Consolidated Statements of Common Shareholders' Equity - USD ($) $ in Millions	Total	Kansas City Power and Light Company [Member]	Common Stock [Member]	Common Stock [Member] Kansas City Power and Light Company [Member]	Retained Earnings [Member]	Retained Earnings [Member] Kansas City Power and Light Company [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Other Comprehensive Income (Loss) [Member] Kansas City Power and Light Company [Member]
Beginning balance at Dec. 31, 2014			$ 2,639.3	$ 1,563.1	$ 967.8	$ 726.8	$ (2.3)	$ (18.7)	$ (14.9)
Beginning balance (in shares) at Dec. 31, 2014			154,254,037	1
Beginning balance, treasury stock (in shares) at Dec. 31, 2014							(91,281)
Issuance of common stock			$ 3.2
Issuance of common stock (in shares)			122,420
Equity compensation expense, net of forfeitures			$ 0.3
Unearned Compensation [Abstract]
Issuance of restricted common stock			(2.0)
Compensation expense recognized			0.5
Other			0.0
Net income	$ 18.9	$ 13.2			18.9	13.2
Dividends:
Common stock ($0.2625 and $0.245 per share)					(37.8)
Preferred stock - at required rates					(0.4)
Performance shares					(0.2)
Treasury shares acquired							$ (1.3)
Treasury shares acquired (in shares)							(50,899)
Treasury shares reissued							$ 1.2
Treasury shares reissued (in shares)							47,085
Derivative hedging activity, net of tax	1.4	1.4						1.4	1.4
Change in unrecognized pension expense, net of tax	0.1							0.1
Ending balance at Mar. 31, 2015	3,570.0	2,289.6	$ 2,641.3	$ 1,563.1	948.3	740.0	$ (2.4)	(17.2)	(13.5)
Ending balance, treasury stock (in shares) at Mar. 31, 2015							(95,095)
Ending balance (in shares) at Mar. 31, 2015			154,376,457	1
Beginning balance at Dec. 31, 2015	$ 3,656.5	2,433.1	$ 2,646.7	$ 1,563.1	1,024.4	879.6	$ (2.6)	(12.0)	(9.6)
Beginning balance (in shares) at Dec. 31, 2015			154,504,900	1
Beginning balance, treasury stock (in shares) at Dec. 31, 2015	(101,229)						(101,229)
Issuance of common stock			$ 10.0
Issuance of common stock (in shares)			336,356
Equity compensation expense, net of forfeitures			$ 0.8
Unearned Compensation [Abstract]
Issuance of restricted common stock			(2.8)
Compensation expense recognized			0.6
Other			0.3
Net income	$ 26.4	24.6			26.4	24.6
Dividends:
Common stock ($0.2625 and $0.245 per share)					(40.5)
Preferred stock - at required rates					(0.4)
Performance shares					(0.3)
Treasury shares acquired							$ (4.0)
Treasury shares acquired (in shares)							(134,484)
Treasury shares reissued							$ 2.8
Treasury shares reissued (in shares)							105,403
Derivative hedging activity, net of tax	1.4	1.4						1.4	1.4
Change in unrecognized pension expense, net of tax	0.1							0.1
Ending balance at Mar. 31, 2016	$ 3,650.9	$ 2,459.1	$ 2,655.6	$ 1,563.1	$ 1,009.6	$ 904.2	$ (3.8)	$ (10.5)	$ (8.2)
Ending balance, treasury stock (in shares) at Mar. 31, 2016	(130,310)						(130,310)
Ending balance (in shares) at Mar. 31, 2016			154,841,256	1