Commitments and Contingencies Commitments and Contingencies Contractual Commitments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Lease Expense [Abstract]
Lease expense	$ 16.8	$ 16.0	$ 18.5
Operating Leases [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	12.3
Operating Leases, Future Minimum Payments, Due in Two Years	10.6
Operating Leases, Future Minimum Payments, Due in Three Years	9.7
Operating Leases, Future Minimum Payments, Due in Four Years	9.9
Operating Leases, Future Minimum Payments, Due in Five Years	9.6
Operating Leases, Future Minimum Payments, Due Thereafter	121.5
Operating Leases, Future Minimum Payments Due, Total	173.6
Capital Leases [Abstract]
Capital Leases, Future Minimum Payments Due, Next Twelve Months	0.4
Capital Leases, Future Minimum Payments Due in Two Years	0.4
Capital Leases, Future Minimum Payments Due in Three Years	0.4
Capital Leases, Future Minimum Payments Due in Four Years	0.4
Capital Leases, Future Minimum Payments Due in Five Years	0.4
Capital Leases, Future Minimum Payments Due Thereafter	3.5
Capital Leases, Future Minimum Payments Due, Total	5.5
Total Commitments [Abstract]
Total Commitments, Due in Next Twelve Months	450.8
Total Commitments, Due within Two Years	353.4
Total Commitments, Due within Three Years	297.9
Total Commitments, Due within Four Years	294.5
Total Commitments, Due within Five Years	252.8
Total Commitments, Due Thereafter	728.1
Total Commitments Due	2,377.5
Public Utilities, Inventory, Fuel [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	311.4
Unrecorded Unconditional Purchase Obligation, Due within Two Years	283.2
Unrecorded Unconditional Purchase Obligation, Due within Three Years	212.7
Unrecorded Unconditional Purchase Obligation, Due within Four Years	196.9
Unrecorded Unconditional Purchase Obligation, Due within Five Years	190.3
Unrecorded Unconditional Purchase Obligation, Due after Five Years	52.5
Unrecorded Unconditional Purchase Obligation, Total	1,247.0
Purchased Power [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	47.3
Unrecorded Unconditional Purchase Obligation, Due within Two Years	47.3
Unrecorded Unconditional Purchase Obligation, Due within Three Years	47.3
Unrecorded Unconditional Purchase Obligation, Due within Four Years	47.3
Unrecorded Unconditional Purchase Obligation, Due within Five Years	47.3
Unrecorded Unconditional Purchase Obligation, Due after Five Years	509.5
Unrecorded Unconditional Purchase Obligation, Total	746.0
Capacity [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	1.2
Unrecorded Unconditional Purchase Obligation, Due within Two Years	0.0
Unrecorded Unconditional Purchase Obligation, Due within Three Years	0.0
Unrecorded Unconditional Purchase Obligation, Due within Four Years	0.0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0.0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0.0
Unrecorded Unconditional Purchase Obligation, Total	1.2
Non-regulated natural gas transportation [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	3.5
Unrecorded Unconditional Purchase Obligation, Due within Two Years	0.9
Unrecorded Unconditional Purchase Obligation, Due within Three Years	0.0
Unrecorded Unconditional Purchase Obligation, Due within Four Years	0.0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0.0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0.0
Unrecorded Unconditional Purchase Obligation, Total	4.4
Other purchase commitments [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	74.7
Unrecorded Unconditional Purchase Obligation, Due within Two Years	11.0
Unrecorded Unconditional Purchase Obligation, Due within Three Years	27.8
Unrecorded Unconditional Purchase Obligation, Due within Four Years	40.0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	5.2
Unrecorded Unconditional Purchase Obligation, Due after Five Years	41.1
Unrecorded Unconditional Purchase Obligation, Total	199.8
Kansas City Power and Light Company [Member]
Lease Expense [Abstract]
