Supplemental Cash Flow Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Cash flows affected by changes in:
Receivables	$ 10.9	$ 17.1
Accounts receivable pledged as collateral	0	(1.0)
Fuel inventories	4.8	(7.5)
Materials and supplies	0.9	(0.6)
Accounts payable	(77.9)	(70.5)
Accrued taxes	34.6	30.5
Accrued interest	16.4	20.5
Deferred refueling outage costs	4.1	(28.6)
Pension and post-retirement benefit obligations	22.4	12.7
Allowance for equity funds used during construction	(4.7)	(1.3)
Fuel recovery mechanism	(6.6)	(4.0)
Solar rebates paid	(12.2)	(4.9)
Other operating activities	(11.4)	1.5
Total other operating activities	(18.7)	(36.1)
Cash paid during the period:
Interest Paid, Net	26.8	23.1
Income Taxes Paid	0.1	0.1
Non-cash investing activities:
Liabilities accrued for capital expenditures	37.7	37.0
Kansas City Power and Light Company [Member]
Cash flows affected by changes in:
Receivables	13.7	21.5
Fuel inventories	1.8	(6.7)
Materials and supplies	0.5	(0.3)
Accounts payable	(45.3)	(32.2)
Accrued taxes	38.1	26.2
Accrued interest	12.1	14.0
Deferred refueling outage costs	4.1	(28.6)
Pension and post-retirement benefit obligations	22.0	13.4
Allowance for equity funds used during construction	(4.7)	(1.3)
Fuel recovery mechanism	4.6	(1.0)
Solar rebates paid	(2.7)	(1.5)
Other operating activities	(17.6)	(2.8)
Total other operating activities	26.6	0.7
Cash paid during the period:
Interest Paid, Net	15.5	15.1
Non-cash investing activities:
Liabilities accrued for capital expenditures	$ 29.4	$ 33.3