Property, Plant and Equipment (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Electric [Abstract]
Property Plant and Equipment Accumulated Depreciation Nonutility and Other	$ (659)	$ (688)
Gas [Abstract]
Non-utility and other	1,921	1,884
Total	23,631	22,541
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(8,947)	(8,795)
Net Property, Plant and Equipment	14,684	13,746
Electric Generation [Member]
Electric [Abstract]
Generation	10,383	9,785
Generation	(3,880)	(3,946)
Electric Distribution [Member]
Electric [Abstract]
Distribution	7,306	7,003
Distribution	(2,837)	(2,580)
Electric Generation, Transmission and Distribution Equipment [Member]
Electric [Abstract]
Total Electric	(6,717)	(6,526)
Public Utilities, Property, Plant and Equipment, Plant in Service	17,689	16,788
Gas Distribution [Member]
Electric [Abstract]
Distribution	2,735	2,561
Distribution	(1,075)	(1,041)
Storage [Member]
Gas [Abstract]
Storage	434	406
Storage	(133)	(127)
Other [Member]
Gas [Abstract]
Other	852	902
Other	(363)	(413)
Gas Distribution and Storage [Member]
Electric [Abstract]
Total Electric	(1,571)	(1,581)
Public Utilities, Property, Plant and Equipment, Plant in Service	$ 4,021	$ 3,869