Reportable Business Segments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Segment Reporting Information [Line Items]
Revenues	$ 846	$ 1,228	$ 2,396	$ 3,323
Segment Reporting Information, Intersegment Revenue	0	0	0	0
Operating Income (Loss)	106	114	335	374
Assets	10,467		10,467		10,687
Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Revenues	360	448	1,209	1,655
Segment Reporting Information, Intersegment Revenue	6	4	11	9
Operating Income (Loss)	9	13	130	155
Assets	4,503		4,503		4,636
Competitive Natural Gas Sales and Services [Member]
Segment Reporting Information [Line Items]
Revenues	302	581	822	1,278
Segment Reporting Information, Intersegment Revenue	6	5	11	14
Operating Income (Loss)	(4)	3	(3)	13
Assets	1,023		1,023		1,089
Interstate Pipelines [Member]
Segment Reporting Information [Line Items]
Revenues	88	111	170	224
Segment Reporting Information, Intersegment Revenue	37	31	82	65
Operating Income (Loss)	52	60	112	136
Assets	3,935		3,935		3,867
Field Services [Member]
Segment Reporting Information [Line Items]
Revenues	96	88	195	166
Segment Reporting Information, Intersegment Revenue	8	10	14	22
Operating Income (Loss)	51	39	98	75
Assets	1,976		1,976		1,894
Other Operations [Member]
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Segment Reporting Information, Intersegment Revenue	0	0	0	0
Operating Income (Loss)	(2)	(1)	(2)	(5)
Assets	363		363		660
Reconciling Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Segment Reporting Information, Intersegment Revenue	(57)	(50)	(118)	(110)
Operating Income (Loss)	0	0	0	0
Assets	$ (1,333)		$ (1,333)		$ (1,459)