Segment Information (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	$ 301	$ 219	$ 65
Electric Utility [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	33	30	28
Gas Utility [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	2	0	2
Gas Storage and Pipelines [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	8	4	5
Power and Industrial Projects [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	238	161	11
Energy Trading [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	70	89	93
Corporate and Other [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	$ (50)	$ (65)	$ (74)