	(12.1)	0
Other operating activities (Note 3)	(7)	(16.3)
Net cash from operating activities	87.6	127.3
Cash Flows from Investing Activities
Utility capital expenditures	(116.6)	(133.6)
Allowance for borrowed funds used during construction	(1.5)	(1.4)
Purchases of nuclear decommissioning trust investments	(5.9)	(10.5)
Proceeds from nuclear decommissioning trust investments	5	9.7
Proceeds from time deposit	1,000	0
Other investing activities	(12.5)	(17.9)
Net cash from investing activities	868.5	(153.7)
Cash Flows from Financing Activities
Issuance of common stock	1.5	0.7
Issuance of long-term debt	4,291.9	0
Issuance fees	(31.2)	(0.2)
Repayment of long-term debt	(1.1)	(1.1)
Net change in short-term borrowings	119.9	69.3
Net change in collateralized short-term borrowings	(0.2)	0
Dividends paid	(74.3)	(40.9)
Purchase of treasury stock	(3.4)	(4.9)
Net cash from financing activities	4,303.1	22.9
Net Change in Cash and Cash Equivalents	5,259.2	(3.5)
Cash and Cash Equivalents at Beginning of Year	1,293.1	11.3
Cash and Cash Equivalents at End of Period	6,552.3	7.8
Kansas City Power and Light Company [Member]
Cash Flows from Operating Activities
Net income (loss)	14.2	24.6
Adjustments to reconcile income to net cash from operating activities:
Depreciation and amortization	65.3	61.1
Amortization of:
Nuclear fuel	8	8.3
Other	8.1	8.4
Deferred income taxes, net	9.2	10.4
Investment tax credit amortization	(0.3)	(0.2)
Other operating activities (Note 3)	(21.1)	75.8
Net cash from operating activities	83.4	188.4
Cash Flows from Investing Activities
Utility capital expenditures	(84)	(83.2)
Allowance for borrowed funds used during construction	(1.2)	(0.9)
Purchases of nuclear decommissioning trust investments	(5.9)	(10.5)
Proceeds from nuclear decommissioning trust investments	5	9.7
Other investing activities	(5.1)	(8.6)
Net cash from investing activities	(91.2)	(93.5)
Cash Flows from Financing Activities
Issuance fees	0	(0.2)
Net change in short-term borrowings	62.4	(94.5)
Dividends paid	(57)	0
Net cash from financing activities	5.4	(94.7)
Net Change in Cash and Cash Equivalents	(2.4)	0.2
Cash and Cash Equivalents at Beginning of Year	4.5	2.3
Cash and Cash Equivalents at End of Period	$ 2.1	$ 2.5

Consolidated Statements of Comm

Consolidated Statements of Common 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
Beginning balance at Dec. 31, 2015			$ 2,646.7	$ 1,563.1	$ 39	$ 0	$ 1,024.4	879.6	$ (2.6)	$ (12)	$ (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			$ 10
Issuance of stock (in shares)			336,356
Equity compensation expense, net of forfeitures			$ 0.8
Unearned Compensation [Abstract]
Issuance of restricted common stock			(2.8)
Forfeiture of restricted common stock			0
Compensation expense recognized			0.6
Other			0.3
Net income (loss)	$ 26.4	$ 24.6					26.4	24.6
Dividends:
Common stock ($0.275 and $0.2625 per share)							(40.5)	0
Preferred stock - at required rates							(0.4)
Performance shares							(0.3)
Treasury shares acquired									$ (4)
Treasury shares acquired (in shares)									(134,484)
Treasury shares reissued									$ 2.8
Treasury shares reissued (in shares)									105,403
Derivative hedging activity, net of tax	1.4	1.4								1.4	1.4
Change in unrecognized pension expense, net of tax	0.1									0.1
Ending balance at Mar. 31, 2016	3,689.9	2,459.1	$ 2,655.6	$ 1,563.1	$ 39	$ 0	1,009.6	904.2	$ (3.8)	(10.5)	(8.2)
Ending balance, treasury stock (in shares) at Mar. 31, 2016									(130,310)
Ending balance (in shares) at Mar. 31, 2016			154,841,256	1	390,000	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	2,541.5	$ 4,217	$ 1,563.1	$ 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			$ 9.5
Issuance of stock (in shares)			249,170
Equity compensation expense, net of forfeitures			$ 1.1
Unearned Compensation [Abstract]
Issuance of restricted common stock			(2.3)
Forfeiture of restricted common stock			0.2
Compensation expense recognized			0.7
Other			(0.7)
Net income (loss)	$ (9.6)	14.2					(9.6)	14.2
Dividends:
Common stock ($0.275 and $0.2625 per share)							(59.2)	(57)
Preferred stock - at required rates							(15.1)
Performance shares							(0.1)
Treasury shares acquired									$ (3)
Treasury shares acquired (in shares)									(104,129)
Treasury shares reissued									$ 3
Treasury shares reissued (in shares)									103,094
Derivative hedging activity, net of tax	1.4	1.3								1.4	1.3
Change in unrecognized pension expense, net of tax	0.1									0.1
Ending balance at Mar. 31, 2017	$ 6,088	$ 2,499.3	$ 4,225.5	$ 1,563.1	$ 0	$ 836.2	$ 1,035.2	$ 939.1	$ (3.8)	$ (5.1)	$ (2.9)
Ending balance, treasury stock (in shares) at Mar. 31, 2017	(129,122)								(129,122)
Ending balance (in shares) at Mar. 31, 2017			215,728,275	1	0	862,500

Consolidated Statements of Com7

Consolidated Statements of Common Shareholders' Equity (Parenthetical) - $ / shares	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Stock Transactions, Parenthetical Disclosures [Abstract]
Common Stock, Dividends, Per Share, Declared	$ 0.275	$ 0.2625

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 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 to be used to fund the cash consideration for the anticipated acquisition of Westar Energy, Inc. (Westar). 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 17 for additional information. Basic and Diluted Earnings per Common Share Calculation To determine basic earnings per common share (EPS), preferred stock dividend requirements are deducted from net income before dividing by the average number of common shares outstanding. To determine diluted EPS, preferred stock dividend requirements are added to earnings available for common shareholders for the periods in which the assumed conversion of Great Plains Energy's 7.00% Series B Mandatory Convertible Preferred Stock (Series B Preferred Stock) has a dilutive effect 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 and the number of common shares that would be issued under an assumed conversion of Series B Preferred Stock using the if-converted method. The following table reconciles Great Plains Energy's basic and diluted EPS. Three Months Ended March 31 2017 2016 Income (loss) (millions, except per share amounts) Net income (loss) $ (9.6 ) $ 26.4 Less: preferred stock dividend requirements 15.1 0.4 Earnings (loss) available for common shareholders $ (24.7 ) $ 26.0 Common Shares Outstanding Average number of common shares outstanding 215.3 154.4 Add: effect of dilutive securities — 0.6 Diluted average number of common shares outstanding 215.3 155.0 Basic and diluted EPS $ (0.11 ) $ 0.17 Anti-dilutive shares excluded from the computation of diluted EPS are detailed in the following table. Three Months Ended March 31 2017 2016 Assumed conversion of Series B Preferred Stock 29,930,385 — Performance shares 460,169 372,093 Restricted stock shares 328,512 — Dividends Declared In May 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 June 20, 2017 , to shareholders of record as of May 30, 2017 . The Great Plains Energy Board also declared a regular quarterly dividend on Great Plains Energy's Series B Preferred Stock. The dividend will be payable June 15, 2017 , to shareholders of record as of June 1, 2017 . In May 2017 , KCP&L's Board of Directors declared a cash dividend payable to Great Plains Energy of $75.0 million payable on June 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 other 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. The new guidance is to be applied retrospectively for the presentation of service cost and other 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 are evaluating the effect it will have on their consolidated financial statements and related disclosures. 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 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 retrospective or cumulative effect transition method. The Companies have completed a review of the majority of their revenue arrangements and do not expect the standard to have a material impact on their consolidated financial statements. However, the Companies are still evaluating the impacts on revenue recognition of their remaining revenue arrangements and contracts where collectability is uncertain. The Companies are in the process of determining their method of adoption, which depends in part on completing the evaluation of the remaining items noted above.

