Great Plains Energy (GXP) 10-Q 2 May 18 2018 Q1 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 30, 2018
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		215,795,884
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Current Assets
Cash and cash equivalents	$ 1,142.1	$ 1,125.4
Receivables, net	108.2	151.7
Accounts receivable pledged as collateral	180	180
Fuel inventories, at average cost	105	103.2
Materials and supplies, at average cost	172.3	171.2
Deferred refueling outage costs	5.9	6.8
Interest rate derivative instruments	98.4	91.4
Prepaid expenses and other assets	37.7	33.4
Total	1,849.6	1,863.1
Utility Plant, at Original Cost
Electric	13,733.1	13,674.1
Less - accumulated depreciation	5,305.1	5,224
Net utility plant in service	8,428	8,450.1
Construction work in progress	494.4	458.6
Plant to be retired, net	142	143.6
Nuclear fuel, net of amortization of $211.9 and $204.2	65.7	72.4
Total	9,130.1	9,124.7
Investments and Other Assets
Nuclear decommissioning trust fund	255.3	258.4
Regulatory assets	901.7	913.9
Goodwill	169	169
Other	142.7	128.8
Total	1,468.7	1,470.1
Total	12,448.4	12,457.9
Current Liabilities
Notes payable	23	11
Collateralized note payable	180	180
Commercial paper	523.8	376.8
Current maturities of long-term debt	1.1	351.1
Accounts payable	186	340
Accrued taxes	72.7	35.1
Accrued interest	57.4	42.8
Accrued compensation and benefits	40.4	50.1
Pension and post-retirement liability	2.7	2.7
Other	62.9	59.2
Total	1,150	1,448.8
Deferred Credits and Other Liabilities
Deferred income taxes	639.5	621.7
Deferred tax credits	124.5	124.8
Asset retirement obligations	257.5	262.5
Pension and post-retirement liability	532.4	535
Regulatory liabilities	1,112.4	1,106.3
Other	81.8	81.4
Total	2,748.1	2,731.7
Shareholders' equity
Common stock	4,232.1	4,233.1
Retained earnings	713.6	737.9
Treasury stock - 90,960 and 137,589 shares, at cost	(2.7)	(4)
Accumulated other comprehensive loss	(1.2)	(2.2)
Total shareholders' equity	4,941.8	4,964.8
Long-term debt (Note 11)	3,608.5	3,312.6
Total	8,550.3	8,277.4
Commitments and Contingencies (Note 12)
Total	12,448.4	12,457.9
KCPL [Member]
Current Assets
Cash and cash equivalents	13.8	2.2
Receivables, net	74.3	106.3
Related party receivables	69.1	84.7
Accounts receivable pledged as collateral	130	130
Fuel inventories, at average cost	72	71
Materials and supplies, at average cost	127.8	126
Deferred refueling outage costs	5.9	6.8
Refundable income taxes	7.2	5.4
Prepaid expenses and other assets	31.3	27.6
Total	531.4	560
Utility Plant, at Original Cost
Electric	10,251.8	10,213.2
Less - accumulated depreciation	4,130	4,070.3
Net utility plant in service	6,121.8	6,142.9
Construction work in progress	384.7	350.3
Nuclear fuel, net of amortization of $211.9 and $204.2	65.7	72.4
Total	6,572.2	6,565.6
Investments and Other Assets
Nuclear decommissioning trust fund	255.3	258.4
Regulatory assets	681.9	691.9
Other	49.5	48
Total	986.7	998.3
Total	8,090.3	8,123.9
Current Liabilities
Collateralized note payable	130	130
Commercial paper	288.3	167.5
Current maturities of long-term debt	0	350
Accounts payable	147.6	249
Accrued taxes	55.8	29
Accrued interest	40.7	32.4
Accrued compensation and benefits	40.4	50.1
Pension and post-retirement liability	1.4	1.4
Other	50.7	46.8
Total	754.9	1,056.2
Deferred Credits and Other Liabilities
Deferred income taxes	628.3	616.1
Deferred tax credits	121.5	121.8
Asset retirement obligations	227	231.4
Pension and post-retirement liability	509.7	512.2
Regulatory liabilities	782.7	779.2
Other	62.6	61.6
Total	2,331.8	2,322.3
Shareholders' equity
Common stock	1,563.1	1,563.1
Retained earnings	909.9	949.7
Accumulated other comprehensive loss	1.3	0.4
Total shareholders' equity	2,474.3	2,513.2
Long-term debt (Note 11)	2,529.3	2,232.2
Total	5,003.6	4,745.4
Commitments and Contingencies (Note 12)
Total	$ 8,090.3	$ 8,123.9

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Utility Plant, at Original Cost
Nuclear fuel, amortization	$ 211.9	$ 204.2
Shareholder's equity
Common stock - shares authorized (in shares)	600,000,000	600,000,000
Common stock-shares issued (in shares)	215,886,844	215,801,723
Treasury stock- shares (in shares)	90,960	137,589
KCPL [Member]
Utility Plant, at Original Cost
Nuclear fuel, amortization	$ 211.9	$ 204.2
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, 2018	Mar. 31, 2017
Operating Revenues
Electric revenues	$ 583.9	$ 570.7
Operating Expenses
Fuel and purchased power	154.3	126.5
Transmission	25.4	23.1
Utility operating and maintenance expenses	180.2	174.1
Costs to achieve the anticipated merger with Westar Energy, Inc.	2.9	39.4
Depreciation and amortization	93.7	90.3
General taxes	41.1	57.1
Other	0	1.1
Total	497.6	511.6
Operating income	86.3	59.1
Other Income (Expense)
Non-operating income	14.5	6.6
Non-operating expenses	(13.2)	(15.4)
Total	1.3	(8.8)
Interest charges	(48.1)	(66.6)
Income (loss) before income tax (expense) benefit and income from equity investments	39.5	(16.3)
Income tax (expense) benefit	(5.5)	5.8
Income from equity investments, net of income taxes	1	0.9
Net income (loss)	35	(9.6)
Preferred stock dividend requirements	0	15.1
Earnings (loss) available for common shareholders	$ 35	$ (24.7)
Average number of basic common shares outstanding	215.7	215.3
Average number of diluted common shares outstanding	216	215.3
Basic and diluted earnings (loss) per common share	$ 0.16	$ (0.11)
Cash dividends per common share	$ 0.275	$ 0.275
Comprehensive Income (Loss)
Net income (loss)	$ 35	$ (9.6)
Derivative hedging activity
Reclassification to expenses, net of tax	0.9	1.4
Derivative hedging activity, net of tax	0.9	1.4
Defined benefit pension plans
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	1.5
Comprehensive income (loss)	36	(8.1)
KCPL [Member]
Operating Revenues
Electric revenues	397.1	395.9
Operating Expenses
Fuel and purchased power	101.8	78.9
Transmission	15.7	14.3
Utility operating and maintenance expenses	121	119.6
Costs to achieve the anticipated merger with Westar Energy, Inc.	1.5	7.9
Depreciation and amortization	66.9	65.3
General taxes	29	44.6
Other	0.2	0.3
Total	336.1	330.9
Operating income	61	65
Other Income (Expense)
Non-operating income	3.6	2.5
Non-operating expenses	(7.9)	(8.9)
Total	(4.3)	(6.4)
Interest charges	(33)	(35.6)
Income (loss) before income tax (expense) benefit and income from equity investments	23.7	23
Income tax (expense) benefit	(3.5)	(8.8)
Net income (loss)	20.2	14.2
Comprehensive Income (Loss)
Net income (loss)	20.2	14.2
Derivative hedging activity
Reclassification to expenses, net of tax	0.9	1.3
Derivative hedging activity, net of tax	0.9	1.3
Defined benefit pension plans
Total other comprehensive income	0.9	1.3
Comprehensive income (loss)	$ 21.1	$ 15.5

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash Flows from Operating Activities
Net income (loss)	$ 35	$ (9.6)
Adjustments to reconcile income (loss) to net cash from operating activities:
Depreciation and amortization	93.7	90.3
Amortization of:
Nuclear fuel	7.7	8
Other	8.7	24.9
Deferred income taxes, net	5.8	(5.6)
Investment tax credit amortization	(0.3)	(0.4)
Income from equity investments, net of income taxes	(1)	(0.9)
Fair value impacts of interest rate swaps	(7)	(12.1)
Other operating activities (Note 4)	(29.1)	(7)
Net cash from operating activities	113.5	87.6
Cash Flows from Investing Activities
Utility capital expenditures	(119.7)	(116.6)
Allowance for borrowed funds used during construction	(2.4)	(1.5)
Purchases of nuclear decommissioning trust investments	(12.1)	(5.9)
Proceeds from nuclear decommissioning trust investments	11.3	5
Proceeds from time deposit	0	1,000
Other investing activities	(17.1)	(12.5)
Net cash from investing activities	(140)	868.5
Cash Flows from Financing Activities
Issuance of common stock	0	1.5
Issuance of long-term debt	299.7	4,291.9
Issuance fees	(3.1)	(31.2)
Repayment of long-term debt	(351.1)	(1.1)
Net change in short-term borrowings	159	119.9
Net change in collateralized short-term borrowings	0	(0.2)
Dividends paid	(59.3)	(74.3)
Other financing activities	(2)	(3.4)
Net cash from financing activities	43.2	4,303.1
Net Change in Cash and Cash Equivalents	16.7	5,259.2
Cash and Cash Equivalents at Beginning of Year	1,125.4	1,293.1
Cash and Cash Equivalents at End of Period	1,142.1	6,552.3
KCPL [Member]
Cash Flows from Operating Activities
Net income (loss)	20.2	14.2
Adjustments to reconcile income (loss) to net cash from operating activities:
Depreciation and amortization	66.9	65.3
Amortization of:
Nuclear fuel	7.7	8
Other	6.6	8.1
Deferred income taxes, net	5.6	9.2
Investment tax credit amortization	(0.3)	(0.3)
Other operating activities (Note 4)	(1.7)	(21.1)
Net cash from operating activities	105	83.4
Cash Flows from Investing Activities
Utility capital expenditures	(93.5)	(84)
Allowance for borrowed funds used during construction	(2)	(1.2)
Purchases of nuclear decommissioning trust investments	(12.1)	(5.9)
Proceeds from nuclear decommissioning trust investments	11.3	5
Other investing activities	(4.5)	(5.1)
Net cash from investing activities	(100.8)	(91.2)
Cash Flows from Financing Activities
Issuance of long-term debt	299.7	0
Issuance fees	(3.1)	0
Repayment of long-term debt	(350)	0
Net change in short-term borrowings	120.8	62.4
Dividends paid	(60)	(57)
Net cash from financing activities	7.4	5.4
Net Change in Cash and Cash Equivalents	11.6	(2.4)
Cash and Cash Equivalents at Beginning of Year	2.2	4.5
Cash and Cash Equivalents at End of Period	$ 13.8	$ 2.1

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Common Stock [Member]	Preferred Stock [Member]Preference Stock [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	KCPL [Member]	KCPL [Member]Common Stock [Member]	KCPL [Member]Retained Earnings [Member]	KCPL [Member]Accumulated Other Comprehensive Income (Loss) [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of adoption of ASU 2016-09									$ (0.7)
Beginning balance at Dec. 31, 2016		$ 4,217	$ 836.2	$ 1,119.2	$ (3.8)	$ (6.6)		$ 1,563.1	982.6	$ (4.2)
Beginning balance (in shares) at Dec. 31, 2016		215,479,105	862,500					1
Beginning balance, treasury stock (in shares) at Dec. 31, 2016					(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)			(9.6)			$ 14.2		14.2
Dividends:
Common stock ($0.275 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					1.4	1.3			1.3
Change in unrecognized pension expense, net of tax	0.1					0.1
Ending balance at Mar. 31, 2017	6,088	$ 4,225.5	$ 836.2	1,035.2	$ (3.8)	(5.1)	2,499.3	$ 1,563.1	939.1	(2.9)
Ending balance, treasury stock (in shares) at Mar. 31, 2017					(129,122)
Ending balance (in shares) at Mar. 31, 2017		215,728,275	862,500					1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of adoption of ASU 2016-09									0
Beginning balance at Dec. 31, 2017	$ 4,964.8	$ 4,233.1	$ 0	737.9	$ (4)	(2.2)	2,513.2	$ 1,563.1	949.7	0.4
Beginning balance (in shares) at Dec. 31, 2017		215,801,723	0					1
Beginning balance, treasury stock (in shares) at Dec. 31, 2017	(137,589)				(137,589)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock		$ 3.3
Issuance of stock (in shares)		85,121
Equity compensation expense, net of forfeitures		$ 1.3
Unearned Compensation [Abstract]
Issuance of restricted common stock		(2)
Forfeiture of restricted common stock		0
Compensation expense recognized		0.5
Other		(4.1)
Net income (loss)	$ 35			35			20.2		20.2
Dividends:
Common stock ($0.275 per share)				(59.3)					(60)
Preferred stock - at required rates				0
Performance shares				0
Treasury shares acquired					$ (1.7)
Treasury shares acquired (in shares)					(56,589)
Treasury shares reissued					$ 3
Treasury shares reissued (in shares)					103,218
Derivative hedging activity, net of tax	0.9					0.9	0.9			0.9
Change in unrecognized pension expense, net of tax	0.1					0.1
Ending balance at Mar. 31, 2018	$ 4,941.8	$ 4,232.1	$ 0	$ 713.6	$ (2.7)	$ (1.2)	$ 2,474.3	$ 1,563.1	$ 909.9	$ 1.3
Ending balance, treasury stock (in shares) at Mar. 31, 2018	(90,960)				(90,960)
Ending balance (in shares) at Mar. 31, 2018		215,886,844	0					1

Consolidated Statements of Sha7

Consolidated Statements of Shareholders' Equity (Parenthetical) - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Stock Transactions, Parenthetical Disclosures [Abstract]
Common Stock, Dividends, Per Share, Declared	$ 0.275	$ 0.275

