Investment in Unconsolidated Affiliates Reconciliation of Equity in Earnings of Unconsolidated Affiliates (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020		Dec. 31, 2020
Reconciliation of Equity in Earnings of Unconsolidated Affiliates [Line Items]
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity		$ 1,318.6			$ 1,332.3
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest		25.50%	25.50%
Proportionate Unconsolidated Affiliate Net Income		$ 39.5	$ 26.3
Equity in Earnings Amortization of Basis Difference	[1]	13.7	7.2
Income (Loss) from Equity Method Investments, Total		53.2	(746.5)	[2]
Asset Impairment Charges	[3]	0.0	(780.0)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		52.7	(491.8)
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Reconciliation of Equity in Earnings of Unconsolidated Affiliates [Line Items]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		$ 155.0	$ 103.0
OGE Holdings [Member]
Reconciliation of Equity in Earnings of Unconsolidated Affiliates [Line Items]
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest		25.50%
OGE Energy [Member]
Reconciliation of Equity in Earnings of Unconsolidated Affiliates [Line Items]
Equity in Earnings Amortization of Basis Difference		$ 13.7

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

[2] In 2020, OGE Energy recorded a $780.0 million impairment on its investment in Enable, as further discussed in Note 4

[3] Effective March 31, 2020, OGE Energy estimated the fair value of its investment in Enable was below the book value and concluded the decline in value was not temporary due to the severity of the decline and recent rapid deterioration, as well as the near term future outlook, of the midstream oil and gas industry. Accordingly, OGE Energy recorded a $780.0 million impairment on its investment in Enable in 2020. Further discussion can be found in OGE Energy's 2020 Form 10-K.