Capitalized Exploratory Well Costs and Undeveloped Leasehold Costs - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2018	Sep. 30, 2018
Projects with Exploratory Well Costs Capitalized for More than One Year Since The Commencement of Drilling [Line Items]
Capitalized undeveloped leasehold cost		$ 2,600
Onshore US
Projects with Exploratory Well Costs Capitalized for More than One Year Since The Commencement of Drilling [Line Items]
Capitalized undeveloped leasehold cost		2,400
Eagle Ford
Projects with Exploratory Well Costs Capitalized for More than One Year Since The Commencement of Drilling [Line Items]
Capitalized undeveloped leasehold cost		129
Other Int'l
Projects with Exploratory Well Costs Capitalized for More than One Year Since The Commencement of Drilling [Line Items]
Capitalized undeveloped leasehold cost		53
Held for Sale | Delaware Basin
Projects with Exploratory Well Costs Capitalized for More than One Year Since The Commencement of Drilling [Line Items]
Capitalized undeveloped leasehold cost		259
Held for Sale | Eagle Ford Shale
Projects with Exploratory Well Costs Capitalized for More than One Year Since The Commencement of Drilling [Line Items]
Capitalized undeveloped leasehold cost		$ 20
Held for Sale | Gulf of Mexico
Projects with Exploratory Well Costs Capitalized for More than One Year Since The Commencement of Drilling [Line Items]
Capitalized undeveloped leasehold cost	$ 43
Held for Sale | Other US Onshore Properties
Projects with Exploratory Well Costs Capitalized for More than One Year Since The Commencement of Drilling [Line Items]
Capitalized undeveloped leasehold cost	$ 36