Impairment - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Impairments [Line Items]
Impairment charge, pre-tax			$ 0	$ 4,203	$ 67
Fair value of estimated impairment charges determined using internal projected discounted cash flows	$ 1,100
Norway
Impairments [Line Items]
Impairment charge, pre-tax		$ 2,503
Impairment charge, after-tax		$ 550
Midstream
Impairments [Line Items]
Impairment charge, pre-tax					67
Impairment charge, after-tax and noncontrolling interest					$ 21
Stampede Field
Impairments [Line Items]
Impairment charge, pre-tax	1,095
Percentage of working interest prior to unitizing				100.00%
Impairment charge, after-tax	1,095
Tubular Bells Field
Impairments [Line Items]
Impairment charge, pre-tax	605
Impairment charge, after-tax	$ 605