Divestitures and Assets Held for Sale (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property, Plant, and Equipment [Line Items]
Proceeds from divestitures	$ 657	$ 555	$ 70
Net gains (losses) on divestitures	(71)	22	29
Net properties and equipment associated with assets held for sale		320
Goodwill and other intangible assets associated with assets held for sale		38
Other long-term liabilities associated with assets held for sale		75
Remaining balance of assets associated with assets held for sale
Oil and Gas Exploration and Production Reporting Segment [Member] | Fair Value, Inputs, Level 3 [Member]
Property, Plant, and Equipment [Line Items]
Losses on assets held for sale		390
Midstream Reporting Segment [Member] | Fair Value, Inputs, Level 3 [Member]
Property, Plant, and Equipment [Line Items]
Losses on assets held for sale		32
Assets Held For Use [Member]
Property, Plant, and Equipment [Line Items]
Proceeds from divestitures	433
Net gains (losses) on divestitures	(43)
Assets Held For Use [Member] | Peregrino Field [Member]
Property, Plant, and Equipment [Line Items]
Proceeds from divestitures		419
Assets Held For Sale [Member] | Oil and Gas Exploration and Production Reporting Segment [Member]
Property, Plant, and Equipment [Line Items]
Losses on assets held for sale	$ 28