Goodwill and other intangible assets - Intangible assets (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 43,993	$ 43,988
Accumulated amortization	14,948	14,661
Net carrying value	29,045	29,327
Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	8,866	8,858
Accumulated amortization	1,162	1,045
Net carrying value	7,704	7,813
Customer relationships [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	28,287	28,305
Accumulated amortization	8,051	7,901
Net carrying value	20,236	20,404
Trademarks and trade names [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,624	5,619
Accumulated amortization	850	846
Net carrying value	4,774	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	126	98
Net carrying value	3,466	3,494
Customer relationships and contracts [Member] | Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	4,092	4,092
Accumulated amortization	855	791
Net carrying value	3,237	3,301
Other intangible assets [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	4,803	4,826
Accumulated amortization	1,851	1,805
Net carrying value	2,952	3,021
Other intangible assets [Member] | Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	1,182	1,174
Accumulated amortization	181	156
Net carrying value	1,001	1,018
Patents and technology [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,279	5,238
Accumulated amortization	4,196	4,109
Net carrying value	$ 1,083	$ 1,129