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Employee plans - Summary of Changes in Level 3 Fair Value of Plan Assets (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022
Other Postretirement Plans |  |
Change in plan assets |  |
Fair value of plan assets at beginning of year | $ 5.2 | $ 5.6
Fair value of plan assets at end of year | 3.2 | 5.2
U.S. Plans | Other Postretirement Plans | Insurance Contracts |  |
Change in plan assets |  |
Fair value of plan assets at beginning of year | 5.2 |
Fair value of plan assets at end of year | 3.2 | 5.2
U.S. Plans | Other Postretirement Plans | Level 3 | Insurance Contracts |  |
Change in plan assets |  |
Fair value of plan assets at beginning of year | 5.2 | 5.6
Realized gains (losses) | (2.8) | (0.7)
Purchases or acquisitions | 0.8 | 0.3
Sales or dispositions | 0.0 | 0.0
Currency and unrealized gains (losses) relating to instruments still held | 0.0 | 0.0
Fair value of plan assets at end of year | 3.2 | 5.2
U.S. Plans | Pension Plans |  |
Change in plan assets |  |
Fair value of plan assets at beginning of year | 2,440.1 | 3,139.3
Fair value of plan assets at end of year | 1,817.9 | 2,440.1
U.S. Plans | Pension Plans | Level 3 |  |
Change in plan assets |  |
Fair value of plan assets at beginning of year | 0.0 |
Fair value of plan assets at end of year | 0.0 | 0.0
International Plans | Pension Plans |  |
Change in plan assets |  |
Fair value of plan assets at beginning of year | 1,444.3 | 2,431.6
Fair value of plan assets at end of year | 1,486.2 | 1,444.3
International Plans | Pension Plans | Level 3 |  |
Change in plan assets |  |
Fair value of plan assets at beginning of year | 100.3 |
Fair value of plan assets at end of year | 510.6 | 100.3
International Plans | Pension Plans | Level 3 | Insurance Contracts |  |
Change in plan assets |  |
Fair value of plan assets at beginning of year | 100.3 | 110.2
Realized gains (losses) | 0.0 | 0.0
Purchases or acquisitions | 375.6 | 5.2
Sales or dispositions | (13.8) | (10.0)
Currency and unrealized gains (losses) relating to instruments still held | 48.5 | (5.1)
Fair value of plan assets at end of year | $ 510.6 | $ 100.3

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- Definition Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets sold. + 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)(iv)(02)(A) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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- Definition Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held. + 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)(iv)(02)(A) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Definition Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee. + 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)(iv)(02) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 6: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 7: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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- Definition Amount, measured using unobservable input, of decrease in plan asset of defined benefit plan from sale. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(02)(B) -SubTopic 20 -Topic 715 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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