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies [Text Block]	1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Organization Great Plains Energy, a Missouri corporation incorporated in 2001, is a public utility holding company and does not own or operate any significant assets other than the stock of its subsidiaries and cash and cash equivalents. Great Plains Energy's wholly owned direct subsidiaries with significant operations are as follows: • KCP&L is an integrated, regulated electric utility that provides electricity to customers primarily in the states of Missouri and Kansas. KCP&L has one active wholly owned subsidiary, Kansas City Power & Light Receivables Company (KCP&L Receivables Company). • KCP&L Greater Missouri Operations Company (GMO) is an integrated, regulated electric utility that provides electricity to customers in the state of Missouri. GMO also provides regulated steam service to certain customers in the St. Joseph, Missouri area. GMO has one active wholly owned subsidiary, GMO Receivables Company. 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, 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 the electric utility segment (Electric Utility). See Note 17 for additional information. Basic and Diluted Earnings (Loss) per Common Share Calculation To determine basic earnings (loss) per common share (EPS), preferred stock dividend requirements are deducted from net income (loss) 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 2018 2017 Income (loss) (millions, except per share amounts) Net income (loss) $ 35.0 $ (9.6 ) Less: preferred stock dividend requirements — 15.1 Earnings (loss) available for common shareholders $ 35.0 $ (24.7 ) Common Shares Outstanding Average number of common shares outstanding 215.7 215.3 Add: effect of dilutive securities 0.3 — Diluted average number of common shares outstanding 216.0 215.3 Basic and diluted EPS $ 0.16 $ (0.11 ) There were no anti-dilutive shares excluded from the computation of diluted EPS for the three months ended March 31, 2018. Anti-dilutive shares excluded from the computation of diluted EPS for the three months ended March 31, 2017 were 29,930,385 shares of Series B Preferred Stock assumed to be converted, 460,169 performance shares and 328,512 restricted stock shares. Dividends Declared In May 2018 , 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, 2018 , to shareholders of record as of May 30, 2018 . In May 2018 , KCP&L's Board of Directors declared a cash dividend payable to Great Plains Energy of $60.0 million payable on June 19, 2018 . New Accounting Standards In March 2017, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2017-07, Compensation-Retirement Benefits , which requires an employer to disaggregate the service cost component from the other components of net benefit cost. The service cost component is to be reported in the same line item or items as other compensation costs arising from services rendered by the pertinent employees during the period. The non-service cost components are to be reported separately from service costs and outside of a subtotal of income from operations. The amendments in this update allow only the service cost component to be eligible for capitalization as part of utility plant. The non-service cost components that are no longer eligible for capitalization as part of utility plant will be recorded as a regulatory asset. The new guidance is to be applied retrospectively for the presentation of service cost and non-service cost components in the income statement and prospectively for the capitalization of the service cost component and is effective for interim and annual periods beginning after December 15, 2017. The Companies adopted ASU No. 2017-07 on January 1, 2018, and accordingly have retrospectively adjusted prior periods. The following table reflects the retrospective adjustments in the line items of Great Plains Energy's and KCP&L's consolidated statements of comprehensive income associated with the adoption of ASU No. 2017-07. Three Months Ended March 31, 2017 As Previously Reported Effect of Change As Reported Great Plains Energy (millions) Utility operating and maintenance expenses $ 185.4 $ (11.3 ) $ 174.1 Other operating expense 1.5 (0.4 ) 1.1 Operating expenses 523.3 (11.7 ) 511.6 Operating income 47.4 11.7 59.1 Non-operating expenses (3.7 ) (11.7 ) (15.4 ) Other income (expense) 2.9 (11.7 ) (8.8 ) KCP&L Utility operating and maintenance expenses $ 126.4 $ (6.8 ) $ 119.6 Operating expenses 337.7 (6.8 ) 330.9 Operating income 58.2 6.8 65.0 Non-operating expenses (2.1 ) (6.8 ) (8.9 ) Other income (expense) 0.4 (6.8 ) (6.4 ) In February 2016, the FASB issued ASU No. 2016-02, Leases , which requires an entity that is a lessee to record a right-of-use asset and a lease liability for lease payments on the balance sheet for all leases with terms longer than 12 months. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. The new guidance is effective for interim and annual periods beginning after December 15, 2018, with early adoption permitted, and is required to be applied using a modified retrospective approach . Great Plains Energy and KCP&L plan to adopt the new guidance on January 1, 2019. The Companies expect that the new guidance will affect the balance sheet by increasing the assets and liabilities recorded related to operating leases and continue to evaluate the effect that ASU No. 2016-02 will have on their income statement, statement of cash flows and related disclosures. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers , which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. 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 ASU replaced most existing revenue recognition guidance in Generally Accepted Accounting Principles (GAAP) when it became effective. The Companies adopted ASU No. 2014-09 and its related amendments (ASC 606) on January 1, 2018 using the modified retrospective transition method for all contracts not completed as of the date of adoption. Results for reporting periods beginning after January 1, 2018 are presented under ASC 606 while historical periods have not been adjusted and continue to be reported in accordance with the legacy guidance in ASC 605 - Revenue Recognition . There was no cumulative effect adjustment to the opening balance of retained earnings in 2018 for Great Plains Energy or KCP&L as a result of the adoption of the new guidance. The impact to both electric revenues and general taxes on Great Plains Energy's and KCP&L's statements of comprehensive income in 2018 as a result of adopting ASC 606 was a decrease of $17.9 million . This impact was related to sales taxes and franchise fees collected from KCP&L's Missouri customers, which prior to ASC 606, were recorded gross on Great Plains Energy's and KCP&L's statements of comprehensive income.

Revenue Recognition

Revenue Recognition	3 Months Ended
	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer [Text Block]	2. REVENUE RECOGNITION Great Plains Energy's and KCP&L's revenues disaggregated by customer class and for Great Plains Energy's direct subsidiaries are summarized in the following table. All of Great Plains Energy's revenues pertain to Electric Utility. Three Months Ended March 31, 2018 KCP&L GMO Great Plains Energy Customer class (millions) Residential $ 154.9 $ 88.1 $ 243.0 Commercial 181.8 64.2 246.0 Industrial 32.2 19.9 52.1 Other 2.7 1.8 4.5 Total electric retail $ 371.6 $ 174.0 $ 545.6 Wholesale 3.1 2.9 6.0 Transmission 3.3 4.6 7.9 Industrial steam — 4.3 4.3 Total revenue from contracts with customers $ 378.0 $ 185.8 $ 563.8 Other revenue 19.1 1.0 20.1 Electric revenue $ 397.1 $ 186.8 $ 583.9 Retail Revenues Great Plains Energy's and KCP&L's retail revenues are generated by the regulated sale of electricity to KCP&L's and GMO's residential, commercial and industrial customers within their franchised service territories. Great Plains Energy and KCP&L recognize revenue on the sale of electricity to their customers over time as the service is provided in the amount they have a right to invoice. Retail customers are billed on a monthly basis at the tariff rates approved by the MPSC and KCC based on customer kWh usage. Revenues recorded include electric services provided but not yet billed by KCP&L and GMO. Unbilled revenues are recorded for kWh usage in the period following the customers' billing cycle to the end of the month. KCP&L's and GMO's estimate is based on net system kWh usage less actual billed kWhs. KCP&L's and GMO's estimated unbilled kWhs are allocated and priced by regulatory jurisdiction across the rate classes based on actual billing rates. KCP&L and GMO also collect sales taxes and franchise fees from customers concurrent with revenue-producing activities that are levied by state and local governments. These items are excluded from revenue upon the adoption of ASC 606 and thus presented net on Great Plains Energy's and KCP&L's statements of comprehensive income. Wholesale Revenues Great Plains Energy's and KCP&L's wholesale revenue are generated by the sale of wholesale power and capacity in circumstances when the power that KCP&L and GMO generate is not required for customers in their service territory. These sales primarily occur within the Southwest Power Pool, Inc. (SPP) Integrated Marketplace. Great Plains Energy and KCP&L also purchase power from the SPP Integrated Marketplace and record sale and purchase activity on a net basis in wholesale revenue or purchased power. In addition, Great Plains Energy and KCP&L sell wholesale power and capacity through bilateral contracts between KCP&L and GMO and other counterparties, such as municipalities. For both wholesale sales to the SPP Integrated Marketplace and through bilateral contracts, Great Plains Energy and KCP&L recognize revenue on the sale of wholesale electricity to their customers over time as the service is provided in the amount they have a right to invoice. With regards to the SPP Integrated Marketplace, wholesale sales are billed weekly based on the fixed transaction price determined by the market at the time of the sale and the MWh quantity purchased. With regards to bilateral contracts, wholesale sales are billed monthly based on the contractually determined transaction price and the kWh quantity purchased. Transmission Revenues Great Plains Energy's and KCP&L's transmission revenues are generated by the use of KCP&L's and GMO's transmission network by the SPP, which operates the network, on behalf of other power providers. Great Plains Energy and KCP&L recognize revenue on the sale of transmission service to their customers over time as the service is provided in the amount they have a right to invoice. Transmission service to the SPP is billed monthly based on a fixed transaction price determined by KCP&L's and GMO's FERC formula transmission rates along with other SPP-specific charges and the MW quantity purchased. Industrial Steam Revenues Great Plains Energy's industrial steam revenues are generated by the regulated sale of industrial steam to GMO's steam customers. Great Plains Energy recognizes revenue on the sale of industrial steam to its customers over time as the service is provided in the amount that it has the right to invoice. Steam customers are billed on a monthly basis at the tariff rate approved by the MPSC based on customer MMBtu usage. Optional Exemption Great Plains Energy and KCP&L do not disclose the value of unsatisfied performance obligations on certain bilateral wholesale contracts with an original expected duration of greater than one year for which the Companies recognize revenue in the amount they have the right to invoice.

Anticipated Merger with Westar

Anticipated Merger with Westar Energy, Inc.	3 Months Ended
	Mar. 31, 2018
Anticipated Merger with Westar Energy, Inc. [Abstract]
Anticipated Buiness Combination Disclosure [Text Block]	3 . ANTICIPATED MERGER WITH WESTAR ENERGY, INC. In May 2016, Great Plains Energy entered into an Agreement and Plan of Merger dated as of May 29, 2016, by and among Great Plains Energy, Westar Energy, Inc. (Westar) and GP Star, Inc. (GP Star) (Original Merger Agreement). Pursuant to the Original Merger Agreement, Great Plains Energy would have acquired Westar for (i) $51.00 in cash and (ii) a number of shares of Great Plains Energy common stock, equal to an exchange ratio for each share of Westar common stock issued and outstanding immediately prior to the effective time of the merger, with Westar becoming a wholly owned subsidiary of Great Plains Energy. The acquisition was subject to various shareholder and regulatory approvals, including from The State Corporation Commission of the State of Kansas (KCC), the Public Service Commission of the State of Missouri (MPSC) and The Federal Energy Regulatory Commission (FERC). In April 2017, KCC issued an order denying Great Plains Energy's, KCP&L's and Westar's joint application for approval of the acquisition of Westar by Great Plains Energy citing concerns with the purchase price, Great Plains Energy's capital structure, quantifiable and demonstrable customer benefits and staffing levels in Westar's service territory, among other items. In July 2017, Great Plains Energy entered into an Amended and Restated Agreement and Plan of Merger dated as of July 9, 2017, by and among Great Plains Energy, Westar, Monarch Energy Holding, Inc., a Missouri corporation (Holdco), and King Energy, Inc., a Kansas corporation and wholly owned subsidiary of Holdco (Merger Sub) (Amended Merger Agreement). Pursuant to the Amended Merger Agreement, subject to the satisfaction or waiver of certain conditions, Great Plains Energy will merge with and into Holdco, with Holdco surviving such merger, and Merger Sub will merge with and into Westar, with Westar surviving such merger. Pursuant to the Amended Merger Agreement, at closing each outstanding share of Great Plains Energy's and Westar's common stock will be converted into the right to receive 0.5981 and 1.0 , respectively, of validly issued, fully paid and nonassessable shares of common stock, no par value, of Holdco. Following the mergers, Holdco, with a new name that has yet to be publicly announced, will be the parent of Great Plains Energy's direct subsidiaries, including KCP&L, and Westar. The anticipated merger with Westar has been structured as a merger of equals in a tax-free exchange of shares that involves no premium paid or received with respect to either Great Plains Energy or Westar. Following the completion of the anticipated merger, Westar shareholders will own approximately 52.5 percent and Great Plains Energy shareholders will own approximately 47.5 percent of the combined company. Regulatory and Shareholder Approvals Great Plains Energy's anticipated merger with Westar was unanimously approved by Great Plains Energy's Board of Directors (Great Plains Energy Board) and Westar's Board of Directors (Westar Board). In November 2017, shareholders of Great Plains Energy and Westar approved all proposals necessary for the merger of Great Plains Energy and Westar at each company's respective shareholder meeting. In the first quarter of 2018, regulatory approvals were obtained from the Nuclear Regulatory Commission (NRC), FERC and The Federal Communications Commission (FCC). The anticipated merger remains subject to regulatory approvals from KCC and the MPSC as well as other contractual conditions. KCC Approval In August 2017, Great Plains Energy, KCP&L and Westar filed a joint application with KCC for approval of the anticipated merger with Westar. In March 2018, Great Plains Energy, KCP&L and Westar reached a non-unanimous settlement agreement with KCC staff and certain other intervenors in the case recommending the approval of the merger subject to certain conditions included in the settlement agreement. The conditions include $7.5 million of one-time bill credits to be paid following the close of the merger to KCP&L's Kansas retail electric customers; $2.8 million in annual bill credits to be paid in each of 2019 through 2022 to KCP&L's Kansas retail electric customers; a 5-year base rate moratorium following KCP&L's 2018 Kansas rate case, subject to certain conditions; an Earnings Review and Sharing Plan for the years 2019 through 2022 which may result in KCP&L being subject to refunding 50% of earned return on equity in excess of authorized return on equity to its Kansas retail electric customers; the recovery of certain merger transition costs; and other organizational, financing, customer service and social responsibility commitments. The non-unanimous settlement agreement must still be approved by KCC. A decision from KCC on the joint application is expected by June 5, 2018. MPSC Approval In August 2017, Great Plains Energy, KCP&L, GMO and Westar filed a joint application with the MPSC for approval of the anticipated merger with Westar. In January 2018 and March 2018, Great Plains Energy, KCP&L, GMO and Westar reached stipulations and agreements with the MPSC staff and certain other intervenors in the case recommending the approval of the merger subject to certain conditions included in the stipulations and agreements. The stipulations and agreements impose certain conditions on Holdco, KCP&L and GMO in the areas of financing, ratemaking, customer service, corporate social responsibility and also include other general provisions. The stipulations and agreements 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 merger and that in the event KCP&L's or GMO's credit ratings are downgraded below investment grade as a result of their affiliation with Holdco or any of Holdco's affiliates, KCP&L and GMO will be restricted from paying a dividend unless approved by the MPSC or until their credit ratings are restored to investment grade. The stipulations and agreements also provide upfront bill credits of $14.9 million and $14.2 million to KCP&L's and GMO's Missouri retail electric customers, respectively. The stipulations and agreements must still be approved by the MPSC. While there is not a statutory deadline for an MPSC ruling on the joint application, a decision from the MPSC is expected in the second quarter of 2018. Other Approvals In September 2017, Great Plains Energy and Westar filed applications with FERC and the NRC for approval of the merger. In October 2017, the Securities and Exchange Commission (SEC) declared effective a registration statement on Form S-4 of Holdco including a joint proxy statement of Great Plains Energy and Westar that was used in connection with Great Plains Energy's and Westar's special shareholder meetings on November 21, 2017, and the registration of shares of Holdco common stock to be issued to Great Plains Energy's and Westar's shareholders at the closing of the anticipated merger. In November 2017, 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 under the Hart-Scott-Rodino (HSR) Act. In December 2017, the FTC granted Great Plains Energy's request for early termination of the waiting period under the HSR Act with respect to the anticipated merger. In February 2018, FERC issued an order authorizing the merger. In March 2018, the NRC issued an order approving the indirect ownership transfer of Wolf Creek Generating Station (Wolf Creek) and FCC consented to Transfer of Control applications that were filed by Great Plains Energy, KCP&L, GMO and Westar. Termination Fees The Amended Merger Agreement provides that in connection with a termination of the agreement under specified circumstances relating to a failure to obtain regulatory approvals by July 9, 2018 (which date may be extended to January 9, 2019), a final and nonappealable order enjoining the consummation of the anticipated merger in connection with regulatory approvals or failure by Great Plains Energy to comply with its obligations under the Amended Merger Agreement to consummate the closing of the anticipated merger once all of the conditions have been satisfied, Great Plains Energy may be required to pay Westar a termination fee of $190 million . In addition, in the event that the Amended Merger Agreement is terminated by Westar under certain circumstances to enter into a definitive acquisition agreement with respect to a superior proposal, Westar may be required to pay Great Plains Energy a termination fee of $190 million . Similarly, in the event that the Amended Merger Agreement is terminated by Great Plains Energy under certain circumstances to enter into a definitive acquisition agreement with respect to a superior proposal, Great Plains Energy may be required to pay Westar a termination fee of $190 million .

