Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	$ 234	$ 44	$ 645	$ 167
Electric Utility [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	7	7	22	25
Gas Utility [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	1	1	3	2
Gas Storage and Pipelines [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	1	1	5	7
Unconventional Gas Production [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	1	0	1	0
Power and Industrial Projects [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	225	30	608	119
Energy Trading [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	10	17	34	54
Corporate and Other [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	$ (11)	$ (12)	$ (28)	$ (40)