Derivative Instruments (Detail 5) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 550		$ 437
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(480)		(396)
Derivative, Collateral, Obligation to Return Cash	14	[1]	7	[1]
Derivative Asset, Fair Value, Amount Offset Against Collateral	56		34
Derivative Liability, Fair Value, Gross Liability	694		650
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	480		396
Derivative, Collateral, Right to Reclaim Cash	76	[1]	46	[1]
Derivative Liability, Fair Value, Amount Offset Against Collateral	138		208
Derivative, Fair Value, Net	(144)		(213)
Derivative Fair Value, Amount Not Offset Against Collateral, Net	0		0
Derivative, Collateral, Right to Reclaim Cash, Net	62	[1]	39	[1]
Derivative, Fair Value, Amount Offset Against Collateral, Net	(82)		(174)
Commodity Option [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	541		433
Derivative Liability, Fair Value, Gross Liability	565		450
Derivative, Fair Value, Net	(24)		(17)
Commodity Exchange Traded Futures and Swaps Contracts [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	434		385
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(420)		(379)
Derivative, Collateral, Obligation to Return Cash	14	[1]	6	[1]
Derivative Asset, Fair Value, Amount Offset Against Collateral	0		0
Derivative Liability, Fair Value, Gross Liability	495		424
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	420		379
Derivative, Collateral, Right to Reclaim Cash	75	[1]	45	[1]
Derivative Liability, Fair Value, Amount Offset Against Collateral	0		0
Commodity Forward Contract [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	107		48
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(60)		(17)
Derivative, Collateral, Obligation to Return Cash	0	[1]	1	[1]
Derivative Asset, Fair Value, Amount Offset Against Collateral	47		30
Derivative Liability, Fair Value, Gross Liability	70		26
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	60		17
Derivative, Collateral, Right to Reclaim Cash	1	[1]	1	[1]
Derivative Liability, Fair Value, Amount Offset Against Collateral	9		8
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	9		4
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0		0
Derivative, Collateral, Obligation to Return Cash	0	[1]	0	[1]
Derivative Asset, Fair Value, Amount Offset Against Collateral	9		4
Derivative Liability, Fair Value, Gross Liability	129		200
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0		0
Derivative, Collateral, Right to Reclaim Cash	0	[1]	0	[1]
Derivative Liability, Fair Value, Amount Offset Against Collateral	129		200
Derivative, Fair Value, Net	$ (120)		$ (196)

[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 9 for a further discussion of our collateral.