Impairment (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Impairments [Line Items]
Impairment charge, pre-tax	$ 0	$ 2,126
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

The charge against earnings resulting from the aggregate write down of tangible assets from their carrying value to their fair value.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109226691&loc=d3e2921-110230

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109222650&loc=d3e1361-107760

Name:	us-gaap_TangibleAssetImpairmentCharges
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration