Pensions and other benefits - Pension Plan Asset Allocation and Weighted-Average Policy Range (Details) - Pensions	Dec. 31, 2021	Dec. 31, 2020
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	100.00%
Percentage of plan assets	100.00%	100.00%
Cash and cash equivalents
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	1.20%
Percentage of plan assets	3.10%	2.00%
Fixed income
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	24.10%
Percentage of plan assets	24.10%	28.10%
Public equity
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	45.10%
Percentage of plan assets	50.50%	49.30%
Real estate and infrastructure
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	9.80%
Percentage of plan assets	6.70%	6.30%
Private debt
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	9.80%
Percentage of plan assets	4.60%	3.30%
Absolute return
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	10.00%
Percentage of plan assets	11.00%	11.00%
Minimum \| Fixed income
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Policy range	20.00%
Minimum \| Public equity
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Policy range	35.00%
Minimum \| Real estate and infrastructure
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Policy range	4.00%
Minimum \| Private debt
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Policy range	4.00%
Minimum \| Absolute return
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Policy range	4.00%
Maximum \| Cash and cash equivalents
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Policy range	10.00%
Maximum \| Fixed income
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Policy range	40.00%
Maximum \| Public equity
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Policy range	55.00%
Maximum \| Real estate and infrastructure
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Policy range	13.00%
Maximum \| Private debt
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Policy range	13.00%
Maximum \| Absolute return
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Policy range	13.00%

Defined Benefit Plan, Assets, Policy Range

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=123450688&loc=d3e4179-114921

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

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- Definition

Percentage of actual investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

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