Investment in Unconsolidated Affiliates (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020		Sep. 30, 2019	Dec. 31, 2019
Expected Settlement Charge			$ 15.3
Limited Partner Units Owned	111.0		111.0
Distribution Made to Limited Partner, Distributions Declared, Per Unit			$ 0.16525		$ 0.33050
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	$ 15.8	$ 38.3	$ (703.8)	[1]	$ 104.8
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	1,346.4		1,346.4			$ 652.5
Enable Midstream Partners [Member]
Distributions from unconsolidated affiliates	$ 18.3	$ 36.7	$ 73.3		$ 107.3
OGE Holdings [Member]
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest			25.50%
Enable Midstream Partners [Member]
Share Price	$ 4.14		$ 4.14

[1] In March 2020, the Company recorded a $780.0 million impairment on its investment in Enable, as further discussed in Notes 4 and 5.