Property, plant and equipment and assets held for lease - Depreciation expense (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 2,035	$ 1,876
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	649	542
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	1,225	1,175
Finance and Financial Products [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 161	$ 159