Segment Information (Details 1) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Segment Reporting Information [Line Items]
Operating Revenue	$ 2,225	$ 2,013	$ 4,741	$ 4,252
Net Income (Loss) Attributable to Parent	105	146	339	302
Electric [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1,265	1,290	2,484	2,488
Net Income (Loss) Attributable to Parent	89	127	204	223
Gas [Member]
Segment Reporting Information [Line Items]
Operating Revenue	248	214	852	723
Net Income (Loss) Attributable to Parent	8	4	104	56
Gas Storage and Pipelines [Member]
Segment Reporting Information [Line Items]
Operating Revenue	31	27	58	52
Net Income (Loss) Attributable to Parent	16	17	33	34
Power and Industrial Projects [Member]
Segment Reporting Information [Line Items]
Operating Revenue	429	449	919	898
Net Income (Loss) Attributable to Parent	7	10	19	18
Energy Trading [Member]
Segment Reporting Information [Line Items]
Operating Revenue	451	239	844	500
Net Income (Loss) Attributable to Parent	(2)	4	5	2
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1	1	1	2
Net Income (Loss) Attributable to Parent	(13)	(15)	(26)	(30)
Corporate Elimination [Member]
Segment Reporting Information [Line Items]
Operating Revenue	(200)	(207)	(417)	(411)
Segment, Discontinued Operations [Member]
Segment Reporting Information [Line Items]
Net Income (Loss) Attributable to Parent	$ 0	$ (1)	$ 0	$ (1)