Investment in Unconsolidated Affiliates (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	May 01, 2013
Expected Settlement Charge			$ 14.5
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	$ 33.6	$ 34.5	$ 98.6	$ 79.5
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	721.4		721.4		$ 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	$ 105.9	$ 105.9
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%