Segment Information (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
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	$ 207	$ 81	$ 411	$ 123
Electric Utility [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	8	9	15	18
Gas Utility [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	1	1	2	1
Gas Storage and Pipelines [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	3	4	4	6
Power and Industrial Projects [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	192	63	383	89
Energy Trading [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	10	15	24	37
Corporate and Other [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	$ (7)	$ (11)	$ (17)	$ (28)