Investment in Unconsolidated Affiliate and Related Party Transactions Reconciliation of Equity in Earnings of Unconsolidated Affiliates (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Enable net income		$ 360.0	$ 485.3	$ 400.3
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest		25.50%	25.60%	25.70%
Proportionate Unconsolidated Affiliate Net Income		$ 91.8	$ 124.4	$ 102.7
OGE Energy's portion of Enable net income				102.7
Amortization of basis difference and dilution recognition	[1]	22.1	28.4	28.5
Equity in earnings of unconsolidated affiliates		113.9	152.8	131.2
Natural Gas Midstream Operations [Member]
Schedule of Equity Method Investments [Line Items]
Equity in earnings of unconsolidated affiliates		$ 113.9	$ 152.8	$ 131.2
OGE Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest		25.50%
OGE Energy [Member]
Schedule of Equity Method Investments [Line Items]
Amortization of basis difference and dilution recognition	[2]	$ 27.8

[1] Includes loss on dilution, net of proportional basis difference recognition.

[2] Includes proportional basis difference recognition due to dilution.