Capitalized Exploratory Well Costs and Undeveloped Leasehold Costs - Rollforward of Undeveloped Leasehold Costs (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($)
Proved Developed and Undeveloped Reserves [Roll Forward]
Undeveloped Leasehold Costs, Beginning of Period	$ 2,306
Additions to Undeveloped Leasehold Costs	50
Transfers to Proved Properties	(11)
Assets Sold	(2)
Undeveloped Leasehold Costs, End of Period	$ 2,343