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Derivative Financial Instruments and Hedging - Schedule of Derivative Instruments Gain (Loss) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in OCI on Derivatives | $ 9.7 | $ (6.4) | $ 14.3
Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in OCI on Derivatives | 7.4 | (4.9) |
Cost of Sales and Interest Expense [Member] | Cash Flow Hedging [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) | 3.1 | 8.9 |
Nickel and other raw material contracts [Member] | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in OCI on Derivatives | 11.3 | (6.4) |
Nickel and other raw material contracts [Member] | Cost of Sales [Member] | Cash Flow Hedging [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) | 3.9 | 7.7 |
Natural gas contracts [Member] | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in OCI on Derivatives | (4.0) | 1.5 |
Natural gas contracts [Member] | Cost of Sales [Member] | Cash Flow Hedging [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) | (0.9) | 0.4 |
Foreign Exchange Contract [Member] | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in OCI on Derivatives | 1.0 | 0.5 |
Foreign Exchange Contract [Member] | Cost of Sales [Member] | Cash Flow Hedging [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) | 0.5 | 1.0 |
Interest Rate Swap [Member] | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in OCI on Derivatives | (0.9) | (0.5) |
Interest Rate Swap [Member] | Interest Expense [Member] | Cash Flow Hedging [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) | $ (0.4) | $ (0.2) |

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