Suspended Exploratory Well Costs - Aging of Suspended Well Balances (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Exploratory Well Costs Associated with Wells Suspended for a Period Greater Than One Year [Abstract]
Exploratory well costs capitalized for a period of one year or less	$ 452	$ 393	$ 836
Exploratory well costs capitalized for a period greater than one year	672	1,129	1,396
Balance at December 31	$ 1,124	$ 1,522	$ 2,232	$ 2,062