Impairment (Detail) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020 USD ($) $ / bbl	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Impairments [Line Items]
Impairment charge, pre-tax		$ 2,126	$ 0	$ 0
Oil and Gas Properties
Impairments [Line Items]
Fair value of estimated impairment charges determined using internal projected discounted cash flows	$ 1,050
Weighted average crude oil benchmark price for impaired assets (US dollar per barrel) | $ / bbl	48.82
Discount rate used in fair value measurements	10.00%
Oil and Gas Properties | West Texas Intermediate
Impairments [Line Items]
Future strip crude oil price (US dollar per barrel) used in impairment | $ / bbl	50
Oil and Gas Properties | Brent
Impairments [Line Items]
Future strip crude oil price (US dollar per barrel) used in impairment | $ / bbl	55
Oil and Gas Properties | North Malay Basin Field | Malaysia
Impairments [Line Items]
Impairment charge, pre-tax		755
Impairment charge, after income taxes		755
Oil and Gas Properties | South Arne Field | DENMARK
Impairments [Line Items]
Impairment charge, pre-tax		670
Impairment charge, after income taxes		594
Oil and Gas Properties | Stampede Field | Gulf of Mexico
Impairments [Line Items]
Impairment charge, pre-tax		410
Impairment charge, after income taxes		410
Oil and Gas Properties | Tubular Bells Field | Gulf of Mexico
Impairments [Line Items]
Impairment charge, pre-tax		270
Impairment charge, after income taxes		$ 270
Other Assets
Impairments [Line Items]
Impairment charge, pre-tax	$ 21
Impairment charge, after income taxes	$ 20