Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash flows affected by changes in:
Receivables	$ (64.0)	$ (36.0)
Accounts receivable pledged as collateral	1.3	8.0
Fuel inventories	14.5	(12.2)
Materials and supplies	(4.8)	0.3
Accounts payable	(84.1)	(108.2)
Accrued taxes	54.3	47.5
Accrued interest	0.3	(1.3)
Deferred refueling outage costs	9.5	(17.7)
Pension and post-retirement benefit obligations	38.8	25.0
Allowance for equity funds used during construction	(2.4)	(3.5)
Fuel recovery mechanisms	(2.3)	25.6
Other	(39.7)	(0.9)
Total other operating activities	(78.6)	(73.4)
Cash paid during the period:
Interest	96.8	91.9
Income taxes	0.2	0.2
Non-cash investing activities:
Liabilities accrued for capital expenditures	30.6	34.8
Kansas City Power and Light Company [Member]
Cash flows affected by changes in:
Receivables	(37.6)	(1.4)
Fuel inventories	9.7	(11.9)
Materials and supplies	(3.6)	0.1
Accounts payable	(48.0)	(69.7)
Accrued taxes	106.1	94.4
Accrued interest	(1.5)	(1.5)
Deferred refueling outage costs	9.5	(17.7)
Pension and post-retirement benefit obligations	39.0	25.1
Allowance for equity funds used during construction	(2.1)	(2.7)
Fuel recovery mechanisms	(19.4)	0.6
Other	(32.2)	(0.4)
Total other operating activities	19.9	14.9
Cash paid during the period:
Interest	65.5	61.2
Non-cash investing activities:
Liabilities accrued for capital expenditures	$ 16.5	$ 31.4