v3.26.1
Goodwill and other intangible assets - Intangible assets (Detail) - USD ($)
$ in Millions
Jun. 30, 2026
Dec. 31, 2025
Insurance and Other [Member]    
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]    
Gross carrying amount $ 51,986 $ 51,067
Accumulated amortization 18,037 17,265
Net carrying value 33,949 33,802
Railroad, Utilities and Energy [Member]    
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]    
Gross carrying amount [1] 1,978 1,983
Accumulated amortization [1] 992 943
Net carrying value [1] 986 1,040
Customer relationships [Member] | Insurance and Other [Member]    
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]    
Gross carrying amount 31,768 31,215
Accumulated amortization 10,066 9,638
Net carrying value 21,702 21,577
Trademarks and trade names [Member] | Insurance and Other [Member]    
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]    
Gross carrying amount 9,170 9,007
Accumulated amortization 1,219 1,143
Net carrying value 7,951 7,864
Customer relationships and contracts [Member] | Railroad, Utilities and Energy [Member]    
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]    
Gross carrying amount [1] 1,540 1,541
Accumulated amortization [1] 854 809
Net carrying value [1] 686 732
Other intangible assets [Member] | Insurance and Other [Member]    
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]    
Gross carrying amount 5,635 5,608
Accumulated amortization 2,429 2,288
Net carrying value 3,206 3,320
Other intangible assets [Member] | Railroad, Utilities and Energy [Member]    
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]    
Gross carrying amount [1] 438 442
Accumulated amortization [1] 138 134
Net carrying value [1] 300 308
Patents and technology [Member] | Insurance and Other [Member]    
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]    
Gross carrying amount 5,413 5,237
Accumulated amortization 4,323 4,196
Net carrying value $ 1,090 $ 1,041
[1] Included in other assets.