Derivative Financial Instruments and Hedging - Schedule of Derivative Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	$ 16.5	$ 9.1
Fair value of derivative liability	5.5	18.7
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	16.4	8.5
Fair value of derivative liability	5.5	18.7
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	0.1	0.6
Foreign Exchange Contract [Member] | Designated as Hedging Instrument [Member] | Prepaid expenses and other current assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	0.0	2.4
Foreign Exchange Contract [Member] | Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	0.0	0.2
Foreign Exchange Contract [Member] | Designated as Hedging Instrument [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liability	0.0	0.1
Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [Member] | Prepaid expenses and other current assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	0.1	0.6
Nickel and other raw material contracts [Member] | Designated as Hedging Instrument [Member] | Prepaid expenses and other current assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	10.5	2.2
Nickel and other raw material contracts [Member] | Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	5.5	3.3
Nickel and other raw material contracts [Member] | Designated as Hedging Instrument [Member] | Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liability	2.1	6.7
Nickel and other raw material contracts [Member] | Designated as Hedging Instrument [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liability	2.2	9.4
Natural gas contracts [Member] | Designated as Hedging Instrument [Member] | Prepaid expenses and other current assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	0.1	0.2
Natural gas contracts [Member] | Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	0.3	0.2
Natural gas contracts [Member] | Designated as Hedging Instrument [Member] | Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liability	0.9	2.5
Natural gas contracts [Member] | Designated as Hedging Instrument [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liability	$ 0.3	$ 0.0