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Business Segment Information - Financial Segment Information (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Segment Reporting [Abstract]
Write-down of oil and gas properties	$ 65	$ 521

The expense recorded to reduce the value of oil and gas assets consisting of proved properties and unproved properties as the estimate of future successful production from these properties is reduced.

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