Anticipated Acquisition of West

Anticipated Acquisition of Westar Energy, Inc.	3 Months Ended
	Mar. 31, 2017
Anticipated Acquisition of Westar Energy, Inc. [Abstract]
Anticipated Buiness Combination Disclosure [Text Block]	2 . ANTICIPATED ACQUISITION OF WESTAR ENERGY, INC. On May 29, 2016, Great Plains Energy entered into an Agreement and Plan of Merger (Merger Agreement) by and among Great Plains Energy, Westar, and, from and after its accession to the Merger Agreement, GP Star, Inc., a wholly owned subsidiary of Great Plains Energy in the State of Kansas (Merger Sub). Pursuant to the Merger Agreement, subject to the satisfaction or waiver of certain conditions, Merger Sub will merge with and into Westar, with Westar continuing as the surviving corporation. Upon closing, pursuant to the Merger Agreement, Great Plains Energy will acquire Westar for (i) $51.00 in cash and (ii) a number, rounded to the nearest 1/10,000 of a share, of shares of Great Plains Energy common stock, equal to the Exchange Ratio (as described below) 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 Exchange Ratio is calculated as follows: If the volume-weighted average share price of Great Plains Energy common stock on the New York Stock Exchange for the twenty consecutive full trading days ending on (and including) the third trading day immediately prior to the closing date of the merger (the Great Plains Energy Average Stock Price) is: (a) greater than $33.2283 , the Exchange Ratio will be 0.2709 ; (b) greater than or equal to $28.5918 but less than or equal to $33.2283 , the Exchange Ratio will be an amount equal to the quotient obtained by dividing (x) $9.00 by (y) the Great Plains Energy Average Stock Price; or (c) less than $28.5918 , the Exchange Ratio will be 0.3148 . Financing Great Plains Energy's plan to finance the cash portion of the merger consideration with equity and debt financing includes (i) $750 million of mandatory convertible preferred equity pursuant to a stock purchase agreement with OCM Credit Portfolio LP (OMERS), (ii) approximately $2.35 billion of equity comprised of a combination of Great Plains Energy common stock and additional mandatory convertible preferred stock, which, as discussed below, was completed in October 2016, and (iii) approximately $4.3 billion in debt, which, as discussed below, was completed in March 2017. On May 29, 2016, in connection with the Merger Agreement, Great Plains Energy entered into a commitment letter for a 364-day senior unsecured bridge term loan facility in an aggregate principal amount of $8.017 billion (which has subsequently been reduced to $864.5 million as of March 31, 2017) to support the anticipated transaction and provide flexibility for the timing of long-term financing. See Note 9 for additional information. 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 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 merger. On October 3, 2016, Great Plains Energy completed a registered public offering of 60.5 million shares of common stock, without par value, at a public offering price of $26.45 per share, for total gross proceeds of approximately $1.6 billion (net proceeds of approximately $1.55 billion after issuance costs). Concurrent with this offering, Great Plains Energy also completed a registered public offering of 17.3 million depositary shares, each representing a 1/20th interest in a share of Great Plains Energy's Series B Preferred Stock, without par value, at a public offering price of $50 per depositary share for total gross proceeds of $862.5 million (net proceeds of approximately $836.2 million after issuance costs). In the event that the merger is terminated or if Great Plains Energy determines in its reasonable judgment that the anticipated acquisition of Westar will not close or if the anticipated acquisition of Westar has not closed by November 30, 2017, then Great Plains Energy could at its sole option (but is not required to) redeem all of the Series B Preferred Stock. 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 exceeds a certain threshold amount, then a repurchase price that is equal to a make-whole formula. On March 9, 2017, Great Plains Energy issued, at a discount, $4.3 billion of unsecured senior notes. See Note 10 for additional information. In the event that the anticipated acquisition of Westar does not close by November 30, 2017, or in the event that the Merger Agreement is earlier terminated, then Great Plains Energy would be required to redeem all of the $4.3 billion unsecured senior notes it issued on March 9, 2017, in connection with the anticipated acquisition. Additionally, if at any time prior to November 30, 2017, Great Plains Energy determines in its reasonable judgment that the anticipated acquisition of Westar will not close prior to November 30, 2017, then Great Plains Energy could at its sole option (but is not required to) redeem the unsecured senior notes. The redemption price in each case would be 101% of the aggregate principle amount of the senior notes. In the event that Great Plains Energy would redeem the senior notes, any deferred debt issuance costs would be written off. Regulatory and Shareholder Approvals Great Plains Energy's anticipated acquisition of Westar was unanimously approved by the Great Plains Energy Board and Westar's Board of Directors (Westar Board). In September 2016, shareholders of Great Plains Energy and Westar approved all proposals necessary for Great Plains Energy's acquisition of Westar at each company's respective shareholder meeting. The anticipated acquisition remains subject to regulatory approvals 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); as well as other customary conditions. KCC Approval In June 2016, Great Plains Energy, KCP&L and Westar filed a joint application with KCC for approval of the anticipated acquisition of Westar by Great Plains Energy. Under applicable Kansas regulations, KCC has 300 days following the filing to rule on the transaction. On April 19, 2017, KCC issued its order denying Great Plains Energy's, KCP&L's and Westar's joint application for approval of the anticipated 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 May 4, 2017, Great Plains Energy, KCP&L and Westar filed with KCC a petition for reconsideration of KCC's April 19, 2017, order and to set the matter for further proceedings so that Great Plains Energy, KCP&L and Westar may work together to determine whether it is feasible to develop a revised acquisition proposal addressing KCC's concerns and, if so, file such revised acquisition proposal along with a supplemental application by May 31, 2017. Under applicable Kansas regulations, KCC has 30 days following the filing of the petition for reconsideration to either deny or grant the petition. MPSC Approval On February 22, 2017, the MPSC issued an order directing Great Plains Energy to file an application with the MPSC for approval of the anticipated acquisition of Westar. Great Plains Energy filed its application on February 23, 2017. An evidentiary hearing in the case was held in April 2017. Following the order by the KCC described above, the MPSC approved a request by Great Plains Energy and other joint applicants to suspend the acquisition procedural schedule. Great Plains Energy and the joint applicants agreed to file a status report on any developments related to the KCC proceeding for the proposed acquisition by no later than May 31, 2017. Prior to receiving the MPSC order to file an application for approval of the anticipated acquisition of Westar, Great Plains Energy had reached separate stipulations and agreements with the MPSC staff and the Office of the Public Counsel (OPC) in which the MPSC staff and OPC agreed that they would not file complaints alleging that MPSC approval was necessary in order for Great Plains Energy to acquire Westar. The stipulations and agreements impose certain conditions on Great Plains Energy, KCP&L and GMO in the areas of financing, ratemaking, customer service, corporate social responsibility and also include other general provisions. The stipulation and agreement with the MPSC staff, among other things, provides that retail rates for KCP&L Missouri and GMO customers will not increase as a result of the acquisition and that in the event KCP&L's or GMO's credit ratings are downgraded below investment grade as a result of the acquisition, KCP&L and GMO will be restricted from paying a dividend to Great Plains Energy unless approved by the MPSC or until their credit ratings are restored to investment grade. The stipulations and agreements must still be approved by the MPSC and are being considered as part of Great Plains Energy's application for approval of the anticipated acquisition of Westar. FERC Approval In July 2016, Great Plains Energy and Westar filed a joint application with FERC for approval of the anticipated acquisition of Westar by Great Plains Energy. Approval of the application requires action by the FERC commissioners because it is a contested application. The Federal Power Act requires a quorum of three or more commissioners to act on a contested application. Following the resignation of the FERC Chairman effective February 3, 2017, the FERC is comprised only of two commissioners and is therefore unable to act on the application. A new commissioner must be appointed by the President of the United States, with the advice and consent of the United States Senate, before FERC will be able to act on the application. If the FERC commissioners do not issue an order on the application by November 1, 2017, approval of the application may be deemed granted by operation of law. Great Plains Energy is unable to predict when FERC will regain a quorum or how the change in commissioners will impact the review of the application. Other Approvals In July 2016, Great Plains Energy and Westar filed applications with FERC and NRC for approval of the merger. In August 2016, the Securities and Exchange Commission (SEC) declared effective a registration statement including a joint proxy statement with Westar (the Proxy Statement Prospectus) used in connection with the Great Plains Energy and Westar special shareholder meetings that occurred in September 2016. In September 2016, shareholders of Great Plains Energy and Westar approved all proposals necessary for Great Plains Energy's acquisition of Westar at each company's respective shareholder meeting. In September 2016, Great Plains Energy and Westar filed their respective Pre-Merger Notification and Report forms with the Federal Trade Commission (FTC) and the Department of Justice (DOJ) under the Hart-Scott-Rodino (HSR) Act. In October 2016, the FTC granted Great Plains Energy's request for early termination of the waiting period under the HSR Act with respect to the anticipated acquisition, and the DOJ also notified Great Plains Energy that it has closed its investigation of the antitrust aspects of the anticipated acquisition. In January 2017, The Federal Communications Commission (FCC) consented to the Transfer of Control application filed by Great Plains Energy and Westar relating to the anticipated acquisition. In April 2017, the Nuclear Regulatory Commission (NRC) issued an order approving the indirect ownership transfer of control of Wolf Creek Generating Station (Wolf Creek). Termination Fees The Merger Agreement provides that in connection with the termination of the Merger Agreement under specified circumstances relating to a failure to obtain required regulatory approvals prior to May 31, 2017 (which date may be extended to November 30, 2017, under certain circumstances (the End Date)), a final and nonappealable order enjoining the consummation of the merger in connection with regulatory approvals or failure by Great Plains Energy to consummate the merger once all of the conditions have been satisfied, Great Plains Energy will be required to pay Westar a termination fee of $380 million . In addition, in the event that the Merger Agreement is terminated by (a) either party because the closing has not occurred by the End Date or (b) Westar, as a result of Great Plains Energy's uncured breach of the Merger Agreement, and prior to such termination, an acquisition proposal for Great Plains Energy is publicly disclosed or made to Great Plains Energy, if Great Plains Energy enters into an agreement or consummates a transaction with respect to an acquisition proposal within twelve months following such termination, then Great Plains Energy may be required to pay Westar a termination fee of $180 million . Similarly, in the event that the Merger Agreement is terminated by (x) either party because the closing has not occurred by the End Date or (y) Great Plains Energy, as a result of Westar's uncured breach of the Merger Agreement, and prior to such termination, an acquisition proposal for Westar is publicly disclosed or made to Westar, if Westar enters into an agreement or consummates a transaction with respect to an acquisition proposal within twelve months following such termination, then Westar may be required to pay Great Plains Energy a termination fee of $280 million .

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	3 Months Ended
	Mar. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Cash Flow, Supplemental Disclosures [Text Block]	3. SUPPLEMENTAL CASH FLOW INFORMATION Great Plains Energy Other Operating Activities Three Months Ended March 31 2017 2016 Cash flows affected by changes in: (millions) Receivables $ 55.5 $ 39.7 Accounts receivable pledged as collateral 0.2 — Fuel inventories 1.8 6.3 Materials and supplies (4.2 ) (2.1 ) Accounts payable (136.8 ) (120.4 ) Accrued taxes 36.3 38.0 Accrued interest 26.5 14.4 Deferred refueling outage costs 4.0 4.9 Pension and post-retirement benefit obligations 11.6 23.7 Allowance for equity funds used during construction (1.0 ) (0.9 ) Fuel recovery mechanisms (14.1 ) (4.6 ) Other 13.2 (15.3 ) Total other operating activities $ (7.0 ) $ (16.3 ) Cash paid during the period: Interest $ 34.2 $ 33.3 Income taxes $ — $ 0.1 Non-cash investing activities: Liabilities accrued for capital expenditures $ 22.6 $ 24.7 KCP&L Other Operating Activities Three Months Ended March 31 2017 2016 Cash flows affected by changes in: (millions) Receivables $ 36.2 $ 36.5 Fuel inventories (0.5 ) 4.9 Materials and supplies (3.1 ) (2.0 ) Accounts payable (88.8 ) (75.5 ) Accrued taxes 35.5 102.2 Accrued interest 10.1 9.9 Deferred refueling outage costs 4.0 4.9 Pension and post-retirement benefit obligations 10.3 23.9 Allowance for equity funds used during construction (1.0 ) (0.6 ) Fuel recovery mechanisms (10.8 ) (14.3 ) Other (13.0 ) (14.1 ) Total other operating activities $ (21.1 ) $ 75.8 Cash paid during the period: Interest $ 22.5 $ 22.2 Non-cash investing activities: Liabilities accrued for capital expenditures $ 19.9 $ 16.5

Receivables

Receivables	3 Months Ended
	Mar. 31, 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. March 31 December 31 2017 2016 Great Plains Energy (millions) Customer accounts receivable - billed $ 10.2 $ 26.2 Customer accounts receivable - unbilled 51.9 79.1 Allowance for doubtful accounts - customer accounts receivable (4.4 ) (4.0 ) Other receivables 52.7 64.7 Total $ 110.4 $ 166.0 KCP&L Customer accounts receivable - billed $ 9.0 $ 25.5 Customer accounts receivable - unbilled 47.7 63.7 Allowance for doubtful accounts - customer accounts receivable (1.8 ) (1.8 ) Other receivables 44.1 51.7 Total $ 99.0 $ 139.1 Great Plains Energy's and KCP&L's other receivables at March 31, 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 March 31, 2017 , and December 31, 2016 , Great Plains Energy's accounts receivable pledged as collateral and the corresponding short-term collateralized note payable were $172.2 million and $172.4 million , respectively. At March 31, 2017 , and December 31, 2016 , KCP&L's accounts receivable pledged as collateral and the corresponding short-term collateralized note payable were $110.0 million . KCP&L's agreement expires in September 2017 and allows for $110 million in aggregate outstanding principal amount of borrowings at any time. GMO's agreement expires in September 2017 and allows for $65 million in aggregate outstanding principal of borrowings from mid-November through mid-June and then increases to $80 million from mid-June through mid-November.

