Investment in Unconsolidated Affiliates (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended					9 Months Ended
	Apr. 30, 2014	Sep. 30, 2015		Jun. 30, 2015	Sep. 30, 2014		Sep. 30, 2015		Sep. 30, 2014		Apr. 16, 2014	May. 01, 2013
Distribution Made to Limited Partner, Distributions Declared, Per Unit		$ 0.31800		$ 0.31600
Threshold for Per Unit Incentive Distributions		$ 0.330625					$ 0.330625
Incentive Distribution Percentage Level							50.00%
Equity in earnings of unconsolidated affiliates		$ (71.9)	[1]		$ 44.7	[1]	$ (12.0)	[2]	$ 131.9	[2]
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity		800.0					800.0
Enogex LLC [Member]
Percentage of Enogex LLC Contributed												100.00%
Increase in fair value of net assets		2,200.0					2,200.0
Enable Midstream Partners [Member]
Goodwill, Impairment Loss		1,086.4					1,086.4
Partners' Capital Account, Units, Sold in Public Offering	25,000,000
Distributions from unconsolidated affiliates		$ 35.1			$ 33.6		$ 104.0		$ 110.1
CenterPoint [Member]
Percent of Subordinated Limited Partner Units											61.40%
OGE Holdings [Member]
Percent of Subordinated Limited Partner Units											61.40%
Common Units Held by Limited Partners of the LLC or LP.							42,832,291
Subordinated Units Held by Limited Partners of the LLC or LP.							68,150,514
Percent of Incentive Distribution Rights		60.00%					60.00%
OGE Energy [Member]
Goodwill, Impairment Loss		$ 108.4					$ 108.4
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest							26.30%

[1] The Company recorded a $108.4 million pre-tax charge during the three months ended September 30, 2015 for its share of Enable's goodwill impairment, as adjusted for the basis differences. See Note 3 for further discussion of Enable's goodwill impairment.

[2] The Company recorded a $108.4 million pre-tax charge during the nine months ended September 30, 2015 for its share of Enable's goodwill impairment, as adjusted for the basis differences. See Note 3 of this Form 10-Q for further discussion of Enable's goodwill impairment.