Goodwill and other intangible assets - Intangible assets (Detail) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 43,637	$ 42,461
Accumulated amortization	13,636	13,274
Net carrying value	30,001	29,187
Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	9,438	1,914
Accumulated amortization	703	622
Net carrying value	8,735	1,292
Customer relationships [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	28,247	27,765
Accumulated amortization	7,376	7,174
Net carrying value	20,871	20,591
Trademarks and trade names [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,605	5,603
Accumulated amortization	832	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	2,566	217
Accumulated amortization	44	39
Net carrying value	2,522	178
Customer relationships and contracts [Member] | Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	6,214	1,507
Accumulated amortization	612	541
Net carrying value	5,602	966
Other intangible assets [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	4,775	4,150
Accumulated amortization	1,596	1,530
Net carrying value	3,179	2,620
Other intangible assets [Member] | Railroad, Utilities and Energy [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	658	190
Accumulated amortization	47	42
Net carrying value	611	148
Patents and technology [Member] | Insurance and Other [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,010	4,943
Accumulated amortization	3,832	3,748
Net carrying value	$ 1,178	$ 1,195