Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Significant Accounting Policies [Line Items]
Number of consolidated variable interest entities	5
Amount of removal costs recognized as a component of depreciation expense recorded as a regulatory liability	$ 346	$ 339
Amortization Period, Transition Property (in years)	12 to 14 years
Amount of capitalized interest and allowance for funds used during construction	6	4	3
Allowance for doubtful accounts	2	1
Provision for doubtful accounts	2	2	1
Restricted cash accounts	54	42
Amount of cash and cash equivalents that is held by transition and system restoration bond subsidiaries solely to support servicing the transition and system restoration bonds	266	220
Customer deposits included in other current liabilities	$ 27	$ 23