Schedule of Derivative Instruments in Condensed Consolidated Balance Sheets (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Liability Derivatives:
Total derivative instruments	$ (1,112)	$ (1,719)
Designated as Hedging Instrument
Asset Derivatives:
Asset commodity contracts	144	55
Liability Derivatives:
Liability commodity contracts	(37)	(38)
Designated as Hedging Instrument | Commodity contracts | Short-term derivative instruments
Asset Derivatives:
Asset commodity contracts	108	54
Designated as Hedging Instrument | Commodity contracts | Long-term derivative instruments
Asset Derivatives:
Asset commodity contracts	36	1
Designated as Hedging Instrument | Foreign currency contracts | Long-term derivative instruments
Liability Derivatives:
Liability commodity contracts	(37)	(38)
Not designated as hedging instruments
Liability Derivatives:
Liability commodity contracts	(1,219)	(1,736)
Not designated as hedging instruments | Commodity contracts | Short-term derivative instruments
Liability Derivatives:
Liability commodity contracts	(225)	(232)
Not designated as hedging instruments | Commodity contracts | Long-term derivative instruments
Liability Derivatives:
Liability commodity contracts	(953)	(1,462)
Not designated as hedging instruments | Interest rate contracts | Short-term derivative instruments
Liability Derivatives:
Liability commodity contracts	(2)	0
Not designated as hedging instruments | Interest rate contracts | Long-term derivative instruments
Liability Derivatives:
Liability commodity contracts	$ (39)	$ (42)