Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (38.4)	[1]
Other comprehensive income before reclassifications	1.2	[1]
Amounts reclassified from accumulated other comprehensive loss	11.9	[1]
Net current period other comprehensive income	13.1	[1]	11.4		6.3
Ending balance	(25.3)	[1]	(38.4)	[1]
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(35.4)	[1]
Other comprehensive income before reclassifications	0	[1]
Amounts reclassified from accumulated other comprehensive loss	11.6	[1]
Net current period other comprehensive income	11.6	[1]
Ending balance	(23.8)	[1]
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(3.0)	[1]
Other comprehensive income before reclassifications	1.2	[1]
Amounts reclassified from accumulated other comprehensive loss	0.3	[1]
Net current period other comprehensive income	1.5	[1]
Ending balance	(1.5)	[1]
Kansas City Power and Light Company [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(25.8)
Net current period other comprehensive income	5.6		5.6		5.0
Ending balance	(20.2)		(25.8)
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	(25.8)	[1]
Amounts reclassified from accumulated other comprehensive loss	5.6	[1]
Net current period other comprehensive income	5.6	[1]
Ending balance	$ (20.2)	[1]

[1] Net of tax