Commitments and Contingencies (Details) $ in Millions		12 Months Ended
		Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Loss Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due, Next Twelve Months		$ 130.1
Operating Leases, Future Minimum Payments, Due in Two Years		108.4
Operating Leases, Future Minimum Payments, Due in Three Years		114.3
Operating Leases, Future Minimum Payments, Due in Four Years		128.4
Operating Leases, Future Minimum Payments, Due in Five Years		114.0
Operating Leases, Future Minimum Payments Due		595.2
Utilities Operating Expense, Purchased Power under Long-term Contracts		57.3	$ 57.7	$ 57.6
OG&E minimum fuel purchase commitments [Member]
Loss Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due		235.9
Purchase Obligation, Due in Next Twelve Months		72.5
Unrecorded Unconditional Purchase Obligation, Due within Two Years		50.4
Unrecorded Unconditional Purchase Obligation, Due within Three Years		50.4
Unrecorded Unconditional Purchase Obligation, Due within Four Years		36.7
Unrecorded Unconditional Purchase Obligation, Due within Five Years		25.9
OG&E expected wind purchase commitments [Member]
Loss Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due		280.3
Purchase Obligation, Due in Next Twelve Months		55.2
Unrecorded Unconditional Purchase Obligation, Due within Two Years		55.6
Unrecorded Unconditional Purchase Obligation, Due within Three Years		56.0
Unrecorded Unconditional Purchase Obligation, Due within Four Years		56.6
Unrecorded Unconditional Purchase Obligation, Due within Five Years		56.9
OG&E long-term service agreement commitments [Member]
Loss Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due		79.0
Purchase Obligation, Due in Next Twelve Months		2.4
Unrecorded Unconditional Purchase Obligation, Due within Two Years		2.4
Unrecorded Unconditional Purchase Obligation, Due within Three Years		7.9
Unrecorded Unconditional Purchase Obligation, Due within Four Years		35.1
Unrecorded Unconditional Purchase Obligation, Due within Five Years		31.2
OG&E total cogeneration payments [Member]
Loss Contingencies [Line Items]
Utilities Operating Expense, Purchased Power under Long-term Contracts			14.7	112.4
OG&E capacity payments [Member]
Loss Contingencies [Line Items]
Utilities Operating Expense, Purchased Power under Long-term Contracts			7.4	60.0
CPV Keenan [Member]
Loss Contingencies [Line Items]
Utilities Operating Expense, Purchased Power under Long-term Contracts		27.5	27.2	27.0
Edison Mission Energy [Member]
Loss Contingencies [Line Items]
Utilities Operating Expense, Purchased Power under Long-term Contracts		22.8	23.1	21.7
NextEra Energy [Member]
Loss Contingencies [Line Items]
Utilities Operating Expense, Purchased Power under Long-term Contracts		7.0	7.4	6.8
FPL Energy [Member]
Loss Contingencies [Line Items]
Utilities Operating Expense, Purchased Power under Long-term Contracts	[1]	$ 0.0	$ 0.0	$ 2.1
OG&E long-term service agreement commitments [Member] | McClain Plant [Member]
Loss Contingencies [Line Items]
Factored-Fired Hours		128,000
Factored-Fired Starts		4,800
OG&E long-term service agreement commitments [Member] | Redbud Plant [Member]
Loss Contingencies [Line Items]
Factored-Fired Hours		144,000
Factored-Fired Starts		4,500
Additional Factored-Fired Hours		24,000
Maximum [Member]
Loss Contingencies [Line Items]
Loss Contingency, Range of Possible Loss, Maximum		$ 1,000.0

[1] OG&E's purchased power contract with FPL Energy for 50 MWs expired in 2018.