Leases, Codification Topic 842 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017	Jan. 01, 2019
Leases [Abstract]
Lessee, Operating Lease, Contingent Liability	$ 6.8		$ 16.2
Operating Lease, Cost	6.0		4.9		$ 6.2
Operating Leased Assets [Line Items]
Cash Paid on Operating Leases	5.6
Operating Lease, Right-of-Use Asset	40.9	[1]				$ 34.5
Operating Lease, Liability	$ 45.8	[2]				$ 39.1
Operating Lease, Weighted Average Remaining Lease Term	13 years 1 month 6 days
Operating Lease, Weighted Average Discount Rate, Percent	3.90%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 10.7
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	0.0		22.1	[3],[4]
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	6.2		3.9	[3],[4]
Lessee, Operating Lease, Liability, Payments, Due Year Two	5.8		3.5	[3],[4]
Lessee, Operating Lease, Liability, Payments, Due Year Three	5.2		2.9	[3],[4]
Lessee, Operating Lease, Liability, Payments, Due Year Four	5.2		2.9	[3],[4]
Lessee, Operating Lease, Liability, Payments, Due Year Five	3.1		3.0	[3],[4]
Lessee, Operating Lease, Liability, Payments, Due after Year Five	34.7		34.6	[3],[4]
Lessee, Operating Lease, Liability, Payments, Due	60.2		72.9	[3],[4]
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	14.4
Lessee, Operating Lease, Contingent Liability	$ 6.8		$ 16.2

[1] Included in Property, Plant and Equipment in the 2019 Consolidated Balance Sheet.

[2] Included in Other Deferred Credits and Other Liabilities in the 2019 Consolidated Balance Sheet.

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

[4] 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.