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v3.20.2

Fair Value Measurements - Significant Unobservable Inputs (Details) $ in Millions | 9 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Sep. 30, 2020 USD ($) MWh T | Jun. 30, 2020 USD ($) | Dec. 31, 2019 USD ($) | Sep. 30, 2019 USD ($) | Jun. 30, 2019 USD ($) | Dec. 31, 2018 USD ($)
LME Swap [Member] |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |  |  |
Fair value | $ 6.6 | $ 6.1 | $ 10.6 |  |  |
LME Swap [Member] | Discounted Cash Flow [Member] | Level 3 [Member] |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |  |  |
Derivative asset, percentage | 0.1000 |  |  |  |  |
Contingent obligation [Member] |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |  |  |
Fair value | $ 0.0 |  |  |  |  |
Contingent obligation [Member] | Minimum [Member] | Discounted Cash Flow [Member] | Level 3 [Member] |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |  |  |
Derivative asset (in tones) | T | 1,754 |  |  |  |  |
Contingent obligation [Member] | Maximum [Member] | Discounted Cash Flow [Member] | Level 3 [Member] |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |  |  |
Derivative asset (in tones) | T | 2,312 |  |  |  |  |
Hawesville L4 Power Price Swaps [Member] |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |  |  |
Fair value | $ (0.8) | $ (1.5) | $ (2.9) | $ (1.5) | $ (2.7) | $ 0.0
Hawesville L4 Power Price Swaps [Member] | Discounted Cash Flow [Member] | Level 3 [Member] |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |  |  |
Derivative liability (in MwH) | MWh | 0.45 |  |  |  |  |

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