Property, plant and equipment - Depreciation expense (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 2,392	$ 2,314
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	614	575
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 1,778	$ 1,739