Reportable Business Segments (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenues from External Customers		$ 1,251	$ 978	$ 4,731	$ 3,105
Operating Income (Loss)		26	26	273	210
Total Assets		9,376		9,376		$ 9,218
Equity in earnings of unconsolidated affiliate, net		68	73	199	164
Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Revenues from External Customers		390	370	1,767	1,672
Operating Income (Loss)		19	22	220	202
Energy Services [Member]
Segment Reporting Information [Line Items]
Revenues from External Customers		861	608	2,964	1,433
Operating Income (Loss)		7	5	58	11
Midstream Investments [Member]
Segment Reporting Information [Line Items]
Revenues from External Customers	[1]	0	0	0	0
Operating Income (Loss)	[1]	0	0	0	0
Other Operations [Member]
Segment Reporting Information [Line Items]
Revenues from External Customers		0	0	0	0
Operating Income (Loss)		0	(1)	(5)	(3)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues from External Customers		(18)	(13)	(58)	(38)
Total Assets		(582)		(582)		(563)
Intersegment Eliminations [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Revenues from External Customers		(8)	(7)	(24)	(21)
Intersegment Eliminations [Member] | Energy Services [Member]
Segment Reporting Information [Line Items]
Revenues from External Customers		(10)	(6)	(34)	(17)
Intersegment Eliminations [Member] | Midstream Investments [Member]
Segment Reporting Information [Line Items]
Revenues from External Customers	[1]	0	0	0	0
Intersegment Eliminations [Member] | Other Operations [Member]
Segment Reporting Information [Line Items]
Revenues from External Customers		0	0	0	0
Operating Segments [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Total Assets		6,067		6,067		6,099
Operating Segments [Member] | Energy Services [Member]
Segment Reporting Information [Line Items]
Total Assets		1,337		1,337		1,102
Operating Segments [Member] | Midstream Investments [Member]
Segment Reporting Information [Line Items]
Total Assets	[1]	2,481		2,481		2,505
Operating Segments [Member] | Other Operations [Member]
Segment Reporting Information [Line Items]
Total Assets		73		73		$ 75
Enable Midstream Partners [Member]
Segment Reporting Information [Line Items]
Equity in earnings of unconsolidated affiliate, net		68	73	199	164
Enable Midstream Partners [Member] | Midstream Investments [Member]
Segment Reporting Information [Line Items]
Equity in earnings of unconsolidated affiliate, net		$ 68	$ 73	$ 199	$ 164

[1] Midstream Investments’ equity earnings are as follows: Three Months Ended September 30, Nine Months Ended September 30, 2017 2016 2017 2016 (in millions)Enable $68 $73 $199 $164