v3.3.0.814
Derivative Instruments (Detail 5) (Details) - USD ($)
$ in Millions
Sep. 30, 2015
Dec. 31, 2014
Derivative Instruments Subject to Master Netting Arrangement [Line Items]    
Derivative Asset, Fair Value, Gross Asset $ 2,147 $ 2,497
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (1,704) (2,087)
Derivative, Collateral, Obligation to Return Cash [1] (113) (269)
Derivative Liability, Fair Value, Gross Liability (1,835) (2,226)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 1,704 2,087
Derivative, Collateral, Right to Reclaim Cash [1] 13 15
Derivative, Fair Value, Net 312 271
Derivative Fair Value, Amount Not Offset Against Collateral, Net 0 0
Margin/Cash (Received) Posted Subject to Master Netting Arrangement [1] (100) (254)
Derivative Asset, Fair Value, Amount Offset Against Collateral 330 141
Derivative Liability, Fair Value, Amount Offset Against Collateral (118) (124)
Derivative, Fair Value, Amount Offset Against Collateral, Net 212 17
Commodity Exchange Traded Futures and Swaps Contracts [Member]    
Derivative Instruments Subject to Master Netting Arrangement [Line Items]    
Derivative Asset, Fair Value, Gross Asset 1,584 2,134
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (1,473) (1,865)
Derivative, Collateral, Obligation to Return Cash [1] (111) (269)
Derivative Liability, Fair Value, Gross Liability (1,477) (1,870)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 1,473 1,865
Derivative, Collateral, Right to Reclaim Cash [1] 4 5
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 561 359
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (231) (222)
Derivative, Collateral, Obligation to Return Cash [1] (2) 0
Derivative Liability, Fair Value, Gross Liability (248) (242)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 231 222
Derivative, Collateral, Right to Reclaim Cash [1] 9 10
Derivative Asset, Fair Value, Amount Offset Against Collateral 328 137
Derivative Liability, Fair Value, Amount Offset Against Collateral (8) (10)
Interest Rate Swap [Member]    
Derivative Instruments Subject to Master Netting Arrangement [Line Items]    
Derivative Asset, Fair Value, Gross Asset 2 4
Derivative Asset, Fair Value, Amount Not Offset Against Collateral 0 0
Derivative, Collateral, Obligation to Return Cash [1] 0 0
Derivative Liability, Fair Value, Gross Liability (110) (114)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 0 0
Derivative, Collateral, Right to Reclaim Cash [1] 0 0
Derivative, Fair Value, Net (108) (110)
Derivative Asset, Fair Value, Amount Offset Against Collateral 2 4
Derivative Liability, Fair Value, Amount Offset Against Collateral $ (110) $ (114)
[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.