Impairments and Exploration Expense - Exploration Expenses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Exploration Expenses [Line Items]
Exploration Expense	$ 294	$ 83	$ 352	$ 289
Exploration Abandonment and Impairment Expense			294	196
Diaba [Member]
Exploration Expenses [Line Items]
Capitalized Exploratory Well Cost, Charged to Expense			64
Unproved Property Impairments [Member]
Exploration Expenses [Line Items]
Exploration Expense	172	28	217	172
Unproved Property Impairments [Member] | Diaba [Member]
Exploration Expenses [Line Items]
Exploration Expense			159
Exploration Abandonment and Impairment Expense			95
Unproved Property Impairments [Member] | Tchicuate [Member]
Exploration Expenses [Line Items]
Exploration Abandonment and Impairment Expense			43
Unproved Property Impairments [Member] | Gulf of Mexico Assets [Member]
Exploration Expenses [Line Items]
Exploration Expense				118
Dry Well Costs [Member]
Exploration Expenses [Line Items]
Exploration Expense	77	9	77	24
Geological and Geophysical [Member]
Exploration Expenses [Line Items]
Exploration Expense	2	1	3	1
Other Exploration Expenses [Member]
Exploration Expenses [Line Items]
Exploration Expense	$ 43	$ 45	$ 55	$ 92