Investment in Unconsolidated Affiliates (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020		Dec. 31, 2020
Limited Partner Units Owned		111.0		111.0
Distribution Made to Limited Partner, Distributions Declared, Per Unit				$ 0.16525
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest		25.50%	25.50%	25.50%	25.50%
Equity in earnings (losses) of unconsolidated affiliates	[1]	$ 41.2	$ 15.8	$ 127.9	$ (703.8)	[2]
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity		1,290.2		1,290.2			$ 1,332.3
Enable Midstream Partners [Member]
Distributions from unconsolidated affiliates		$ 18.3	$ 18.3	$ 55.0	$ 73.3
OGE Holdings [Member]
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest				25.50%
Energy Transfer
Common Stock, Terms of Conversion				0.8595
Enable Midstream Partners [Member]
Share Price		$ 8.12		$ 8.12

[1] 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.

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