Supplementary Information (Costs Incurred For Oil And Natural Gas Producing Activities) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Disclosure Supplementary Information Costs Incurred For Oil And Natural Gas Producing Activities [Abstract]
Proved	$ 12	$ 4	$ 139	$ 256
Unproved	87	19	393	158
Exploration	238	165	473	336
Development	145	107	303	190
Total costs incurred for oil and natural gas properties	$ 482	$ 295	$ 1,308	$ 940