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Derivative Financial Instruments and Hedging - Schedule of Derivative Instruments Gain (Loss) (Details) - Cash Flow Hedging [Member] - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Other Comprehensive Income (Loss) [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion) |  | $ 11.1 | $ 13.2
Cost of Sales [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) | [1] | 4.5 | (4.1)
Selling and administrative expenses [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in Income on Derivatives (Ineffective Portion and Amount Excluded from Effectiveness Testing) | [2] | 0.0 | (0.8)
Nickel and other raw material contracts [Member] | Other Comprehensive Income (Loss) [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion) |  | 14.1 | 9.4
Nickel and other raw material contracts [Member] | Cost of Sales [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) | [1] | (2.1) | (12.1)
Nickel and other raw material contracts [Member] | Selling and administrative expenses [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in Income on Derivatives (Ineffective Portion and Amount Excluded from Effectiveness Testing) | [2] | 0.0 | 0.0
Natural gas contracts [Member] | Other Comprehensive Income (Loss) [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion) |  | (2.8) | 3.8
Natural gas contracts [Member] | Cost of Sales [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) | [1] | (3.3) | (8.4)
Natural gas contracts [Member] | Selling and administrative expenses [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in Income on Derivatives (Ineffective Portion and Amount Excluded from Effectiveness Testing) | [2] | 0.0 | (0.8)
Foreign Exchange Contract [Member] | Other Comprehensive Income (Loss) [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion) |  | (0.2) | 0.0
Foreign Exchange Contract [Member] | Cost of Sales [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) | [1] | 9.9 | 16.4
Foreign Exchange Contract [Member] | Selling and administrative expenses [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in Income on Derivatives (Ineffective Portion and Amount Excluded from Effectiveness Testing) | [2] | $ 0.0 | $ 0.0
[1] | The gains (losses) reclassified from accumulated OCI into income related to the effective portion of the derivatives are presented in cost of sales in the same period or periods in which the hedged item affects earnings.
[2] | The gains (losses) recognized in income on derivatives related to the ineffective portion and the amount excluded from effectiveness testing are presented in selling and administrative expenses.

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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 The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4D -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624177-113959 + Details
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- Definition The portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments representing (a) the amount of the hedge ineffectiveness and (b) the amount, if any, excluded from the assessment of hedge effectiveness. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 25 -Section 50 -Paragraph 1 -Subparagraph (a)(1),(2) -URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986 + Details
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- Definition The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959 + Details
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