Lease expense	15.0	$ 14.0	$ 16.0
Operating Leases [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	11.9
Operating Leases, Future Minimum Payments, Due in Two Years	10.6
Operating Leases, Future Minimum Payments, Due in Three Years	9.7
Operating Leases, Future Minimum Payments, Due in Four Years	9.9
Operating Leases, Future Minimum Payments, Due in Five Years	9.6
Operating Leases, Future Minimum Payments, Due Thereafter	121.5
Operating Leases, Future Minimum Payments Due, Total	173.2
Capital Leases [Abstract]
Capital Leases, Future Minimum Payments Due, Next Twelve Months	0.2
Capital Leases, Future Minimum Payments Due in Two Years	0.2
Capital Leases, Future Minimum Payments Due in Three Years	0.2
Capital Leases, Future Minimum Payments Due in Four Years	0.2
Capital Leases, Future Minimum Payments Due in Five Years	0.2
Capital Leases, Future Minimum Payments Due Thereafter	1.8
Capital Leases, Future Minimum Payments Due, Total	2.8
Total Commitments [Abstract]
Total Commitments, Due in Next Twelve Months	368.4
Total Commitments, Due within Two Years	299.0
Total Commitments, Due within Three Years	249.8
Total Commitments, Due within Four Years	263.5
Total Commitments, Due within Five Years	224.7
Total Commitments, Due Thereafter	570.1
Total Commitments Due	1,975.5
Reimbursement by Other Owners per Year (2016)	1.5
Reimbursement By Other Owners in 2017	0.9
Reimbursements by Other Owners per Year (2018 to 2025)	0.4
Reimbursements by Other Owners Total	6.0
Kansas City Power and Light Company [Member] | Supply Commitment [Member]
Total Commitments [Abstract]
Capacity Sales Agreements per Year 2016	6.0
Capacity Sales Agreements per Year 2017	1.9
Capacity Sales Agreements per Year 2018	2.1
Capacity Sales Agreements per Year 2019	1.9
Capacity Sales Agreements per Year 2020	2.0
Kansas City Power and Light Company [Member] | Public Utilities, Inventory, Fuel [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	264.7
Unrecorded Unconditional Purchase Obligation, Due within Two Years	243.2
Unrecorded Unconditional Purchase Obligation, Due within Three Years	178.2
Unrecorded Unconditional Purchase Obligation, Due within Four Years	182.3
Unrecorded Unconditional Purchase Obligation, Due within Five Years	175.8
Unrecorded Unconditional Purchase Obligation, Due after Five Years	52.5
Unrecorded Unconditional Purchase Obligation, Total	1,096.7
Kansas City Power and Light Company [Member] | Purchased Power [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	34.8
Unrecorded Unconditional Purchase Obligation, Due within Two Years	34.8
Unrecorded Unconditional Purchase Obligation, Due within Three Years	34.8
Unrecorded Unconditional Purchase Obligation, Due within Four Years	34.8
Unrecorded Unconditional Purchase Obligation, Due within Five Years	34.8
Unrecorded Unconditional Purchase Obligation, Due after Five Years	359.8
Unrecorded Unconditional Purchase Obligation, Total	533.8
Kansas City Power and Light Company [Member] | Capacity [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	1.2
Unrecorded Unconditional Purchase Obligation, Due within Two Years	0.0
Unrecorded Unconditional Purchase Obligation, Due within Three Years	0.0
Unrecorded Unconditional Purchase Obligation, Due within Four Years	0.0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0.0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0.0
Unrecorded Unconditional Purchase Obligation, Total	1.2
Kansas City Power and Light Company [Member] | Other purchase commitments [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	55.6
Unrecorded Unconditional Purchase Obligation, Due within Two Years	10.2
Unrecorded Unconditional Purchase Obligation, Due within Three Years	26.9
Unrecorded Unconditional Purchase Obligation, Due within Four Years	36.3
Unrecorded Unconditional Purchase Obligation, Due within Five Years	4.3
Unrecorded Unconditional Purchase Obligation, Due after Five Years	34.5
Unrecorded Unconditional Purchase Obligation, Total	$ 167.8