Property, plant and equipment and assets held for lease - Depreciation expense (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 5,727	$ 5,520
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	1,636	1,595
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	3,604	3,459
Finance and Financial Products [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 487	$ 466