Employee plans - Schedule of Weighted-Average Assumptions (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Plans | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.53%	4.50%	3.87%
Expected long-term rate of return on assets	6.50%	6.80%	6.80%
Weighted-average assumptions used to determine benefit obligations at December 31 were as follows:
Discount rate	2.85%	3.53%	4.50%
Pension Plans | International Plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate	1.82%	2.55%	2.24%
Expected long-term rate of return on assets	3.50%	4.18%	4.38%
Weighted-average assumptions used to determine benefit obligations at December 31 were as follows:
Discount rate	1.23%	1.82%	2.55%
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate	5.13%	5.67%	5.30%
Expected long-term rate of return on assets	5.50%	5.50%	5.50%
Weighted-average assumptions used to determine benefit obligations at December 31 were as follows:
Discount rate	2.21%	5.13%	5.67%