Nuclear Plant Decommissioning Trust (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2017
Nuclear decommissioning trust fund [Roll Forward]
Beginning balance January 1	$ 222.9	$ 200.7
Contributions	1.6	3.3
Earned income, net of fees	2.0	4.1
Net realized gains	0.3	0.3
Net unrealized gains	11.6	14.5
Ending balance	238.4	222.9
Kansas City Power and Light Company [Member]
Nuclear decommissioning trust fund [Roll Forward]
Beginning balance January 1	222.9	200.7
Contributions	1.6	3.3
Earned income, net of fees	2.0	4.1
Net realized gains	0.3	0.3
Net unrealized gains	11.6	14.5
Ending balance	$ 238.4	$ 222.9
Kansas City Power and Light Company [Member] | Wolf Creek [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	47.00%		47.00%