Capitalized Exploratory Well Costs and Undeveloped Leasehold Costs (Details) $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2017 USD ($) MMBoe	Apr. 24, 2017 USD ($)	Dec. 31, 2016 USD ($)
Capitalized Exploratory Well Costs [Roll Forward]
Capitalized Exploratory Well Costs, December 31, 2016	$ 768
Additions to Capitalized Exploratory Well Costs Pending Determination of Proved Reserves	6
Reclassified to Proved Oil and Gas Properties Based on Determination of Proved Reserves	(203)
Capitalized Exploratory Well Costs, June 30, 2017	571
Proved undeveloped reserves (MMBOEs) | MMBoe		551
Exploratory Well Costs Capitalized for a Period of One Year or Less		$ 19		$ 69
Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling		552		699
Balance at End of Period	768	$ 571		$ 768
Capitalized undeveloped leasehold cost	3,100
Onshore US
Capitalized Exploratory Well Costs [Roll Forward]
Capitalized undeveloped leasehold cost	1,200
Eagle Ford
Capitalized Exploratory Well Costs [Roll Forward]
Capitalized undeveloped leasehold cost	185
Other Int'l
Capitalized Exploratory Well Costs [Roll Forward]
Capitalized undeveloped leasehold cost	52
Deepwater Gulf of Mexico
Capitalized Exploratory Well Costs [Roll Forward]
Capitalized undeveloped leasehold cost	86
Gulf of Mexico and Falkland Island
Capitalized Exploratory Well Costs [Roll Forward]
Capitalized undeveloped leasehold cost	$ 18
Clayton Williams Energy
Capitalized Exploratory Well Costs [Roll Forward]
Proved undeveloped reserves (MMBOEs) | MMBoe		69
Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Undeveloped Leaseholds			$ 1,581