Business segment data - Narrative (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Revenues	$ 64,381	$ 63,024	$ 56,840	$ 61,265	$ 65,368	$ 64,972	$ 63,598	$ 60,678	$ 245,510	$ 254,616	$ 247,837
Sales, Service and Leasing Revenues [Member]
Segment Reporting Information [Line Items]
Revenues									$ 132,300	$ 140,800	$ 139,100
United States [Member] | Geographic Concentration [Member] | Sales, Service and Leasing Revenues [Member]
Segment Reporting Information [Line Items]
Concentration percentage									86.00%	85.00%	84.00%
United States [Member] | Geographic Concentration [Member] | Property, Plant and Equipment and Equipment Held for Lease [Member]
Segment Reporting Information [Line Items]
Concentration percentage									89.00%
Railroad, Utilities and Energy [Member]
Segment Reporting Information [Line Items]
Revenues									$ 41,764	$ 43,453	$ 43,673
Railroad, Utilities and Energy [Member] | United States [Member] | Geographic Concentration [Member] | Revenues [Member]
Segment Reporting Information [Line Items]
Concentration percentage									96.00%	96.00%	96.00%