Pensions and other benefits - Pension Plan Asset Allocation and Weighted-Average Policy Range (Details) - Pensions	Dec. 31, 2024	Dec. 31, 2023
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	100.00%
Percentage of plan assets as at December 31	100.00%	100.00%
Cash and cash equivalents
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	2.70%
Percentage of plan assets as at December 31	2.20%	2.20%
Fixed income
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	38.20%
Percentage of plan assets as at December 31	36.00%	31.20%
Public equity
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	29.60%
Percentage of plan assets as at December 31	30.70%	35.80%
Real estate and infrastructure
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	14.70%
Percentage of plan assets as at December 31	11.70%	11.30%
Private debt
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	7.40%
Percentage of plan assets as at December 31	7.90%	8.40%
Absolute return
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Asset allocation target	7.40%
Percentage of plan assets as at December 31	11.50%	11.10%
Minimum \| Fixed income
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Policy range	26.00%
Minimum \| Public equity
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Policy range	24.00%
Minimum \| Real estate and infrastructure
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Policy range	6.00%
Minimum \| Private debt
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Policy range	3.00%
Minimum \| Absolute return
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Policy range	3.00%
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	43.00%
Maximum \| Public equity
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Policy range	40.00%
Maximum \| Real estate and infrastructure
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Policy range	20.00%
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.

+ Details

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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
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480482/715-20-55-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

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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
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

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