Property, plant and equipment and assets held for lease - Depreciation expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 6,673	$ 6,215	$ 5,418
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	1,680	1,632	1,691
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	4,383	3,981	3,232
Finance and Financial Products [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 610	$ 602	$ 495