Supplemental Oil and Gas Disclosures (Unaudited) - Principal Sources of Change In Discounted Future Net Cash Flows (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Extractive Industries [Abstract]
Sales, net of production costs	$ (3,479)	$ (4,056)	$ (10,350)
Net change in prices and production costs	(3,835)	(21,710)	(1,029)
Discoveries and improved recovery, net of related costs	1,153	1,953	6,297
Change in future development costs	309	705	(1,136)
Previously estimated development costs incurred during the period	986	1,991	4,462
Revision of quantities	(574)	(2,292)	256
Purchases of minerals in-place	8	22	508
Accretion of discount	1,313	3,642	4,442
Change in income taxes	1,070	7,264	836
Sales of properties	(52)	(5,240)	(4,780)
Change in production rates and other	567	(3,343)	(442)
Change in the discounted future net cash flows, Total	$ (2,534)	$ (21,064)	$ (936)