Regulatory Assets, Liabilities, And Balancing Accounts (Long-Term Regulatory Liabilities) (Details) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Regulatory Assets [Line Items]
Long-term regulatory liabilities	$ 4,596	$ 4,525
Cost Of Removal Obligation [Member]
Regulatory Assets [Line Items]
Long-term regulatory liabilities	3,394	3,229
Recoveries In Excess Of ARO [Member]
Regulatory Assets [Line Items]
Long-term regulatory liabilities	559	600
Public Purpose Programs [Member]
Regulatory Assets [Line Items]
Long-term regulatory liabilities	500	573
Other Long-Term Regulatory Liabilities [Member]
Regulatory Assets [Line Items]
Long-term regulatory liabilities	$ 143	$ 123