Derivative Financial Instruments and Hedging (Details2) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	$ 3.0	$ 9.1
Derivative Fair Value Of Derivative Liability	20.8	18.7
Designated as Hedging Instrument
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	3.0	8.5
Derivative Fair Value Of Derivative Liability	20.5	18.7
Designated as Hedging Instrument | Nickel and other raw material contracts | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	1.3	2.2
Designated as Hedging Instrument | Nickel and other raw material contracts | Other assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	1.2	3.3
Designated as Hedging Instrument | Nickel and other raw material contracts | Accrued liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	8.1	6.7
Designated as Hedging Instrument | Nickel and other raw material contracts | Other long-term liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	9.6	9.4
Designated as Hedging Instrument | Natural gas contracts | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	0.1	0.2
Designated as Hedging Instrument | Natural gas contracts | Other assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	0.2	0.2
Designated as Hedging Instrument | Natural gas contracts | Accrued liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	1.9	2.5
Designated as Hedging Instrument | Natural gas contracts | Other long-term liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	0.2	0.0
Designated as Hedging Instrument | Foreign exchange contracts | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	0.2	2.4
Designated as Hedging Instrument | Foreign exchange contracts | Other assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	0.0	0.2
Designated as Hedging Instrument | Foreign exchange contracts | Accrued liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	0.7	0.0
Designated as Hedging Instrument | Foreign exchange contracts | Other long-term liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	0.0	0.1
Not Designated as Hedging Instrument
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	0.0	0.6
Not Designated as Hedging Instrument | Accrued liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	0.3	0.0
Not Designated as Hedging Instrument | Foreign exchange contracts | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	0.0	0.6
Not Designated as Hedging Instrument | Foreign exchange contracts | Accrued liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	$ 0.3	$ 0.0