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Impairments - Impairments of Unproved Properties (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended		3 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Jun. 30, 2012 U.S. onshore [Member]	Jun. 30, 2012 Gulf Of Mexico [Member]
Property, Plant, and Equipment [Line Items]
Impairment of unproved properties	$ 1,389	$ 423	$ 720	$ 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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