Employee benefits - Discount rate and assumed health care cost trend rates (Details)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Pension Plans | Minimum
Weighted average assumptions used to determine net periodic benefit cost for the years ended December 31:
Discount rate for benefit obligation	2.79%	2.41%	3.22%
Discount rate for interest cost	2.30%	1.76%	2.81%
Expected return on plan asset	4.30%	4.60%	5.00%
Weighted average assumptions used to determine benefit obligation at December 31:
Discount rate for benefit obligation	5.34%	2.79%
Pension Plans | Maximum
Weighted average assumptions used to determine net periodic benefit cost for the years ended December 31:
Discount rate for benefit obligation	2.83%	2.48%	3.27%
Discount rate for interest cost	2.33%	1.80%	2.83%
Expected return on plan asset	5.40%	5.50%	5.80%
Weighted average assumptions used to determine benefit obligation at December 31:
Discount rate for benefit obligation	5.37%	2.83%
OPEB Plan
Weighted average assumptions used to determine net periodic benefit cost for the years ended December 31:
Discount rate for benefit obligation	2.94%	2.65%	3.38%
Discount rate for service cost	3.21%	3.09%	3.72%
Discount rate for interest cost	2.51%	2.03%	2.98%
Initial health care cost trend rates	4.75%	5.00%	5.00%
Ultimate health care cost trend rate	4.50%	4.50%	5.00%
Year that the ultimate trend rate is reached	2023	2023	2020
Weighted average assumptions used to determine benefit obligation at December 31:
Discount rate for benefit obligation	5.42%	2.94%
Initial health care cost trend rates	7.50%	4.75%
Ultimate health care cost trend rate	4.50%	4.50%
Year that the ultimate trend rate is reached	2035	2023