Goodwill and other intangible assets - Intangible assets (Detail) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 44,018	$ 43,988
Accumulated amortization	15,230	14,661
Net carrying value	28,788	29,327
Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	8,858	8,858
Accumulated amortization	1,290	1,045
Net carrying value	7,568	7,813
Customer relationships [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	28,274	28,305
Accumulated amortization	8,214	7,901
Net carrying value	20,060	20,404
Trademarks and trade names [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,625	5,619
Accumulated amortization	859	846
Net carrying value	4,766	4,773
Trademarks and trade names [Member] | Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	3,592	3,592
Accumulated amortization	161	98
Net carrying value	3,431	3,494
Customer relationships and contracts [Member] | Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	4,093	4,092
Accumulated amortization	920	791
Net carrying value	3,173	3,301
Other intangible assets [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	4,765	4,826
Accumulated amortization	1,863	1,805
Net carrying value	2,902	3,021
Other intangible assets [Member] | Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	1,173	1,174
Accumulated amortization	209	156
Net carrying value	964	1,018
Patents and technology [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,354	5,238
Accumulated amortization	4,294	4,109
Net carrying value	$ 1,060	$ 1,129