Goodwill and other intangible assets - Intangible assets (Detail) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 40,638	$ 40,664
Accumulated amortization	12,427	12,178
Net carrying value	28,211	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	561	542
Net carrying value	1,132	1,151
Trademarks and trade names [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,171	5,176
Accumulated amortization	807	802
Net carrying value	4,364	4,374
Customer relationships [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	27,323	27,335
Accumulated amortization	6,616	6,450
Net carrying value	20,707	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	404	396
Net carrying value	274	282
Other intangible assets [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	3,326	3,390
Accumulated amortization	1,457	1,442
Net carrying value	1,869	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	157	146
Net carrying value	858	869
Patents and technology [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	4,818	4,763
Accumulated amortization	3,547	3,484
Net carrying value	$ 1,271	$ 1,279