Nuclear Plant

Nuclear Plant	3 Months Ended
	Mar. 31, 2017
Nuclear Plant [Abstract]
Nuclear Plant	5. NUCLEAR PLANT KCP&L owns 47% of 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 Decommissioning Trust Fund The following table summarizes the change in Great Plains Energy's and KCP&L's nuclear decommissioning trust fund. March 31 December 31 2017 2016 Decommissioning Trust (millions) Beginning balance January 1 $ 222.9 $ 200.7 Contributions 0.9 3.3 Earned income, net of fees 1.1 4.1 Net realized gains 0.2 0.3 Net unrealized gains 7.4 14.5 Ending balance $ 232.5 $ 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. March 31, 2017 December 31, 2016 Cost Basis Unrealized Gains Unrealized Losses Fair Value Cost Basis Unrealized Gains Unrealized Losses Fair Value (millions) Equity securities $ 93.9 $ 68.6 $ (0.8 ) $ 161.7 $ 93.3 $ 62.1 $ (1.5 ) $ 153.9 Debt securities 63.2 2.4 (0.4 ) 65.2 63.4 2.3 (0.5 ) 65.2 Other 5.6 — — 5.6 3.8 — — 3.8 Total $ 162.7 $ 71.0 $ (1.2 ) $ 232.5 $ 160.5 $ 64.4 $ (2.0 ) $ 222.9 The weighted average maturity of debt securities held by the trust at March 31, 2017 , was approximately 8 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 March 31 2017 2016 (millions) Realized gains $ 0.3 $ 0.7 Realized losses (0.1 ) (0.7 )

Regulatory Matters

Regulatory Matters	3 Months Ended
	Mar. 31, 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 the 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 will not be 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 the KCC that (i) requested a decrease in retail revenues of $3.6 million ; (ii) requested to cancel the May 2017 evidentiary hearing; and (iii) requested an order by June 7, 2017, which would facilitate a June 28, 2017, effective date for the decrease to retail revenues. 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 a return on equity of 9.5% and a rate-making equity ratio of approximately 49.2% . Pursuant to the order, KCP&L will file tariff sheets sufficient to recover revenues approved in compliance with the order no later than May 9, 2017. KCP&L anticipates the increase to retail revenues will be approximately $30 million to $35 million . The MPSC staff has until May 15, 2017, to file its recommendation concerning approval of KCP&L's tariff sheets. New rates are expected to be effective by May 28, 2017.

Pension Plans and Other Employe

Pension Plans and Other Employee Benefits	3 Months Ended
	Mar. 31, 2017
Compensation and Retirement Disclosure [Abstract]
Pension Plans and Other Employee Benefits	7. 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 table provides 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 March 31 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 1.3 1.5 Expected return on plan assets (12.8 ) (12.3 ) (0.6 ) (0.8 ) Prior service cost 0.2 0.2 — 0.3 Recognized net actuarial (gain)/loss 12.4 13.0 (0.1 ) (0.4 ) Net periodic benefit costs before regulatory adjustment 24.2 24.6 1.1 1.3 Regulatory adjustment 0.8 (1.0 ) 1.3 1.5 Net periodic benefit costs $ 25.0 $ 23.6 $ 2.4 $ 2.8 For the three months ended March 31, 2017 , Great Plains Energy contributed $16.0 million to the pension plans and expects to contribute an additional $63.6 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

Equity Compensation	3 Months Ended
	Mar. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity Compensation	8. 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, limited stock appreciation rights, director shares, director deferred share units and performance shares 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 March 31 2017 2016 Great Plains Energy (millions) Equity compensation expense $ 1.2 $ 3.7 Income tax benefit 0.6 1.5 KCP&L Equity compensation expense $ 0.8 $ 2.5 Income tax benefit 0.4 1.0 Performance Shares Performance share activity for the three months ended March 31, 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 (182,676 ) 28.78 Forfeited (32,264 ) 27.74 Ending balance March 31, 2017 646,593 29.09 * weighted-average At March 31, 2017 , the remaining weighted-average contractual term was 1.9 years. The weighted-average grant-date fair value of shares granted was $31.26 and $31.41 for the three months ended March 31, 2017, and 2016, respectively. At March 31, 2017 , there was $11.7 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 $5.3 million and $7.4 million for the three months ended March 31, 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 for the three months ended March 31, 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 (84,473 ) 27.05 Forfeited (7,320 ) 27.58 Ending balance March 31, 2017 236,719 27.71 * weighted-average At March 31, 2017 , the remaining weighted-average contractual term was 1.9 years. The weighted-average grant-date fair value of shares granted was $28.60 and $29.42 for the three months ended March 31, 2017, and 2016, respectively. At March 31, 2017 , there was $3.9 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 $2.3 million and $1.6 million for the three months ended March 31, 2017, and 2016, respectively.

Short-term Borrowings and Short

Short-term Borrowings and Short-term Bank Lines of Credit	3 Months Ended
	Mar. 31, 2017
Short-term Borrowings and Short-term Bank Lines of Credit [Abstract]
Short-term Borrowings and Short-term Bank Lines of Credit [Text Block]	9 . 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 March 31, 2017 , Great Plains Energy was in compliance with this covenant. In June 2016, the facility was amended, among other things, to increase the maximum consolidated indebtedness to consolidated capitalization ratio of 0.65 to 1.00 to a level such that, if Great Plains Energy would not be in compliance with the covenant as of the date of the closing of the anticipated acquisition of Westar, the ratio would increase up to a maximum of 0.75 to 1.00 for one year. At March 31, 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 March 31, 2017 , KCP&L was in compliance with this covenant. At March 31, 2017 , KCP&L had $195.3 million of commercial paper outstanding at a weighted-average interest rate of 1.20% , 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 March 31, 2017 , GMO was in compliance with this covenant. At March 31, 2017 , GMO had $259.4 million of commercial paper outstanding at a weighted-average interest rate of 1.21% , 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 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. The aggregate principal amount of the facility has been reduced most recently in connection with the March 2017 Great Plains Energy senior note issuance and as of March 31, 2017, the available aggregate principal amount of the facility was $864.5 million . The facility is scheduled to expire on May 31, 2017 , unless otherwise extended in connection with any extension of the Merger Agreement.

Long-Term Debt

Long-Term Debt	3 Months Ended
	Mar. 31, 2017
Debt Disclosure [Abstract]
Long-Term Debt	10. LONG-TERM DEBT Great Plains Energy's and KCP&L's long-term debt is detailed in the following table. March 31 December 31 Year Due 2017 2016 KCP&L (millions) General Mortgage Bonds 2.47% EIRR bonds (a) 2017-2023 $ 110.5 $ 110.5 7.15% Series 2009A (8.59% rate) (b) 2019 400.0 400.0 Senior Notes 5.85% Series (5.72% rate) (b) 2017 250.0 250.0 6.375% Series (7.49% rate) (b) 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) (b) 2035 250.0 250.0 5.30% Series 2041 400.0 400.0 EIRR Bonds 0.773% Series 2007A and 2007B (c) 2035 146.5 146.5 2.875% Series 2008 2038 23.4 23.4 Current maturities (631.0 ) (281.0 ) Unamortized discount and debt issuance costs (14.9 ) (15.4 ) Total KCP&L excluding current maturities (d) 1,934.5 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) (b) 2017 100.0 100.0 2.50% Series 2020 750.0 — 4.85% Series 2021 350.0 350.0 5.292% Series 2022 287.5 287.5 3.15% Series 2022 1,150.0 — 3.90% Series 2027 1,400.0 — 4.85% Series 2047 1,000.0 — Current maturities (101.1 ) (101.1 ) Unamortized discount and premium, net and debt issuance costs (40.5 ) (1.8 ) Total Great Plains Energy excluding current maturities (d) $ 7,275.9 $ 3,365.2 (a) Weighted-average interest rates at March 31, 2017 (b) Rate after amortizing gains/losses recognized in other comprehensive income (OCI) on settlements of interest rate hedging instruments (c) Variable rate (d) At March 31, 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: • $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 . Great Plains Energy plans to use proceeds from the offering to finance a portion of the cash consideration for the anticipated acquisition of Westar. In the event that the anticipated acquisition of Westar does not close by November 30, 2017, or in the event that the Merger Agreement is earlier terminated, then Great Plains Energy would be required to redeem all of the $4.3 billion unsecured senior notes. Additionally, if at any time prior to November 30, 2017, Great Plains Energy determines in its reasonable judgment that the anticipated acquisition of Westar will not close prior to November 30, 2017, then Great Plains Energy could at its sole option (but is not required to) redeem the unsecured senior notes. The redemption price in each case would be 101% of the aggregate principle amount of the senior notes.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	11 . 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 $ 43.4 $ 36.6 $ 11.5 $ 14.0 KCP&L 34.9 16.5 7.6 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 (CO 2 ) 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 CO 2 , 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 as the threshold of at least 55 countries representing at least 55% of global greenhouse gas emissions have joined it through ratification. 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. 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 CO 2 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 CO 2 emission performance rates for existing affected fossil fuel-fired electric generating units. Nationwide, by 2030, the EPA projects the Clean Power Plan would achieve CO 2 emission reductions from the power sector of approximately 32% from CO 2 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 March 2017, United States President Donald Trump issued an Executive Order, Promoting Energy Independence and Economic Growth, that contains a number of climate-related actions. As to the Clean Power Plan and related rules, the order instructs the EPA to review the final rules addressing greenhouse gas emissions from existing, new and modified power plants and suspend, revise or rescind the rules if appropriate. The order directs the EPA Administrator to notify the Attorney General of actions pursuant to this order so that the Attorney General may request courts that are judicially reviewing the above rules and associated litigation to stay or otherwise delay further the litigation while EPA reviews them. Compliance with the Clean Power Plan 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 review 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. Future water permit renewals at GMO's Sibley and Lake Road Stations could also be impacted by the allowable amount of heat that can be contained in the returned water. Great Plains Energy and KCP&L cannot predict the outcome of these matters; however, while less significant outcomes are possible, these matters 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 April 2017, the EPA announced its decision to review and reconsider the new requirements and issued an administrative stay to delay the compliance deadlines. 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 March 31, 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 March 31, 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

Legal Proceedings	3 Months Ended
	Mar. 31, 2017
Legal Proceedings [Abstract]
Contingencies Disclosure [Text Block]	12. 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 accordance with the terms of the settlement agreement, the $7.5 million of cash consideration will accrue interest at the FERC interest rate beginning on January 1, 2017, until the date paid. The settlement agreement is subject to approval by FERC. At March 31, 2017, and December 31, 2016, Great Plains Energy had accrued for the cash consideration and any applicable interest pursuant to the settlement agreement.