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	3 Months Ended
	Mar. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Cash Flow, Supplemental Disclosures [Text Block]	4. SUPPLEMENTAL CASH FLOW INFORMATION Great Plains Energy Other Operating Activities Three Months Ended March 31 2018 2017 Cash flows affected by changes in: (millions) Receivables $ 43.2 $ 55.5 Accounts receivable pledged as collateral — 0.2 Fuel inventories (1.8 ) 1.8 Materials and supplies (1.1 ) (4.2 ) Accounts payable (142.1 ) (136.8 ) Accrued taxes 37.6 36.3 Accrued interest 14.6 26.5 Deferred refueling outage costs 0.9 4.0 Pension and post-retirement benefit obligations 10.5 11.6 Allowance for equity funds used during construction (1.4 ) (1.0 ) Fuel recovery mechanisms (3.5 ) (14.1 ) ARO settlements (4.5 ) (4.3 ) Other 18.5 17.5 Total other operating activities $ (29.1 ) $ (7.0 ) Cash paid during the period: Interest $ 31.3 $ 34.2 Non-cash investing activities: Liabilities accrued for capital expenditures $ 25.4 $ 22.6 KCP&L Other Operating Activities Three Months Ended March 31 2018 2017 Cash flows affected by changes in: (millions) Receivables $ 47.9 $ 36.2 Fuel inventories (1.0 ) (0.5 ) Materials and supplies (1.8 ) (3.1 ) Accounts payable (90.0 ) (88.8 ) Accrued taxes 25.0 35.5 Accrued interest 8.3 10.1 Deferred refueling outage costs 0.9 4.0 Pension and post-retirement benefit obligations 9.0 10.3 Allowance for equity funds used during construction (1.4 ) (1.0 ) Fuel recovery mechanisms 1.2 (10.8 ) ARO settlements (3.6 ) (3.9 ) Other 3.8 (9.1 ) Total other operating activities $ (1.7 ) $ (21.1 ) Cash paid during the period: Interest $ 22.7 $ 22.5 Non-cash investing activities: Liabilities accrued for capital expenditures $ 19.5 $ 19.9

Receivables

Receivables	3 Months Ended
	Mar. 31, 2018
Receivables [Abstract]
Loans Notes Trade And Other Receivables Disclosure And Transfers And Servicing Of Financial Asset [Text Block]	5. RECEIVABLES Great Plains Energy's and KCP&L's receivables are detailed in the following table. March 31 December 31 2018 2017 Great Plains Energy (millions) Customer accounts receivable - billed $ — $ 3.7 Customer accounts receivable - unbilled 80.3 103.2 Allowance for doubtful accounts - customer accounts receivable (5.0 ) (4.7 ) Other receivables 32.9 49.5 Total $ 108.2 $ 151.7 KCP&L Customer accounts receivable - billed $ — $ 1.6 Customer accounts receivable - unbilled 50.4 67.6 Allowance for doubtful accounts - customer accounts receivable (2.3 ) (2.2 ) Other receivables 26.2 39.3 Total $ 74.3 $ 106.3 Great Plains Energy's and KCP&L's other receivables at March 31, 2018 and December 31, 2017 , consisted primarily of receivables from partners in jointly owned electric utility plants and wholesale sales receivables. As of March 31, 2018, other receivables for Great Plains Energy included $2.7 million of receivables from contracts with customers. As of March 31, 2018, other receivables for KCP&L included $1.1 million of receivables from contracts with customers. Great Plains Energy's and KCP&L's impairment losses recognized on receivables were $2.4 million and $1.7 million , respectively, for the three months ended March 31, 2018 and $2.2 million and $1.5 million , respectively, for the three months ended March 31, 2017. 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, 2018 and December 31, 2017 , Great Plains Energy's accounts receivable pledged as collateral and the corresponding short-term collateralized note payable were $180.0 million . At March 31, 2018 and December 31, 2017 , KCP&L's accounts receivable pledged as collateral and the corresponding short-term collateralized note payable were $130.0 million . KCP&L's agreement expires in September 2018 and allows for $130 million in aggregate outstanding principal amount of borrowings at any time. GMO's agreement expires in September 2018 and allows for $50 million in aggregate outstanding principal amount of borrowings from mid-November through mid-June and then $65 million from mid-June through mid-November.

Nuclear Plant

Nuclear Plant	3 Months Ended
	Mar. 31, 2018
Nuclear Plant [Abstract]
Nuclear Plant	6. 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 has elected to build a dry cask storage facility to expand its existing on-site spent nuclear fuel storage to provide additional capacity prior to 2025. Wolf Creek has finalized a settlement agreement through 2019 with the DOE for reimbursement of a significant portion of the costs to construct this facility that would not have otherwise been incurred had the DOE begun accepting spent nuclear fuel. Management expects the majority of the remaining cost to construct the dry cask storage facility that would not have otherwise been incurred will ultimately be reimbursed by the DOE. 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 Great Plains Energy's and KCP&L's nuclear decommissioning trust fund is reported at fair value on the balance sheets and is invested in equity and debt securities. The following table summarizes the unrealized gains and losses for equity and debt securities in the nuclear decommissioning trust fund. Three Months Ended March 31 2018 2017 (millions) Net unrealized gains - equity securities $ 83.7 $ 67.8 Net unrealized gains - debt securities 0.7 2.0 Total $ 84.4 $ 69.8

Regulatory Matters

Regulatory Matters	3 Months Ended
	Mar. 31, 2018
Regulated Operations [Abstract]
Regulatory Matters	7 . REGULATORY MATTERS KCP&L Missouri 2018 Rate Case Proceedings In January 2018, KCP&L filed an application with the MPSC to request an increase to its retail revenues of $8.9 million before rebasing fuel and purchased power expense, with a return on equity of 9.85% and a rate-making equity ratio of 50.03% . The request reflects the impact of the Tax Cuts and Jobs Act and increases in infrastructure investment costs, transmission related costs and property tax costs. KCP&L also requested an additional $7.5 million increase associated with rebasing fuel and purchased power expense. An evidentiary hearing in the case is expected to occur in September 2018 with new rates expected to go into effect in December 2018. GMO Missouri 2018 Rate Case Proceedings In January 2018, GMO filed an application with the MPSC to request a decrease to its retail revenues of $2.4 million before rebasing fuel and purchased power expense, with a return on equity of 9.85% and a rate-making equity ratio of 54.4% . The request reflects the impact of the Tax Cuts and Jobs Act and increases in infrastructure investment costs and transmission related costs. GMO also requested a $21.7 million increase associated with rebasing fuel and purchased power expense. An evidentiary hearing in the case is expected to occur in September 2018 with new rates expected to go into effect in December 2018. KCP&L Kansas 2018 Rate Case Proceedings In May 2018, KCP&L filed an application with KCC to request an increase to its retail revenues of $26.2 million before rebasing property tax expense, with a return on equity of 9.85% and a rate-making equity ratio of 49.8% . The request reflects the impact of the Tax Cuts and Jobs Act and increases in infrastructure investment costs. KCP&L also requested an additional $6.7 million increase associated with rebasing property tax expense. An evidentiary hearing in the case is expected in the fourth quarter of 2018 with new rates expected to go into effect in December 2018.

Pension Plans and Other Employe

Pension Plans and Other Employee Benefits	3 Months Ended
	Mar. 31, 2018
Retirement Benefits [Abstract]
Pension Plans and Other Employee Benefits	8. PENSION PLANS AND OTHER EMPLOYEE BENEFITS Great Plains Energy maintains defined benefit pension plans for the majority of KCP&L's and GMO's active and inactive employees, including officers, and its 47% ownership share of Wolf Creek Nuclear Operating Corporation (WCNOC) defined benefit plans. For the majority of employees, pension benefits under these plans reflect the employees' compensation, years of service and age at retirement. Effective in 2014, the non-union plan was closed to future employees. Great Plains Energy also provides certain post-retirement health care and life insurance benefits for substantially all retired employees of KCP&L, GMO and its 47% ownership share of WCNOC. KCP&L and GMO record pension and post-retirement expense in accordance with rate orders from the MPSC and KCC that allow the difference between pension and post-retirement costs under GAAP and costs for ratemaking to be recognized as a regulatory asset or liability. This difference between financial and regulatory accounting methods is due to timing and will be eliminated over the life of the plans. The following 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 2018 2017 2018 2017 Components of net periodic benefit costs (millions) Service cost $ 12.2 $ 11.0 $ 0.5 $ 0.5 Interest cost 12.7 13.4 1.2 1.3 Expected return on plan assets (13.9 ) (12.8 ) (0.7 ) (0.6 ) Prior service cost 0.2 0.2 — — Recognized net actuarial (gain)/loss 11.4 12.4 — (0.1 ) Net periodic benefit costs before regulatory adjustment 22.6 24.2 1.0 1.1 Regulatory adjustment 0.6 0.8 — 1.3 Net periodic benefit costs $ 23.2 $ 25.0 $ 1.0 $ 2.4 The components of net periodic benefit costs other than the service cost component are included in non-operating expenses on Great Plains Energy's and KCP&L's consolidated statements of comprehensive income. For the three months ended March 31, 2018 , Great Plains Energy contributed $13.7 million to the pension plans and expects to contribute an additional $70.3 million in 2018 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 2018 , Great Plains Energy expects to make contributions of $4.6 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, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity Compensation	9. EQUITY COMPENSATION Great Plains Energy's Long-Term Incentive Plan is an equity compensation plan approved by Great Plains Energy's shareholders. The Long-Term Incentive Plan permits the grant of restricted stock, restricted stock units, bonus shares, stock options, stock appreciation rights, director shares, director deferred share units, performance shares and other stock-based awards to directors, officers and other employees of Great Plains Energy and KCP&L. Forfeiture rates are based on historical forfeitures and future expectations and are reevaluated annually. The following table summarizes Great Plains Energy's and KCP&L's equity compensation expense and the associated income tax benefit. Three Months Ended March 31 2018 2017 Great Plains Energy (millions) Equity compensation expense $ 1.8 $ 1.2 Income tax benefit 0.4 0.6 KCP&L Equity compensation expense $ 1.2 $ 0.8 Income tax benefit 0.2 0.4 Performance Shares Performance share activity for the three months ended March 31, 2018 , is summarized in the following table. Performance Shares Grant Date Fair Value* Beginning balance January 1, 2018 545,087 $ 29.12 Granted 209,937 29.35 Earned (115,833 ) 24.01 Forfeited (2,097 ) 30.65 Performance adjustment (49,052 ) 24.01 Ending balance March 31, 2018 588,042 30.63 * weighted-average At March 31, 2018 , the remaining weighted-average contractual term was 1.8 years. The weighted-average grant-date fair value of shares granted was $29.35 and $31.26 for the three months ended March 31, 2018 , and 2017, respectively. At March 31, 2018 , there was $10.7 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 $2.8 million and $5.3 million for the three months ended March 31, 2018 , and 2017, 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 2018, inputs for expected volatility, dividend yield and risk-free rates were 17% , 3.72% and 2.34% , respectively. Restricted Stock Restricted stock activity for the three months ended March 31, 2018 , is summarized in the following table. Nonvested Restricted Stock Grant Date Fair Value* Beginning balance January 1, 2018 192,402 $ 27.87 Granted and issued 70,001 29.08 Vested (56,878 ) 26.12 Forfeited (700 ) 28.87 Ending balance March 31, 2018 204,825 28.77 * weighted-average At March 31, 2018 , the remaining weighted-average contractual term was 1.9 years. The weighted-average grant-date fair value of shares granted was $29.08 and $28.60 for the three months ended March 31, 2018 , and 2017, respectively. At March 31, 2018 , there was $3.5 million of total unrecognized compensation expense, net of forfeiture rates, related to nonvested restricted stock granted under the Long-Term Incentive Plan, which will be recognized over the remaining weighted-average contractual term. Total fair value of shares vested was $1.5 million and $2.3 million for the three months ended March 31, 2018 , and 2017, respectively.

Short-term Borrowings and Short

Short-term Borrowings and Short-term Bank Lines of Credit	3 Months Ended
	Mar. 31, 2018
Short-term Borrowings and Short-term Bank Lines of Credit [Abstract]
Short-term Borrowings and Short-term Bank Lines of Credit [Text Block]	10 . SHORT-TERM BORROWINGS AND SHORT-TERM BANK LINES OF CREDIT Great Plains Energy's $200 Million Revolving Credit Facility Great Plains Energy's $200 million revolving credit facility with a group of banks expires in October 2019 . The facility's terms permit transfers of unused commitments between this facility and the KCP&L and GMO facilities discussed below, with the total amount of the facility not exceeding $400 million at any one time. A default by Great Plains Energy or any of its significant subsidiaries on other indebtedness totaling more than $50.0 million is a default under the facility. Under the terms of this facility, Great Plains Energy is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times. At March 31, 2018 , Great Plains Energy was in compliance with this covenant. At March 31, 2018 , Great Plains Energy had $23.0 million of outstanding cash borrowings at a weighted-average interest rate of 3.23% and had issued $1.0 million in letters of credit under the credit facility. At December 31, 2017 , Great Plains Energy had $11.0 million of outstanding cash borrowings at a weighted-average interest rate of 2.94% 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, 2018 , KCP&L was in compliance with this covenant. At March 31, 2018 , KCP&L had $288.3 million of commercial paper outstanding at a weighted-average interest rate of 2.39% , had issued letters of credit totaling $2.7 million and had no outstanding cash borrowings under the credit facility. At December 31, 2017 , KCP&L had $167.5 million of commercial paper outstanding at a weighted-average interest rate of 1.95% , had issued letters of credit totaling $2.7 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, 2018 , GMO was in compliance with this covenant. At March 31, 2018 , GMO had $235.5 million of commercial paper outstanding at a weighted-average interest rate of 2.38% , had issued letters of credit totaling $2.1 million and had no outstanding cash borrowings under the credit facility. At December 31, 2017 , GMO had $209.3 million of commercial paper outstanding at a weighted-average interest rate of 1.85% , had issued letters of credit totaling $2.1 million and had no outstanding cash borrowings under the credit facility.

