Fair Value Measurement Information for Financial Assets or liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	$ 6
Total Derivatives	(1,112)	(1,719)
Fair Value Assets And Liabilities Measured On Recurring Basis	(1,078)	(1,686)
Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	24	34
Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assets Measured On Recurring Basis Other Assets	87	61
Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Obligations, Fair Value Disclosure	(83)	(62)
Commodity derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives assets	144	55
Derivative Liabilities	(1,178)	(1,694)
Interest rate derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives liabilities	(41)	(42)
Foreign currency derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contracts, Liability, Fair Value Disclosure	(37)	(38)
Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	6
Total Derivatives	0	0
Fair Value Assets And Liabilities Measured On Recurring Basis	34	33
Quoted Prices in Active Markets (Level 1) | Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	24	34
Quoted Prices in Active Markets (Level 1) | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assets Measured On Recurring Basis Other Assets	87	61
Quoted Prices in Active Markets (Level 1) | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Obligations, Fair Value Disclosure	(83)	(62)
Quoted Prices in Active Markets (Level 1) | Commodity derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives assets	0	0
Derivative Liabilities	0	0
Quoted Prices in Active Markets (Level 1) | Interest rate derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives liabilities	0	0
Quoted Prices in Active Markets (Level 1) | Foreign currency derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contracts, Liability, Fair Value Disclosure	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	0
Total Derivatives	(37)	(65)
Fair Value Assets And Liabilities Measured On Recurring Basis	(37)	(65)
Significant Other Observable Inputs (Level 2) | Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Significant Other Observable Inputs (Level 2) | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assets Measured On Recurring Basis Other Assets	0	0
Significant Other Observable Inputs (Level 2) | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Obligations, Fair Value Disclosure	0	0
Significant Other Observable Inputs (Level 2) | Commodity derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives assets	112	46
Derivative Liabilities	(73)	(31)
Significant Other Observable Inputs (Level 2) | Interest rate derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives liabilities	(39)	(42)
Significant Other Observable Inputs (Level 2) | Foreign currency derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contracts, Liability, Fair Value Disclosure	(37)	(38)
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	0
Total Derivatives	(1,075)	(1,654)
Fair Value Assets And Liabilities Measured On Recurring Basis	(1,075)	(1,654)
Significant Unobservable Inputs (Level 3) | Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Significant Unobservable Inputs (Level 3) | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assets Measured On Recurring Basis Other Assets	0	0
Significant Unobservable Inputs (Level 3) | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Obligations, Fair Value Disclosure	0	0
Significant Unobservable Inputs (Level 3) | Commodity derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives assets	32	9
Derivative Liabilities	(1,105)	(1,663)
Significant Unobservable Inputs (Level 3) | Interest rate derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives liabilities	(2)	0
Significant Unobservable Inputs (Level 3) | Foreign currency derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contracts, Liability, Fair Value Disclosure	$ 0	$ 0