Related Party Transactions and

Related Party Transactions and Relationships	3 Months Ended
	Mar. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions and Relationships	13 . 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 $47.9 million and $47.2 million , respectively, for the three months ended March 31, 2017 and 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 March 31, 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. March 31 December 31 2017 2016 (millions) Net receivable from GMO $ 47.3 $ 64.6 Net receivable from Great Plains Energy 21.8 2.6

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	14. 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. 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 anticipated acquisition of Westar. Settlement of the interest rate swaps is contingent on the consummation of the anticipated acquisition of Westar. The interest rate swaps have been designated as economic hedges (non-hedging derivatives). 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 acquisition of Westar. 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 at March 31, 2017, and December 31, 2016, was 0.35 . At March 31, 2017, and December 31, 2016, the fair value of the interest rate swaps was $91.4 million and $79.3 million , respectively, and was recorded on Great Plains Energy's balance sheet in interest rate derivative instruments. For the three months ended March 31, 2017, Great Plains Energy recognized a $12.1 million gain in interest charges for the change in fair value. 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 March 31, 2017 , the book value and fair value of Great Plains Energy's long-term debt, including current maturities, were $8.1 billion and $8.3 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 March 31, 2017 , and 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. At March 31, 2017, and December 31, 2016, GMO's Supplemental Executive Retirement Plan (SERP) rabbi trusts included $15.4 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 March 31 Level 1 Level 2 Level 3 KCP&L (millions) Assets Nuclear decommissioning trust (a) Equity securities $ 161.7 $ 161.7 $ — $ — Debt securities U.S. Treasury 28.2 28.2 — — U.S. Agency 1.7 — 1.7 — State and local obligations 4.1 — 4.1 — Corporate bonds 31.1 — 31.1 — Foreign governments 0.1 — 0.1 — Cash equivalents 5.6 5.6 — — Total nuclear decommissioning trust 232.5 195.5 37.0 — Self-insured health plan trust (b) Equity securities 0.7 0.7 — — Debt securities 2.6 — 2.6 — Cash and cash equivalents 8.0 8.0 — — Total self-insured health plan trust 11.3 8.7 2.6 — Total $ 243.8 $ 204.2 $ 39.6 $ — Other Great Plains Energy Assets Interest rate derivative instruments (c) 91.4 — — 91.4 Total $ 91.4 $ — $ — $ 91.4 Great Plains Energy Assets Nuclear decommissioning trust (a) $ 232.5 $ 195.5 $ 37.0 $ — Self-insured health plan trust (b) 11.3 8.7 2.6 — Interest rate derivative instruments (c) 91.4 — — 91.4 Total $ 335.2 $ 204.2 $ 39.6 $ 91.4 Description December 31 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 March 31, 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 0.35 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 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. Management expects that the contingency factor will decrease as the Company obtains certain regulatory approvals connected with the anticipated acquisition of Westar but could also increase in response to facts and circumstances that in the view of a market participant, would increase the likelihood that the anticipated acquisition of 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 table reconciles the beginning and ending balances for all Level 3 assets measured at fair value on a recurring basis. Great Plains Energy Fair Value Measurements Using Significant Unobservable Inputs (Level 3) Derivative Instruments 2017 (millions) Net asset at January 1 $ 79.3 Total unrealized gains: included in interest charges 12.1 Net asset at March 31 $ 91.4 Total unrealized gains relating to assets still on the consolidated balance sheet at March 31: included in interest charges $ 12.1

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	3 Months Ended
	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss) [Text Block]	15 . 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) Three Months Ended March 31, 2017 Beginning balance January 1 $ (4.5 ) $ (2.1 ) $ (6.6 ) Amounts reclassified from accumulated other comprehensive loss 1.4 0.1 1.5 Net current period other comprehensive income 1.4 0.1 1.5 Ending balance March 31 $ (3.1 ) $ (2.0 ) $ (5.1 ) Three Months Ended March 31, 2016 Beginning balance January 1 $ (10.1 ) $ (1.9 ) $ (12.0 ) Amounts reclassified from accumulated other comprehensive loss 1.4 0.1 1.5 Net current period other comprehensive income 1.4 0.1 1.5 Ending balance March 31 $ (8.7 ) $ (1.8 ) $ (10.5 ) (a) Net of tax KCP&L Gains and Losses on Cash Flow Hedges (a) (millions) Three Months Ended March 31, 2017 Beginning balance January 1 $ (4.2 ) Amounts reclassified from accumulated other comprehensive loss 1.3 Net current period other comprehensive income 1.3 Ending balance March 31 $ (2.9 ) Three Months Ended March 31, 2016 Beginning balance January 1 $ (9.6 ) Amounts reclassified from accumulated other comprehensive loss 1.4 Net current period other comprehensive income 1.4 Ending balance March 31 $ (8.2 ) (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 March 31 2017 2016 (millions) Gains and (losses) on cash flow hedges (effective portion) Interest rate contracts $ (2.3 ) $ (2.3 ) Interest charges (2.3 ) (2.3 ) Income (loss) before income tax (expense) benefit and income from equity investments 0.9 0.9 Income tax (expense) benefit $ (1.4 ) $ (1.4 ) 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 (loss) before income tax (expense) benefit and income from equity investments 0.1 0.1 Income tax (expense) benefit $ (0.1 ) $ (0.1 ) Net income (loss) Total reclassifications, net of tax $ (1.5 ) $ (1.5 ) 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 March 31 2017 2016 (millions) Gains and (losses) on cash flow hedges (effective portion) Interest rate contracts $ (2.2 ) $ (2.3 ) Interest charges (2.2 ) (2.3 ) Income before income tax expense 0.9 0.9 Income tax benefit Total reclassifications, net of tax $ (1.3 ) $ (1.4 ) Net income

Taxes

Taxes	3 Months Ended
	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Income Tax Disclosure [Text Block]	16. TAXES Components of income tax expense (benefit) are detailed in the following tables. Great Plains Energy Three Months Ended March 31 2017 2016 Current income taxes (millions) Federal $ — $ (0.1 ) State 0.2 0.2 Total 0.2 0.1 Deferred income taxes Federal (4.5 ) 9.7 State (1.1 ) 2.3 Total (5.6 ) 12.0 Investment tax credit amortization (0.4 ) (0.4 ) Income tax expense (benefit) $ (5.8 ) $ 11.7 KCP&L Three Months Ended March 31 2017 2016 Current income taxes (millions) Federal $ (0.1 ) $ 0.4 State — 0.1 Total (0.1 ) 0.5 Deferred income taxes Federal 7.8 8.4 State 1.4 2.0 Total 9.2 10.4 Investment tax credit amortization (0.3 ) (0.2 ) Income tax expense $ 8.8 $ 10.7 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. Great Plains Energy Three Months Ended March 31 2017 2016 Federal statutory income tax rate 35.0 % 35.0 % Differences between book and tax depreciation not normalized — 0.5 Amortization of investment tax credits (0.4 ) (0.9 ) Federal income tax credits (1.5 ) (8.0 ) State income taxes 4.2 4.2 Transaction costs 3.1 — Other (2.5 ) — Effective income tax rate 37.9 % 30.8 % KCP&L Three Months Ended March 31 2017 2016 Federal statutory income tax rate 35.0 % 35.0 % Differences between book and tax depreciation not normalized (0.1 ) 0.4 Amortization of investment tax credits (0.3 ) (0.7 ) Federal income tax credits (1.8 ) (7.8 ) State income taxes 4.0 3.9 Other 1.5 (0.5 ) Effective income tax rate 38.3 % 30.3 %

Segments and Related Informatio

Segments and Related Information	3 Months Ended
	Mar. 31, 2017
Segment Reporting [Abstract]
Segments and Related Information	17 . 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 costs to achieve the anticipated acquisition of Westar. The summary of significant accounting policies applies to the reportable segment. Segment performance is evaluated based on net income. The following tables reflect summarized financial information concerning Great Plains Energy's reportable segment. Three Months Ended March 31, 2017 Electric Utility Other Eliminations Great Plains Energy (millions) Operating revenues $ 570.7 $ — $ — $ 570.7 Depreciation and amortization (90.3 ) — — (90.3 ) Interest (charges) income (50.1 ) (24.5 ) 8.0 (66.6 ) Income tax (expense) benefit (10.1 ) 15.9 — 5.8 Net income (loss) 16.1 (25.7 ) — (9.6 ) Three Months Ended March 31, 2016 Electric Utility Other Eliminations Great Plains Energy (millions) Operating revenues $ 572.1 $ — $ — $ 572.1 Depreciation and amortization (85.2 ) — — (85.2 ) Interest (charges) income (49.1 ) (10.1 ) 8.0 (51.2 ) Income tax (expense) benefit (13.1 ) 1.4 — (11.7 ) Net income (loss) 29.0 (2.6 ) — 26.4 Electric Utility Other Eliminations Great Plains Energy March 31, 2017 (millions) Assets $ 11,465.6 $ 6,729.5 $ (397.6 ) $ 17,797.5 Capital expenditures (a) 116.6 — — 116.6 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 Accoun25

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2017
Accounting Policies [Abstract]
Organization [Policy Text Block]	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 to be used to fund the cash consideration for the anticipated acquisition of Westar Energy, Inc. (Westar). 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 17 for additional information.
Basic and Diluted Earnings per Common Share Calculation [Policy Text Block]	Basic and Diluted Earnings per Common Share Calculation To determine basic earnings per common share (EPS), preferred stock dividend requirements are deducted from net income before dividing by the average number of common shares outstanding. To determine diluted EPS, preferred stock dividend requirements are added to earnings available for common shareholders for the periods in which the assumed conversion of Great Plains Energy's 7.00% Series B Mandatory Convertible Preferred Stock (Series B Preferred Stock) has a dilutive effect 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 and the number of common shares that would be issued under an assumed conversion of Series B Preferred Stock using the if-converted method.
New Accounting Pronouncements, Policy [Policy Text Block]	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 other 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. The new guidance is to be applied retrospectively for the presentation of service cost and other 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 are evaluating the effect it will have on their consolidated financial statements and related disclosures. 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 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 retrospective or cumulative effect transition method. The Companies have completed a review of the majority of their revenue arrangements and do not expect the standard to have a material impact on their consolidated financial statements. However, the Companies are still evaluating the impacts on revenue recognition of their remaining revenue arrangements and contracts where collectability is uncertain. The Companies are in the process of determining their method of adoption, which depends in part on completing the evaluation of the remaining items noted above.