Long-Term Debt

Long-Term Debt	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Long-Term Debt	11. LONG-TERM DEBT Great Plains Energy's and KCP&L's long-term debt is detailed in the following table. March 31 December 31 Year Due 2018 2017 KCP&L (millions) General Mortgage Bonds 2.95% EIRR bonds 2023 $ 79.5 $ 79.5 7.15% Series 2009A (8.59% rate) (a) 2019 400.0 400.0 Senior Notes 6.375% Series (7.49% rate) (a) 2018 — 350.0 3.15% Series 2023 300.0 300.0 3.65% Series 2025 350.0 350.0 6.05% Series (5.78% rate) (a) 2035 250.0 250.0 5.30% Series 2041 400.0 400.0 4.20% Series 2047 300.0 300.0 4.20% Series 2048 300.0 — EIRR Bonds 1.349% Series 2007A and 2007B (b) 2035 146.5 146.5 2.875% Series 2008 2038 23.4 23.4 Current maturities — (350.0 ) Unamortized discount and debt issuance costs (20.1 ) (17.2 ) Total KCP&L excluding current maturities (c) 2,529.3 2,232.2 Other Great Plains Energy GMO First Mortgage Bonds 9.44% Series 2019-2021 3.4 4.6 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 4.85% Series 2021 350.0 350.0 5.292% Series 2022 287.5 287.5 Current maturities (1.1 ) (1.1 ) Unamortized discount and premium, net and debt issuance costs (1.5 ) (1.5 ) Total Great Plains Energy excluding current maturities (c) $ 3,608.5 $ 3,312.6 (a) Rate after amortizing gains/losses recognized in other comprehensive income (OCI) on settlements of interest rate hedging instruments (b) Variable rate (c) At March 31, 2018 and December 31, 2017, 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 KCP&L Senior Notes In March 2018, KCP&L issued, at a discount, $300.0 million of 4.20% unsecured Senior Notes, maturing in 2048 . KCP&L also repaid its $350.0 million of 6.375% unsecured Senior Notes at maturity in March 2018.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	12 . 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 five 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. 2018 2019 2020 2021 2022 (millions) Great Plains Energy $ 14.6 $ 2.8 $ 7.7 $ 20.1 $ 63.1 KCP&L 14.5 2.8 7.7 20.1 63.1 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 baseload generation capacity is primarily coal-fired and is estimated to produce about one ton of carbon dioxide (CO 2 ) per MWh, or approximately 17 million tons and 13 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 emission 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. The Paris Agreement does not result in any new, legally binding obligations on the U.S. to meet a particular greenhouse gas emissions target, but establishes a framework for international cooperation on climate change. In June 2017, U.S. President Donald Trump announced the U.S. would withdraw from the Paris Agreement. Under the rules of the Paris Agreement, the earliest any country can withdraw is November 2020. Other international agreements legally binding on the U.S. 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 U.S. Court of Appeals for the District of Columbia Circuit and any subsequent review by the U.S. Supreme Court if such review is sought. In October 2017, the EPA proposed to repeal the Clean Power Plan on the basis that it exceeded the EPA's statutory authority. In December 2017, the EPA issued an advance notice of proposed rulemaking (ANPRM) to solicit comments as the agency considers proposing a future rule to replace the Clean Power Plan. In the ANPRM, the EPA is considering proposing emission guidelines to limit greenhouse gas emissions from existing electric utility generating units. Compliance with the Clean Power Plan or any replacement rule has the potential of having significant financial and operational impacts on Great Plains Energy and KCP&L; however, the ultimate financial and operational consequences to Great Plains Energy and KCP&L cannot be determined until the outcome of the EPA's proposal to repeal the Clean Power Plan and pending litigation is known. Clean Water Act The Clean Water Act and associated regulations enacted by the EPA form a comprehensive program to restore and preserve water quality. Like the Clean Air Act, states are required to establish regulations and programs to address all requirements of the Clean Water Act, and have the flexibility to enact more stringent requirements. All of Great Plains Energy's and KCP&L's generating facilities, and certain of their other facilities, are subject to the Clean Water Act. In May 2014, the EPA finalized regulations pursuant to Section 316(b) of the Clean Water Act regarding cooling water intake structures pursuant to a court approved settlement. KCP&L generation facilities with cooling water intake structures are subject to the best technology available standards based on studies completed to comply with such standards. The rule provides flexibility to work with the states to develop the best technology available to minimize aquatic species impacted by being pinned against intake screens (impingement) or drawn into cooling water systems (entrainment). Estimated costs to comply with Section 316(b) of the Clean Water Act are included in the estimated capital expenditures table above. KCP&L holds a permit from the Missouri Department of Natural Resources (MDNR) covering water discharge from its Hawthorn Station. The permit authorizes KCP&L to, among other things, withdraw water from the Missouri River for cooling purposes and return the heated water to the Missouri River. KCP&L has applied for a renewal of this permit and the EPA has submitted an interim objection letter regarding the allowable amount of heat that can be contained in the returned water. Until this matter is resolved, KCP&L continues to operate under its current permit. Great Plains Energy and KCP&L cannot predict the outcome of this matter; however, while less significant outcomes are possible, this matter may require a reduction in generation, installation of cooling towers or other technology to cool the water, or both, any of which could have a significant impact on Great Plains Energy's and KCP&L's results of operations, financial position and cash flows. 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 took effect in October 2015 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 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, 2018 and December 31, 2017 , 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, 2018 and December 31, 2017 , Great Plains Energy had $1.5 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 $1.6 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.

Related Party Transactions and

Related Party Transactions and Relationships	3 Months Ended
	Mar. 31, 2018
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 $46.4 million and $47.9 million , respectively, for the three months ended March 31, 2018 and 2017. 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, 2018 and December 31, 2017, 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 2018 2017 (millions) Net receivable from GMO $ 50.5 $ 65.8 Net receivable from Great Plains Energy 18.6 18.9

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2018
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. Interest Rate Derivatives In June 2016, Great Plains Energy entered into four interest rate swaps, with a total notional amount of $4.4 billion , to hedge against interest rate fluctuations on future issuances of long-term debt expected to be issued to finance a portion of the cash consideration for the acquisition of Westar under the Original Merger Agreement. The interest rate swaps were designated as economic hedges (non-hedging derivatives). Settlement of the interest rate swaps was contingent on the consummation of the acquisition of Westar. In 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. In July 2017, the interest rate swap agreements were amended to make their cash settlement contingent on the consummation of the anticipated merger with Westar under the Amended Merger Agreement by November 30, 2018. Also in July 2017, Great Plains Energy redeemed its $4.3 billion senior notes that the interest rate swaps were entered into to hedge. The fair value of the interest rate swaps recorded on Great Plains Energy's balance sheets reflects a contingency factor that management believes is representative of what a market participant would use in valuing these instruments in order to account for the contingent nature of the cash settlement of the interest rate swaps. The contingency factor was 0.3 and 0.35 at March 31, 2018 and December 31, 2017 , respectively. At March 31, 2018 and December 31, 2017 , the fair value of the interest rate swaps was $98.4 million and $91.4 million , respectively, and was recorded on Great Plains Energy's consolidated balance sheets in interest rate derivative instruments. Due to the redemption of Great Plains Energy's $4.3 billion senior notes in July 2017 and the fact that the interest rate swaps no longer serve as economic hedges, Great Plains Energy recorded changes in the fair value of the interest rate swaps after July 2017 in non-operating income on Great Plains Energy's consolidated statements of comprehensive income (loss). All changes in the fair value of the interest rate swaps prior to July 2017 were recorded in interest charges. For the three months ended March 31, 2018 , Great Plains Energy recognized a $7.0 million gain for the change in fair value of the interest rate swaps in non-operating income. For the three months ended March 31, 2017 , Great Plains Energy recognized a $12.1 million gain for the change in fair value of the interest rate swaps in interest charges. Fair Value of Long-Term Debt Great Plains Energy and KCP&L record long-term debt on the balance sheet at amortized cost. The fair value of long-term debt is measured as a Level 2 liability. At March 31, 2018 , the book value and fair value of Great Plains Energy's long-term debt, including current maturities, were $3.6 billion and $3.8 billion , respectively. At December 31, 2017 , the book value and fair value of Great Plains Energy's long-term debt, including current maturities, were $3.7 billion and $4.0 billion , respectively. At March 31, 2018 , the book value and fair value of KCP&L's long-term debt, including current maturities, were $2.5 billion and $2.7 billion , respectively. At December 31, 2017 , the book value and fair value of KCP&L's long-term debt, including current maturities, were $2.6 billion and $2.8 billion , respectively. Supplemental Executive Retirement Plan At March 31, 2018 and December 31, 2017 , GMO's Supplemental Executive Retirement Plan (SERP) rabbi trusts included $14.2 million and $14.7 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 $ 179.6 $ 179.6 $ — $ — Debt securities U.S. Treasury 35.0 35.0 — — U.S. Agency 0.4 — 0.4 — State and local obligations 2.1 — 2.1 — Corporate bonds 32.7 — 32.7 — Foreign governments 0.1 — 0.1 — Cash equivalents 4.4 4.4 — — Other 1.0 1.0 — — Total nuclear decommissioning trust 255.3 220.0 35.3 — Self-insured health plan trust (b) Equity securities 0.4 0.4 — — Debt securities 2.1 0.1 2.0 — Cash and cash equivalents 8.6 8.6 — — Total self-insured health plan trust 11.1 9.1 2.0 — Total $ 266.4 $ 229.1 $ 37.3 $ — Other Great Plains Energy Assets Interest rate derivative instruments (c) $ 98.4 $ — $ — $ 98.4 Total $ 98.4 $ — $ — $ 98.4 Great Plains Energy Assets Nuclear decommissioning trust (a) $ 255.3 $ 220.0 $ 35.3 $ — Self-insured health plan trust (b) 11.1 9.1 2.0 — Interest rate derivative instruments (c) 98.4 — — 98.4 Total $ 364.8 $ 229.1 $ 37.3 $ 98.4 Description December 31 Level 1 Level 2 Level 3 KCP&L (millions) Assets Nuclear decommissioning trust (a) Equity securities $ 183.8 $ 183.8 $ — $ — Debt securities U.S. Treasury 35.3 35.3 — — U.S. Agency 0.4 — 0.4 — State and local obligations 2.1 — 2.1 — Corporate bonds 34.1 — 34.1 — Foreign governments 0.1 — 0.1 — Cash equivalents 2.5 2.5 — — Other 0.1 0.1 — — Total nuclear decommissioning trust 258.4 221.7 36.7 — Self-insured health plan trust (b) Equity securities 0.5 0.5 — — Debt securities 2.7 0.3 2.4 — Cash and cash equivalents 7.7 7.7 — — Total self-insured health plan trust 10.9 8.5 2.4 — Total $ 269.3 $ 230.2 $ 39.1 $ — 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) $ 258.4 $ 221.7 $ 36.7 $ — Self-insured health plan trust (b) 10.9 8.5 2.4 — Interest rate derivative instruments (c) 91.4 — — 91.4 Total $ 360.7 $ 230.2 $ 39.1 $ 91.4 (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) The fair value of interest rate derivative instruments is based on a settlement value, discounted by 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 these instruments. At March 31, 2018 and December 31, 2017 , the settlement value was $140.6 million with a contingency factor of 0.3 and 0.35 , respectively. A decrease in the contingency factor would result in a higher fair value measurement. The contingency factor will increase or decrease in response to facts and circumstances that in the view of a market participant, would increase or decrease the likelihood that the merger with Westar is not consummated. Because of the unobservable nature of the contingency factor, the interest rate derivatives have been classified as Level 3. The following 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 2018 2017 (millions) Net asset at January 1 $ 91.4 $ 79.3 Total realized/unrealized gains: included in interest charges — 12.1 included in non-operating income 7.0 — Net asset at March 31 $ 98.4 $ 91.4 Total unrealized gains relating to assets still on the consolidated balance sheet at March 31: included in interest charges $ — $ 12.1 included in non-operating income 7.0 —

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	3 Months Ended
	Mar. 31, 2018
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 income (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) Three Months Ended March 31, 2018 (millions) Beginning balance January 1 $ 0.4 $ (2.6 ) $ (2.2 ) Amounts reclassified from accumulated other comprehensive loss 0.9 0.1 1.0 Net current period other comprehensive income 0.9 0.1 1.0 Ending balance March 31 $ 1.3 $ (2.5 ) $ (1.2 ) 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 ) (a) Net of tax KCP&L Gains and Losses on Cash Flow Hedges (a) Three Months Ended March 31, 2018 (millions) Beginning balance January 1 $ 0.4 Amounts reclassified from accumulated other comprehensive income 0.9 Net current period other comprehensive income 0.9 Ending balance March 31 $ 1.3 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 ) (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 income (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 2018 2017 (millions) Gains (losses) on cash flow hedges (effective portion) Interest rate contracts $ (1.2 ) $ (2.3 ) Interest charges (1.2 ) (2.3 ) Income before income tax expense and income from equity investments 0.3 0.9 Income tax benefit $ (0.9 ) $ (1.4 ) Net income (loss) Amortization of defined benefit pension items Net losses included in net periodic benefit costs $ (0.1 ) $ (0.2 ) Non-operating expenses (0.1 ) (0.2 ) Income before income tax expense and income from equity investments — 0.1 Income tax benefit $ (0.1 ) $ (0.1 ) Net income (loss) Total reclassifications, net of tax $ (1.0 ) $ (1.5 ) Net income (loss) KCP&L Details about Accumulated Other Comprehensive Loss Components Amount Reclassified from Accumulated Other Comprehensive Income (Loss) Affected Line Item in the Income Statement Three Months Ended March 31 2018 2017 (millions) Gains (losses) on cash flow hedges (effective portion) Interest rate contracts $ (1.2 ) $ (2.2 ) Interest charges (1.2 ) (2.2 ) Income before income tax expense 0.3 0.9 Income tax benefit Total reclassifications, net of tax $ (0.9 ) $ (1.3 ) Net income

Taxes

Taxes	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Tax Disclosure [Text Block]	16. TAXES Components of income tax expense are detailed in the following tables. Great Plains Energy Three Months Ended March 31 2018 2017 Current income taxes (millions) Federal $ — $ — State — 0.2 Total — 0.2 Deferred income taxes Federal 3.2 (4.5 ) State 2.6 (1.1 ) Total 5.8 (5.6 ) Investment tax credit amortization (0.3 ) (0.4 ) Income tax expense (benefit) $ 5.5 $ (5.8 ) KCP&L Three Months Ended March 31 2018 2017 Current income taxes (millions) Federal $ (1.3 ) $ (0.1 ) State (0.5 ) — Total (1.8 ) (0.1 ) Deferred income taxes Federal 3.6 7.8 State 2.0 1.4 Total 5.6 9.2 Investment tax credit amortization (0.3 ) (0.3 ) Income tax expense $ 3.5 $ 8.8 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 2018 2017 Federal statutory income tax rate 21.0 % 35.0 % Effect of regulatory treatment of book and tax differences (9.6 ) — Amortization of investment tax credits (0.4 ) (0.4 ) Federal income tax credits (4.1 ) (1.5 ) State income taxes 5.2 4.2 Transaction-related costs 0.1 3.1 Other 1.4 (2.5 ) Effective income tax rate 13.6 % 37.9 % KCP&L Three Months Ended March 31 2018 2017 Federal statutory income tax rate 21.0 % 35.0 % Effect of regulatory treatment of book and tax differences (7.2 ) (0.1 ) Amortization of investment tax credits (0.4 ) (0.3 ) Federal income tax credits (5.3 ) (1.8 ) State income taxes 5.1 4.0 Other 1.7 1.5 Effective income tax rate 14.9 % 38.3 % The decrease in Great Plains Energy's and KCP&L's effective income tax rates for the three months ended March 31, 2018 , compared to the same period in 2017, is primarily driven by the impacts of the Tax Cuts and Jobs Act which reduced the federal statutory income tax rate from 35% to 21% beginning in 2018. Tax Reform In December 2017, the U.S. Congress passed and President Donald Trump signed Public Law No. 115-97, commonly referred to as the Tax Cuts and Jobs Act. The Tax Cuts and Jobs Act represents the first major reform in U.S. income tax law since 1986. Most notably, the Tax Cuts and Jobs Act reduces the current top corporate income tax rate from 35% to 21% beginning in 2018, repeals the corporate Alternative Minimum Tax (AMT), makes existing AMT tax credit carryforwards refundable, and changes the deductibility and taxability of certain items, among other things. KCP&L and GMO currently recover the cost of income taxes in rates from their customers based on the 35% federal corporate income tax rate. Both KCP&L and GMO have announced their intentions to pass the income tax savings generated by the tax rate change, currently estimated at approximately $100 million annually, through to customers as part of general rate cases recently filed in both Missouri and Kansas. In January 2018, KCC issued an order requiring certain regulated public utilities, including KCP&L, to begin recording a regulatory liability for the difference between the new corporate tax rate and amounts currently collected in rates. The treatment of the regulatory liability will be addressed by KCC in future orders. As a result of the KCC order discussed above and the probability that KCP&L and GMO will be required to make similar refunds to their Missouri customers, Great Plains Energy and KCP&L have recorded regulatory liabilities as of March 31, 2018 of $21.9 million and $15.2 million , respectively. The actual regulatory treatment of tax reform and these regulatory liabilities will not be known until orders specifying the treatment are received from the MPSC and KCC and any amounts ultimately refunded to customers could differ from the amounts recorded.

