Leases (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019		Sep. 30, 2019		Dec. 31, 2018		Jan. 01, 2019
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Contingent Liability	$ 6.8		$ 6.8		$ 16.2
Lessee, Operating Lease, Liability, Payments, Due Year Two	5.3		5.3		2.9	[1],[2]
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	0.6		0.6		21.1	[1],[2]
Operating Lease, Cost	1.3		3.8
Cash Paid on Operating Leases			4.3
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability			10.7
Operating Lease, Right-of-Use Asset	$ 40.4	[3]	$ 40.4	[3]			$ 32.3
Operating Lease, Weighted Average Remaining Lease Term	13 years 7 months 6 days		13 years 7 months 6 days
Operating Lease, Weighted Average Discount Rate, Percent	3.90%		3.90%
Lessee, Operating Lease, Liability, Payments, Due Year Three	$ 5.2		$ 5.2		2.9	[1],[2]
Lessee, Operating Lease, Liability, Payments, Due Year Four	5.2		5.2		2.9	[1],[2]
Lessee, Operating Lease, Liability, Payments, Due Year Five	5.2		5.2		2.9	[1],[2]
Lessee, Operating Lease, Liability, Payments, Due after Year Five	37.8		37.8		37.6	[1],[2]
Lessee, Operating Lease, Liability, Payments, Due	59.3		59.3		70.3	[1],[2]
Unrecorded Unconditional Purchase Obligation, Imputed Interest	14.1		14.1
Operating Lease, Liability	$ 45.2	[4]	$ 45.2	[4]			$ 36.9
Operating Leases, Rent Expense, Net					$ 4.1

[1] Amounts included for comparability and accounted for in accordance with ASC 840, "Leases."

[2] At the end of the railcar lease term, which was February 1, 2019, OG&E had the option to either purchase the railcars at a stipulated fair market value or renew the lease. OG&E renewed the lease effective February 1, 2019. If OG&E chose not to purchase the railcars or renew the lease agreement and the actual fair value of the railcars was less than the stipulated fair market value, OG&E would have been responsible for the difference in those values up to a maximum of $16.2 million.

[3] Included in Property, Plant and Equipment in the 2019 Condensed Balance Sheet.

[4] Included in Other Deferred Credits and Other Liabilities in the 2019 Condensed Balance Sheet.