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Fair Value Disclosures (Reconciliations Of Fair Value Measurements Using Significant Unobservable Inputs (Level 3)) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Natural Gas [Member]
   
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning balance as of January 1 $ (17) $ (23)
Included in regulatory assets (3) (1)
Settlements 6 5
Ending balance as of March 31 (14) (19)
Life Insurance Contracts [Member]
   
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning balance as of January 1 17 19
Included in income 1 3
Issuances   (1)
Settlements   (4)
Ending balance as of March 31 $ 18 $ 17