Segments and Related Informatio

Segments and Related Information	3 Months Ended
	Mar. 31, 2018
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 certain costs to achieve the anticipated merger with Westar. The summary of significant accounting policies applies to the reportable segment. Segment performance is evaluated based on net income (loss). The following tables reflect summarized financial information concerning Great Plains Energy's reportable segment. Three Months Ended March 31, 2018 Electric Utility Other Eliminations Great Plains Energy (millions) Operating revenues $ 583.9 $ — $ — $ 583.9 Depreciation and amortization (93.7 ) — — (93.7 ) Interest (charges) income (47.8 ) (8.3 ) 8.0 (48.1 ) Income tax expense (2.9 ) (2.6 ) — (5.5 ) Net income 28.0 7.0 — 35.0 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 ) Electric Utility Other Eliminations Great Plains Energy March 31, 2018 (millions) Assets $ 11,529.0 $ 1,304.1 $ (384.7 ) $ 12,448.4 Capital expenditures (a) 119.7 — — 119.7 December 31, 2017 Assets $ 11,508.1 $ 1,285.7 $ (335.9 ) $ 12,457.9 Capital expenditures (a) 573.5 — — 573.5 (a) Capital expenditures reflect year to date amounts for the periods presented.

Summary of Significant Accoun25

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2018
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. 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 one active wholly owned subsidiary, GMO Receivables Company. 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, 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 the electric utility segment (Electric Utility). See Note 17 for additional information.
Basic and Diluted Earnings per Common Share Calculation [Policy Text Block]	Basic and Diluted Earnings (Loss) per Common Share Calculation To determine basic earnings (loss) per common share (EPS), preferred stock dividend requirements are deducted from net income (loss) 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 non-service cost components are to be reported separately from service costs and outside of a subtotal of income from operations. The amendments in this update allow only the service cost component to be eligible for capitalization as part of utility plant. The non-service cost components that are no longer eligible for capitalization as part of utility plant will be recorded as a regulatory asset. The new guidance is to be applied retrospectively for the presentation of service cost and non-service cost components in the income statement and prospectively for the capitalization of the service cost component and is effective for interim and annual periods beginning after December 15, 2017. The Companies adopted ASU No. 2017-07 on January 1, 2018, and accordingly have retrospectively adjusted prior periods. The following table reflects the retrospective adjustments in the line items of Great Plains Energy's and KCP&L's consolidated statements of comprehensive income associated with the adoption of ASU No. 2017-07. Three Months Ended March 31, 2017 As Previously Reported Effect of Change As Reported Great Plains Energy (millions) Utility operating and maintenance expenses $ 185.4 $ (11.3 ) $ 174.1 Other operating expense 1.5 (0.4 ) 1.1 Operating expenses 523.3 (11.7 ) 511.6 Operating income 47.4 11.7 59.1 Non-operating expenses (3.7 ) (11.7 ) (15.4 ) Other income (expense) 2.9 (11.7 ) (8.8 ) KCP&L Utility operating and maintenance expenses $ 126.4 $ (6.8 ) $ 119.6 Operating expenses 337.7 (6.8 ) 330.9 Operating income 58.2 6.8 65.0 Non-operating expenses (2.1 ) (6.8 ) (8.9 ) Other income (expense) 0.4 (6.8 ) (6.4 ) In February 2016, the FASB issued ASU No. 2016-02, Leases , which requires an entity that is a lessee to record a right-of-use asset and a lease liability for lease payments on the balance sheet for all leases with terms longer than 12 months. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. The new guidance is effective for interim and annual periods beginning after December 15, 2018, with early adoption permitted, and is required to be applied using a modified retrospective approach . Great Plains Energy and KCP&L plan to adopt the new guidance on January 1, 2019. The Companies expect that the new guidance will affect the balance sheet by increasing the assets and liabilities recorded related to operating leases and continue to evaluate the effect that ASU No. 2016-02 will have on their income statement, statement of cash flows and related disclosures. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers , which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. 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 ASU replaced most existing revenue recognition guidance in Generally Accepted Accounting Principles (GAAP) when it became effective. The Companies adopted ASU No. 2014-09 and its related amendments (ASC 606) on January 1, 2018 using the modified retrospective transition method for all contracts not completed as of the date of adoption. Results for reporting periods beginning after January 1, 2018 are presented under ASC 606 while historical periods have not been adjusted and continue to be reported in accordance with the legacy guidance in ASC 605 - Revenue Recognition . There was no cumulative effect adjustment to the opening balance of retained earnings in 2018 for Great Plains Energy or KCP&L as a result of the adoption of the new guidance. The impact to both electric revenues and general taxes on Great Plains Energy's and KCP&L's statements of comprehensive income in 2018 as a result of adopting ASC 606 was a decrease of $17.9 million . This impact was related to sales taxes and franchise fees collected from KCP&L's Missouri customers, which prior to ASC 606, were recorded gross on Great Plains Energy's and KCP&L's statements of comprehensive income.

Summary of Significant Accoun26

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2018
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 2018 2017 Income (loss) (millions, except per share amounts) Net income (loss) $ 35.0 $ (9.6 ) Less: preferred stock dividend requirements — 15.1 Earnings (loss) available for common shareholders $ 35.0 $ (24.7 ) Common Shares Outstanding Average number of common shares outstanding 215.7 215.3 Add: effect of dilutive securities 0.3 — Diluted average number of common shares outstanding 216.0 215.3 Basic and diluted EPS $ 0.16 $ (0.11 )
Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block]	The following table reflects the retrospective adjustments in the line items of Great Plains Energy's and KCP&L's consolidated statements of comprehensive income associated with the adoption of ASU No. 2017-07. Three Months Ended March 31, 2017 As Previously Reported Effect of Change As Reported Great Plains Energy (millions) Utility operating and maintenance expenses $ 185.4 $ (11.3 ) $ 174.1 Other operating expense 1.5 (0.4 ) 1.1 Operating expenses 523.3 (11.7 ) 511.6 Operating income 47.4 11.7 59.1 Non-operating expenses (3.7 ) (11.7 ) (15.4 ) Other income (expense) 2.9 (11.7 ) (8.8 ) KCP&L Utility operating and maintenance expenses $ 126.4 $ (6.8 ) $ 119.6 Operating expenses 337.7 (6.8 ) 330.9 Operating income 58.2 6.8 65.0 Non-operating expenses (2.1 ) (6.8 ) (8.9 ) Other income (expense) 0.4 (6.8 ) (6.4 )

Revenue Recognition (Tables)

Revenue Recognition (Tables)	3 Months Ended
	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue [Table Text Block]	Great Plains Energy's and KCP&L's revenues disaggregated by customer class and for Great Plains Energy's direct subsidiaries are summarized in the following table. All of Great Plains Energy's revenues pertain to Electric Utility. Three Months Ended March 31, 2018 KCP&L GMO Great Plains Energy Customer class (millions) Residential $ 154.9 $ 88.1 $ 243.0 Commercial 181.8 64.2 246.0 Industrial 32.2 19.9 52.1 Other 2.7 1.8 4.5 Total electric retail $ 371.6 $ 174.0 $ 545.6 Wholesale 3.1 2.9 6.0 Transmission 3.3 4.6 7.9 Industrial steam — 4.3 4.3 Total revenue from contracts with customers $ 378.0 $ 185.8 $ 563.8 Other revenue 19.1 1.0 20.1 Electric revenue $ 397.1 $ 186.8 $ 583.9

Supplemental Cash Flow Inform28

Supplemental Cash Flow Information (Tables)	3 Months Ended
	Mar. 31, 2018
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 2018 2017 Cash flows affected by changes in: (millions) Receivables $ 43.2 $ 55.5 Accounts receivable pledged as collateral — 0.2 Fuel inventories (1.8 ) 1.8 Materials and supplies (1.1 ) (4.2 ) Accounts payable (142.1 ) (136.8 ) Accrued taxes 37.6 36.3 Accrued interest 14.6 26.5 Deferred refueling outage costs 0.9 4.0 Pension and post-retirement benefit obligations 10.5 11.6 Allowance for equity funds used during construction (1.4 ) (1.0 ) Fuel recovery mechanisms (3.5 ) (14.1 ) ARO settlements (4.5 ) (4.3 ) Other 18.5 17.5 Total other operating activities $ (29.1 ) $ (7.0 ) Cash paid during the period: Interest $ 31.3 $ 34.2 Non-cash investing activities: Liabilities accrued for capital expenditures $ 25.4 $ 22.6 KCP&L Other Operating Activities Three Months Ended March 31 2018 2017 Cash flows affected by changes in: (millions) Receivables $ 47.9 $ 36.2 Fuel inventories (1.0 ) (0.5 ) Materials and supplies (1.8 ) (3.1 ) Accounts payable (90.0 ) (88.8 ) Accrued taxes 25.0 35.5 Accrued interest 8.3 10.1 Deferred refueling outage costs 0.9 4.0 Pension and post-retirement benefit obligations 9.0 10.3 Allowance for equity funds used during construction (1.4 ) (1.0 ) Fuel recovery mechanisms 1.2 (10.8 ) ARO settlements (3.6 ) (3.9 ) Other 3.8 (9.1 ) Total other operating activities $ (1.7 ) $ (21.1 ) Cash paid during the period: Interest $ 22.7 $ 22.5 Non-cash investing activities: Liabilities accrued for capital expenditures $ 19.5 $ 19.9

Receivables (Tables)

Receivables (Tables)	3 Months Ended
	Mar. 31, 2018
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 2018 2017 Great Plains Energy (millions) Customer accounts receivable - billed $ — $ 3.7 Customer accounts receivable - unbilled 80.3 103.2 Allowance for doubtful accounts - customer accounts receivable (5.0 ) (4.7 ) Other receivables 32.9 49.5 Total $ 108.2 $ 151.7 KCP&L Customer accounts receivable - billed $ — $ 1.6 Customer accounts receivable - unbilled 50.4 67.6 Allowance for doubtful accounts - customer accounts receivable (2.3 ) (2.2 ) Other receivables 26.2 39.3 Total $ 74.3 $ 106.3

Nuclear Plant (Tables)

Nuclear Plant (Tables)	3 Months Ended
	Mar. 31, 2018
Nuclear Plant [Abstract]
Unrealized Gains Losses In Nuclear Decommissioning Trust Fund [Table Text Block]	The following table summarizes the unrealized gains and losses for equity and debt securities in the nuclear decommissioning trust fund. Three Months Ended March 31 2018 2017 (millions) Net unrealized gains - equity securities $ 83.7 $ 67.8 Net unrealized gains - debt securities 0.7 2.0 Total $ 84.4 $ 69.8

Pension Plans and Other Emplo31

Pension Plans and Other Employee Benefits (Tables)	3 Months Ended
	Mar. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Schedule of Net Benefit Costs [Table Text Block]	Pension Benefits Other Benefits Three Months Ended March 31 2018 2017 2018 2017 Components of net periodic benefit costs (millions) Service cost $ 12.2 $ 11.0 $ 0.5 $ 0.5 Interest cost 12.7 13.4 1.2 1.3 Expected return on plan assets (13.9 ) (12.8 ) (0.7 ) (0.6 ) Prior service cost 0.2 0.2 — — Recognized net actuarial (gain)/loss 11.4 12.4 — (0.1 ) Net periodic benefit costs before regulatory adjustment 22.6 24.2 1.0 1.1 Regulatory adjustment 0.6 0.8 — 1.3 Net periodic benefit costs $ 23.2 $ 25.0 $ 1.0 $ 2.4

Equity Compensation (Tables)

Equity Compensation (Tables)	3 Months Ended
	Mar. 31, 2018
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Equity compensation expense and associated income tax benefits	Three Months Ended March 31 2018 2017 Great Plains Energy (millions) Equity compensation expense $ 1.8 $ 1.2 Income tax benefit 0.4 0.6 KCP&L Equity compensation expense $ 1.2 $ 0.8 Income tax benefit 0.2 0.4
Performance share activity	Performance Shares Grant Date Fair Value* Beginning balance January 1, 2018 545,087 $ 29.12 Granted 209,937 29.35 Earned (115,833 ) 24.01 Forfeited (2,097 ) 30.65 Performance adjustment (49,052 ) 24.01 Ending balance March 31, 2018 588,042 30.63
Restricted stock activity	Nonvested Restricted Stock Grant Date Fair Value* Beginning balance January 1, 2018 192,402 $ 27.87 Granted and issued 70,001 29.08 Vested (56,878 ) 26.12 Forfeited (700 ) 28.87 Ending balance March 31, 2018 204,825 28.77

Long-Term Debt (Tables)

Long-Term Debt (Tables)	3 Months Ended
	Mar. 31, 2018
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 2018 2017 KCP&L (millions) General Mortgage Bonds 2.95% EIRR bonds 2023 $ 79.5 $ 79.5 7.15% Series 2009A (8.59% rate) (a) 2019 400.0 400.0 Senior Notes 6.375% Series (7.49% rate) (a) 2018 — 350.0 3.15% Series 2023 300.0 300.0 3.65% Series 2025 350.0 350.0 6.05% Series (5.78% rate) (a) 2035 250.0 250.0 5.30% Series 2041 400.0 400.0 4.20% Series 2047 300.0 300.0 4.20% Series 2048 300.0 — EIRR Bonds 1.349% Series 2007A and 2007B (b) 2035 146.5 146.5 2.875% Series 2008 2038 23.4 23.4 Current maturities — (350.0 ) Unamortized discount and debt issuance costs (20.1 ) (17.2 ) Total KCP&L excluding current maturities (c) 2,529.3 2,232.2 Other Great Plains Energy GMO First Mortgage Bonds 9.44% Series 2019-2021 3.4 4.6 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 4.85% Series 2021 350.0 350.0 5.292% Series 2022 287.5 287.5 Current maturities (1.1 ) (1.1 ) Unamortized discount and premium, net and debt issuance costs (1.5 ) (1.5 ) Total Great Plains Energy excluding current maturities (c) $ 3,608.5 $ 3,312.6 (a) Rate after amortizing gains/losses recognized in other comprehensive income (OCI) on settlements of interest rate hedging instruments (b) Variable rate (c) At March 31, 2018 and December 31, 2017, 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, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule Of Environmental Capital Expenditures [Table Text Block]	2018 2019 2020 2021 2022 (millions) Great Plains Energy $ 14.6 $ 2.8 $ 7.7 $ 20.1 $ 63.1 KCP&L 14.5 2.8 7.7 20.1 63.1

Related Party Transactions an35

Related Party Transactions and Relationships (Tables)	3 Months Ended
	Mar. 31, 2018
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 2018 2017 (millions) Net receivable from GMO $ 50.5 $ 65.8 Net receivable from Great Plains Energy 18.6 18.9

