Supplemental cash flow information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for income taxes	$ 2,237	$ 2,575
Liabilities assumed in connection with business acquisitions	17,319	2,792
Equity securities exchanged in connection with business acquisition	4,239
Insurance and Other [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	499	312
Railroad, Utilities and Energy [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	2,130	2,043
Finance and Financial Products [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	$ 263	$ 274