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v3.20.2

Fair Value Measurements - Significant Unobservable Inputs (Details) $ in Millions | 6 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Jun. 30, 2020 USD ($) MWh T | Mar. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Jun. 30, 2019 USD ($) | Mar. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |  |  |
Locational margin price average term | 3 years |  |  |  |  |
LME Swap [Member] |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |  |  |
Fair value | $ 6.1 | $ 7.8 | $ 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 | 1,594 |  |  |  |  |
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 | 2,179 |  |  |  |  |
Hawesville L4 Power Price Swaps [Member] |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |  |  |
Fair value | $ (1.5) | $ (3.2) | $ (2.9) | $ (2.7) | $ 0.0 | $ 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 | 0.52 |  |  |  |  |

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