Supplemental cash flow information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for income taxes	$ 4,535	$ 4,014	$ 5,401
Liabilities assumed in connection with business acquisitions	2,812	6,334	9,224
Equity securities exchanged in connection with business acquisitions		2,478
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	346	360	343
Railroad, Utilities and Energy [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	2,717	2,487	1,958
Finance and Financial Products [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	$ 403	$ 465	$ 573