Business segment data - Narrative (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues	$ 65,368	$ 64,972	$ 63,598	$ 60,678	$ 63,714	$ 63,450	$ 62,200	$ 58,473	$ 254,616	$ 247,837	$ 239,933
Sales, Service and Leasing Revenues [Member]
Segment Reporting Information [Line Items]
Revenues									$ 140,800	$ 139,100	$ 132,800
United States [Member] | Geographic Concentration [Member] | Sales, Service and Leasing Revenues [Member]
Segment Reporting Information [Line Items]
Concentration percentage									85.00%	84.00%	85.00%
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									$ 43,453	$ 43,673	$ 40,005
Railroad, Utilities and Energy [Member] | United States [Member] | Geographic Concentration [Member] | Revenues [Member]
Segment Reporting Information [Line Items]
Concentration percentage									96.00%	96.00%	95.00%