Investment in Unconsolidated Affiliates (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Apr. 30, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	May 13, 2014	May 01, 2013
Limited Partner Units Owned		111,000,000		111,000,000
Distribution Made to Limited Partner, Distributions Declared, Per Unit				$ 0.31800
Equity in earnings of unconsolidated affiliates		$ 34.5	$ (71.9)	$ 79.5	$ (12.0)
percentage of subsidiary contributed							24.95%
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity		761.5		761.5		$ 783.5
Enogex LLC [Member]
Percentage of Enogex LLC Contributed								100.00%
Increase in fair value of net assets								$ 2,200.0
Enable Midstream Partners [Member]
Goodwill, Impairment Loss						$ 1,086.4
Partners' Capital Account, Units, Sold in Public Offering	25,000,000
Distributions from unconsolidated affiliates		$ 35.3	$ 35.1	$ 105.9	$ 104.0
CenterPoint [Member]
Percent of Incentive Distribution Rights		40.00%		40.00%
OGE Holdings [Member]
Subordinated Units Held by Limited Partners of the LLC or LP.				68,200,000
Percent of Incentive Distribution Rights		60.00%		60.00%
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest		26.30%	26.30%	26.30%	26.30%
OGE Energy [Member]
Goodwill, Impairment Loss		$ 0.0	$ (177.7)	$ 0.6	$ (177.7)