Capitalized Exploratory Well Costs and Undeveloped Leasehold Costs - Aging of Capitalized Exploratory Well Costs (Details) $ in Millions	Jun. 30, 2020 USD ($) project	Dec. 31, 2019 USD ($) project
Extractive Industries [Abstract]
Exploratory Well Costs Capitalized for a Period of One Year or Less	$ 30	$ 22
Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling	214	258
Capitalized Exploratory Well Costs, End of Period	$ 244	$ 280
Number of Projects with Exploratory Well Costs That Have Been Capitalized for a Period Greater Than One Year Since Commencement of Drilling | project	4	5