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Retirement Benefit Plans - Funded status of plans with ABO in excess of plan assets (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Accumulated benefit obligation | $ (681.2) | $ (594.0)
Plan assets | 494.8 | 423.3
Funded status of plan | (186.4) | (170.7)
Germany |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Funded status of plan | (75.7) | (77.5)
United States |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Funded status of plan | (43.2) | (53.0)
Other |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Funded status of plan | $ (67.5) | $ (40.2)

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- Definition Amount of funded (unfunded) status of defined benefit plan, measured as difference between fair value of plan assets and benefit obligation. Includes, but is not limited to, overfunded (underfunded) status. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=64852052&loc=d3e1703-114919 + Details
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- Definition Amount of accumulated benefit obligation for defined benefit pension plan with accumulated benefit obligation in excess of plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2417-114920 + Details
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- Definition Fair value of plan assets for defined benefit pension plan with accumulated benefit obligation in excess of plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2417-114920 + Details
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