Supplemental cash flow information (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for income taxes	$ 1,199	$ 2,358
Liabilities assumed in connection with business acquisitions	94	76
Right-of-use assets obtained in exchange for new operating lease liabilities	361
Insurance and Other [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	540	646
Railroad, Utilities and Energy [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	$ 1,370	$ 1,402