v3.26.1
Goodwill and other intangible assets - Intangible assets (Detail) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Insurance and Other [Member]    
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]    
Gross carrying amount $ 51,898 $ 51,067
Accumulated amortization 17,623 17,265
Net carrying value 34,275 33,802
Railroad, Utilities and Energy [Member]    
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]    
Gross carrying amount [1] 1,981 1,983
Accumulated amortization [1] 969 943
Net carrying value [1] 1,012 1,040
Customer relationships [Member] | Insurance and Other [Member]    
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]    
Gross carrying amount 31,779 31,215
Accumulated amortization 9,853 9,638
Net carrying value 21,926 21,577
Trademarks and trade names [Member] | Insurance and Other [Member]    
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]    
Gross carrying amount 9,181 9,007
Accumulated amortization 1,189 1,143
Net carrying value 7,992 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] 832 809
Net carrying value [1] 708 732
Other intangible assets [Member] | Insurance and Other [Member]    
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]    
Gross carrying amount 5,632 5,608
Accumulated amortization 2,362 2,288
Net carrying value 3,270 3,320
Other intangible assets [Member] | Railroad, Utilities and Energy [Member]    
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]    
Gross carrying amount [1] 441 442
Accumulated amortization [1] 137 134
Net carrying value [1] 304 308
Patents and technology [Member] | Insurance and Other [Member]    
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]    
Gross carrying amount 5,306 5,237
Accumulated amortization 4,219 4,196
Net carrying value $ 1,087 $ 1,041
[1] Included in other assets.