Dispositions - Schedule of Pre-tax Income (Loss) Associated with Interests Excluding Financial Statement Impacts Resulting from Asset Sales (Parenthetical) (Detail) - USD ($) $ in Millions	1 Months Ended		9 Months Ended	12 Months Ended
	Dec. 31, 2017	Nov. 30, 2017	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disposition Of Businesses [Line Items]
Impairment				$ 4,203	$ 67	$ 1,616
Norway
Disposition Of Businesses [Line Items]
Impairment			$ 2,503
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Equatorial Guinea
Disposition Of Businesses [Line Items]
Gains (loss) on sales of assets		$ 486
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Norway
Disposition Of Businesses [Line Items]
Gains (loss) on sales of assets	$ (857)
Impairment				$ 2,503