Commitments and Contingencies (Details) $ in Millions		12 Months Ended
		Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Feb. 01, 2019 USD ($)
Loss Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due, Next Twelve Months		$ 22.1
Operating Leases, Future Minimum Payments, Due in Two Years		3.9
Operating Leases, Future Minimum Payments, Due in Three Years		3.5
Operating Leases, Future Minimum Payments, Due in Four Years		2.9
Operating Leases, Future Minimum Payments, Due in Five Years		2.9
Operating Leases, Future Minimum Payments, Due Thereafter		37.6
Operating Leases, Future Minimum Payments Due		72.9
Operating Leases, Rent Expense, Net		4.9	$ 6.2	$ 9.3
Purchase Obligation, Due in Next Twelve Months		198.0
Unrecorded Unconditional Purchase Obligation, Due within Two Years		104.1
Unrecorded Unconditional Purchase Obligation, Due within Three Years		104.1
Unrecorded Unconditional Purchase Obligation, Due within Four Years		104.5
Unrecorded Unconditional Purchase Obligation, Due within Five Years		117.0
Long-term Purchase Commitment, Amount		627.7
Utilities Operating Expense, Purchased Power under Long-term Contracts		57.6	61.1	61.0
OG&E Railcar Lease Agreement [Member]
Loss Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due, Next Twelve Months		18.6
Operating Leases, Future Minimum Payments, Due in Two Years		0.0
Operating Leases, Future Minimum Payments, Due in Three Years		0.0
Operating Leases, Future Minimum Payments, Due in Four Years		0.0
Operating Leases, Future Minimum Payments, Due in Five Years		0.0
Operating Leases, Future Minimum Payments, Due Thereafter		0.0
Operating Leases, Future Minimum Payments Due		18.6
OG&E Wind Farm Land Lease Agreements [Member]
Loss Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due, Next Twelve Months		2.5
Operating Leases, Future Minimum Payments, Due in Two Years		2.9
Operating Leases, Future Minimum Payments, Due in Three Years		2.9
Operating Leases, Future Minimum Payments, Due in Four Years		2.9
Operating Leases, Future Minimum Payments, Due in Five Years		2.9
Operating Leases, Future Minimum Payments, Due Thereafter		37.6
Operating Leases, Future Minimum Payments Due		51.7
OGE Energy Building Lease [Member]
Loss Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due, Next Twelve Months		1.0
Operating Leases, Future Minimum Payments, Due in Two Years		1.0
Operating Leases, Future Minimum Payments, Due in Three Years		0.6
Operating Leases, Future Minimum Payments, Due in Four Years		0.0
Operating Leases, Future Minimum Payments, Due in Five Years		0.0
Operating Leases, Future Minimum Payments, Due Thereafter		0.0
Operating Leases, Future Minimum Payments Due		2.6
OG&E cogeneration capacity and fixed operation and maintenance payments [Member]
Loss Contingencies [Line Items]
Purchase Obligation, Due in Next Twelve Months	[1]	10.9
Unrecorded Unconditional Purchase Obligation, Due within Two Years	[1]	0.0
Unrecorded Unconditional Purchase Obligation, Due within Three Years	[1]	0.0
Unrecorded Unconditional Purchase Obligation, Due within Four Years	[1]	0.0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	[1]	0.0
Long-term Purchase Commitment, Amount	[1]	10.9
OG&E expected cogeneration energy payments [Member]
Loss Contingencies [Line Items]
Purchase Obligation, Due in Next Twelve Months	[1]	2.4
Unrecorded Unconditional Purchase Obligation, Due within Two Years	[1]	0.0
Unrecorded Unconditional Purchase Obligation, Due within Three Years	[1]	0.0
Unrecorded Unconditional Purchase Obligation, Due within Four Years	[1]	0.0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	[1]	0.0
Long-term Purchase Commitment, Amount	[1]	2.4
OG&E minimum fuel purchase commitments [Member]
Loss Contingencies [Line Items]
Purchase Obligation, Due in Next Twelve Months		75.8
Unrecorded Unconditional Purchase Obligation, Due within Two Years		44.6
Unrecorded Unconditional Purchase Obligation, Due within Three Years		44.6
Unrecorded Unconditional Purchase Obligation, Due within Four Years		44.6
Unrecorded Unconditional Purchase Obligation, Due within Five Years		44.6
Long-term Purchase Commitment, Amount		254.2
OG&E expected wind purchase commitments [Member]
Loss Contingencies [Line Items]
Purchase Obligation, Due in Next Twelve Months		56.3
Unrecorded Unconditional Purchase Obligation, Due within Two Years		56.9
Unrecorded Unconditional Purchase Obligation, Due within Three Years		57.1
Unrecorded Unconditional Purchase Obligation, Due within Four Years		57.5
Unrecorded Unconditional Purchase Obligation, Due within Five Years		58.0
Long-term Purchase Commitment, Amount		285.8
OG&E long-term service agreement commitments [Member]
Loss Contingencies [Line Items]
Purchase Obligation, Due in Next Twelve Months		46.8
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		2.4
Unrecorded Unconditional Purchase Obligation, Due within Five Years		14.4
Long-term Purchase Commitment, Amount		68.4
Environmental compliance plan expenditures [Member]
Loss Contingencies [Line Items]
Purchase Obligation, Due in Next Twelve Months		5.8
Unrecorded Unconditional Purchase Obligation, Due within Two Years		0.2
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
Long-term Purchase Commitment, Amount		$ 6.0
Public Utility Regulatory Policy Act of 1978 [Member]
Loss Contingencies [Line Items]
Percentage of output purchased		100.00%
OG&E total cogeneration payments [Member]
Loss Contingencies [Line Items]
Long-term Purchase Commitment, Amount		$ 112.4	115.2	124.8
OG&E capacity payments [Member]
Loss Contingencies [Line Items]
Long-term Purchase Commitment, Amount		60.0	63.0	66.3
CPV Keenan [Member]
Loss Contingencies [Line Items]
Utilities Operating Expense, Purchased Power under Long-term Contracts		27.0	29.0	29.2
Edison Mission Energy [Member]
Loss Contingencies [Line Items]
Utilities Operating Expense, Purchased Power under Long-term Contracts		21.7	22.1	21.1
FPL Energy [Member]
Loss Contingencies [Line Items]
Utilities Operating Expense, Purchased Power under Long-term Contracts	[2]	2.1	2.6	3.4
NextEra Energy [Member]
Loss Contingencies [Line Items]
Utilities Operating Expense, Purchased Power under Long-term Contracts		$ 6.8	$ 7.4	$ 7.3
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		$ 16.2			$ 6.8

[1] Cogeneration capacity, fixed operation and maintenance and energy payments will end in 2019, as a result of contract expiration. As described below, OG&E intends to acquire the AES and Oklahoma Cogeneration LLC power plants, pending regulatory approval.

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