Segment Information - Operating Revenues (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating revenues	$ 571	$ 674	$ 1,905	$ 2,395
Less gross gas costs	191	222	769	1,157
Operating Segments [Member] \| Wholesale Services [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating revenues	(95)	4	(32)	94
Less gross gas costs	1	0	4	9
Third Party Gross Revenues [Member] \| Operating Segments [Member] \| Wholesale Services [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating revenues	1,061	1,291	2,500	3,436
Intercompany Revenues [Member] \| Operating Segments [Member] \| Wholesale Services [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating revenues	58	89	143	239
Total Gross Revenues [Member] \| Operating Segments [Member] \| Wholesale Services [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating revenues	1,119	1,380	2,643	3,675
Third Party Gross Costs [Member] \| Operating Segments [Member] \| Wholesale Services [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Less gross gas costs	$ 1,214	$ 1,376	$ 2,675	$ 3,581

The aggregate cost of goods produced and sold and services rendered during the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.2)
-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

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+ References

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