Investment in Unconsolidated Affiliate (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2020	May 01, 2013
Schedule of Equity Method Investments [Line Items]
Limited Partner Units Owned		111.0
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest		25.50%		25.50%	25.60%
Distribution Made to Limited Partner, Distributions Declared, Per Unit		$ 0.16525
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity		$ 1,332.3		$ 652.5
Equity in earnings (losses) of unconsolidated affiliates	[1]	(668.0)	[2]	113.9	$ 152.8
Share Price						$ 30.36
Enable Midstream Partners [Member]
Schedule of Equity Method Investments [Line Items]
Distributions received		$ 91.7		144.0	141.2
Share Price		$ 5.26
Enogex LLC [Member]
Schedule of Equity Method Investments [Line Items]
Increase in fair value of net assets							$ 2,200.0
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]
Percentage Share of Management Rights		50.00%
CenterPoint [Member]
Schedule of Equity Method Investments [Line Items]
Percentage Share of Management Rights		50.00%
Energy Transfer
Schedule of Equity Method Investments [Line Items]
Common Stock, Terms of Conversion		0.8595
Natural Gas Midstream Operations [Member]
Schedule of Equity Method Investments [Line Items]
Equity in earnings (losses) of unconsolidated affiliates		$ (668.0)	[2]	$ 113.9	$ 152.8

[1] For the year ended December 31, 2020, Enable recorded a $225.0 million impairment on its SESH equity method investment. 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 and was offset by basis differences that flow through the amortization of basis difference and dilution recognition line item above.

[2] In March 2020, OGE Energy recorded a $780.0 million impairment on its investment in Enable, as further discussed in Notes 5 and 7.