Property, Plant and Equipment (Details Textuals) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Public Utility Property, Plant and Equipment [Line Items]
AFUDC capitalized	$ 20	$ 10
Capitalized Computer Software, Amortization	75	65	65
Capitalized Computer Software, Gross	561	623
Capitalized Computer Software, Accumulated Amortization	295	300
Capitalized Computer Software Future Amortization Expense	46
Capital Leased Assets, Gross	32	57
Capital Leases, Lessee Balance Sheet, Assets by Major Class, Accumulated Depreciation	$ 3	$ 34
Electric [Member]
Public Utility Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	3.30%	3.30%	3.30%
Gas [Member]
Public Utility Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	2.40%	2.30%	2.50%
Minimum [Member]
Public Utility Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Finite-Lived Intangible Assets, Useful Life	3 years
Maximum [Member]
Public Utility Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	55 years
Finite-Lived Intangible Assets, Useful Life	15 years