Supplemental cash flow information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for income taxes	$ 4,719	$ 4,535	$ 4,014
Liabilities assumed in connection with business acquisitions	16,555	2,812	6,334
Equity securities exchanged in connection with business acquisitions	4,239		2,478
Treasury stock acquired in connection with business acquisition			400
Conversions and other exchanges of investments	4,154	1,597
Insurance and Other [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	555	346	360
Railroad, Utilities and Energy [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	2,788	2,717	2,487
Finance and Financial Products [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	$ 389	$ 403	$ 465