Property, Plant and Equipment - Net Changes in Capitalized Exploratory Well Costs (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) Well	Dec. 31, 2014 USD ($) Well	Dec. 31, 2013 USD ($) Well
Capitalized Exploratory Well Costs [Abstract]
Beginning balance	$ 1,416	$ 2,045	$ 2,259
Additions to capitalized exploratory well costs pending the determination of proved reserves	424	292	237
Reclassifications to wells, facilities and equipment based on the determination of proved reserves	(72)	(629)	(106)
Capitalized exploratory well costs charged to expense	(356)	(235)	(267)
Dispositions and other	3	(57)	(78)
Ending balance	$ 1,415	$ 1,416	$ 2,045
Number of wells at end of year | Well	35	37	50