Goodwill and other intangible assets - Intangible assets - Narrative (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Intangible asset amortization expense	$ 1,828	$ 1,233	$ 1,252
Estimated amortization expense - 2024	2,059
Estimated amortization expense - 2025	1,988
Estimated amortization expense - 2026	1,898
Estimated amortization expense - 2027	1,754
Estimated amortization expense - 2028	1,684
Intangible assets with indefinite lives, excluding goodwill	18,900	$ 18,300
Railroad, Utilities and Energy [Member] | PTC [Member] | Other Assets [Member]
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Other intangible assets	$ 6,600