Capitalized Exploratory Well Costs and Undeveloped Leasehold Costs - Changes in Capitalized Exploratory Well Costs (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Increase (Decrease) in Capitalized Exploratory Well Costs that are Pending Determination of Proved Reserves [Roll Forward]
Capitalized Exploratory Well Costs, Beginning of Period		$ 354	$ 520	$ 768
Additions to Capitalized Exploratory Well Costs Pending Determination of Proved Reserves		26	7	20
Divestitures		0	(168)	0
Reclassified to Proved Oil and Gas Properties, Based on Determination of Proved Reserves, or to Assets Held for Sale		0	(1)	(203)
Capitalized Exploratory Well Costs Charged to Expense	$ (100)	(100)	(4)	(65)
Capitalized Exploratory Well Costs, End of Period	$ 280	$ 280	$ 354	$ 520