Consolidated Statements of Common Shareholders' Equity and Noncontrolling Interest (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]	Noncontrolling Interest [Member]
Beginning balance at Dec. 31, 2011			$ 2,330.6	$ 1,563.1	$ 684.7	$ 513.8	$ (5.6)	$ (49.8)	$ (31.4)	$ 1.0
Beginning balance (in shares) at Dec. 31, 2011			136,406,306	1			(264,567)
Issuance of common stock			290.3
Issuance of common stock (in shares)			17,248,954
Equity compensation expense, net of forfeitures			0.1
Unearned Compensation [Abstract]
Issuance of restricted common stock			(3.2)
Forfeiture of restricted common stock			1.0
Compensation expense recognized			1.6
Stockholders' Equity, Other			0.5
Net income (loss) attributable to Great Plains Energy	49.0				49.0	46.0
Loss on reissuance of treasury stock					(0.3)
Dividends:
Common stock					(57.9)	(50.0)
Preferred stock - at required rates					(0.8)
Performance shares					0
Treasury shares acquired							(2.9)
Treasury shares acquired (in shares)							(145,701)
Treasury shares reissued							3.5
Treasury shares reissued (in shares)							169,800
Derivative hedging activity, net of tax	6.1	2.6						6.1	2.6
Change in unrecognized pension expense, net of tax	0.1							0.1
Net income (loss) attributable to noncontrolling interest	0.2									(0.2)
Distribution										(0.6)
Ending balance at Jun. 30, 2012	3,247.0	2,044.1	2,620.9	1,563.1	674.7	509.8	(5.0)	(43.6)	(28.8)	0.2
Ending balance (in shares) at Jun. 30, 2012			153,655,260	1			(240,468)
Beginning balance at Mar. 31, 2012
Unearned Compensation [Abstract]
Net income (loss) attributable to Great Plains Energy	58.1
Dividends:
Derivative hedging activity, net of tax	3.2	1.4
Change in unrecognized pension expense, net of tax	0
Net income (loss) attributable to noncontrolling interest	0
Ending balance at Jun. 30, 2012	3,247.0	2,044.1		1,563.1
Ending balance (in shares) at Jun. 30, 2012				1
Beginning balance at Dec. 31, 2012	3,340.0	2,096.7	2,624.7	1,563.1	758.8	559.4	(5.1)	(38.4)	(25.8)	0
Beginning balance (in shares) at Dec. 31, 2012			153,779,806	1			(250,236)
Issuance of common stock			2.6
Issuance of common stock (in shares)			114,918
Equity compensation expense, net of forfeitures			0.2
Unearned Compensation [Abstract]
Issuance of restricted common stock			(1.7)
Forfeiture of restricted common stock			0
Compensation expense recognized			1.0
Stockholders' Equity, Other			0.5
Net income (loss) attributable to Great Plains Energy	89.6				89.6	60.4
Loss on reissuance of treasury stock					0
Dividends:
Common stock					(66.8)	(46.0)
Preferred stock - at required rates					(0.8)
Performance shares					(0.2)
Treasury shares acquired							(1.2)
Treasury shares acquired (in shares)							(55,731)
Treasury shares reissued							3.7
Treasury shares reissued (in shares)							184,721
Derivative hedging activity, net of tax	6.1	2.8						6.1	2.8
Change in unrecognized pension expense, net of tax	0.2							0.2
Net income (loss) attributable to noncontrolling interest	0									0
Distribution										0
Ending balance at Jun. 30, 2013	3,373.2	2,113.9	2,627.3	1,563.1	780.6	573.8	(2.6)	(32.1)	(23.0)	0
Ending balance (in shares) at Jun. 30, 2013			153,894,724	1			(121,246)
Beginning balance at Mar. 31, 2013
Unearned Compensation [Abstract]
Net income (loss) attributable to Great Plains Energy	63.6
Dividends:
Derivative hedging activity, net of tax	2.9	1.3
Change in unrecognized pension expense, net of tax	0.2
Net income (loss) attributable to noncontrolling interest	0
Ending balance at Jun. 30, 2013	$ 3,373.2	$ 2,113.9		$ 1,563.1
Ending balance (in shares) at Jun. 30, 2013				1