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Impairments - Impairments of Unproved Properties (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]
Impairment of unproved properties	$ 1,544	$ 625	$ 682
Onshore Domestic [Member]
Property, Plant, and Equipment [Line Items]
Impairment of unproved properties	721
Gulf Of Mexico [Member]
Property, Plant, and Equipment [Line Items]
Impairment of unproved properties	$ 124

The adjustment to expense previously capitalized costs of drilling exploratory wells when proved reserves are not found or when the entity obtains information that raises substantial doubt about the economic or operational viability of the project.

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