Property, plant and equipment - Depreciation expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 9,631	$ 9,392	$ 8,457
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	3,117	2,898	2,276
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 6,514	$ 6,494	$ 6,181