Goodwill and other intangible assets - Intangible assets (Detail) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 43,772	$ 42,461
Accumulated amortization	13,953	13,274
Net carrying value	29,819	29,187
Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	8,655	1,914
Accumulated amortization	808	622
Net carrying value	7,847	1,292
Customer relationships [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	28,276	27,765
Accumulated amortization	7,558	7,174
Net carrying value	20,718	20,591
Trademarks and trade names [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,626	5,603
Accumulated amortization	838	822
Net carrying value	4,788	4,781
Trademarks and trade names [Member] | Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	2,228	217
Accumulated amortization	51	39
Net carrying value	2,177	178
Customer relationships and contracts [Member] | Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,334	1,507
Accumulated amortization	695	541
Net carrying value	4,639	966
Other intangible assets [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	4,810	4,150
Accumulated amortization	1,656	1,530
Net carrying value	3,154	2,620
Other intangible assets [Member] | Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	1,093	190
Accumulated amortization	62	42
Net carrying value	1,031	148
Patents and technology [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,060	4,943
Accumulated amortization	3,901	3,748
Net carrying value	$ 1,159	$ 1,195