Supplemental cash flow information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for income taxes	$ 1,774	$ 2,237
Liabilities assumed in connection with business acquisitions	685	17,319
Equity securities exchanged in connection with business acquisition		4,239
Equity securities surrendered in connection with warrant exercise	4,965
Insurance and Other [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	747	499
Railroad, Utilities and Energy [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	2,111	2,130
Finance and Financial Products [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	$ 296	$ 263