Accumulated Other Comprehensive Income (Loss) Reclassification (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges	$ (51.2)	$ (47.3)
Fuel	(90.6)	(107.6)
Utility operating and maintenance expenses	(179.4)	(171.5)
Income before income tax expense and income from equity investments	37.4	25.1
Income tax benefit	(11.7)	(6.5)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	(1.5)	(1.5)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income tax expense and income from equity investments	(2.3)	(2.3)
Income tax benefit	0.9	0.9
Net income	(1.4)	(1.4)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Interest Rate Contract [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges	(2.3)	(2.3)
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Utility operating and maintenance expenses	(0.2)	(0.2)
Income before income tax expense and income from equity investments	(0.2)	(0.2)
Income tax benefit	0.1	0.1
Net income	(0.1)	(0.1)
Kansas City Power and Light Company [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges	(35.3)	(31.5)
Fuel	(61.5)	(74.8)
Utility operating and maintenance expenses	(123.7)	(118.3)
Income before income tax expense and income from equity investments	35.3	16.5
Income tax benefit	(10.7)	(3.3)
Kansas City Power and Light Company [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income tax expense and income from equity investments	(2.3)	(2.3)
Income tax benefit	0.9	0.9
Net income	(1.4)	(1.4)
Kansas City Power and Light Company [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Interest Rate Contract [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges	$ (2.3)	$ (2.3)