Investment in Unconsolidated Affiliates Reconciliation of Equity in Earnings of Unconsolidated Affiliates (Details) - USD ($) $ in Millions		3 Months Ended						9 Months Ended
		Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020		Dec. 31, 2020
Reconciliation of Equity in Earnings of Unconsolidated Affiliates [Line Items]
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity		$ 1,290.2						$ 1,290.2			$ 1,332.3
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest		25.50%			25.50%			25.50%	25.50%
Proportionate Unconsolidated Affiliate Net Income		$ 27.5			$ (44.0)			$ 87.0	$ (8.9)
Equity in Earnings Amortization of Basis Difference	[1]	13.7			59.8			40.9	85.1
Income (Loss) from Equity Method Investments, Total	[2]	41.2			15.8			127.9	(703.8)	[3]
Asset Impairment Charges	[4]	0.0			0.0			0.0	(780.0)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		252.5	$ 112.9	$ 52.7	177.4	$ 85.9	$ (491.8)	418.1	(228.5)
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		$ 107.0			$ (173.0)			$ 341.0	$ (35.0)
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	[5]							$ 42.1

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

[2] For the three and nine months ended September 30, 2020, Enable recorded a $225.0 million impairment on its SESH equity method investment, which is included in their net loss for each period. Enable estimated the fair value of this equity method investment was below the carrying value at September 30, 2020 and concluded the decline in value was other than temporary due to the expiration of a transportation contract and the current status of renewal negotiations. The impairment ran through OGE Energy's portion of Enable net income (loss) and was offset by basis differences that flow through the amortization of basis difference and dilution recognition line item above.

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

[4] 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.(C) For the three and nine months ended September 30, 2020, Enable recorded a $225.0 million impairment on its SESH equity method investment, which is included in their net loss for each period. Enable estimated the fair value of this equity method investment was below the carrying value at September 30, 2020 and concluded the decline in value was other than temporary due to the expiration of a transportation contract and the current status of renewal negotiations. The impairment ran through OGE Energy's portion of Enable net income (loss) and was offset by basis differences that flow through the amortization of basis difference and dilution recognition line item above.

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