v2.4.0.8
Derivative Instruments (Detail 5) (Details) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2013
Dec. 31, 2012
Derivative Instruments Subject to Master Netting Arrangement [Line Items]    
Derivative, Fair Value, Gross Amount Not Offset Against Collateral, Net $ (186) $ (213)
Derivative Fair Value, Amount Not Offset Against Collateral, Net 0 0
Derivative Asset, Fair Value, Amount Offset Against Collateral 41 34
Derivative Asset, Fair Value, Gross Asset 619 437
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (527) (396)
Derivative Liability, Fair Value, Gross Liability (805) (650)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 527 396
Margin/Cash (Received) Posted Subject to Master Netting Arrangement 62 [1] 39 [1]
Derivative Liability, Fair Value, Amount Offset Against Collateral (165) (208)
Derivative, Fair Value, Amount Offset Against Collateral, Net (124) (174)
Derivative, Collateral, Right to Reclaim Cash 113 [1] 46 [1]
Derivative, Collateral, Obligation to Return Cash (51) [1] (7) [1]
Commodity Exchange Traded Futures and Swaps Contracts [Member]
    
Derivative Instruments Subject to Master Netting Arrangement [Line Items]    
Derivative Asset, Fair Value, Amount Offset Against Collateral 0 0
Derivative Asset, Fair Value, Gross Asset 505 385
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (454) (379)
Derivative Liability, Fair Value, Gross Liability (566) (424)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 454 379
Derivative Liability, Fair Value, Amount Offset Against Collateral 0 0
Derivative, Collateral, Right to Reclaim Cash 112 [1] 45 [1]
Derivative, Collateral, Obligation to Return Cash (51) [1] (6) [1]
Commodity Forward Contract [Member]
    
Derivative Instruments Subject to Master Netting Arrangement [Line Items]    
Derivative Asset, Fair Value, Amount Offset Against Collateral 33 30
Derivative Asset, Fair Value, Gross Asset 106 48
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (73) (17)
Derivative Liability, Fair Value, Gross Liability (95) (26)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 73 17
Derivative Liability, Fair Value, Amount Offset Against Collateral (21) (8)
Derivative, Collateral, Right to Reclaim Cash 1 [1] 1 [1]
Derivative, Collateral, Obligation to Return Cash 0 [1] (1) [1]
Interest Rate Swap [Member]
    
Derivative Instruments Subject to Master Netting Arrangement [Line Items]    
Derivative, Fair Value, Gross Amount Not Offset Against Collateral, Net (136) (196)
Derivative Asset, Fair Value, Amount Offset Against Collateral 8 4
Derivative Asset, Fair Value, Gross Asset 8 4
Derivative Asset, Fair Value, Amount Not Offset Against Collateral 0 0
Derivative Liability, Fair Value, Gross Liability (144) (200)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 0 0
Derivative Liability, Fair Value, Amount Offset Against Collateral (144) (200)
Derivative, Collateral, Right to Reclaim Cash 0 [1] 0 [1]
Derivative, Collateral, Obligation to Return Cash $ 0 [1] $ 0 [1]
[1] Negative balances represent margin deposits posted with us by our counterparties related to our derivative activities that are subject to a master netting arrangement. Positive balances reflect margin deposits posted by us with our counterparties related to our derivative activities that are subject to a master netting arrangement. See Note 6 for a further discussion of our collateral.