Property, plant and equipment - Depreciation expense (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 7,175	$ 7,078
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	1,845	1,776
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 5,330	$ 5,302