Goodwill and other intangible assets - Intangible assets (Detail) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 40,732	$ 40,664
Accumulated amortization	12,994	12,178
Net carrying value	27,738	28,486
Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	1,693	1,693
Accumulated amortization	603	542
Net carrying value	1,090	1,151
Trademarks and trade names [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,158	5,176
Accumulated amortization	816	802
Net carrying value	4,342	4,374
Customer relationships [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	27,337	27,335
Accumulated amortization	6,957	6,450
Net carrying value	20,380	20,885
Customer relationships [Member] | Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	678	678
Accumulated amortization	421	396
Net carrying value	257	282
Other intangible assets [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	3,280	3,390
Accumulated amortization	1,480	1,442
Net carrying value	1,800	1,948
Trademarks, Trade Names and Other [Member] | Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	1,015	1,015
Accumulated amortization	182	146
Net carrying value	833	869
Patents and technology [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	4,957	4,763
Accumulated amortization	3,741	3,484
Net carrying value	$ 1,216	$ 1,279