Commitments and Contingencies (Details) $ in Millions		12 Months Ended
		Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Loss Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due, Next Twelve Months		$ 141.1
Operating Leases, Future Minimum Payments, Due in Two Years		113.5
Operating Leases, Future Minimum Payments, Due in Three Years		109.2
Operating Leases, Future Minimum Payments, Due in Four Years		121.0
Operating Leases, Future Minimum Payments, Due in Five Years		122.5
Operating Leases, Future Minimum Payments Due		607.3
Utilities Operating Expense, Purchased Power under Long-term Contracts		57.7	$ 57.6	$ 61.1
OG&E minimum fuel purchase commitments [Member]
Loss Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due		271.4
Purchase Obligation, Due in Next Twelve Months		82.6
Unrecorded Unconditional Purchase Obligation, Due within Two Years		55.1
Unrecorded Unconditional Purchase Obligation, Due within Three Years		50.4
Unrecorded Unconditional Purchase Obligation, Due within Four Years		50.4
Unrecorded Unconditional Purchase Obligation, Due within Five Years		32.9
OG&E expected wind purchase commitments [Member]
Loss Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due		282.4
Purchase Obligation, Due in Next Twelve Months		55.7
Unrecorded Unconditional Purchase Obligation, Due within Two Years		56.0
Unrecorded Unconditional Purchase Obligation, Due within Three Years		56.4
Unrecorded Unconditional Purchase Obligation, Due within Four Years		56.8
Unrecorded Unconditional Purchase Obligation, Due within Five Years		57.5
OG&E long-term service agreement commitments [Member]
Loss Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due		53.1
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		2.4
Unrecorded Unconditional Purchase Obligation, Due within Four Years		13.8
Unrecorded Unconditional Purchase Obligation, Due within Five Years		32.1
Environmental compliance plan expenditures [Member]
Loss Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due		0.4
Purchase Obligation, Due in Next Twelve Months		0.4
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
OG&E total cogeneration payments [Member]
Loss Contingencies [Line Items]
Long-term Purchase Commitment, Amount		14.7	112.4	115.2
OG&E capacity payments [Member]
Loss Contingencies [Line Items]
Long-term Purchase Commitment, Amount		7.4	60.0	63.0
CPV Keenan [Member]
Loss Contingencies [Line Items]
Utilities Operating Expense, Purchased Power under Long-term Contracts		27.2	27.0	29.0
Edison Mission Energy [Member]
Loss Contingencies [Line Items]
Utilities Operating Expense, Purchased Power under Long-term Contracts		23.1	21.7	22.1
FPL Energy [Member]
Loss Contingencies [Line Items]
Utilities Operating Expense, Purchased Power under Long-term Contracts	[1]	0.0	2.1	2.6
NextEra Energy [Member]
Loss Contingencies [Line Items]
Utilities Operating Expense, Purchased Power under Long-term Contracts		$ 7.4	$ 6.8	$ 7.4
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

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