Supplemental cash flow information (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for income taxes	$ 1,082	$ 1,055
Liabilities assumed in connection with business acquisitions	167	16,997
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	390	253
Railroad, Utilities and Energy [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	1,410	1,406
Finance and Financial Products [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	$ 211	$ 184