Supplemental cash flow information (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for income taxes	$ 1,128	$ 2,151
Equity securities exchanged in connection with business acquisitions		2,478
Liabilities assumed in connection with business acquisitions	2,478	1,038
Treasury stock acquired in connection with business acquisition		400
Insurance and Other [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	185	181
Railroad, Utilities and Energy [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	1,319	1,209
Finance and Financial Products [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	$ 215	$ 237