Property, plant and equipment - Depreciation expense (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 2,106	$ 2,072
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	564	576
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 1,542	$ 1,496