Capitalized Exploratory Well Costs and Undeveloped Leasehold Costs - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Delaware Basin
Projects with Exploratory Well Costs Capitalized for More than One Year Since The Commencement of Drilling [Line Items]
Capitalized undeveloped leasehold cost	$ 2,100
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	100
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	70
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	$ 59