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2018
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 $ 179.6 $ 179.6 $ — $ — Debt securities U.S. Treasury 35.0 35.0 — — U.S. Agency 0.4 — 0.4 — State and local obligations 2.1 — 2.1 — Corporate bonds 32.7 — 32.7 — Foreign governments 0.1 — 0.1 — Cash equivalents 4.4 4.4 — — Other 1.0 1.0 — — Total nuclear decommissioning trust 255.3 220.0 35.3 — Self-insured health plan trust (b) Equity securities 0.4 0.4 — — Debt securities 2.1 0.1 2.0 — Cash and cash equivalents 8.6 8.6 — — Total self-insured health plan trust 11.1 9.1 2.0 — Total $ 266.4 $ 229.1 $ 37.3 $ — Other Great Plains Energy Assets Interest rate derivative instruments (c) $ 98.4 $ — $ — $ 98.4 Total $ 98.4 $ — $ — $ 98.4 Great Plains Energy Assets Nuclear decommissioning trust (a) $ 255.3 $ 220.0 $ 35.3 $ — Self-insured health plan trust (b) 11.1 9.1 2.0 — Interest rate derivative instruments (c) 98.4 — — 98.4 Total $ 364.8 $ 229.1 $ 37.3 $ 98.4 Description December 31 Level 1 Level 2 Level 3 KCP&L (millions) Assets Nuclear decommissioning trust (a) Equity securities $ 183.8 $ 183.8 $ — $ — Debt securities U.S. Treasury 35.3 35.3 — — U.S. Agency 0.4 — 0.4 — State and local obligations 2.1 — 2.1 — Corporate bonds 34.1 — 34.1 — Foreign governments 0.1 — 0.1 — Cash equivalents 2.5 2.5 — — Other 0.1 0.1 — — Total nuclear decommissioning trust 258.4 221.7 36.7 — Self-insured health plan trust (b) Equity securities 0.5 0.5 — — Debt securities 2.7 0.3 2.4 — Cash and cash equivalents 7.7 7.7 — — Total self-insured health plan trust 10.9 8.5 2.4 — Total $ 269.3 $ 230.2 $ 39.1 $ — 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) $ 258.4 $ 221.7 $ 36.7 $ — Self-insured health plan trust (b) 10.9 8.5 2.4 — Interest rate derivative instruments (c) 91.4 — — 91.4 Total $ 360.7 $ 230.2 $ 39.1 $ 91.4 (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) The fair value of interest rate derivative instruments is based on a settlement value, discounted by 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 these instruments. At March 31, 2018 and December 31, 2017 , the settlement value was $140.6 million with a contingency factor of 0.3 and 0.35 , respectively. A decrease in the contingency factor would result in a higher fair value measurement. The contingency factor will increase or decrease in response to facts and circumstances that in the view of a market participant, would increase or decrease the likelihood that the merger with Westar is not consummated. Because of the unobservable nature of the contingency factor, the interest rate derivatives have been classified as Level 3.
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 2018 2017 (millions) Net asset at January 1 $ 91.4 $ 79.3 Total realized/unrealized gains: included in interest charges — 12.1 included in non-operating income 7.0 — Net asset at March 31 $ 98.4 $ 91.4 Total unrealized gains relating to assets still on the consolidated balance sheet at March 31: included in interest charges $ — $ 12.1 included in non-operating income 7.0 —

Accumulated Other Comprehensi37

Accumulated Other Comprehensive Income (Loss) (Tables)	3 Months Ended
	Mar. 31, 2018
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 income (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) Three Months Ended March 31, 2018 (millions) Beginning balance January 1 $ 0.4 $ (2.6 ) $ (2.2 ) Amounts reclassified from accumulated other comprehensive loss 0.9 0.1 1.0 Net current period other comprehensive income 0.9 0.1 1.0 Ending balance March 31 $ 1.3 $ (2.5 ) $ (1.2 ) 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 ) (a) Net of tax KCP&L Gains and Losses on Cash Flow Hedges (a) Three Months Ended March 31, 2018 (millions) Beginning balance January 1 $ 0.4 Amounts reclassified from accumulated other comprehensive income 0.9 Net current period other comprehensive income 0.9 Ending balance March 31 $ 1.3 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 ) (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 income (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 2018 2017 (millions) Gains (losses) on cash flow hedges (effective portion) Interest rate contracts $ (1.2 ) $ (2.3 ) Interest charges (1.2 ) (2.3 ) Income before income tax expense and income from equity investments 0.3 0.9 Income tax benefit $ (0.9 ) $ (1.4 ) Net income (loss) Amortization of defined benefit pension items Net losses included in net periodic benefit costs $ (0.1 ) $ (0.2 ) Non-operating expenses (0.1 ) (0.2 ) Income before income tax expense and income from equity investments — 0.1 Income tax benefit $ (0.1 ) $ (0.1 ) Net income (loss) Total reclassifications, net of tax $ (1.0 ) $ (1.5 ) Net income (loss) KCP&L Details about Accumulated Other Comprehensive Loss Components Amount Reclassified from Accumulated Other Comprehensive Income (Loss) Affected Line Item in the Income Statement Three Months Ended March 31 2018 2017 (millions) Gains (losses) on cash flow hedges (effective portion) Interest rate contracts $ (1.2 ) $ (2.2 ) Interest charges (1.2 ) (2.2 ) Income before income tax expense 0.3 0.9 Income tax benefit Total reclassifications, net of tax $ (0.9 ) $ (1.3 ) Net income

Taxes (Tables)

Taxes (Tables)	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	Great Plains Energy Three Months Ended March 31 2018 2017 Current income taxes (millions) Federal $ — $ — State — 0.2 Total — 0.2 Deferred income taxes Federal 3.2 (4.5 ) State 2.6 (1.1 ) Total 5.8 (5.6 ) Investment tax credit amortization (0.3 ) (0.4 ) Income tax expense (benefit) $ 5.5 $ (5.8 ) KCP&L Three Months Ended March 31 2018 2017 Current income taxes (millions) Federal $ (1.3 ) $ (0.1 ) State (0.5 ) — Total (1.8 ) (0.1 ) Deferred income taxes Federal 3.6 7.8 State 2.0 1.4 Total 5.6 9.2 Investment tax credit amortization (0.3 ) (0.3 ) Income tax expense $ 3.5 $ 8.8
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	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 2018 2017 Federal statutory income tax rate 21.0 % 35.0 % Effect of regulatory treatment of book and tax differences (9.6 ) — Amortization of investment tax credits (0.4 ) (0.4 ) Federal income tax credits (4.1 ) (1.5 ) State income taxes 5.2 4.2 Transaction-related costs 0.1 3.1 Other 1.4 (2.5 ) Effective income tax rate 13.6 % 37.9 % KCP&L Three Months Ended March 31 2018 2017 Federal statutory income tax rate 21.0 % 35.0 % Effect of regulatory treatment of book and tax differences (7.2 ) (0.1 ) Amortization of investment tax credits (0.4 ) (0.3 ) Federal income tax credits (5.3 ) (1.8 ) State income taxes 5.1 4.0 Other 1.7 1.5 Effective income tax rate 14.9 % 38.3 %

Segments and Related Informat39

Segments and Related Information (Tables)	3 Months Ended
	Mar. 31, 2018
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, 2018 Electric Utility Other Eliminations Great Plains Energy (millions) Operating revenues $ 583.9 $ — $ — $ 583.9 Depreciation and amortization (93.7 ) — — (93.7 ) Interest (charges) income (47.8 ) (8.3 ) 8.0 (48.1 ) Income tax expense (2.9 ) (2.6 ) — (5.5 ) Net income 28.0 7.0 — 35.0 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 ) Electric Utility Other Eliminations Great Plains Energy March 31, 2018 (millions) Assets $ 11,529.0 $ 1,304.1 $ (384.7 ) $ 12,448.4 Capital expenditures (a) 119.7 — — 119.7 December 31, 2017 Assets $ 11,508.1 $ 1,285.7 $ (335.9 ) $ 12,457.9 Capital expenditures (a) 573.5 — — 573.5 (a) Capital expenditures reflect year to date amounts for the periods presented.

Summary of Significant Accoun40

Summary of Significant Accounting Policies Equity Method Investment (Details) - Transource Energy, LLC [Member]	3 Months Ended
	Mar. 31, 2018Rate
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 Accoun41

Summary of Significant Accounting Policies Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income [Abstract]
Net income (loss)	$ 35	$ (9.6)
Less: preferred stock dividend requirements	0	15.1
Earnings (loss) available for common shareholders	$ 35	$ (24.7)
Common Shares Outstanding [Abstract]
Average number of common shares outstanding (in shares)	215.7	215.3
Add: effect of dilutive securities (in shares)	0.3	0
Diluted average number of common shares outstanding (in shares)	216	215.3
Earnings Per Share [Abstract]
Basic and Diluted EPS	$ 0.16	$ (0.11)
Series B Preferred Stock [Member]
Preferred Stock, Dividend Rate, Percentage		7.00%

Summary of Significant Accoun42

Summary of Significant Accounting Policies Antidilutive Securities (Details) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0
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
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
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

Summary of Significant Accoun43

Summary of Significant Accounting Policies Summary of Significant Accounting Policies New Accounting Pronouncements (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Utility operating and maintenance expenses	$ 180.2	$ 174.1
Other operating expense	0	1.1
Operating expenses	497.6	511.6
Operating income	86.3	59.1
Non-operating expenses	(13.2)	(15.4)
Other income (expense)	1.3	(8.8)
Adjustments for New Accounting Pronouncement [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Utility operating and maintenance expenses		174.1
Other operating expense		1.1
Operating expenses		511.6
Operating income		59.1
Non-operating expenses		(15.4)
Other income (expense)		(8.8)
Adjustments for New Accounting Pronouncement [Member] | Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Utility operating and maintenance expenses		185.4
Other operating expense		1.5
Operating expenses		523.3
Operating income		47.4
Non-operating expenses		(3.7)
Other income (expense)		2.9
Adjustments for New Accounting Pronouncement [Member] | Restatement Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Utility operating and maintenance expenses		(11.3)
Other operating expense		(0.4)
Operating expenses		(11.7)
Operating income		11.7
Non-operating expenses		(11.7)
Other income (expense)		(11.7)
KCPL [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Utility operating and maintenance expenses	121	119.6
Other operating expense	0.2	0.3
Operating expenses	336.1	330.9
Operating income	61	65
Non-operating expenses	(7.9)	(8.9)
Other income (expense)	$ (4.3)	(6.4)
KCPL [Member] | Adjustments for New Accounting Pronouncement [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Utility operating and maintenance expenses		119.6
Operating expenses		330.9
Operating income		65
Non-operating expenses		(8.9)
Other income (expense)		(6.4)
KCPL [Member] | Adjustments for New Accounting Pronouncement [Member] | Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Utility operating and maintenance expenses		126.4
Operating expenses		337.7
Operating income		58.2
Non-operating expenses		(2.1)
Other income (expense)		0.4
KCPL [Member] | Adjustments for New Accounting Pronouncement [Member] | Restatement Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Utility operating and maintenance expenses		(6.8)
Operating expenses		(6.8)
Operating income		6.8
Non-operating expenses		(6.8)
Other income (expense)		$ (6.8)

Summary of Significant Accoun44

Summary of Significant Accounting Policies Subsequent Events (Details) - Subsequent Event [Member]	May 31, 2018$ / shares
Common Stock [Member]
Dividends Declared [Abstract]
Dividends Payable, Amount Per Share	$ 0.275
Dividends Payable, Date of Record	May 30, 2018
Dividends Payable, Date Declared, Month and Year	2018-05
Dividends Payable, Date to be Paid	Jun. 20, 2018
KCPL [Member]
Dividends Declared [Abstract]
Dividends Payable, Amount Per Share	$ 60,000,000
Dividends Payable, Date Declared, Month and Year	2018-05
Dividends Payable, Date to be Paid	Jun. 19, 2018

Summary of Significant Accoun45

Summary of Significant Accounting Policies Revenue, Initial Application Period Cumulative Effect Transition (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
General taxes	$ (41.1)	$ (57.1)
Electric Revenue	(583.9)	(570.7)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
General taxes	17.9
Electric Revenue	17.9
KCPL [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
General taxes	(29)	(44.6)
Electric Revenue	(397.1)	$ (395.9)
KCPL [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
General taxes	17.9
Electric Revenue	$ 17.9

Revenue Recognition (Details)

Revenue Recognition (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Electric Revenue	$ 583.9	$ 570.7
KCPL [Member]
Disaggregation of Revenue [Line Items]
Electric Revenue	397.1	$ 395.9
Electric Utility Segment [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	563.8
Other Revenue	20.1
Electric Revenue	583.9
Electric Utility Segment [Member] | KCPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	378
Other Revenue	19.1
Electric Revenue	397.1
Electric Utility Segment [Member] | Kcpl Greater Missouri Operations Member
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	185.8
Other Revenue	1
Electric Revenue	186.8
Electric Utility Customer Class Residential [Member] | Electric Utility Segment [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	243
Electric Utility Customer Class Residential [Member] | Electric Utility Segment [Member] | KCPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	154.9
Electric Utility Customer Class Residential [Member] | Electric Utility Segment [Member] | Kcpl Greater Missouri Operations Member
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	88.1
Electric Utility Customer Class Commercial [Member] | Electric Utility Segment [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	246
Electric Utility Customer Class Commercial [Member] | Electric Utility Segment [Member] | KCPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	181.8
Electric Utility Customer Class Commercial [Member] | Electric Utility Segment [Member] | Kcpl Greater Missouri Operations Member
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	64.2
Electric Utility Customer Class Industrial [Member] | Electric Utility Segment [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	52.1
Electric Utility Customer Class Industrial [Member] | Electric Utility Segment [Member] | KCPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	32.2
Electric Utility Customer Class Industrial [Member] | Electric Utility Segment [Member] | Kcpl Greater Missouri Operations Member
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	19.9
Electric Utility Customer Class Other Retail [Member] | Electric Utility Segment [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	4.5
Electric Utility Customer Class Other Retail [Member] | Electric Utility Segment [Member] | KCPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	2.7
Electric Utility Customer Class Other Retail [Member] | Electric Utility Segment [Member] | Kcpl Greater Missouri Operations Member
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1.8
Electric Utility Customer Class Total Electric Retail [Member] | Electric Utility Segment [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	545.6
Electric Utility Customer Class Total Electric Retail [Member] | Electric Utility Segment [Member] | KCPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	371.6
Electric Utility Customer Class Total Electric Retail [Member] | Electric Utility Segment [Member] | Kcpl Greater Missouri Operations Member
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	174
Electric Utility Customer Class Wholesale [Member] | Electric Utility Segment [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	6
Electric Utility Customer Class Wholesale [Member] | Electric Utility Segment [Member] | KCPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	3.1
Electric Utility Customer Class Wholesale [Member] | Electric Utility Segment [Member] | Kcpl Greater Missouri Operations Member
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	2.9
Electric Utility Customer Class Transmission [Member] | Electric Utility Segment [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	7.9
Electric Utility Customer Class Transmission [Member] | Electric Utility Segment [Member] | KCPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	3.3
Electric Utility Customer Class Transmission [Member] | Electric Utility Segment [Member] | Kcpl Greater Missouri Operations Member
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	4.6
Electric Utility Customer Class Industrial Steam [Member] | Electric Utility Segment [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	4.3
Electric Utility Customer Class Industrial Steam [Member] | Electric Utility Segment [Member] | KCPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Electric Utility Customer Class Industrial Steam [Member] | Electric Utility Segment [Member] | Kcpl Greater Missouri Operations Member
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 4.3

