Long-Term Debt Subsequent Event (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
Subsequent Event [Line Items]
Subsequent Event Amount	$ 11.8
Subsequent Event Description	In July 2013, the IRS provided guidance to the Company regarding the audit of certain income tax accounting methods for the capitalization of assets. Based on this new guidance, the Company expects to reduce unrecognized tax benefits for these income tax accounting methods by $11.8 million for Great Plains Energy and KCP&L in the third quarter of 2013. This $11.8 million reduction in unrecognized tax benefits will be offset by an increase to deferred income tax liabilities since a significant portion of the unrecognized tax benefits were related to temporary tax differences.
Kansas City Power and Light Company [Member] | Subsequent Event [Member] | EIRR Bonds Remarketed Same Series [Member] | Corporate Debt Securities [Member] | EIRR bonds 4.90 percent Series 2008 [Member]
Subsequent Event [Line Items]
Subsequent Event Amount	$ 23.4
Subsequent Event Date	Jul. 01, 2013
Subsequent Event Description	In July 2013, KCP&L remarketed its unsecured Series 2008 EIRR bonds maturing in 2038 totaling $23.4 million at a fixed rate of 2.875% through July 1, 2018.