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Employee benefit plans - Weighted-Average Asset Allocations (Details) | Dec. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Retirement Plans | U.S. |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 100.00% | 100.00%
Retirement Plans | U.S. | Equity securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 19.50% | 22.20%
Retirement Plans | U.S. | Debt securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 78.00% | 76.60%
Retirement Plans | U.S. | Cash and short-term investments |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 2.50% | 1.20%
Retirement Plans | RTS |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 100.00% | 100.00%
Retirement Plans | RTS | Equity securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 22.20% | 18.60%
Retirement Plans | RTS | Debt securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 77.80% | 81.20%
Retirement Plans | RTS | Cash and short-term investments |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 0.00% | 0.20%
Retirement Plans | U.K. |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 100.00% | 100.00%
Retirement Plans | U.K. | Equity securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 21.00% | 20.00%
Retirement Plans | U.K. | Debt securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 77.10% | 79.10%
Retirement Plans | U.K. | Cash and short-term investments |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 1.90% | 0.90%
Retirement Plans | Canada |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 100.00% | 100.00%
Retirement Plans | Canada | Equity securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 31.40% | 29.40%
Retirement Plans | Canada | Debt securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 68.60% | 70.60%
Retirement Plans | Canada | Cash and short-term investments |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 0.00% | 0.00%
Retiree Health and Life Insurance Plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 100.00% | 100.00%
Retiree Health and Life Insurance Plans | Equity securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 0.00% | 0.00%
Retiree Health and Life Insurance Plans | Debt securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 100.00% | 100.00%
Retiree Health and Life Insurance Plans | Cash and short-term investments |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total | 0.00% | 0.00%

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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 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 + Details
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