v3.6.0.2
Derivative Instruments (Detail 5) (Details) - USD ($)
$ in Millions
Dec. 31, 2016
Dec. 31, 2015
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset $ 2,268 $ 2,011
Derivative Asset, Not Offset, Policy Election Deduction (1,686) (1,804)
Derivative, Collateral, Obligation to Return Cash [1] (32) (137)
Derivative Asset, Fair Value, Amount Offset Against Collateral 550 70
Derivative Liability, Fair Value, Gross Liability (2,106) (2,207)
Derivative Liability, Not Offset, Policy Election Deduction 1,686 1,804
Derivative, Collateral, Right to Reclaim Cash [1] 104 5
Derivative Liability, Fair Value, Amount Offset Against Collateral (316) (398)
Net derivative assets (liabilities) 162 (196)
Derivative Fair Value, Amount Not Offset Against Collateral, Net 0 0
Derivative, Collateral, Right to Reclaim Cash, Net [1] 72 (132)
Derivative, Fair Value, Amount Offset Against Collateral, Net 234 (328)
Commodity Exchange Traded Futures and Swaps Contracts [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 1,542 1,736
Derivative Asset, Not Offset, Policy Election Deduction (1,521) (1,602)
Derivative, Collateral, Obligation to Return Cash [1] (21) (134)
Derivative Asset, Fair Value, Amount Offset Against Collateral 0 0
Derivative Liability, Fair Value, Gross Liability (1,570) (1,604)
Derivative Liability, Not Offset, Policy Election Deduction 1,521 1,602
Derivative, Collateral, Right to Reclaim Cash [1] 49 2
Derivative Liability, Fair Value, Amount Offset Against Collateral 0 0
Commodity Forward Contract [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 697 274
Derivative Asset, Not Offset, Policy Election Deduction (165) (202)
Derivative, Collateral, Obligation to Return Cash [1] (11) (3)
Derivative Asset, Fair Value, Amount Offset Against Collateral 521 69
Derivative Liability, Fair Value, Gross Liability (478) (513)
Derivative Liability, Not Offset, Policy Election Deduction 165 202
Derivative, Collateral, Right to Reclaim Cash [1] 55 3
Derivative Liability, Fair Value, Amount Offset Against Collateral (258) (308)
Interest Rate Contract [Member]    
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 29 1
Derivative Asset, Not Offset, Policy Election Deduction 0 0
Derivative, Collateral, Obligation to Return Cash [1] 0 0
Derivative Asset, Fair Value, Amount Offset Against Collateral 29 1
Derivative Liability, Fair Value, Gross Liability (58) (90)
Derivative Liability, Not Offset, Policy Election Deduction 0 0
Derivative, Collateral, Right to Reclaim Cash [1] 0 0
Derivative Liability, Fair Value, Amount Offset Against Collateral (58) (90)
Net derivative assets (liabilities) $ (29) $ (89)
[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 9 for a further discussion of our collateral.