Property, plant and equipment - Depreciation expense (Detail) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2024	Jun. 30, 2023
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 4,779	$ 4,652
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	1,226	1,158
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 3,553	$ 3,494

Amount, excluding lessor's underlying asset for which right to use has been conveyed to lessee under operating lease, of depreciation expense.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479773/842-30-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 360
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482099/360-10-50-1

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