Anticipated Merger with Westa47

Anticipated Merger with Westar Energy, Inc. (Details) $ / shares in Units, $ in Millions	Jul. 09, 2017Rate	May 29, 2016$ / shares	Mar. 31, 2018USD ($)Rate	Mar. 31, 2018USD ($)shares	Mar. 31, 2017USD ($)Rateshares	Jul. 31, 2017USD ($)
Anticipated Merger With Westar Energy, Inc. [Line Items]
Cash consideration to be transferred (per share) | $ / shares		$ 51
Issuance of long-term debt				$ 299.7	$ 4,291.9
Westar Energy Inc [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Holdco Common Stock Conversion Ratio | Rate	1
Ownership in Holdco - Percentage | Rate	52.50%
Merger Termination Fee Westar Termination				190
Great Plains Energy [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Holdco Common Stock Conversion Ratio | Rate	0.5981
Merger Termination Fee Regulatory Approvals				190
Merger Termination Fee Great Plains Energy				190
Ownership in Holdco - Percentage | Rate	47.50%
Great Plains Energy [Member] | GPE 4.3 Billion Senior Notes [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Long-term Debt, Gross					4,300	$ 4,300
KCPL [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Issuance of long-term debt				$ 299.7	$ 0
KCC Merger ROE Refund | Rate			50.00%
MPSC Merger Bill Credits			$ 14.9
KCC Merger One Time Bill Credits			7.5
KCC Merger Annual Bill Credit			2.8
Kcpl Greater Missouri Operations Member
Anticipated Merger With Westar Energy, Inc. [Line Items]
MPSC Merger Bill Credits			$ 14.2
Series B Preferred Stock [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Preferred Stock, Dividend Rate, Percentage | Rate					7.00%
Common Stock [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Stock Issued During Period, Shares, New Issues | shares				85,121	249,170

Supplemental Cash Flow Inform48

Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows affected by changes in:
Receivables	$ 43.2	$ 55.5
Accounts receivable pledged as collateral	0	0.2
Fuel inventories	(1.8)	1.8
Materials and supplies	(1.1)	(4.2)
Accounts payable	(142.1)	(136.8)
Accrued taxes	37.6	36.3
Accrued interest	14.6	26.5
Deferred refueling outage costs	0.9	4
Pension and post-retirement benefit obligations	10.5	11.6
Allowance for equity funds used during construction	(1.4)	(1)
Fuel recovery mechanisms	(3.5)	(14.1)
ARO settlements	(4.5)	(4.3)
Other	18.5	17.5
Total other operating activities	(29.1)	(7)
Cash paid during the period:
Interest	31.3	34.2
Non-cash investing activities:
Liabilities accrued for capital expenditures	25.4	22.6
KCPL [Member]
Cash flows affected by changes in:
Receivables	47.9	36.2
Fuel inventories	(1)	(0.5)
Materials and supplies	(1.8)	(3.1)
Accounts payable	(90)	(88.8)
Accrued taxes	25	35.5
Accrued interest	8.3	10.1
Deferred refueling outage costs	0.9	4
Pension and post-retirement benefit obligations	9	10.3
Allowance for equity funds used during construction	(1.4)	(1)
Fuel recovery mechanisms	1.2	(10.8)
ARO settlements	(3.6)	(3.9)
Other	3.8	(9.1)
Total other operating activities	(1.7)	(21.1)
Cash paid during the period:
Interest	22.7	22.5
Non-cash investing activities:
Liabilities accrued for capital expenditures	$ 19.5	$ 19.9

Receivables Accounts, Notes, an

Receivables Accounts, Notes, and Financing (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other receivables	$ 32.9	$ 49.5
Total	108.2	151.7
KCPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other receivables	26.2	39.3
Total	74.3	106.3
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts	(5)	(4.7)
Trade Accounts Receivable [Member] | KCPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts	(2.3)	(2.2)
Trade Accounts Receivable [Member] | Billed Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	0	3.7
Trade Accounts Receivable [Member] | Billed Revenues [Member] | KCPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	0	1.6
Trade Accounts Receivable [Member] | Unbilled Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	80.3	103.2
Trade Accounts Receivable [Member] | Unbilled Revenues [Member] | KCPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	$ 50.4	$ 67.6

Receivables Narrative (Details)

Receivables Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Other receivables	$ 32.9		$ 49.5
Other Receivables, Contracts with Customers	2.7
Sale Of Accounts Receivable - KCPL and GMO
Accounts receivable pledged as collateral	180		180
Collateralized note payable	180		180
Impairment losses recognized on receivables
Impairment losses recognized on receivables	2.4	$ 2.2
KCPL Greater Missouri Operations [Member]
Sale Of Accounts Receivable - KCPL and GMO
Maximum amount of outstanding principal under receivables agreement from mid-November to mid-June	50
Maximum amount of outstanding principal under receivables agreement from mid-June to mid-November	65
KCPL [Member]
Other receivables	26.2		39.3
Other Receivables, Contracts with Customers	1.1
Sale Of Accounts Receivable - KCPL and GMO
Accounts receivable pledged as collateral	130		130
Collateralized note payable	130		$ 130
Maximum amount of outstanding principal under receivables agreement	130
KCPL [Member] | Impairment losses recognized on receivables
Impairment losses recognized on receivables	$ 1.7	$ 1.5

Nuclear Plant (Details)

Nuclear Plant (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018
Investments in decommissioning trust fund [Line Items]
Net unrealized gains	$ 84.4	$ 69.8
Equity Securities [Member]
Investments in decommissioning trust fund [Line Items]
Net unrealized gains	83.7	67.8
Debt Securities [Member]
Investments in decommissioning trust fund [Line Items]
Net unrealized gains	$ 0.7	$ 2
KCPL [Member] | Wolf Creek [Member]
Investments in decommissioning trust fund [Line Items]
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	47.00%		47.00%

Regulatory Matters (Details)

Regulatory Matters (Details) - Missouri Public Service Commission [Member] $ in Millions	1 Months Ended
	Jan. 31, 2018USD ($)Rate
KCPL Greater Missouri Operations [Member]
Regulatory Proceedings [Line Items]
Annual revenue increase, requested, portion related to rebasing | $	$ 21.7
Annual revenue increase (decrease), requested, not including rebasing | $	$ (2.4)
Return on equity, requested (in hundredths) | Rate	9.85%
Rate-making equity ratio, requested (in hundredths) | Rate	54.40%
KCPL [Member]
Regulatory Proceedings [Line Items]
Annual revenue increase, requested, portion related to rebasing | $	$ 7.5
Annual revenue increase (decrease), requested, not including rebasing | $	$ 8.9
Return on equity, requested (in hundredths) | Rate	9.85%
Rate-making equity ratio, requested (in hundredths) | Rate	50.03%

Regulatory Matters Regulatory M

Regulatory Matters Regulatory Matters Subsequent Events (Details) - USD ($) $ in Millions	1 Months Ended
	May 31, 2018	Jan. 31, 2018
Kcpl Greater Missouri Operations Member | MissouriPublicServiceCommission [Member]
Subsequent Event [Line Items]
Public Utilities, Requested Return on Equity, Percentage		9.85%
Annual revenue increase (decrease), requested, not including rebasing		$ (2.4)
Annual revenue increase, requested, portion related to rebasing		$ 21.7
Public Utilities, Requested Equity Capital Structure, Percentage		54.40%
KCPL [Member] | MissouriPublicServiceCommission [Member]
Subsequent Event [Line Items]
Public Utilities, Requested Return on Equity, Percentage		9.85%
Annual revenue increase (decrease), requested, not including rebasing		$ 8.9
Annual revenue increase, requested, portion related to rebasing		$ 7.5
Public Utilities, Requested Equity Capital Structure, Percentage		50.03%
KCPL [Member] | Kansas Corporation Commission [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Public Utilities, Requested Return on Equity, Percentage	9.85%
Annual revenue increase (decrease), requested, not including rebasing	$ 26.2
Annual revenue increase, requested, portion related to rebasing	$ 6.7
Public Utilities, Requested Equity Capital Structure, Percentage	49.80%

Pension Plans and Other Emplo54

Pension Plans and Other Employee Benefits (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Amounts recognized in the consolidated balance sheets [Abstract]
Current pension and other post-retirement liability			$ (2.7)		$ (2.7)
Noncurrent pension liability and other post-retirement liability			(532.4)		(535)
KCPL [Member]
Amounts recognized in the consolidated balance sheets [Abstract]
Current pension and other post-retirement liability			(1.4)		(1.4)
Noncurrent pension liability and other post-retirement liability			(509.7)		$ (512.2)
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 13.7
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year			70.3
Components of net periodic benefit costs [Abstract]
Service cost	12.2	$ 11
Interest cost	12.7	13.4
Expected return on plan assets	(13.9)	(12.8)
Prior service cost	0.2	0.2
Recognized net actuarial (gain)/loss	11.4	12.4
Net periodic benefit costs before regulatory adjustment	22.6	24.2
Regulatory adjustment	0.6	0.8
Net periodic benefit costs	23.2	25
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year			$ 4.6
Components of net periodic benefit costs [Abstract]
Service cost	0.5	0.5
Interest cost	1.2	1.3
Expected return on plan assets	(0.7)	(0.6)
Prior service cost	0	0
Recognized net actuarial (gain)/loss	0	(0.1)
Net periodic benefit costs before regulatory adjustment	1	1.1
Regulatory adjustment	0	1.3
Net periodic benefit costs	$ 1	$ 2.4
Wolf Creek [Member] | KCPL [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, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation expense	$ 1.8	$ 1.2
Income tax benefit	$ 0.4	$ 0.6
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility (in hundredths)	17.00%
Expected dividend yield (in hundredths)	3.72%
Risk-free interest rate (in hundredths)	2.34%
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares)	545,087
Granted (in shares)	209,937
Earned (in shares)	(115,833)
Forfeited (in shares)	(2,097)
Performance adjustment (in shares)	(49,052)
Ending balance (in shares)	588,042
Weighted average beginning balance (in dollars per share)	$ 29.12
Weighted average granted (in dollars per share)	29.35	$ 31.26
Weighted average earned (in dollars per share)	24.01
Weighted average forfeited (in dollars per share)	30.65
Weighted average performance adjustment (in dollars per share)	24.01
Weighted average ending balance (in dollars per share)	$ 30.63
Total unrecognized compensation expense	$ 10.7
Remaining weighted-average contractual term (in years)	1 year 9 months
Fair value of performance shares earned and paid	$ 2.8	$ 5.3
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)	192,402
Granted (in shares)	70,001
Vested (in shares)	(56,878)
Forfeited (in shares)	(700)
Ending balance (in shares)	204,825
Weighted average beginning balance (in dollars per share)	$ 27.87
Weighted average granted (in dollars per share)	29.08	$ 28.60
Weighted average vested (in dollars per share)	26.12
Weighted average forfeited (in dollars per share)	28.87
Weighted average ending balance (in dollars per share)	$ 28.77
Total unrecognized compensation expense	$ 3.5
Total fair value of shares vested	$ 1.5	$ 2.3
Remaining weighted-average contractual term (in years)	1 year 11 months
KCPL [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation expense	$ 1.2	0.8
Income tax benefit	$ 0.2	$ 0.4

Short-term Borrowings and Sho56

Short-term Borrowings and Short-term Bank Lines of Credit (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Short-term Debt [Line Items]
Amount of outstanding cash borrowings	$ 23	$ 11
Commercial paper outstanding	523.8	376.8
KCPL Greater Missouri Operations [Member]
Short-term Debt [Line Items]
Commercial paper outstanding	$ 235.5	$ 209.3
Weighted-average interest rate from outstanding borrowings	2.38%	1.85%
KCPL Greater Missouri Operations [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 450
Credit facility expiration date	Oct. 31, 2019
Maximum transfer of unused commitments	$ 200
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	2.1	2.1
KCPL [Member]
Short-term Debt [Line Items]
Commercial paper outstanding	$ 288.3	$ 167.5
Weighted-average interest rate from outstanding borrowings	2.39%	1.95%
KCPL [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 600
Credit facility expiration date	Oct. 31, 2019
Maximum transfer of unused commitments	$ 200
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	2.7	2.7
Great Plains Energy [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 200
Credit facility expiration date	Oct. 31, 2019
Maximum borrowing capacity with transfer of unused commitments	$ 400
Line of Credit Facility, Covenant Terms	A default by Great Plains Energy or any of its significant subsidiaries on other indebtedness totaling more than $50.0 million is a default under the facility.  Under the terms of this facility, Great Plains Energy is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times.
Line of Credit Facility, Covenant Compliance	in compliance
Amount of outstanding cash borrowings	$ 23	$ 11
Weighted-average interest rate from outstanding borrowings	3.23%	2.94%
Amount of letters of credit outstanding	$ 1	$ 1

Long-Term Debt (Details)

Long-Term Debt (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2018	Dec. 31, 2017	Jul. 31, 2017	Mar. 31, 2017
Debt Instrument [Line Items]
Current maturities			$ (1.1)		$ (351.1)
Long-term debt excluding current maturities			3,608.5		3,312.6
Other Consolidated Entities [Member]
Debt Instrument [Line Items]
Current maturities			(1.1)		(1.1)
Unamortized discount and premium, net and debt issuance costs			(1.5)		(1.5)
KCPL [Member]
Debt Instrument [Line Items]
Current maturities			0		(350)
Unamortized discount and premium, net and debt issuance costs			(20.1)		(17.2)
Long-term debt excluding current maturities			2,529.3		2,232.2
KCPL [Member] | Secured Debt [Member] | General Mortgage bonds Series 2009A due 2019 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			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%
KCPL [Member] | Secured Debt [Member] | General Mortgage bonds EIRR series 2005 [Member]
Debt Instrument [Line Items]
EIRR bonds repurchased and held			50		50
KCPL [Member] | Secured Debt [Member] | General Mortgage Bonds EIRR Due 2023 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			79.5		79.5
EIRR bonds repurchased and held			21.9		21.9
Debt Instrument, Maturity Date		Dec. 31, 2023
Interest rates (in hundredths)				2.95%
KCPL [Member] | Senior Notes [Member] | Senior notes due 2018 KCPL [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			0		350
Debt Instrument, Maturity Date		Dec. 31, 2018
Interest rates (in hundredths)	6.375%	6.375%		6.375%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)				7.49%
Repayments of Long-Term Debt	$ 350
KCPL [Member] | Senior Notes [Member] | Senior Notes due 2023 KCPL [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			300		300
Debt Instrument, Maturity Date		Dec. 31, 2023
Interest rates (in hundredths)				3.15%
KCPL [Member] | Senior Notes [Member] | Senior Notes due 2025 KCPL [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			350		350
Debt Instrument, Maturity Date		Dec. 31, 2025
Interest rates (in hundredths)				3.65%
KCPL [Member] | Senior Notes [Member] | Senior notes due 2035 KCPL [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			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%
KCPL [Member] | Senior Notes [Member] | Senior Notes Due 2041 KCPL [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			400		400
Debt Instrument, Maturity Date		Dec. 31, 2041
Interest rates (in hundredths)				5.30%
KCPL [Member] | Senior Notes [Member] | Senior Notes Due 2047 KCPL [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			300		300
Debt Instrument, Maturity Date		Dec. 31, 2047
Interest rates (in hundredths)				4.20%
KCPL [Member] | Senior Notes [Member] | Senior Notes Due 2048 KCPL [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			300		0
Debt Instrument, Maturity Date	Dec. 31, 2048	Dec. 31, 2048
Interest rates (in hundredths)				4.20%
KCPL [Member] | Unsecured Debt [Member] | EIRR Bonds Series 2007A and 2007B due 2035 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			146.5		146.5
Debt Instrument, Maturity Date		Dec. 31, 2035
Variable rate (in hundredths)				1.349%
KCPL [Member] | Unsecured Debt [Member] | EIRR bonds 2.875 percent Series 2008 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			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]
Long-term Debt, Gross			3.4		4.6
Debt Instrument Maturity Date Range End		Dec. 31, 2021
Debt Instrument Maturity Date Range Start		Dec. 31, 2019
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]
Long-term Debt, Gross			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]
Long-term Debt, Gross			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]
Long-term Debt, Gross			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]
Long-term Debt, Gross			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]
Long-term Debt, Gross			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]
Long-term Debt, Gross			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]
Long-term Debt, Gross						$ 4,300	$ 4,300
Great Plains Energy [Member] | Senior Notes [Member] | Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			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]
Long-term Debt, Gross			$ 287.5		$ 287.5
Debt Instrument, Maturity Date		Dec. 31, 2022
Interest rates (in hundredths)				5.292%

Commitments and Contingencies E

Commitments and Contingencies Environmental Matters (Details) T in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)T	Dec. 31, 2017USD ($)
Estimated Environmental Capital Expenditures [Abstract]
Estimate Of Environmental Capital Expenditures Current	$ 14.6
Estimate Of Environmental Capital Expenditures In Two Years	2.8
Estimate Of Environmental Capital Expenditures In Three Years	7.7
Estimate Of Environmental Capital Expenditures In Four Years	20.1
Estimate Of Environmental Capital Expenditures In Five Years	$ 63.1
Climate Change [Abstract]
CO2 produced per year (in millions of tons) | T	17
EPA nationwide CO2 emission reductions by 2030	32.00%
Remediation [Abstract]
Accrued environmental remediation expenses	$ 1.5	$ 1.5
KCPL Greater Missouri Operations [Member]
Remediation [Abstract]
Estimated amount of insurance proceeds available to cover qualified remediation expenses	1.6
KCPL [Member]
Estimated Environmental Capital Expenditures [Abstract]
Estimate Of Environmental Capital Expenditures Current	14.5
Estimate Of Environmental Capital Expenditures In Two Years	2.8
Estimate Of Environmental Capital Expenditures In Three Years	7.7
Estimate Of Environmental Capital Expenditures In Four Years	20.1
Estimate Of Environmental Capital Expenditures In Five Years	$ 63.1
Climate Change [Abstract]
CO2 produced per year (in millions of tons) | T	13
Remediation [Abstract]
Accrued environmental remediation expenses	$ 0.3	$ 0.3

Related Party Transactions an59

Related Party Transactions and Relationships (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
KCPL [Member] | Money Pool [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	$ 0		$ 0
KCPL [Member] | KCPL Greater Missouri Operations [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	50.5		65.8
KCPL [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	46.4	$ 47.9
KCPL [Member] | Great Plains Energy [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	$ 18.6		$ 18.9
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) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Fair Value, Measurements, Recurring [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 98.4		$ 91.4
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Asset, Fair Value, Gross Asset	98.4		91.4
Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance net asset (liability)	91.4	$ 79.3
Net asset at March 31	98.4	91.4
Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Non-Operating Income [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	7	0
Total unrealized gains (losses) relating to assets and liabilities still on the consolidated balance sheet at March 31:	7	0
Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Charges [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	0	12.1
Total unrealized gains (losses) relating to assets and liabilities still on the consolidated balance sheet at March 31:	0	$ 12.1
Interest Rate Contract [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Asset, Fair Value, Gross Asset	98.4		91.4
Interest Rate Contract [Member] | Other Great Plains [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivatives, Interest Rate Swaps, Finalized Settlement Value	140.6		140.6
Derivative Asset, Fair Value, Gross Asset	98.4		91.4
Interest Rate Contract [Member] | Other Great Plains [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 98.4		$ 91.4

Fair Value Measurements Fair Va

Fair Value Measurements Fair Value Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)	Jul. 31, 2017USD ($)	Jun. 30, 2016USD ($)
KCPL Greater Missouri Operations [Member]
SERP rabbi trust [Abstract]
Alternative Investment, Fair Value Disclosure	$ 14.2		$ 14.7
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair value of financial instruments [Abstract]
Long-term Debt	3,600		3,700
Carrying (Reported) Amount, Fair Value Disclosure [Member] | KCPL [Member]
Fair value of financial instruments [Abstract]
Long-term Debt	2,500		2,600
Fair Value, Measurements, Recurring [Member]
Fair value of financial instruments [Abstract]
Derivative Asset, Fair Value, Gross Asset	98.4		91.4
GPE 4.3 Billion Senior Notes [Member] | Great Plains Energy [Member]
Fair value of financial instruments [Abstract]
Long-term Debt, Gross		$ 4,300		$ 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	3,800		4,000
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member] | KCPL [Member]
Fair value of financial instruments [Abstract]
Long-term debt fair value	2,700		2,800
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair value of financial instruments [Abstract]
Derivative Asset, Fair Value, Gross Asset	$ 0		$ 0
Interest Rate Contract [Member]
Fair value of financial instruments [Abstract]
Fair Value Inputs, Contingency Factor, Interest Rate Derivative	0.3		0.35
Derivative Asset, Fair Value, Gross Asset	$ 98.4		$ 91.4
Interest Rate Contract [Member] | Great Plains Energy [Member]
Fair value of financial instruments [Abstract]
Notional Contract Amount					$ 4,400
Derivatives, Interest Rate Swaps, Finalized Settlement Value		140.6
Interest Rate Contract [Member] | Interest Expense [Member]
Fair value of financial instruments [Abstract]
Derivative, Gain (Loss) on Derivative, Net		$ 12.1
Interest Rate Contract [Member] | Non-Operating Income [Member]
Fair value of financial instruments [Abstract]
Derivative, Gain (Loss) on Derivative, Net	$ 7

Fair Value Measurements (Detail

Fair Value Measurements (Details) $ in Millions	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Mar. 31, 2017USD ($)
Interest Rate Contract [Member]
Assets [Abstract]
Derivative instruments, assets	$ 98.4	$ 91.4
Fair Value Inputs, Contingency Factor, Interest Rate Derivative	0.3	0.35
Interest Rate Contract [Member] | Great Plains Energy [Member]
Assets [Abstract]
Derivatives, Interest Rate Swaps, Finalized Settlement Value			$ 140.6
Fair Value, Measurements, Recurring [Member]
Assets [Abstract]
Derivative instruments, assets	$ 98.4	$ 91.4
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	255.3	258.4
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	11.1	10.9
Total assets	364.8	360.7
Fair Value, Measurements, Recurring [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	255.3	258.4
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	11.1	10.9
Total assets	266.4	269.3
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member]
Self-insured health plan trust [Abstract]
Total assets	98.4	91.4
Fair Value, Measurements, Recurring [Member] | Interest Rate Contract [Member] | Other Consolidated Entities [Member]
Assets [Abstract]
Derivative instruments, assets	98.4	91.4
Derivatives, Interest Rate Swaps, Finalized Settlement Value	$ 140.6	$ 140.6
Fair Value Inputs, Contingency Factor, Interest Rate Derivative	0.3	0.35
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	$ 179.6	$ 183.8
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.4	0.5
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | KCPL [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	2.1	2.7
Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	35	35.3
Fair Value, Measurements, Recurring [Member] | US Government Corporations and Agencies Securities [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.4	0.4
Fair Value, Measurements, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	2.1	2.1
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	32.7	34.1
Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.1	0.1
Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	4.4	2.5
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | KCPL [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	8.6	7.7
Fair Value, Measurements, Recurring [Member] | Other Trust Assets [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	1	0.1
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	220	221.7
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	9.1	8.5
Total assets	229.1	230.2
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	220	221.7
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	9.1	8.5
Total assets	229.1	230.2
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other Consolidated Entities [Member]
Self-insured health plan trust [Abstract]
Total assets	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Interest Rate Contract [Member] | Other Consolidated Entities [Member]
Assets [Abstract]
Derivative instruments, assets	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	179.6	183.8
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.4	0.5
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Debt Securities [Member] | KCPL [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.1	0.3
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury and Government [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	35	35.3
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Corporations and Agencies Securities [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US States and Political Subdivisions Debt Securities [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign Government Debt Securities [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Cash Equivalents [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	4.4	2.5
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member] | KCPL [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	8.6	7.7
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other Trust Assets [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	1	0.1
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	35.3	36.7
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	2	2.4
Total assets	37.3	39.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	35.3	36.7
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	2	2.4
Total assets	37.3	39.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other Consolidated Entities [Member]
Self-insured health plan trust [Abstract]
Total assets	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Contract [Member] | Other Consolidated Entities [Member]
Assets [Abstract]
Derivative instruments, assets	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member] | KCPL [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] | Fair Value, Inputs, Level 2 [Member] | Debt Securities [Member] | KCPL [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	2	2.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury and Government [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Corporations and Agencies Securities [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.4	0.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US States and Political Subdivisions Debt Securities [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	2.1	2.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	32.7	34.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign Government Debt Securities [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.1	0.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Cash Equivalents [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member] | KCPL [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other Trust Assets [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Derivative instruments, assets	98.4	91.4
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	98.4	91.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | KCPL [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] | Fair Value, Inputs, Level 3 [Member] | Other Consolidated Entities [Member]
Self-insured health plan trust [Abstract]
Total assets	98.4	91.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Interest Rate Contract [Member] | Other Consolidated Entities [Member]
Assets [Abstract]
Derivative instruments, assets	98.4	91.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member] | KCPL [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] | Fair Value, Inputs, Level 3 [Member] | Debt Securities [Member] | KCPL [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Treasury and Government [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Corporations and Agencies Securities [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US States and Political Subdivisions Debt Securities [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign Government Debt Securities [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Cash Equivalents [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member] | KCPL [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other Trust Assets [Member] | KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	$ 0	$ 0

Accumulated Other Comprehensi63

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (2.2)	$ (6.6)
Amounts reclassified from accumulated other comprehensive loss	1	1.5
Net current period other comprehensive income	1	1.5
Ending balance	(1.2)	(5.1)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	0.4	(4.5)
Amounts reclassified from accumulated other comprehensive loss	0.9	1.4
Net current period other comprehensive income	0.9	1.4
Ending balance	1.3	(3.1)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(2.6)	(2.1)
Amounts reclassified from accumulated other comprehensive loss	0.1	0.1
Net current period other comprehensive income	0.1	0.1
Ending balance	(2.5)	(2)
KCPL [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	0.4
Net current period other comprehensive income	0.9	1.3
Ending balance	1.3
KCPL [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	0.4	(4.2)
Amounts reclassified from accumulated other comprehensive loss	0.9	1.3
Net current period other comprehensive income	0.9	1.3
Ending balance	$ 1.3	$ (2.9)

Accumulated Other Comprehensi64

Accumulated Other Comprehensive Income (Loss) Reclassification (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges	$ (48.1)	$ (66.6)
Utility operating and maintenance expenses	(180.2)	(174.1)
Non-operating expenses	(13.2)	(15.4)
Income (loss) before income tax (expense) benefit and income from equity investments	39.5	(16.3)
Income tax (expense) benefit	(5.5)	5.8
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)	(1)	(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	(1.2)	(2.3)
Income tax (expense) benefit	0.3	0.9
Net income (loss)	(0.9)	(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	(1.2)	(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]
Non-operating expenses	(0.1)	(0.2)
Income (loss) before income tax (expense) benefit and income from equity investments	(0.1)	(0.2)
Income tax (expense) benefit	0	0.1
Net income (loss)	(0.1)	(0.1)
KCPL [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges	(33)	(35.6)
Utility operating and maintenance expenses	(121)	(119.6)
Non-operating expenses	(7.9)	(8.9)
Income (loss) before income tax (expense) benefit and income from equity investments	23.7	23
Income tax (expense) benefit	(3.5)	(8.8)
KCPL [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income tax (expense) benefit and income from equity investments	(1.2)	(2.2)
Income tax (expense) benefit	0.3	0.9
Net income (loss)	(0.9)	(1.3)
KCPL [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Interest Rate Contract [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges	$ (1.2)	$ (2.2)

Income Tax Expense (Details)

Income Tax Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Current income taxes
Federal	$ 0	$ 0
State	0	0.2
Total	0	0.2
Deferred income taxes
Federal	3.2	(4.5)
State	2.6	(1.1)
Total	5.8	(5.6)
Investment tax credit
Investment tax credit amortization	(0.3)	(0.4)
Income tax expense (benefit)	$ 5.5	$ (5.8)
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax (in hundredths)	21.00%	35.00%
Effect of regulatory treatment of book and tax differences	(9.60%)	0.00%
Amortization of investments tax credits (in hundredths)	(0.40%)	(0.40%)
Federal income tax credits (in hundredths)	(4.10%)	(1.50%)
State income taxes (in hundredths)	5.20%	4.20%
Transaction costs (in hundredths)	0.10%	3.10%
Other (in hundredths)	1.40%	(2.50%)
Effective income tax rate (in hundredths)	13.60%	37.90%
KCPL [Member]
Current income taxes
Federal	$ (1.3)	$ (0.1)
State	(0.5)	0
Total	(1.8)	(0.1)
Deferred income taxes
Federal	3.6	7.8
State	2	1.4
Total	5.6	9.2
Investment tax credit
Investment tax credit amortization	(0.3)	(0.3)
Income tax expense (benefit)	$ 3.5	$ 8.8
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax (in hundredths)	21.00%	35.00%
Effect of regulatory treatment of book and tax differences	(7.20%)	(0.10%)
Amortization of investments tax credits (in hundredths)	(0.40%)	(0.30%)
Federal income tax credits (in hundredths)	(5.30%)	(1.80%)
State income taxes (in hundredths)	5.10%	4.00%
Other (in hundredths)	1.70%	1.50%
Effective income tax rate (in hundredths)	14.90%	38.30%

Taxes Tax Reform (Details)

Taxes Tax Reform (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Income Tax Savings From Tax Reform	$ 100
Regulatory Liability, Noncurrent	1,112.4	$ 1,106.3
Revenue Subject to Refund [Member]
Regulatory Liability, Noncurrent	21.9
KCPL [Member]
Regulatory Liability, Noncurrent	782.7	$ 779.2
KCPL [Member] | Revenue Subject to Refund [Member]
Regulatory Liability, Noncurrent	$ 15.2

Segments and Related Informat67

Segments and Related Information (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Operating revenues	$ (583.9)	$ (570.7)
Depreciation and amortization	(93.7)	(90.3)
Interest charges	(48.1)	(66.6)
Income tax expense	(5.5)	5.8
Net income	35	(9.6)
Assets	12,448.4		$ 12,457.9
Capital expenditures	119.7	116.6	573.5
Electric Utility Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	(583.9)
Operating Segments [Member] | Electric Utility Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	(583.9)	(570.7)
Depreciation and amortization	(93.7)	(90.3)
Interest charges	(47.8)	(50.1)
Income tax expense	(2.9)	(10.1)
Net income	28	16.1
Assets	11,529		11,508.1
Capital expenditures	119.7		573.5
Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Depreciation and amortization	0	0
Interest charges	(8.3)	(24.5)
Income tax expense	(2.6)	15.9
Net income	7	(25.7)
Assets	1,304.1		1,285.7
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	0	0
Net income	0	$ 0
Assets	(384.7)		(335.9)
Capital expenditures	$ 0		$ 0