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Employee Benefits, Components of net periodic benefit cost (income) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic postretirement benefit cost | $ 6.6 | $ 4.8 | $ 3.7
VEBAs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Service Cost | 0.0 | 0.0 |
Defined Benefit Plan, Interest Cost | 2.8 | 3.0 |
Net periodic postretirement benefit cost | 6.1 | 4.5 | 3.4
All Other | VEBAs |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Service Cost | 0.1 | 0.0 | 0.0
Defined Benefit Plan, Interest Cost | 2.7 | 3.0 | 2.9
Defined Benefit Plan, Expected Return (Loss) on Plan Assets | 2.9 | 4.1 | 4.1
Defined Benefit Plan, Amortization of Prior Service Cost (Credit) | 5.4 | 4.7 | 4.1
Defined Benefit Plan, Amortization of Gain (Loss) | (0.8) | (0.9) | (0.5)
Net periodic postretirement benefit cost | 6.1 | 4.5 | 3.4
Canadian pension plan | Canadian pension plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic postretirement benefit cost | 0.4 | 0.3 | 0.3
Canadian pension plan | Fabricated Products | Canadian pension plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Service Cost | 0.3 | 0.3 | 0.3
Defined Benefit Plan, Interest Cost | 0.3 | 0.3 | 0.3
Defined Benefit Plan, Expected Return (Loss) on Plan Assets | 0.3 | 0.3 | 0.3
Defined Benefit Plan, Amortization of Prior Service Cost (Credit) | 0.0 | 0.0 | 0.0
Defined Benefit Plan, Amortization of Gain (Loss) | (0.1) | 0.0 | 0.0
Net periodic postretirement benefit cost | $ 0.4 | $ 0.3 | $ 0.3

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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit 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 (h)(4) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 2: 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=112275985&loc=d3e4179-114921 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920 + Details
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- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit 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=112275985&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 (h)(5) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(5) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920 + Details
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- Definition Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit 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=112275985&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 (h)(3) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920 + Details
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