Property, plant and equipment and assets held for lease - Narrative (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 1,202	$ 1,206
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	2,932	2,403
Finance and Financial Products [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 447	$ 427