Organization, Basis of Presentation and Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Regulatory assets on the Balance Sheets
Regulatory Assets	$ 2,375	$ 2,030
Increase (Decrease) in Regulatory Assets	345
Regulatory transition costs
Regulatory assets on the Balance Sheets
Regulatory Assets	281	309
Increase (Decrease) in Regulatory Assets	(28)
Customer receivables for future income taxes
Regulatory assets on the Balance Sheets
Regulatory Assets	508	519
Increase (Decrease) in Regulatory Assets	(11)
Nuclear decommissioning and spent fuel disposal costs
Regulatory assets on the Balance Sheets
Regulatory Assets	(219)	(210)
Increase (Decrease) in Regulatory Assets	(9)
Asset removal costs
Regulatory assets on the Balance Sheets
Regulatory Assets	(372)	(347)
Increase (Decrease) in Regulatory Assets	(25)
Deferred transmission costs
Regulatory assets on the Balance Sheets
Regulatory Assets	390	340
Increase (Decrease) in Regulatory Assets	50
Deferred generation costs
Regulatory assets on the Balance Sheets
Regulatory Assets	379	400
Increase (Decrease) in Regulatory Assets	(21)
Deferred distribution costs
Regulatory assets on the Balance Sheets
Regulatory Assets	231	267
Increase (Decrease) in Regulatory Assets	(36)
Contract valuations
Regulatory assets on the Balance Sheets
Regulatory Assets	463	299
Increase (Decrease) in Regulatory Assets	164
Storm-related costs
Regulatory assets on the Balance Sheets
Regulatory Assets	509	144
Increase (Decrease) in Regulatory Assets	365
Other
Regulatory assets on the Balance Sheets
Regulatory Assets	205	309
Increase (Decrease) in Regulatory Assets	$ (104)