Capitalized Exploratory Well Costs and Undeveloped Leasehold Costs - Rollforward of Undeveloped Lease Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Proved Developed and Undeveloped Reserves [Roll Forward]
Undeveloped Leasehold Costs, Beginning of Period	$ 2,373	$ 2,922
Additions to Undeveloped Leasehold Costs	59	47
Transfers to Proved Properties	(184)	(453)
Assets Sold	(96)	(142)
Impairment	0	(1)
Undeveloped Leasehold Costs, End of Period	$ 2,152	$ 2,373