Subsequent Event - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2018	Nov. 08, 2018	Oct. 31, 2018
Subsequent Event [Line Items]
Cost incurred on unsuccessful exploration wells			$ 13
Offshore Suriname
Subsequent Event [Line Items]
Cost incurred on unsuccessful exploration wells		$ 25
Offshore Suriname | Forecast
Subsequent Event [Line Items]
Cost incurred on unsuccessful exploration wells	$ 10
Offshore Nova Scotia, Canada
Subsequent Event [Line Items]
Cost incurred on unsuccessful exploration wells			$ 94
Offshore Nova Scotia, Canada | Forecast
Subsequent Event [Line Items]
Cost incurred on unsuccessful exploration wells	$ 30
Subsequent Event | Offshore Suriname
Subsequent Event [Line Items]
Project interest percentage					33.00%
Subsequent Event | Offshore Nova Scotia, Canada
Subsequent Event [Line Items]
Project interest percentage				50.00%