Supplemental cash flow information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for income taxes	$ 3,977	$ 1,774
Liabilities assumed in connection with business acquisitions	93	685
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	677	747
Railroad, Utilities and Energy [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	2,129	2,111
Finance and Financial Products [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	$ 257	$ 296