Intangibles Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets	$ 28.6	$ 21.6
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	21.9
Finite-Lived Intangible Assets, Amortization Expense, Year Two	18.7
Finite-Lived Intangible Assets, Amortization Expense, Year Three	16.5
Finite-Lived Intangible Assets, Amortization Expense, Year Four	14.5
Finite-Lived Intangible Assets, Amortization Expense, Year Five	12.4
Kansas City Power and Light Company [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets	24.7	19.2
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	18.9
Finite-Lived Intangible Assets, Amortization Expense, Year Two	17.7
Finite-Lived Intangible Assets, Amortization Expense, Year Three	16.1
Finite-Lived Intangible Assets, Amortization Expense, Year Four	14.1
Finite-Lived Intangible Assets, Amortization Expense, Year Five	12.0
Computer Software, Intangible Asset [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	333.0	300.2
Finite-Lived Intangible Assets, Accumulated Amortization	(191.8)	(190.9)
Computer Software, Intangible Asset [Member] | Kansas City Power and Light Company [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	315.5	277.9
Finite-Lived Intangible Assets, Accumulated Amortization	(177.7)	(175.5)
Asset Improvements [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	28.3	27.4
Finite-Lived Intangible Assets, Accumulated Amortization	(6.1)	(5.5)
Asset Improvements [Member] | Kansas City Power and Light Company [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	13.1	12.2
Finite-Lived Intangible Assets, Accumulated Amortization	$ (1.5)	$ (1.3)