Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Millions				12 Months Ended
	Jan. 29, 2016	Jan. 28, 2016	Jan. 22, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Subsequent Event [Line Items]
Proceeds from Equity Method Investment, Dividends or Distributions				$ 294.0	$ 305.0	$ 129.0
Dividends paid to parent				43.0	405.0	0.0
Subsequent Event [Member]
Subsequent Event [Line Items]
Dividends paid to parent		$ 363.0
Business Acquisition, Name of Acquired Entity	Continuum Energy Services
Amount to be paid to acquire Continuum	$ 77.5
Enable Midstream Partners [Member]
Subsequent Event [Line Items]
Proceeds from Equity Method Investment, Dividends or Distributions				$ 294.0	$ 298.0	$ 106.0
Enable Midstream Partners [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Dividends Payable, Date Declared			Jan. 22, 2016
Common Stock, Dividends, Per Share, Declared			$ 0.318
Proceeds from Equity Method Investment, Dividends or Distributions			$ 74.0
Series A Preferred Stock [Member] | Enable Midstream Partners [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Number of Series A Preferred Units Purchased		14,520,000
Interest Rate on Series A Preferred Units		10.00%
Purchase Price Per Unit of Series A Preferred		$ 25.00
Enable Midstream Partners [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Amount of Debt Redeemed by Enable		$ 363.0