Acquisitions and Divestitures - Additional Information - 2013 Activity - Gulf of Mexico Shelf Divestiture (Detail) - USD ($) $ in Millions		12 Months Ended
	Sep. 30, 2013	Dec. 31, 2015	Dec. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proved properties		$ 89,069	$ 89,852
Unproved properties		$ 2,611	$ 7,014
Fieldwood Energy LLC [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of operations	$ 3,700
Liabilities assumed	$ 1,500
Percentage of ownership interest in assets	50.00%
Effective date of the transaction		Jul. 01, 2013
Proved properties	$ 4,600
Unproved properties	$ 473