Goodwill and other intangible assets - Intangible assets (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 43,988	$ 42,461
Accumulated amortization	14,661	13,274
Net carrying value	29,327	29,187
Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	8,858	1,914
Accumulated amortization	1,045	622
Net carrying value	7,813	1,292
Trademarks and trade names [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,619	5,603
Accumulated amortization	846	822
Net carrying value	4,773	4,781
Trademarks and trade names [Member] | Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	3,592	217
Accumulated amortization	98	39
Net carrying value	3,494	178
Customer relationships [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	28,305	27,765
Accumulated amortization	7,901	7,174
Net carrying value	20,404	20,591
Other intangible assets [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	4,826	4,150
Accumulated amortization	1,805	1,530
Net carrying value	3,021	2,620
Other intangible assets [Member] | Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	1,174	190
Accumulated amortization	156	42
Net carrying value	1,018	148
Customer relationships and contracts [Member] | Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	4,092	1,507
Accumulated amortization	791	541
Net carrying value	3,301	966
Patents and technology [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,238	4,943
Accumulated amortization	4,109	3,748
Net carrying value	$ 1,129	$ 1,195