Acquisitions and Divestitures - Divestitures (Detail) (USD $)	9 Months Ended		3 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Mozambique Offshore Area 1 [Member]
Gain (Loss) on Disposition of Assets [Abstract]
Proceeds from divestitures	$ 451,000,000	$ 440,000,000
Net gains on divestitures	165,000,000	(23,000,000)
Property, Plant and Equipment [Line Items]
Expected working interest sold			10.00%
Expected proceeds from divestiture			$ 2,640,000,000