Supplemental cash flow information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for income taxes	$ 3,201	$ 4,028
Investments in equity securities exchanged in connection with business acquisitions	2,478
Liabilities assumed in connection with business acquisitions	1,459	275
Treasury stock acquired in connection with business acquisition	400
Insurance and Other [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	321	321
Railroad, Utilities and Energy [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	1,864	1,507
Finance and Financial Products [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	$ 332	$ 401