Asset Retirement Obligation - Asset Retirement Obligation (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Asset Retirement Obligation Disclosure [Abstract]
Asset retirement obligation at beginning of year	$ 2,598	$ 2,952
Liabilities incurred	41	68
Liabilities divested	(7)	(490)
Liabilities settled	(57)	(90)
Accretion expense	156	158
Revisions in estimated liabilities	(233)	0
Asset retirement obligation at end of year	2,498	2,598
Less current portion	(66)	(36)
Asset retirement obligation, long-term	$ 2,432	$ 2,562	[1]

[1] Financial information for 2015 has been recast to reflect retrospective application of the successful efforts method of accounting. See Note 1.