Nuclear Plant Decommissioning Trust (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Nuclear decommissioning trust fund [Roll Forward]
Nuclear decommissioning trust fund, beginning balance	$ 183.9	$ 154.7
Contributions to nuclear decommissioning trust fund	2.5	3.3
Earned income, net of fees	2.8	2.7
Net realized gains (losses) on nuclear decommissioning trust fund	0.3	1.7
Net unrealized gains (losses) on nuclear decommissioning trust fund	3.7	21.5
Nuclear decommissioning trust fund, ending balance	193.2	183.9
Wolf Creek [Member] | Missouri Public Service Commission [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Current cost of decommissioning (in 2014 dollars)	765.1
Future cost of decommissioning (in 2045 through 2053 dollars)	2,253.1
Annual Escalation Factor	3.22%
Annual return on trust assets through 2025	5.68%
Annual return on trusts assets in 2053	2.22%
Wolf Creek [Member] | Kansas Corporation Commission [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Current cost of decommissioning (in 2014 dollars)	765.1
Future cost of decommissioning (in 2045 through 2053 dollars)	2,201.5
Annual Escalation Factor	3.15%
Kansas City Power and Light Company [Member]
Nuclear decommissioning trust fund [Roll Forward]
Nuclear decommissioning trust fund, beginning balance	183.9	154.7
Contributions to nuclear decommissioning trust fund	2.5	3.3
Earned income, net of fees	2.8	2.7
Net realized gains (losses) on nuclear decommissioning trust fund	0.3	1.7
Net unrealized gains (losses) on nuclear decommissioning trust fund	3.7	21.5
Nuclear decommissioning trust fund, ending balance	193.2	183.9
Kansas City Power and Light Company [Member] | Wolf Creek [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	47.00%
Kansas City Power and Light Company [Member] | Wolf Creek [Member] | Missouri Public Service Commission [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Current cost of decommissioning (in 2014 dollars)	359.6
Future cost of decommissioning (in 2045 through 2053 dollars)	1,059.0
Kansas City Power and Light Company [Member] | Wolf Creek [Member] | Kansas Corporation Commission [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Current cost of decommissioning (in 2014 dollars)	359.6
Future cost of decommissioning (in 2045 through 2053 dollars)	$ 1,034.7