Property, plant and equipment - Depreciation expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 9,392	$ 8,457	$ 8,308
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	2,388	2,276	2,318
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 7,004	$ 6,181	$ 5,990