Property, Plant and Equipment (Details Textuals) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 years percent	Dec. 31, 2010	Dec. 31, 2009
Public Utility Property, Plant and Equipment [Line Items]
AFUDC capitalized	$ 10	$ 10
Property, Plant and Equipment, Useful Life, Minimum	3
Property, Plant and Equipment, Useful Life, Maximum	55
Finite-Lived Intangible Assets, Useful Life, Minimum	3
Finite-Lived Intangible Assets, Useful Life, Maximum	20
Capitalized Computer Software, Amortization	65	65	66
Capitalized Computer Software, Gross	623	602
Capitalized Computer Software, Accumulated Amortization	300	252
Capitalized Computer Software Future Amortization Expense	64
Capital Leased Assets, Gross	57	153
Capital Leases, Lessee Balance Sheet, Assets by Major Class, Accumulated Depreciation	$ 34	$ 114
Electric Utility [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 Utility [Member]
Public Utility Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	2.30%	2.50%	3.10%