Capitalized Exploratory Well Costs - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($)
Capitalized Exploratory Well Costs [Line Items]
Capitalized exploratory well costs that have been capitalized for period greater than one year	$ 404
Offshore Ghana
Capitalized Exploratory Well Costs [Line Items]
Capitalized well costs percentage	65.00%
Project interest percentage	50.00%
Period to submit plan of development to Ghanaian government	10 months
Northern Portion of Shenzi Field, Gulf of Mexico
Capitalized Exploratory Well Costs [Line Items]
Capitalized well costs percentage	25.00%
Project interest percentage	28.00%
JDA, Gulf of Thailand
Capitalized Exploratory Well Costs [Line Items]
Capitalized well costs percentage	10.00%
Project interest percentage	50.00%