Impairment Exploration Expenses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Exploration Expenses [Line Items]
Capitalized Exploratory Well Cost, Charged to Expense	$ 35	$ 64	$ 23
Exploration Abandonment and Impairment Expense	255	323	220
Total exploration expenses	289	409	323
Unproved property impairments
Exploration Expenses [Line Items]
Total exploration expenses	208	246	195
Dry well costs
Exploration Expenses [Line Items]
Total exploration expenses	47	77	25
Geological and geophysical
Exploration Expenses [Line Items]
Total exploration expenses	21	25	5
Other
Exploration Expenses [Line Items]
Total exploration expenses	13	61	$ 98
Rodo
Exploration Expenses [Line Items]
Capitalized Exploratory Well Cost, Charged to Expense	32
Rodo | Unproved property impairments
Exploration Expenses [Line Items]
Exploration Abandonment and Impairment Expense	$ 16
Various Projects [Member] | Unproved property impairments
Exploration Expenses [Line Items]
Exploration Abandonment and Impairment Expense		95
Tchicuate | Unproved property impairments
Exploration Expenses [Line Items]
Exploration Abandonment and Impairment Expense		43
Diaba
Exploration Expenses [Line Items]
Capitalized Exploratory Well Cost, Charged to Expense		$ 64