Basis of Presentation - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Reclassification of expense from Operating costs and expenses, Exploration expenses, and General and administrative expenses to Other, net due to adopting ASU 2017-07		$ 7		$ 9
Cumulative effect of hedging ineffectiveness					$ 0	$ (37)
Prior Period Adjustment [Abstract]
Sales and other operating revenue	$ 1,534	1,197	$ 2,880	2,455
Marketing, including purchased oil and gas	450	253	808	453
Restatement Adjustment
Prior Period Adjustment [Abstract]
Sales and other operating revenue		(19)		(38)
Marketing, including purchased oil and gas		(19)		(38)
Scenario Previously Reported
Prior Period Adjustment [Abstract]
Sales and other operating revenue		1,216		2,493
Marketing, including purchased oil and gas		$ 272		$ 491
Retained Earnings
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Cumulative effect of hedging ineffectiveness					1	(39)
Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Cumulative effect of hedging ineffectiveness					$ (1)	$ 0
ASU 2017-12 | Retained Earnings
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Cumulative effect of hedging ineffectiveness	1		1
ASU 2017-12 | Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Cumulative effect of hedging ineffectiveness	$ (1)		$ (1)