Dispositions - Schedule of Pre-tax Income (Loss) Associated with Interests Excluding Financial Statement Impacts Resulting from Asset Sales (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disposition Of Businesses [Line Items]
Income (Loss) from Continuing Operations Before Income Taxes Excluding Gain / Loss and Impairment	$ (5,778)	$ (3,854)	$ (4,258)
Disposal Group, Disposed of by Sale, Not Discontinued Operations
Disposition Of Businesses [Line Items]
Income (Loss) from Continuing Operations Before Income Taxes Excluding Gain / Loss and Impairment	14	(290)	(299)
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Equatorial Guinea
Disposition Of Businesses [Line Items]
Income (Loss) from Continuing Operations Before Income Taxes Excluding Gain / Loss and Impairment	69	(95)	(23)
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Norway
Disposition Of Businesses [Line Items]
Income (Loss) from Continuing Operations Before Income Taxes Excluding Gain / Loss and Impairment	$ (55)	$ (195)	$ (276)