Consolidated Statements of Common Shareholders' Equity (USD $) In Millions, except Share data, unless otherwise specified	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, 2012			$ 2,624.7		$ 758.8	$ 559.4	$ (5.1)	$ (38.4)	$ (25.8)
Beginning balance, treasury stock (in shares) at Dec. 31, 2012							(250,236)
Beginning balance (in shares) at Dec. 31, 2012			153,779,806
Issuance of common stock			3.8
Issuance of common stock (in shares)			168,211
Equity compensation expense, net of forfeitures			0.3
Unearned Compensation [Abstract]
Issuance of restricted common stock			(1.7)
Forfeiture of restricted common stock			0.1
Compensation expense recognized			1.5
Stockholders' Equity, Other			0.6
Net income (loss)	232.7	156.8			232.7	156.8
Dividends:
Common stock					(100.3)	(69.0)
Preferred stock - at required rates					(1.2)
Performance shares					(0.2)
Treasury shares acquired							(1.6)
Treasury shares acquired (in shares)							(73,201)
Treasury shares reissued							3.8
Treasury shares reissued (in shares)							188,075
Derivative hedging activity, net of tax	8.9	4.2						8.9	4.2
Change in unrecognized pension expense, net of tax	0.3							0.3
Ending balance at Sep. 30, 2013	3,487.0	2,188.7	2,629.3	1,563.1	889.8	647.2	(2.9)	(29.2)	(21.6)
Ending balance (in shares) at Sep. 30, 2013			153,948,017	1
Ending balance, treasury stock (in shares) at Sep. 30, 2013							(135,362)
Beginning balance at Jun. 30, 2013
Unearned Compensation [Abstract]
Net income (loss)	143.1	96.4
Dividends:
Derivative hedging activity, net of tax	2.8	1.4
Change in unrecognized pension expense, net of tax	0.1
Ending balance at Sep. 30, 2013	3,487.0	2,188.7		1,563.1
Ending balance (in shares) at Sep. 30, 2013				1
Beginning balance at Dec. 31, 2013	3,474.4	2,179.3	2,631.1		871.4	636.4	(2.8)	(25.3)	(20.2)
Beginning balance, treasury stock (in shares) at Dec. 31, 2013	(129,290)						(129,290)
Beginning balance (in shares) at Dec. 31, 2013			153,995,621
Issuance of common stock			5.5
Issuance of common stock (in shares)			214,241
Equity compensation expense, net of forfeitures			0.4
Unearned Compensation [Abstract]
Issuance of restricted common stock			(2.0)
Forfeiture of restricted common stock			0
Compensation expense recognized			1.5
Stockholders' Equity, Other			1.1
Net income (loss)	223.3	146.5			223.3	146.5
Dividends:
Common stock					(106.3)	(54.0)
Preferred stock - at required rates					(1.2)
Performance shares					(0.6)
Treasury shares acquired							(2.2)
Treasury shares acquired (in shares)							(85,062)
Treasury shares reissued							2.6
Treasury shares reissued (in shares)							118,965
Derivative hedging activity, net of tax	6.6	3.9						6.6	3.9
Change in unrecognized pension expense, net of tax	0.3							0.3
Ending balance at Sep. 30, 2014	3,603.4	2,275.7	2,637.6	1,563.1	986.6	728.9	(2.4)	(18.4)	(16.3)
Ending balance (in shares) at Sep. 30, 2014			154,209,862	1
Ending balance, treasury stock (in shares) at Sep. 30, 2014	(95,387)						(95,387)
Beginning balance at Jun. 30, 2014
Unearned Compensation [Abstract]
Net income (loss)	147.4	94.5
Dividends:
Derivative hedging activity, net of tax	1.3	1.2
Change in unrecognized pension expense, net of tax	0.1
Ending balance at Sep. 30, 2014	$ 3,603.4	$ 2,275.7		$ 1,563.1
Ending balance (in shares) at Sep. 30, 2014				1
Ending balance, treasury stock (in shares) at Sep. 30, 2014	(95,387)