Supplemental cash flow information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for income taxes	$ 231	$ 248
Liabilities assumed in connection with business acquisitions	16,842	2,213
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	181	149
Railroad, Utilities and Energy [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	731	697
Finance and Financial Products [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	$ 63	$ 89