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v3.22.1

Fair Value Measurements - Significant Unobservable Inputs (Details) $ in Millions | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Mar. 31, 2022 USD ($) t MT | Dec. 31, 2021 USD ($) MT | Mar. 31, 2021 USD ($) | Dec. 31, 2020 USD ($)
LME Swap [Member] |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |
Fair Value | $ (16.7) | $ (5.1) | $ (6.0) | $ 2.9
Open position to offset fixed prices (in tonnes) | t | 118,341 |  |  |
LME Swap [Member] | Level 3 [Member] | Discount rate, net [Member] |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |
Value/Range of Unobservable Input | 0.0858 | 0.0858 |  |
FX Swap [Member] |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |
Fair Value | $ 0.0 | $ (0.2) | $ (0.2) | $ 0.1
FX Swap [Member] | Level 3 [Member] | Discount rate, net [Member] |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |
Value/Range of Unobservable Input | 0.0858 | 0.0858 |  |
Nordpool Power Price Swap [Member] |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |
Fair Value | $ 0.0 | $ 0.2 |  |
Nordpool Power Price Swap [Member] | Level 3 [Member] | Discount rate, net [Member] |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |
Value/Range of Unobservable Input | 0.0858 | 0.0858 |  |
Contingent Obligation [Member] |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |
Fair Value | $ 0.0 | $ 0.0 |  |
Contingent Obligation [Member] | Level 3 [Member] | Minimum [Member] |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |
Open position to offset fixed prices (in tonnes) | MT | 14,000 | 14,000 |  |
Contingent Obligation [Member] | Level 3 [Member] | Maximum [Member] |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |
Open position to offset fixed prices (in tonnes) | MT | 16,000 | 15,000 |  |

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