Supplemental cash flow information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for income taxes	$ 5,415	$ 4,354	$ 3,286
Liabilities assumed in connection with business acquisitions	766	3,735	747
Right-of-use assets obtained in exchange for new operating lease liabilities	782
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	1,011	1,111	1,260
Railroad, Utilities and Energy [Member]
Supplemental Cash Flow Information [Line Items]
Cash paid during the period for interest	$ 2,879	$ 2,867	$ 2,828