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, 2009			$ 2,313.7	$ 1,563.1	$ 529.2	$ 410.1	$ (5.5)	$ (44.9)	$ (41.5)	$ 1.2
Beginning balance (in shares) at Dec. 31, 2009			135,636,538	1			(213,423)
Distribution										(0.2)
Total Great Plains Energy Common Shareholders' Equity	2,885.9	2,005.0
Derivative hedging activity, net of tax	(10.6)	5.1						(10.6)	5.1
Change in unrecognized pension expense, net of tax	(0.6)							(0.6)
Net income (loss) attributable to Great Plains Energy	211.7				211.7	163.2
Treasury shares acquired							(3.4)
Treasury shares acquired (in shares)							(188,383)
Treasury shares reissued							0
Treasury shares reissued (in shares)							917
Issuance of common stock			6.6
Issuance of common stock (in shares)			347,279
Common stock issuance fees			0
Issuance of restricted common stock			2.3
Issuance of restricted common stock (in shares)			130,137
Equity compensation expense, net of forfeitures			1.0
Unearned Compensation [Abstract]
Issuance of restricted common stock			(2.3)
Forfeiture of restricted common stock			0.8
Compensation expense recognized			2.2
Equity Units allocated fees and expenses and the present value of contract adjustment payments			0
Other			0.1
Equity contribution from Great Plains Energy				0
Dividends:
Common stock					(112.6)	(95.0)
Preferred stock - at required rates					(1.6)
Performance shares					(0.2)
Performance shares amendment					0
Net income attributable to noncontrolling interest										0.2
Ending balance at Dec. 31, 2010			2,324.4	1,563.1	626.5	478.3	(8.9)	(56.1)	(36.4)	1.2
Ending balance (in shares) at Dec. 31, 2010			136,113,954	1			(400,889)
Beginning balance at Jan. 01, 2011
Distribution										0
Total Great Plains Energy Common Shareholders' Equity	2,959.9	2,045.5
Derivative hedging activity, net of tax	6.8	5.0						6.8	5.0
Change in unrecognized pension expense, net of tax	(0.5)							(0.5)
Net income (loss) attributable to Great Plains Energy	174.4				174.4	135.5
Loss On Reissuance Of Treasury Stock					(0.7)
Treasury shares acquired							(2.4)
Treasury shares acquired (in shares)							(125,234)
Treasury shares reissued							5.7
Treasury shares reissued (in shares)							261,556
Issuance of common stock			5.9
Issuance of common stock (in shares)			292,352
Common stock issuance fees			0
Issuance of restricted common stock			0
Issuance of restricted common stock (in shares)			0
Equity compensation expense, net of forfeitures			0.3
Unearned Compensation [Abstract]
Issuance of restricted common stock			(3.5)
Forfeiture of restricted common stock			0.9
Compensation expense recognized			2.3
Equity Units allocated fees and expenses and the present value of contract adjustment payments			0
Other			0.3
Equity contribution from Great Plains Energy				0
Dividends:
Common stock					(113.5)	(100.0)
Preferred stock - at required rates					(1.6)
Performance shares					(0.4)
Performance shares amendment					0
Net income attributable to noncontrolling interest										(0.2)
Ending balance at Dec. 31, 2011			$ 2,330.6	$ 1,563.1	$ 684.7	$ 513.8	$ (5.6)	$ (49.8)	$ (31.4)	$ 1.0
Ending balance (in shares) at Dec. 31, 2011			136,406,306	1			(264,567)