Summary of Significant Accoun26

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 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 March 31 2017 2016 Income (loss) (millions, except per share amounts) Net income (loss) $ (9.6 ) $ 26.4 Less: preferred stock dividend requirements 15.1 0.4 Earnings (loss) available for common shareholders $ (24.7 ) $ 26.0 Common Shares Outstanding Average number of common shares outstanding 215.3 154.4 Add: effect of dilutive securities — 0.6 Diluted average number of common shares outstanding 215.3 155.0 Basic and diluted EPS $ (0.11 ) $ 0.17
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]	Anti-dilutive shares excluded from the computation of diluted EPS are detailed in the following table. Three Months Ended March 31 2017 2016 Assumed conversion of Series B Preferred Stock 29,930,385 — Performance shares 460,169 372,093 Restricted stock shares 328,512 —

Supplemental Cash Flow Inform27

Supplemental Cash Flow Information (Tables)	3 Months Ended
	Mar. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]	Great Plains Energy Other Operating Activities Three Months Ended March 31 2017 2016 Cash flows affected by changes in: (millions) Receivables $ 55.5 $ 39.7 Accounts receivable pledged as collateral 0.2 — Fuel inventories 1.8 6.3 Materials and supplies (4.2 ) (2.1 ) Accounts payable (136.8 ) (120.4 ) Accrued taxes 36.3 38.0 Accrued interest 26.5 14.4 Deferred refueling outage costs 4.0 4.9 Pension and post-retirement benefit obligations 11.6 23.7 Allowance for equity funds used during construction (1.0 ) (0.9 ) Fuel recovery mechanisms (14.1 ) (4.6 ) Other 13.2 (15.3 ) Total other operating activities $ (7.0 ) $ (16.3 ) Cash paid during the period: Interest $ 34.2 $ 33.3 Income taxes $ — $ 0.1 Non-cash investing activities: Liabilities accrued for capital expenditures $ 22.6 $ 24.7 KCP&L Other Operating Activities Three Months Ended March 31 2017 2016 Cash flows affected by changes in: (millions) Receivables $ 36.2 $ 36.5 Fuel inventories (0.5 ) 4.9 Materials and supplies (3.1 ) (2.0 ) Accounts payable (88.8 ) (75.5 ) Accrued taxes 35.5 102.2 Accrued interest 10.1 9.9 Deferred refueling outage costs 4.0 4.9 Pension and post-retirement benefit obligations 10.3 23.9 Allowance for equity funds used during construction (1.0 ) (0.6 ) Fuel recovery mechanisms (10.8 ) (14.3 ) Other (13.0 ) (14.1 ) Total other operating activities $ (21.1 ) $ 75.8 Cash paid during the period: Interest $ 22.5 $ 22.2 Non-cash investing activities: Liabilities accrued for capital expenditures $ 19.9 $ 16.5

Receivables (Tables)

Receivables (Tables)	3 Months Ended
	Mar. 31, 2017
Receivables [Abstract]
Schedule of receivables [Table Text Block]	Great Plains Energy's and KCP&L's receivables are detailed in the following table. March 31 December 31 2017 2016 Great Plains Energy (millions) Customer accounts receivable - billed $ 10.2 $ 26.2 Customer accounts receivable - unbilled 51.9 79.1 Allowance for doubtful accounts - customer accounts receivable (4.4 ) (4.0 ) Other receivables 52.7 64.7 Total $ 110.4 $ 166.0 KCP&L Customer accounts receivable - billed $ 9.0 $ 25.5 Customer accounts receivable - unbilled 47.7 63.7 Allowance for doubtful accounts - customer accounts receivable (1.8 ) (1.8 ) Other receivables 44.1 51.7 Total $ 99.0 $ 139.1

Nuclear Plant (Tables)

Nuclear Plant (Tables)	3 Months Ended
	Mar. 31, 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. March 31 December 31 2017 2016 Decommissioning Trust (millions) Beginning balance January 1 $ 222.9 $ 200.7 Contributions 0.9 3.3 Earned income, net of fees 1.1 4.1 Net realized gains 0.2 0.3 Net unrealized gains 7.4 14.5 Ending balance $ 232.5 $ 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. March 31, 2017 December 31, 2016 Cost Basis Unrealized Gains Unrealized Losses Fair Value Cost Basis Unrealized Gains Unrealized Losses Fair Value (millions) Equity securities $ 93.9 $ 68.6 $ (0.8 ) $ 161.7 $ 93.3 $ 62.1 $ (1.5 ) $ 153.9 Debt securities 63.2 2.4 (0.4 ) 65.2 63.4 2.3 (0.5 ) 65.2 Other 5.6 — — 5.6 3.8 — — 3.8 Total $ 162.7 $ 71.0 $ (1.2 ) $ 232.5 $ 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 March 31 2017 2016 (millions) Realized gains $ 0.3 $ 0.7 Realized losses (0.1 ) (0.7 )

Pension Plans and Other Emplo30

Pension Plans and Other Employee Benefits (Tables)	3 Months Ended
	Mar. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Schedule of Net Benefit Costs [Table Text Block]	The following table provides 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 March 31 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 1.3 1.5 Expected return on plan assets (12.8 ) (12.3 ) (0.6 ) (0.8 ) Prior service cost 0.2 0.2 — 0.3 Recognized net actuarial (gain)/loss 12.4 13.0 (0.1 ) (0.4 ) Net periodic benefit costs before regulatory adjustment 24.2 24.6 1.1 1.3 Regulatory adjustment 0.8 (1.0 ) 1.3 1.5 Net periodic benefit costs $ 25.0 $ 23.6 $ 2.4 $ 2.8

Equity Compensation (Tables)

Equity Compensation (Tables)	3 Months Ended
	Mar. 31, 2017
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Equity compensation expense and associated income tax benefits	Three Months Ended March 31 2017 2016 Great Plains Energy (millions) Equity compensation expense $ 1.2 $ 3.7 Income tax benefit 0.6 1.5 KCP&L Equity compensation expense $ 0.8 $ 2.5 Income tax benefit 0.4 1.0
Performance share activity	Performance Shares Grant Date Fair Value* Beginning balance January 1, 2017 625,100 $ 28.13 Granted 236,433 31.26 Earned (182,676 ) 28.78 Forfeited (32,264 ) 27.74 Ending balance March 31, 2017 646,593 29.09
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 (84,473 ) 27.05 Forfeited (7,320 ) 27.58 Ending balance March 31, 2017 236,719 27.71

Long-Term Debt (Tables)

Long-Term Debt (Tables)	3 Months Ended
	Mar. 31, 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. March 31 December 31 Year Due 2017 2016 KCP&L (millions) General Mortgage Bonds 2.47% EIRR bonds (a) 2017-2023 $ 110.5 $ 110.5 7.15% Series 2009A (8.59% rate) (b) 2019 400.0 400.0 Senior Notes 5.85% Series (5.72% rate) (b) 2017 250.0 250.0 6.375% Series (7.49% rate) (b) 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) (b) 2035 250.0 250.0 5.30% Series 2041 400.0 400.0 EIRR Bonds 0.773% Series 2007A and 2007B (c) 2035 146.5 146.5 2.875% Series 2008 2038 23.4 23.4 Current maturities (631.0 ) (281.0 ) Unamortized discount and debt issuance costs (14.9 ) (15.4 ) Total KCP&L excluding current maturities (d) 1,934.5 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) (b) 2017 100.0 100.0 2.50% Series 2020 750.0 — 4.85% Series 2021 350.0 350.0 5.292% Series 2022 287.5 287.5 3.15% Series 2022 1,150.0 — 3.90% Series 2027 1,400.0 — 4.85% Series 2047 1,000.0 — Current maturities (101.1 ) (101.1 ) Unamortized discount and premium, net and debt issuance costs (40.5 ) (1.8 ) Total Great Plains Energy excluding current maturities (d) $ 7,275.9 $ 3,365.2 (a) Weighted-average interest rates at March 31, 2017 (b) Rate after amortizing gains/losses recognized in other comprehensive income (OCI) on settlements of interest rate hedging instruments (c) Variable rate (d) At March 31, 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

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule Of Environmental Capital Expenditures [Table Text Block]	2017 2018 2019 2020 (millions) Great Plains Energy $ 43.4 $ 36.6 $ 11.5 $ 14.0 KCP&L 34.9 16.5 7.6 13.0

Related Party Transactions an34

Related Party Transactions and Relationships (Tables)	3 Months Ended
	Mar. 31, 2017
Related Party Transactions [Abstract]
Schedule of related party receivables and payables [Table Text Block]	The following table summarizes KCP&L's related party net receivables. March 31 December 31 2017 2016 (millions) Net receivable from GMO $ 47.3 $ 64.6 Net receivable from Great Plains Energy 21.8 2.6

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 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 March 31 Level 1 Level 2 Level 3 KCP&L (millions) Assets Nuclear decommissioning trust (a) Equity securities $ 161.7 $ 161.7 $ — $ — Debt securities U.S. Treasury 28.2 28.2 — — U.S. Agency 1.7 — 1.7 — State and local obligations 4.1 — 4.1 — Corporate bonds 31.1 — 31.1 — Foreign governments 0.1 — 0.1 — Cash equivalents 5.6 5.6 — — Total nuclear decommissioning trust 232.5 195.5 37.0 — Self-insured health plan trust (b) Equity securities 0.7 0.7 — — Debt securities 2.6 — 2.6 — Cash and cash equivalents 8.0 8.0 — — Total self-insured health plan trust 11.3 8.7 2.6 — Total $ 243.8 $ 204.2 $ 39.6 $ — Other Great Plains Energy Assets Interest rate derivative instruments (c) 91.4 — — 91.4 Total $ 91.4 $ — $ — $ 91.4 Great Plains Energy Assets Nuclear decommissioning trust (a) $ 232.5 $ 195.5 $ 37.0 $ — Self-insured health plan trust (b) 11.3 8.7 2.6 — Interest rate derivative instruments (c) 91.4 — — 91.4 Total $ 335.2 $ 204.2 $ 39.6 $ 91.4 Description December 31 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 March 31, 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 0.35 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 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. Management expects that the contingency factor will decrease as the Company obtains certain regulatory approvals connected with the anticipated acquisition of Westar but could also increase in response to facts and circumstances that in the view of a market participant, would increase the likelihood that the anticipated acquisition of Westar is not consummated. Because of the unobservable nature of the contingency factor, the interest rate derivatives have been classified as Level 3.
Unobservable inputs reconciliation	The following table reconciles the beginning and ending balances for all Level 3 assets measured at fair value on a recurring basis. Great Plains Energy Fair Value Measurements Using Significant Unobservable Inputs (Level 3) Derivative Instruments 2017 (millions) Net asset at January 1 $ 79.3 Total unrealized gains: included in interest charges 12.1 Net asset at March 31 $ 91.4 Total unrealized gains relating to assets still on the consolidated balance sheet at March 31: included in interest charges $ 12.1

