Taxes Tax Credit Carryforwards (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
General Business Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 141.1	$ 127.6
Amount of tax credit acquired in business combination	0.5
Tax Credit Carryforward, Description	relate primarily to Advanced Coal Investment Tax Credits and Wind Production tax credits	relate primarily to Advanced Coal Investment Tax Credits and Wind Production tax credits
Tax Credit Carryforward, Valuation Allowance	0.4
General Business Tax Credit Carryforward [Member] | Minimum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2028
General Business Tax Credit Carryforward [Member] | Maximum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2033
Federal Alternative Minimum Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	87.9	87.9
Amount of tax credit acquired in business combination	87.6	87.6
Tax Credit Carryforward, Description	These credits do not expire and can be used to reduce taxes paid in the future.	These credits do not expire and can be used to reduce taxes paid in the future.
State and Local Jurisdiction [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	0.3	2.0
Tax Credit Carryforward, Description	relate primarily to the Company's Missouri affordable housing investment portfolio	relate primarily to the Company's Missouri affordable housing investment portfolio
State and Local Jurisdiction [Member] | Minimum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2014
State and Local Jurisdiction [Member] | Maximum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2016
Kansas City Power and Light Company [Member] | General Business Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 139.6	$ 126.3
Tax Credit Carryforward, Description	relate primarily to Advanced Coal Investment Tax Credits and Wind Production tax credits	relate primarily to Advanced Coal Investment Tax Credits and Wind Production tax credits
Kansas City Power and Light Company [Member] | General Business Tax Credit Carryforward [Member] | Minimum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2028
Kansas City Power and Light Company [Member] | General Business Tax Credit Carryforward [Member] | Maximum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2033