Supplemental Cash Flow Information (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Cash flows affected by changes in:
Receivables	$ (70.4)	$ (44.1)
Accounts receivable pledged as collateral	4.0	(16.0)
Fuel inventories	23.3	11.2
Materials and supplies	1.7	(4.3)
Accounts payable	(75.2)	(91.5)
Accrued taxes	91.2	81.0
Accrued interest	11.4	18.4
Deferred refueling outage costs	15.8	(21.8)
Pension and post-retirement benefit obligations	24.8	40.2
Allowance for equity funds used during construction	(13.2)	(9.1)
Fuel recovery mechanism	(21.3)	(5.3)
Solar rebates paid	(43.9)	(20.1)
Other operating activities	(10.0)	11.3
Total other operating activities	(61.8)	(50.1)
Cash paid during the period:
Interest Paid, Net	115.6	111.3
Income Taxes Paid	0.1	0.1
Non-cash investing activities:
Liabilities accrued for capital expenditures	50.5	34.5
Kansas City Power and Light Company [Member]
Cash flows affected by changes in:
Receivables	(70.5)	(40.2)
Fuel inventories	18.3	10.4
Materials and supplies	0.5	(3.0)
Accounts payable	(34.7)	(66.7)
Accrued taxes	118.2	55.3
Accrued interest	10.8	12.2
Deferred refueling outage costs	15.8	(21.8)
Pension and post-retirement benefit obligations	23.6	41.9
Allowance for equity funds used during construction	(12.3)	(9.1)
Fuel recovery mechanism	1.4	(1.2)
Solar rebates paid	(14.8)	(4.8)
Other operating activities	(23.9)	(11.8)
Total other operating activities	32.4	(38.8)
Cash paid during the period:
Interest Paid, Net	72.9	73.2
Non-cash investing activities:
Liabilities accrued for capital expenditures	$ 44.4	$ 28.3