Accumulated Other Comprehensi36

Accumulated Other Comprehensive Income (Loss) (Tables)	3 Months Ended
	Mar. 31, 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) Three Months Ended March 31, 2017 Beginning balance January 1 $ (4.5 ) $ (2.1 ) $ (6.6 ) Amounts reclassified from accumulated other comprehensive loss 1.4 0.1 1.5 Net current period other comprehensive income 1.4 0.1 1.5 Ending balance March 31 $ (3.1 ) $ (2.0 ) $ (5.1 ) Three Months Ended March 31, 2016 Beginning balance January 1 $ (10.1 ) $ (1.9 ) $ (12.0 ) Amounts reclassified from accumulated other comprehensive loss 1.4 0.1 1.5 Net current period other comprehensive income 1.4 0.1 1.5 Ending balance March 31 $ (8.7 ) $ (1.8 ) $ (10.5 ) (a) Net of tax KCP&L Gains and Losses on Cash Flow Hedges (a) (millions) Three Months Ended March 31, 2017 Beginning balance January 1 $ (4.2 ) Amounts reclassified from accumulated other comprehensive loss 1.3 Net current period other comprehensive income 1.3 Ending balance March 31 $ (2.9 ) Three Months Ended March 31, 2016 Beginning balance January 1 $ (9.6 ) Amounts reclassified from accumulated other comprehensive loss 1.4 Net current period other comprehensive income 1.4 Ending balance March 31 $ (8.2 ) (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 March 31 2017 2016 (millions) Gains and (losses) on cash flow hedges (effective portion) Interest rate contracts $ (2.3 ) $ (2.3 ) Interest charges (2.3 ) (2.3 ) Income (loss) before income tax (expense) benefit and income from equity investments 0.9 0.9 Income tax (expense) benefit $ (1.4 ) $ (1.4 ) 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 (loss) before income tax (expense) benefit and income from equity investments 0.1 0.1 Income tax (expense) benefit $ (0.1 ) $ (0.1 ) Net income (loss) Total reclassifications, net of tax $ (1.5 ) $ (1.5 ) 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 March 31 2017 2016 (millions) Gains and (losses) on cash flow hedges (effective portion) Interest rate contracts $ (2.2 ) $ (2.3 ) Interest charges (2.2 ) (2.3 ) Income before income tax expense 0.9 0.9 Income tax benefit Total reclassifications, net of tax $ (1.3 ) $ (1.4 ) Net income

Taxes (Tables)

Taxes (Tables)	3 Months Ended
	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	Components of income tax expense (benefit) are detailed in the following tables. Great Plains Energy Three Months Ended March 31 2017 2016 Current income taxes (millions) Federal $ — $ (0.1 ) State 0.2 0.2 Total 0.2 0.1 Deferred income taxes Federal (4.5 ) 9.7 State (1.1 ) 2.3 Total (5.6 ) 12.0 Investment tax credit amortization (0.4 ) (0.4 ) Income tax expense (benefit) $ (5.8 ) $ 11.7 KCP&L Three Months Ended March 31 2017 2016 Current income taxes (millions) Federal $ (0.1 ) $ 0.4 State — 0.1 Total (0.1 ) 0.5 Deferred income taxes Federal 7.8 8.4 State 1.4 2.0 Total 9.2 10.4 Investment tax credit amortization (0.3 ) (0.2 ) Income tax expense $ 8.8 $ 10.7
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. Great Plains Energy Three Months Ended March 31 2017 2016 Federal statutory income tax rate 35.0 % 35.0 % Differences between book and tax depreciation not normalized — 0.5 Amortization of investment tax credits (0.4 ) (0.9 ) Federal income tax credits (1.5 ) (8.0 ) State income taxes 4.2 4.2 Transaction costs 3.1 — Other (2.5 ) — Effective income tax rate 37.9 % 30.8 % KCP&L Three Months Ended March 31 2017 2016 Federal statutory income tax rate 35.0 % 35.0 % Differences between book and tax depreciation not normalized (0.1 ) 0.4 Amortization of investment tax credits (0.3 ) (0.7 ) Federal income tax credits (1.8 ) (7.8 ) State income taxes 4.0 3.9 Other 1.5 (0.5 ) Effective income tax rate 38.3 % 30.3 %

Segments and Related Informat38

Segments and Related Information (Tables)	3 Months Ended
	Mar. 31, 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 March 31, 2017 Electric Utility Other Eliminations Great Plains Energy (millions) Operating revenues $ 570.7 $ — $ — $ 570.7 Depreciation and amortization (90.3 ) — — (90.3 ) Interest (charges) income (50.1 ) (24.5 ) 8.0 (66.6 ) Income tax (expense) benefit (10.1 ) 15.9 — 5.8 Net income (loss) 16.1 (25.7 ) — (9.6 ) Three Months Ended March 31, 2016 Electric Utility Other Eliminations Great Plains Energy (millions) Operating revenues $ 572.1 $ — $ — $ 572.1 Depreciation and amortization (85.2 ) — — (85.2 ) Interest (charges) income (49.1 ) (10.1 ) 8.0 (51.2 ) Income tax (expense) benefit (13.1 ) 1.4 — (11.7 ) Net income (loss) 29.0 (2.6 ) — 26.4 Electric Utility Other Eliminations Great Plains Energy March 31, 2017 (millions) Assets $ 11,465.6 $ 6,729.5 $ (397.6 ) $ 17,797.5 Capital expenditures (a) 116.6 — — 116.6 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 Accoun39

Summary of Significant Accounting Policies Equity Method Investment (Details) - Transource Energy, LLC [Member]	3 Months Ended
	Mar. 31, 2017Rate
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 Accoun40

Summary of Significant Accounting Policies Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Income [Abstract]
Net income (loss)	$ (9.6)	$ 26.4
Less: preferred stock dividend requirements	15.1	0.4
Earnings (loss) available for common shareholders	$ (24.7)	$ 26
Common Shares Outstanding [Abstract]
Average number of common shares outstanding (in shares)	215.3	154.4
Add: effect of dilutive securities (in shares)	0	0.6
Diluted average number of common shares outstanding (in shares)	215.3	155
Earnings Per Share [Abstract]
Basic and Diluted EPS	$ (0.11)	$ 0.17
Series B Preferred Stock [Member]
Preferred Stock, Dividend Rate, Percentage	7.00%		7.00%

Summary of Significant Accoun41

Summary of Significant Accounting Policies Antidilutive Securities (Details) - shares	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Performance Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	460,169	372,093
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	328,512	0
Assumed conversion of Series B Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	29,930,385	0

Summary of Significant Accoun42

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

Summary of Significant Accoun43

Summary of Significant Accounting Policies Subsequent Events (Details) - Subsequent Event [Member]	1 Months Ended
	May 31, 2017$ / shares
Kansas City Power and Light Company [Member]
Dividends Declared [Abstract]
Dividends Payable, Amount Per Share	$ 75,000,000
Dividends Payable, Date to be Paid	Jun. 19, 2017
Dividends Payable, Date Declared, Month and Year	2017-05
Common Stock [Member]
Dividends Declared [Abstract]
Dividends Payable, Amount Per Share	$ 0.275
Dividends Payable, Date to be Paid	Jun. 20, 2017
Dividends Payable, Date of Record	May 30, 2017
Dividends Payable, Date Declared, Month and Year	2017-05
7.00% Mandatory Convertible Preferred Stock, Series B
Dividends Declared [Abstract]
Dividends Payable, Date to be Paid	Jun. 15, 2017
Dividends Payable, Date of Record	Jun. 1, 2017
Dividends Payable, Date Declared, Month and Year	2017-05

Anticipated Acquisition of We44

Anticipated Acquisition of Westar Energy, Inc. (Details) $ / shares in Units, $ in Millions	Mar. 09, 2017USD ($)	Oct. 03, 2016USD ($)$ / sharesshares	May 29, 2016USD ($)$ / sharesRateshares	Mar. 31, 2017USD ($)$ / sharesRateshares	Mar. 31, 2016USD ($)shares	Dec. 31, 2016Rate
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Cash consideration to be transferred (per share) | $ / shares			$ 51
Great Plains Energy Average Stock Price - Maximum | $ / shares			33.2283
Great Plains Energy Average Stock Price Minimum | $ / shares			$ 28.5918
Exchange Ratio if Great Plains Energy Avg Stock Price is less than $28.5918			0.3148
Exchange Ratio if Great Plains Energy Avg Stock Price is greater than $33.2283			0.2709
Exchange Ratio Numerator | $ / shares			$ 9
Gross Proceeds from Issuance of Common Stock				$ 1.5	$ 0.7
Anticipated Acquisition Financing, Mandatory Convertible Preferred Equity				750
Anticipated Acquisition Financing, Common And Preferred Equity				2,350
Anticipated Acquisition Financing, Debt				4,300
Issuance of long-term debt				$ 4,291.9	$ 0
Unsecured Debt [Member] | GPE 4.3 Billion Senior Notes [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Debt Instrument, Mandatory Redemption Price, Percentage | Rate				101.00%
Debt Instrument, Optional Redemption Price, Percentage | Rate				101.00%
Great Plains Energy [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Merger Termination Fee, Regulatory Approval				$ 380
Merger Termination Fee Great Plains Energy				180
Great Plains Energy [Member] | GPE 4.3 Billion Senior Notes [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Long-term Debt, Gross				4,300
Great Plains Energy [Member] | Unsecured Debt [Member] | GPE 4.3 Billion Senior Notes [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Proceeds from Issuance of Senior Long-term Debt	$ 4,300
Long-term Debt, Gross				4,300
Westar Energy Inc [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Merger Termination Fee Westar				280
Bridge Loan [Member] | Great Plains Energy [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Amount of bridge facility			$ 8,017	8,017
Amount of bridge facility, as amended				$ 864.5
7.25% Mandatory Convertible Preferred Stock, Series A [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Preferred Shares To Be Issued, Stock Purchase Agreement, Series A Preferred Stock | shares			750,000
Preferred Stock, Dividend Rate, Percentage | Rate			7.25%
Preferred Stock, Purchase Agreement, Proceeds			$ 750
Depositary Shares [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Stock Issued During Period, Shares, New Issues | shares		17,300,000
Shares Issued, Price Per Share | $ / shares		$ 50
Net Proceeds from Issuance of Depositary Shares		$ 836.2
Gross Proceeds from Issuance of Depositary Shares		$ 862.5
Series B Preferred Stock [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Preferred Stock, Dividend Rate, Percentage | Rate				7.00%		7.00%
Preferred Stock, Redemption Price Per Share | $ / shares				$ 1,000
Minimum [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Great Plains Energy Average Stock Price - Less Than Maximum, Greater Than Minimum | $ / shares			$ 28.5918
Maximum [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Great Plains Energy Average Stock Price - Less Than Maximum, Greater Than Minimum | $ / shares			$ 33.2283
Common Stock [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Stock Issued During Period, Shares, New Issues | shares		60,500,000		249,170	336,356
Shares Issued, Price Per Share | $ / shares		$ 26.45
Net Proceeds from Issuance of Common Stock		$ 1,550
Gross Proceeds from Issuance of Common Stock		$ 1,600

