v2.4.0.8
Derivative Instruments (Detail 5) (Details) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2014
Dec. 31, 2013
Derivative Instruments Subject to Master Netting Arrangement [Line Items]    
Derivative Asset, Fair Value, Gross Asset $ 844 $ 550
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (696) (480)
Derivative, Collateral, Obligation to Return Cash (76) [1] (14) [1]
Derivative Liability, Fair Value, Gross Liability (829) (694)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 696 480
Derivative, Collateral, Right to Reclaim Cash 8 [1] 76 [1]
Derivative, Fair Value, Net 15 (144)
Derivative Fair Value, Amount Not Offset Against Collateral, Net 0 0
Margin/Cash (Received) Posted Subject to Master Netting Arrangement (68) [1] 62 [1]
Derivative Asset, Fair Value, Amount Offset Against Collateral 72 56
Derivative Liability, Fair Value, Amount Offset Against Collateral (125) (138)
Derivative, Fair Value, Amount Offset Against Collateral, Net (53) (82)
Commodity Exchange Traded Futures and Swaps Contracts [Member]
    
Derivative Instruments Subject to Master Netting Arrangement [Line Items]    
Derivative Asset, Fair Value, Gross Asset 649 434
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (575) (420)
Derivative, Collateral, Obligation to Return Cash (74) [1] (14) [1]
Derivative Liability, Fair Value, Gross Liability (575) (495)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 575 420
Derivative, Collateral, Right to Reclaim Cash 0 [1] 75 [1]
Derivative Asset, Fair Value, Amount Offset Against Collateral 0 0
Derivative Liability, Fair Value, Amount Offset Against Collateral 0 0
Commodity Forward Contract [Member]
    
Derivative Instruments Subject to Master Netting Arrangement [Line Items]    
Derivative Asset, Fair Value, Gross Asset 190 107
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (121) (60)
Derivative, Collateral, Obligation to Return Cash (2) [1] 0 [1]
Derivative Liability, Fair Value, Gross Liability (141) (70)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 121 60
Derivative, Collateral, Right to Reclaim Cash 8 [1] 1 [1]
Derivative Asset, Fair Value, Amount Offset Against Collateral 67 47
Derivative Liability, Fair Value, Amount Offset Against Collateral (12) (9)
Interest Rate Swap [Member]
    
Derivative Instruments Subject to Master Netting Arrangement [Line Items]    
Derivative Asset, Fair Value, Gross Asset 5 9
Derivative Asset, Fair Value, Amount Not Offset Against Collateral 0 0
Derivative, Collateral, Obligation to Return Cash 0 [1] 0 [1]
Derivative Liability, Fair Value, Gross Liability (113) (129)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 0 0
Derivative, Collateral, Right to Reclaim Cash 0 [1] 0 [1]
Derivative, Fair Value, Net (108) (120)
Derivative Asset, Fair Value, Amount Offset Against Collateral 5 9
Derivative Liability, Fair Value, Amount Offset Against Collateral $ (113) $ (129)
[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 and natural gas and power prepayments posted by us with our counterparties related to our derivative activities that are subject to a master netting arrangement. See Note 7 for a further discussion of our collateral.