Impairment and Other (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Impairments [Line Items]
Loss contingency charge, pre-tax	$ 147
Loss contingency charge, after tax	$ 147
Oil and Gas Properties
Impairments [Line Items]
Impairment charge, pre-tax		$ 2,100
Impairment charge, after income taxes		2,000
Other Assets
Impairments [Line Items]
Impairment charge, pre-tax		21
Impairment charge, after income taxes		$ 20