Property, plant and equipment and assets held for lease - Depreciation expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 7,719	$ 7,411	$ 6,673
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	2,217	2,148	1,680
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	4,852	4,639	4,383
Finance and Financial Products [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 650	$ 624	$ 610