Pensions and other benefits - Actuarial Assumptions (Details)	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Benefit obligation at December 31:
Discount rate		3.01%	2.58%	3.25%
Projected future salary increases		2.75%	2.75%	2.75%
Health care cost trend rate		5.00%	5.00%	5.50%
Benefit cost for year ended December 31:
Discount rate		2.58%	3.25%	4.01%
Expected rate of return on fund assets		6.90%	7.25%	7.50%
Projected future salary increases		2.75%	2.75%	2.75%
Health care cost trend rate		5.00%	5.50%	6.00%
Assumed health care cost trend rate		5.00%	5.50%	6.00%
Forecast
Benefit cost for year ended December 31:
Expected rate of return on fund assets	6.90%

Defined Benefit Plan, Health Care Cost Trend Rate Change

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- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

+ References

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- Definition

Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

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- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan.

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- Definition

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e2919-114920

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- Definition

Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

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- Definition

Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status.

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- Definition

Ultimate trend rate for health care cost for defined benefit postretirement plan.

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