Segment Information (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	$ 848	$ 301	$ 219
Electric [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	29	33	30
Gas [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	4	2	0
Gas Storage and Pipelines [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	6	8	4
Power and Industrial Projects [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	801	238	161
Energy Trading [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	43	70	89
Corporate and Other [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	(37)	(50)	(65)
Segment, Discontinued Operations [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	$ 2	$ 0	$ 0