Supplemental Cash Flow Inform45

Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows affected by changes in:
Receivables	$ 55.5	$ 39.7
Accounts receivable pledged as collateral	0.2	0
Fuel inventories	1.8	6.3
Materials and supplies	(4.2)	(2.1)
Accounts payable	(136.8)	(120.4)
Accrued taxes	36.3	38
Accrued interest	26.5	14.4
Deferred refueling outage costs	4	4.9
Pension and post-retirement benefit obligations	11.6	23.7
Allowance for equity funds used during construction	(1)	(0.9)
Fuel recovery mechanisms	(14.1)	(4.6)
Other	13.2	(15.3)
Total other operating activities	(7)	(16.3)
Cash paid during the period:
Interest	34.2	33.3
Income taxes	0	0.1
Non-cash investing activities:
Liabilities accrued for capital expenditures	22.6	24.7
Kansas City Power and Light Company [Member]
Cash flows affected by changes in:
Receivables	36.2	36.5
Fuel inventories	(0.5)	4.9
Materials and supplies	(3.1)	(2)
Accounts payable	(88.8)	(75.5)
Accrued taxes	35.5	102.2
Accrued interest	10.1	9.9
Deferred refueling outage costs	4	4.9
Pension and post-retirement benefit obligations	10.3	23.9
Allowance for equity funds used during construction	(1)	(0.6)
Fuel recovery mechanisms	(10.8)	(14.3)
Other	(13)	(14.1)
Total other operating activities	(21.1)	75.8
Cash paid during the period:
Interest	22.5	22.2
Non-cash investing activities:
Liabilities accrued for capital expenditures	$ 19.9	$ 16.5

Receivables Accounts, Notes, an

Receivables Accounts, Notes, and Financing (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other receivables	$ 52.7	$ 64.7
Total	110.4	166
Kansas City Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other receivables	44.1	51.7
Total	99	139.1
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts	(4.4)	(4)
Trade Accounts Receivable [Member] | Kansas City Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts	(1.8)	(1.8)
Trade Accounts Receivable [Member] | Billed Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	10.2	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	9	25.5
Trade Accounts Receivable [Member] | Unbilled Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	51.9	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	$ 47.7	$ 63.7

Receivables Narrative (Details)

Receivables Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Sale Of Accounts Receivable - KCPL and GMO
Accounts receivable pledged as collateral	$ 172.2	$ 172.4
Collateralized note payable	172.2	172.4
Kansas City Power and Light Company [Member]
Sale Of Accounts Receivable - KCPL and GMO
Accounts receivable pledged as collateral	110	110
Collateralized note payable	110	$ 110
Maximum amount of outstanding principal under receivables agreement	110
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	65
Maximum amount of outstanding principal under receivables agreement from mid-June to mid-November	$ 80

Nuclear Plant (Details)

Nuclear Plant (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Investments in decommissioning trust fund [Line Items]
Cost Basis	$ 162.7		$ 160.5
Unrealized Gains	71		64.4
Unrealized Losses	(1.2)		(2)
Fair Value	$ 232.5		222.9	$ 200.7
Weighted average maturity of debt securities (in years)	8 years
Realized gains	$ 0.3	$ 0.7
Realized losses	(0.1)	$ (0.7)
Equity Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	93.9		93.3
Unrealized Gains	68.6		62.1
Unrealized Losses	(0.8)		(1.5)
Fair Value	161.7		153.9
Debt Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	63.2		63.4
Unrealized Gains	2.4		2.3
Unrealized Losses	(0.4)		(0.5)
Fair Value	65.2		65.2
Other Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	5.6		3.8
Fair Value	$ 5.6		$ 3.8

Nuclear Plant Decommissioning T

Nuclear Plant Decommissioning Trust (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2017
Nuclear decommissioning trust fund [Roll Forward]
Beginning balance January 1	$ 222.9	$ 200.7
Contributions	0.9	3.3
Earned income, net of fees	1.1	4.1
Net realized gains	0.2	0.3
Net unrealized gains	7.4	14.5
Ending balance	232.5	222.9
Kansas City Power and Light Company [Member]
Nuclear decommissioning trust fund [Roll Forward]
Beginning balance January 1	222.9	200.7
Contributions	0.9	3.3
Earned income, net of fees	1.1	4.1
Net realized gains	0.2	0.3
Net unrealized gains	7.4	14.5
Ending balance	$ 232.5	$ 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%

Regulatory Matters (Details)

Regulatory Matters (Details) - Kansas City Power and Light Company [Member] - USD ($) $ in Millions	1 Months Ended
	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%
Kansas Corporation Commission [Member]
Regulatory Proceedings [Line Items]
Annual revenue decrease, requested	$ 2.8

Regulatory Matters Regulatory M

Regulatory Matters Regulatory Matters Subsequent Events (Details) - Kansas City Power and Light Company [Member] - Subsequent Event [Member] - USD ($) $ in Millions	1 Months Ended
	May 31, 2017	Apr. 30, 2017
MissouriPublicServiceCommission [Member]
Subsequent Event [Line Items]
Return on equity, approved (in hundredths)	9.50%
Ratemaking equity ratio, approved (in hundredths)	49.20%
Kansas Corporation Commission [Member]
Subsequent Event [Line Items]
Public Utilities, KCPL and Commission Staff Recommended Rate Decrease, Amount		$ 3.6
Minimum [Member] | MissouriPublicServiceCommission [Member]
Subsequent Event [Line Items]
Anticipated annual revenue increase authorized	$ 30
Maximum [Member] | MissouriPublicServiceCommission [Member]
Subsequent Event [Line Items]
Anticipated annual revenue increase authorized	$ 35

Pension Plans and Other Emplo52

Pension Plans and Other Employee Benefits (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Contributions by Employer	$ 16
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year	63.6
Components of net periodic benefit costs [Abstract]
Service cost	11	$ 10.5
Interest cost	13.4	13.2
Expected return on plan assets	(12.8)	(12.3)
Prior service cost	0.2	0.2
Recognized net actuarial (gain)/loss	12.4	13
Net periodic benefit costs before regulatory adjustment	24.2	24.6
Regulatory adjustment	0.8	(1)
Net periodic benefit costs	25	23.6
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
Interest cost	1.3	1.5
Expected return on plan assets	(0.6)	(0.8)
Prior service cost	0	0.3
Recognized net actuarial (gain)/loss	(0.1)	(0.4)
Net periodic benefit costs before regulatory adjustment	1.1	1.3
Regulatory adjustment	1.3	1.5
Net periodic benefit costs	$ 2.4	$ 2.8
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%

Equity Compensation (Details)

Equity Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation expense	$ 1.2	$ 3.7
Income tax benefit	$ 0.6	$ 1.5
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)	236,433
Earned (in shares)	(182,676)
Forfeited (in shares)	(32,264)
Ending balance (in shares)	646,593
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)	28.78
Weighted average forfeited (in dollars per share)	27.74
Weighted average ending balance (in dollars per share)	$ 29.09
Total unrecognized compensation expense	$ 11.7
Remaining weighted-average contractual term (in years)	1 year 11 months
Fair value of performance shares earned and paid	$ 5.3	$ 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)	78,840
Vested (in shares)	(84,473)
Forfeited (in shares)	(7,320)
Ending balance (in shares)	236,719
Weighted average beginning balance (in dollars per share)	$ 27.20
Weighted average granted (in dollars per share)	28.60	$ 29.42
Weighted average vested (in dollars per share)	27.05
Weighted average forfeited (in dollars per share)	27.58
Weighted average ending balance (in dollars per share)	$ 27.71
Total unrecognized compensation expense	$ 3.9
Total fair value of shares vested	$ 2.3	$ 1.6
Remaining weighted-average contractual term (in years)	1 year 11 months
Kansas City Power and Light Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation expense	$ 0.8	2.5
Income tax benefit	$ 0.4	$ 1

Short-term Borrowings and Sho54

Short-term Borrowings and Short-term Bank Lines of Credit (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	May 29, 2016
Short-term Debt [Line Items]
Commercial paper outstanding	$ 454,700,000	$ 334,800,000
Great Plains Energy [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 200,000,000
Credit facility expiration date	Oct. 31, 2019
Maximum borrowing capacity with transfer of unused commitments	$ 400,000,000
Line of Credit Facility, Covenant Terms	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. In June 2016, the facility was amended, among other things, to increase the maximum consolidated indebtedness to consolidate capitalization ratio of 0.65 to 1.00 to a level such that, if Great Plains Energy would not be in compliance with the covenant as of the date of the closing of the anticipated acquisition of Westar, the ratio would increase up to a maximum of 0.75 to 1.00 for one year.
Line of Credit Facility, Covenant Compliance	in compliance
Amount of outstanding cash borrowings	$ 0	0
Amount of letters of credit outstanding	1,000,000	1,000,000
Great Plains Energy [Member] | Bridge Loan [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 8,017,000,000		$ 8,017,000,000
Credit facility expiration date	May 31, 2017
Amount of bridge facility, as amended	$ 864,500,000
Kansas City Power and Light Company [Member]
Short-term Debt [Line Items]
Commercial paper outstanding	$ 195,300,000	$ 132,900,000
Weighted-average interest rate from outstanding borrowings	1.20%	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	$ 600,000,000
Credit facility expiration date	Oct. 31, 2019
Maximum transfer of unused commitments	$ 200,000,000
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
Amount of letters of credit outstanding	2,700,000	2,800,000
KCPL Greater Missouri Operations [Member]
Short-term Debt [Line Items]
Commercial paper outstanding	$ 259,400,000	$ 201,900,000
Weighted-average interest rate from outstanding borrowings	1.21%	1.02%
KCPL Greater Missouri Operations [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 450,000,000
Credit facility expiration date	Oct. 31, 2019
Maximum transfer of unused commitments	$ 200,000,000
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
Amount of letters of credit outstanding	$ 2,000,000	$ 1,900,000

Long-Term Debt (Details)

Long-Term Debt (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Current maturities	$ (732.1)	$ (382.1)
Long-term debt excluding current maturities	$ 7,275.9	3,365.2
Unsecured Debt [Member] | GPE 4.3 Billion Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Optional Redemption Price, Percentage	101.00%
Debt Instrument, Mandatory Redemption Price, Percentage	101.00%
Kansas City Power and Light Company [Member]
Debt Instrument [Line Items]
Current maturities	$ (631)	(281)
Unamortized discount and premium, net and debt issuance costs	(14.9)	(15.4)
Long-term debt excluding current maturities	1,934.5	2,284
Kansas City Power and Light Company [Member] | Secured Debt [Member] | General Mortgage Bonds EIRR due 2017-2023 [Member]
Debt Instrument [Line Items]
Principal outstanding	110.5	110.5
EIRR bonds repurchased and held	$ 21.9	21.9
Debt Instrument Maturity Date Range End	Dec. 31, 2023
Debt Instrument Maturity Date Range Start	Dec. 31, 2017
Long-term Debt, Weighted Average Interest Rate	2.47%
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	400
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	50
Kansas City Power and Light Company [Member] | Senior Notes [Member] | Senior notes due 2017 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding	$ 250	250
Debt Instrument, Maturity Date	Dec. 31, 2017
Interest rates (in hundredths)	5.85%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)	5.72%
Kansas City Power and Light Company [Member] | Senior Notes [Member] | Senior notes due 2018 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding	$ 350	350
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	300
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	350
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	250
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	400
Debt Instrument, Maturity Date	Dec. 31, 2041
Interest rates (in hundredths)	5.30%
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)	0.773%
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	125
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	75
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	150
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	3
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	7
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
Great Plains Energy [Member] | Senior Notes [Member] | Senior notes due 2017 [Member]
Debt Instrument [Line Items]
Principal outstanding	$ 100	100
Debt Instrument, Maturity Date	Dec. 31, 2017
Interest rates (in hundredths)	6.875%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)	7.33%
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%
Debt Instrument, Optional Redemption Price, Percentage	101.00%
Debt Instrument, Mandatory Redemption Price, Percentage	101.00%
Great Plains Energy [Member] | Senior Notes [Member] | Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Principal outstanding	$ 350	350
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%
Debt Instrument, Optional Redemption Price, Percentage	101.00%
Debt Instrument, Mandatory Redemption Price, Percentage	101.00%
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%
Debt Instrument, Optional Redemption Price, Percentage	101.00%
Debt Instrument, Mandatory Redemption Price, Percentage	101.00%
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%
Debt Instrument, Optional Redemption Price, Percentage	101.00%
Debt Instrument, Mandatory Redemption Price, Percentage	101.00%
Great Plains Energy [Member] | Unsecured Debt [Member] | GPE 4.3 Billion Senior Notes [Member]
Debt Instrument [Line Items]
Principal outstanding	$ 4,300
Other Consolidated Entities [Member]
Debt Instrument [Line Items]
Current maturities	(101.1)	(101.1)
Unamortized discount and premium, net and debt issuance costs	$ (40.5)	$ (1.8)

