Supplemental cash flow information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for income taxes	$ 2,575	$ 3,201
Equity securities exchanged in connection with business acquisitions		2,478
Liabilities assumed in connection with business acquisitions	2,792	1,459
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	312	321
Railroad, Utilities and Energy [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	2,043	1,864
Finance and Financial Products [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	$ 274	$ 332