v3.7.0.1
Derivative Instruments (Detail 3) (Details) - USD ($)
$ in Millions
Mar. 31, 2017
Dec. 31, 2016
Derivative Instruments Subject to Master Netting Arrangement [Line Items]    
Derivative Asset, Fair Value, Gross Asset $ 2,057 $ 2,268
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (1,430) (1,686)
Derivative, Collateral, Obligation to Return Cash [1] (17) (32)
Derivative Liability, Fair Value, Gross Liability (1,823) (2,106)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 1,430 1,686
Derivative, Collateral, Right to Reclaim Cash [1] 97 104
Derivative, Fair Value, Net 234 162
Derivative Fair Value, Amount Not Offset Against Collateral, Net 0 0
Margin/Cash (Received) Posted Subject to Master Netting Arrangement [1] 80 72
Derivative Asset, Fair Value, Amount Offset Against Collateral 610 550
Derivative Liability, Fair Value, Amount Offset Against Collateral (296) (316)
Derivative, Fair Value, Amount Offset Against Collateral, Net 314 234
Commodity Exchange Traded Futures and Swaps Contracts [Member]    
Derivative Instruments Subject to Master Netting Arrangement [Line Items]    
Derivative Asset, Fair Value, Gross Asset 1,259 1,542
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (1,253) (1,521)
Derivative, Collateral, Obligation to Return Cash [1] (6) (21)
Derivative Liability, Fair Value, Gross Liability (1,298) (1,570)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 1,253 1,521
Derivative, Collateral, Right to Reclaim Cash [1] 45 49
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 761 697
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (172) (165)
Derivative, Collateral, Obligation to Return Cash [1] (11) (11)
Derivative Liability, Fair Value, Gross Liability (470) (478)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 172 165
Derivative, Collateral, Right to Reclaim Cash [1] 52 55
Derivative Asset, Fair Value, Amount Offset Against Collateral 578 521
Derivative Liability, Fair Value, Amount Offset Against Collateral (246) (258)
Interest Rate Hedging Instruments    
Derivative Instruments Subject to Master Netting Arrangement [Line Items]    
Derivative Asset, Fair Value, Gross Asset 37 29
Derivative Asset, Fair Value, Amount Not Offset Against Collateral (5) 0
Derivative, Collateral, Obligation to Return Cash [1] 0 0
Derivative Liability, Fair Value, Gross Liability (55) (58)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral 5 0
Derivative, Collateral, Right to Reclaim Cash [1] 0 0
Derivative, Fair Value, Net (18) (29)
Derivative Asset, Fair Value, Amount Offset Against Collateral 32 29
Derivative Liability, Fair Value, Amount Offset Against Collateral $ (50) $ (58)
[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.