Commitments and Contingencies E

Commitments and Contingencies Environmental Matters (Details) T in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2017USD ($)T	Dec. 31, 2016USD ($)
Estimated Environmental Capital Expenditures [Abstract]
Estimate Of Environmental Capital Expenditures Current	$ 43.4
Estimate Of Environmental Capital Expenditures In Two Years	36.6
Estimate Of Environmental Capital Expenditures In Three Years	11.5
Estimate Of Environmental Capital Expenditures In Four Years	$ 14
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	7.6
Estimate Of Environmental Capital Expenditures In Four Years	$ 13
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

Legal Proceedings Loss Continge

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

Related Party Transactions an58

Related Party Transactions and Relationships (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 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
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	47.3		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	47.9	$ 47.2
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	$ 21.8		$ 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%

Fair Value Measurements Level 3

Fair Value Measurements Level 3 (Details) - Derivative Financial Instruments, Assets [Member] - Fair Value, Inputs, Level 3 [Member] - Fair Value, Measurements, Recurring [Member] $ in Millions	3 Months Ended
	Mar. 31, 2017USD ($)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net asset at January 1	$ 79.3
Net asset at March 31	91.4
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	12.1
Total unrealized gains relating to assets still on the consolidated balance sheet at March 31:	$ 12.1

Fair Value Measurements Fair Va

Fair Value Measurements Fair Value Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jun. 30, 2016USD ($)
Fair value of financial instruments [Abstract]
Notional Contract Amount			$ 4,400
Derivatives, Interest Rate Swaps, Finalized Settlement Value	$ 140.6
Kcpl Greater Missouri Operations Member
SERP rabbi trust [Abstract]
Alternative Investments, Fair Value Disclosure	15.4	$ 16
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair value of financial instruments [Abstract]
Long-term Debt	8,100	3,800
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	2,600
GPE 4.3 Billion Senior Notes [Member] | Great Plains Energy [Member]
Fair value of financial instruments [Abstract]
Long-term Debt, Gross	4,300
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]
Fair value of financial instruments [Abstract]
Long-term debt fair value	8,300	4,000
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	$ 2,700	$ 2,700
Interest Rate Contract [Member]
Fair value of financial instruments [Abstract]
Fair Value Inputs, Contingency Factor	0.35	0.35
Derivative Asset, Fair Value, Gross Asset	$ 91.4	$ 79.3
Interest Rate Contract [Member] | Interest Expense [Member]
Fair value of financial instruments [Abstract]
Derivative, Gain (Loss) on Derivative, Net	$ 12.1

Fair Value Measurements (Detail

Fair Value Measurements (Details) $ in Millions	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Assets [Abstract]
Derivatives, Interest Rate Swaps, Finalized Settlement Value	$ 140.6
Interest Rate Contract [Member]
Assets [Abstract]
Derivative instruments, assets	$ 91.4	$ 79.3
Self-insured health plan trust [Abstract]
Fair Value Inputs, Contingency Factor	0.35	0.35
Fair Value, Measurements, Recurring [Member]
Assets [Abstract]
Derivative instruments, assets	$ 91.4	$ 79.3
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	232.5	222.9
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	11.3	11.3
Total assets	335.2	313.5
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Derivative instruments, assets	0	0
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	195.5	185.5
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	8.7	6.6
Total assets	204.2	192.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Derivative instruments, assets	0	0
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	37	37.4
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	2.6	4.7
Total assets	39.6	42.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Derivative instruments, assets	91.4	79.3
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0	0
Total assets	91.4	79.3
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	232.5	222.9
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	11.3	11.3
Total assets	243.8	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	161.7	153.9
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.7	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	2.6	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	28.2	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	1.7	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	4.1	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	31.1	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	5.6	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	5.6
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	195.5	185.5
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	8.7	6.6
Total assets	204.2	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	161.7	153.9
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.7	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	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	28.2	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
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
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
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
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	5.6	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	5.6
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	37	37.4
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	2.6	4.7
Total assets	39.6	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
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	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	2.6	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
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	1.7	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	4.1	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	31.1	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
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
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
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0	0
Total assets	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
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	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
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
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
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
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
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
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
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
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member]
Self-insured health plan trust [Abstract]
Total assets	91.4	79.3
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Interest Rate Contract [Member]
Assets [Abstract]
Derivative instruments, assets	91.4	$ 79.3
Derivatives, Interest Rate Swaps, Finalized Settlement Value	$ 140.6
Self-insured health plan trust [Abstract]
Fair Value Inputs, Contingency Factor	0.35	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
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
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
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
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 3 [Member]
Self-insured health plan trust [Abstract]
Total assets	91.4	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	$ 91.4	$ 79.3

Accumulated Other Comprehensi62

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (6.6)	$ (12)
Amounts reclassified from accumulated other comprehensive loss	1.5	1.5
Net current period other comprehensive income	1.5	1.5
Ending balance	(5.1)	(10.5)
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	1.4	1.4
Net current period other comprehensive income	1.4	1.4
Ending balance	(3.1)	(8.7)
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	0.1	0.1
Net current period other comprehensive income	0.1	0.1
Ending balance	(2)	(1.8)
Kansas City Power and Light Company [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(4.2)
Net current period other comprehensive income	1.3	1.4
Ending balance	(2.9)
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	1.3	1.4
Net current period other comprehensive income	1.3	1.4
Ending balance	$ (2.9)	$ (8.2)

Accumulated Other Comprehensi63

Accumulated Other Comprehensive Income (Loss) Reclassification (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges	$ (66.6)	$ (51.2)
Utility operating and maintenance expenses	(185.4)	(179.4)
Income (loss) before income tax (expense) benefit and income from equity investments	(16.3)	37.4
Income tax (expense) benefit	5.8	(11.7)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)	(1.5)	(1.5)
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	(2.3)	(2.3)
Income tax (expense) benefit	0.9	0.9
Net income (loss)	(1.4)	(1.4)
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	(2.3)	(2.3)
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)
Income (loss) before income tax (expense) benefit and income from equity investments	(0.2)	(0.2)
Income tax (expense) benefit	0.1	0.1
Net income (loss)	(0.1)	(0.1)
Kansas City Power and Light Company [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges	(35.6)	(35.3)
Utility operating and maintenance expenses	(126.4)	(123.7)
Income (loss) before income tax (expense) benefit and income from equity investments	23	35.3
Income tax (expense) benefit	(8.8)	(10.7)
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	(2.2)	(2.3)
Income tax (expense) benefit	0.9	0.9
Net income (loss)	(1.3)	(1.4)
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	$ (2.2)	$ (2.3)

Income Tax Expense (Details)

Income Tax Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Current income taxes
Federal	$ 0	$ (0.1)
State	0.2	0.2
Total	0.2	0.1
Deferred income taxes
Federal	(4.5)	9.7
State	(1.1)	2.3
Total	(5.6)	12
Investment tax credit
Investment tax credit amortization	(0.4)	(0.4)
Income tax expense (benefit)	$ (5.8)	$ 11.7
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax (in hundredths)	35.00%	35.00%
Differences between book and tax depreciation not normalized (in hundredths)	0.00%	0.50%
Amortization of investments tax credits (in hundredths)	(0.40%)	(0.90%)
Federal income tax credits (in hundredths)	(1.50%)	(8.00%)
State income taxes (in hundredths)	4.20%	4.20%
Transaction costs (in hundredths)	3.10%	0.00%
Other (in hundredths)	(2.50%)	0.00%
Effective income tax rate (in hundredths)	37.90%	30.80%
Kansas City Power and Light Company [Member]
Current income taxes
Federal	$ (0.1)	$ 0.4
State	0	0.1
Total	(0.1)	0.5
Deferred income taxes
Federal	7.8	8.4
State	1.4	2
Total	9.2	10.4
Investment tax credit
Investment tax credit amortization	(0.3)	(0.2)
Income tax expense (benefit)	$ 8.8	$ 10.7
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax (in hundredths)	35.00%	35.00%
Differences between book and tax depreciation not normalized (in hundredths)	(0.10%)	0.40%
Amortization of investments tax credits (in hundredths)	(0.30%)	(0.70%)
Federal income tax credits (in hundredths)	(1.80%)	(7.80%)
State income taxes (in hundredths)	4.00%	3.90%
Other (in hundredths)	1.50%	(0.50%)
Effective income tax rate (in hundredths)	38.30%	30.30%

Segments and Related Informat65

Segments and Related Information (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Operating revenues	$ 570.7	$ 572.1
Depreciation and amortization	(90.3)	(85.2)
Interest charges	(66.6)	(51.2)
Income tax (expense) benefit	5.8	(11.7)
Net income (loss)	(9.6)	26.4
Assets	17,797.5		$ 13,570
Capital expenditures	116.6	133.6	609.4
Operating Segments [Member] | Electric Utility Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	570.7	572.1
Depreciation and amortization	(90.3)	(85.2)
Interest charges	(50.1)	(49.1)
Income tax (expense) benefit	(10.1)	(13.1)
Net income (loss)	16.1	29
Assets	11,465.6		11,444.2
Capital expenditures	116.6		609.4
Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Depreciation and amortization	0	0
Interest charges	(24.5)	(10.1)
Income tax (expense) benefit	15.9	1.4
Net income (loss)	(25.7)	(2.6)
Assets	6,729.5		2,461.3
Capital expenditures	0		0
Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Depreciation and amortization	0	0
Interest charges	8	8
Income tax (expense) benefit	0	0
Net income (loss)	0	$ 0
Assets	(397.6)		(335.5)
Capital expenditures	$ 0		$ 0