Impairment - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Impairments [Line Items]
Impairment charge, pre-tax			$ 4,203	$ 67	$ 1,616
Fair value of estimated impairment charges determined using internal projected discounted cash flows	$ 1,100
Goodwill impairment charge, pre-tax					1,483
Goodwill impairment charge, after-tax					1,483
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
Legacy conventional North Dakota Assets
Impairments [Line Items]
Impairment charge, pre-tax					133
Impairment charge, after-tax					$ 83
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