Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ (6.6)	$ (12.0)
Amounts reclassified from accumulated other comprehensive loss			3.0	3.0
Net current period other comprehensive income	$ 1.5	$ 1.5	3.0	3.0
Ending balance	(3.6)	(9.0)	(3.6)	(9.0)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(4.5)	(10.1)
Amounts reclassified from accumulated other comprehensive loss			2.8	2.8
Net current period other comprehensive income			2.8	2.8
Ending balance	(1.7)	(7.3)	(1.7)	(7.3)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(2.1)	(1.9)
Amounts reclassified from accumulated other comprehensive loss			0.2	0.2
Net current period other comprehensive income			0.2	0.2
Ending balance	(1.9)	(1.7)	(1.9)	(1.7)
Kansas City Power and Light Company [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(4.2)
Net current period other comprehensive income	1.3	1.4	2.6	2.8
Ending balance	(1.6)		(1.6)
Kansas City Power and Light Company [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(4.2)	(9.6)
Amounts reclassified from accumulated other comprehensive loss			2.6	2.8
Net current period other comprehensive income			2.6	2.8
Ending balance	$ (1.6)	$ (6.8)	$ (1.6)	$ (6.8)