Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	$ 2,225	$ 2,013	$ 4,741	$ 4,252
Electric [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	7	8	13	15
Gas [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	1	1	2	2
Gas Storage and Pipelines [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	2	3	4	4
Power and Industrial Projects [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	185	192	390	383
Energy Trading [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	12	10	23	24
Corporate and Other [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	(7)	(7)	(15)	(17)
Segment Inter Co [Member]
Inter-Segment Revenue [Line Items]
Segment Reporting Information, Intersegment Revenue	$ 200	$ 207	$ 417	$ 411