Common Shareholders' Equity Common Shareholders' Equity (Details) (USD $) In Billions, except Share data in Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Common Shareholders' Equity [Abstract]
Shares authorized under the Dividend Reinvestment and Direct Stock Purchase Plan (in shares)	6.0
Number of shares available for grant under the Dividend Reinvestment and Direct Stock Purchase Plan (in shares)	1.5
Shares registered under the defined contribution savings plan (in shares)	14.3
Number of shares available under the defined contribution savings plan (in shares)	2.0
Restrictions on the payment of common stock dividends contained in the articles of incorporation	Great Plains Energy's articles of incorporation restrict the payment of common stock dividends in the event common equity is 25% or less of total capitalization. In addition, if preferred stock dividends are not declared and paid when scheduled, Great Plains Energy could not declare or pay common stock dividends or purchase any common shares. If the unpaid preferred stock dividends equal four or more full quarterly dividends, the preferred shareholders, voting as a single class, could elect the smallest number of directors necessary to constitute a majority of the full Board.
Regulatory restrictions on the payment of dividends	Certain conditions in the MPSC and KCC orders authorizing the holding company structure require Great Plains Energy and KCP&L to maintain consolidated common equity of at least 30% and 35%, respectively, of total capitalization (including only the amount of short-term debt in excess of the amount of construction work in progress). Under the Federal Power Act, KCP&L and GMO generally can pay dividends only out of retained earnings.
Consolidated indebtedness to consolidated total capitalization ratio required under the revolving credit agreement	The revolving credit agreements of Great Plains Energy, KCP&L and GMO contain a covenant requiring each company to maintain a consolidated indebtedness to consolidated total capitalization ratio of not more than 0.65 to 1.00.
Restricted net assets of subsidiaries	$ 2.8