Summary of Significant Accounting Policies Subsequent Events (Details) (Dividend Declared [Member], USD $) In Millions, except Per Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Dividends Declared [Abstract]
Subsequent Event, Date	Nov. 01, 2012
Subsequent Event Description	Great Plains Energy’s Board of Directors declared a quarterly dividend on common stock and also declared regular dividends on Great Plains Energys preferred stock.
Subsequent per common share amount (in dollars per share)	$ 0.2175
Kansas City Power and Light Company [Member]
Dividends Declared [Abstract]
Subsequent Event, Date	Nov. 01, 2012
Subsequent Event Amount	$ 23
Subsequent Event Description	KCP&L’s Board of Directors declared a cash dividend payable to Great Plains Energy