Summary of Significant Accounting Policies (Details) (USD $)	3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Dividend Declared [Member]	Jun. 30, 2012 Restricted Stock [Member]	Jun. 30, 2011 Restricted Stock [Member]	Jun. 30, 2012 Restricted Stock [Member]	Jun. 30, 2011 Restricted Stock [Member]	Jun. 30, 2012 Stock Options [Member]	Jun. 30, 2011 Stock Options [Member]	Jun. 30, 2012 Stock Options [Member]	Jun. 30, 2011 Stock Options [Member]	Jun. 30, 2012 Performance Shares [Member]	Jun. 30, 2011 Performance Shares [Member]	Jun. 30, 2012 Performance Shares [Member]	Jun. 30, 2011 Performance Shares [Member]	Jun. 30, 2012 Subsidiaries [Member]	Jun. 30, 2011 Subsidiaries [Member]	Jun. 30, 2012 Subsidiaries [Member]	Jun. 30, 2011 Subsidiaries [Member]	Jun. 30, 2012 Subsidiaries [Member] Dividend Declared [Member]	Jun. 30, 2012 Carrying (Reported) Amount, Fair Value Disclosure [Member]	Dec. 31, 2011 Carrying (Reported) Amount, Fair Value Disclosure [Member]	Jun. 30, 2012 Carrying (Reported) Amount, Fair Value Disclosure [Member] Subsidiaries [Member]	Dec. 31, 2011 Carrying (Reported) Amount, Fair Value Disclosure [Member] Subsidiaries [Member]	Jun. 30, 2012 Estimate of Fair Value, Fair Value Disclosure [Member]	Dec. 31, 2011 Estimate of Fair Value, Fair Value Disclosure [Member]	Jun. 30, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Subsidiaries [Member]	Dec. 31, 2011 Estimate of Fair Value, Fair Value Disclosure [Member] Subsidiaries [Member]
Fair value of financial instruments [Abstract}
Long-term debt																							$ 3,500,000,000	$ 3,500,000,000	$ 1,900,000,000	$ 1,900,000,000	$ 3,900,000,000	$ 3,900,000,000	$ 2,200,000,000	$ 2,200,000,000
Income [Abstract]
Net income	58,100,000	43,400,000	48,800,000	45,700,000														43,700,000	33,400,000	46,000,000	37,400,000
Less: net income attributable to noncontrolling interest	0	0	(200,000)	(100,000)
Less: preferred stock dividend requirements	400,000	400,000	800,000	800,000
Income from continuing operations available for common shareholders	57,700,000	43,000,000	48,200,000	45,000,000
Common Shares Outstanding [Abstract]
Average number of common shares outstanding (in shares)	139,600,000	135,600,000	137,700,000	135,500,000
Add: effect of dilutive securities (in shares)	2,400,000	3,300,000	2,900,000	3,100,000
Diluted average number of common shares outstanding (in shares)	142,000,000	138,900,000	140,600,000	138,600,000
Earnings per share [Abstract]
Basic EPS from continuing operations (in dollars per share)	$ 0.41	$ 0.32	$ 0.35	$ 0.33
Diluted EPS from continuing operations (in dollars per share)	$ 0.41	$ 0.31	$ 0.34	$ 0.32
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares (in shares)						10,617	12,115	10,617	43,641	0	154,096	0	154,096	0	201,571	0	201,571
Dividends Declared [Abstract]
Subsequent event date					Aug. 01, 2012																	Aug. 01, 2012
Subsequent Event Amount																						$ 23,000,000
Subsequent per share amount (in dollars per share)					$ 0.2125
Subsequent Event Description					Great Plains Energys Board of Directors declared a quarterly dividend and also declared regular dividends on Great Plains Energys preferred stock.																	KCP&Ls Board of Directors declared a cash dividend payable to Great Plains Energy.