Property, plant and equipment - Depreciation expense (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 2,449	$ 2,392
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	784	767
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 1,665	$ 1,625