Investment in Unconsolidated Affiliates (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	May 01, 2013
Expected Settlement Charge			$ 20.2
Limited Partner Units Owned	111.0		111.0
Distribution Made to Limited Partner, Distributions Declared, Per Unit	$ 0.31800
Equity in earnings of unconsolidated affiliates	$ 29.4	$ 16.7	$ 65.0	$ 45.0
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	729.4		729.4		$ 743.7
Enogex LLC [Member]
Percentage of Enogex LLC Contributed						100.00%
Increase in fair value of net assets						$ 2,200.0
Enable Midstream Partners [Member]
Distributions from unconsolidated affiliates	$ 35.3	$ 35.3	$ 70.6	$ 70.6
OGE Holdings [Member]
Subordinated Units Held by Limited Partners of the LLC or LP.			68.2
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest	25.70%	26.30%	25.70%	26.30%