Goodwill and other intangible assets - Intangible assets - Narrative (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Intangible asset amortization expense	$ 1,300	$ 1,300
Intangible assets with indefinite lives, excluding goodwill	18,900		$ 18,900
Railroad, Utilities and Energy [Member]
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Net carrying value	7,447		7,813
Railroad, Utilities and Energy [Member] | Other intangible assets [Member]
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Net carrying value	938		1,018
Railroad, Utilities and Energy [Member] | Pilot [Member] | Other Assets [Member]
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Net carrying value	$ 6,300		$ 6,600