Supplemental Oil and Gas Disclosures - Sources of Change in Standardized Measure of Discounted Future Net Cash Flows (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Standardized measure of discounted future net cash flows beginning of period	$ 5,191	$ 3,161	$ 1,038
Sales of oil and gas produced, net of operating costs	(1,515)	(1,541)	(894)
Net change in prices and production costs	(2,247)	2,004	1,385
Extensions, discoveries and improved recovery, less estimated future costs	667	1,341	816
Development costs incurred during year	636	654	345
Changes in estimated future development costs	585	(35)	105
Purchase of reserves in place, less estimated future costs	0	27	305
Sale of reserves in place, loss estimated future costs	(63)	(409)	20
Revisions of previous quantity estimates	85	75	30
Accretion of discount	548	324	104
Net change in income taxes	260	(396)	(83)
Other	(16)	(14)	(10)
Net changes	(1,060)	2,030	2,123
Standardized measure of discounted future net cash flows end of period	$ 4,131	$ 5,191	$ 3,161