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Regulatory Assets, Liabilities, And Balancing Accounts (Long-Term Regulatory Liabilities) (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2012
Dec. 31, 2011
Regulatory Liabilities [Line Items]    
Total long-term regulatory liabilities $ 4,927 $ 4,733
Cost Of Removal Obligations [Member]
   
Regulatory Liabilities [Line Items]    
Total long-term regulatory liabilities 3,524 3,460
Recoveries In Excess Of AROs [Member]
   
Regulatory Liabilities [Line Items]    
Total long-term regulatory liabilities 707 611
Public Purpose Programs [Member]
   
Regulatory Liabilities [Line Items]    
Total long-term regulatory liabilities 526 499
Other Long-Term Regulatory Liabilities [Member]
   
Regulatory Liabilities [Line Items]    
Total long-term regulatory liabilities $ 170 $ 163