Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows affected by changes in:
Receivables	$ (10.4)	$ (64.0)
Accounts receivable pledged as collateral	0.2	1.3
Fuel inventories	19.5	14.5
Materials and supplies	(6.3)	(4.8)
Accounts payable	(141.7)	(84.1)
Accrued taxes	50.7	54.3
Accrued interest	41.9	0.3
Deferred refueling outage costs	8.1	9.5
Pension and post-retirement benefit obligations	39.1	38.8
Allowance for equity funds used during construction	(1.7)	(2.4)
Fuel recovery mechanisms	(11.7)	(2.3)
Other	(6.4)	(39.7)
Total other operating activities	(18.7)	(78.6)
Cash paid during the period:
Interest	107.7	96.8
Income taxes	0.1	0.2
Non-cash investing activities:
Liabilities accrued for capital expenditures	31.8	30.6
Kansas City Power and Light Company [Member]
Cash flows affected by changes in:
Receivables	(1.3)	(37.6)
Fuel inventories	9.4	9.7
Materials and supplies	(4.5)	(3.6)
Accounts payable	(90.6)	(48.0)
Accrued taxes	56.7	106.1
Accrued interest	(1.6)	(1.5)
Deferred refueling outage costs	8.1	9.5
Pension and post-retirement benefit obligations	36.8	39.0
Allowance for equity funds used during construction	(1.7)	(2.1)
Fuel recovery mechanisms	(3.6)	(19.4)
Other	(13.0)	(32.2)
Total other operating activities	(5.3)	19.9
Cash paid during the period:
Interest	66.6	65.5
Non-cash investing activities:
Liabilities accrued for capital expenditures	$ 26.5	$ 16.5