Regulatory Assets, Liabilities, And Balancing Accounts (Long-Term Regulatory Liabilities) (Details) - Entity [Domain] - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	$ 6,330	$ 6,290
Cost Of Removal Obligations [Member]
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	4,414	4,211
Recoveries In Excess Of AROs [Member]
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	719	754
Public Purpose Programs [Member]
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	708	701
Other Long Term Regulatory Assets (Liabilities) [Member]
Regulatory Liabilities [Line Items]
Total long-term regulatory liabilities	$ 489	$ 624