Supplemental cash flow information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for income taxes	$ 26	$ 231
Liabilities assumed in connection with business acquisitions	142	16,842
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	306	181
Railroad, Utilities and Energy [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	737	731
Finance and Financial Products [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	$ 78	$ 63