Investment in Unconsolidated Affiliates (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020		Dec. 31, 2020
Expected Settlement Charge			$ 18.1
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	$ 33.5	$ 26.9	$ 86.7	$ (719.6)	[1]
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	1,303.9		1,303.9			$ 1,332.3
Enable Midstream Partners [Member]
Distributions from unconsolidated affiliates	$ 18.4	$ 18.3	$ 36.7	$ 55.0
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	$ 9.11		$ 9.11

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