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Derivatives, Hedging Programs and Other Financial Instruments - Summary of Derivative Positions (Details) mmlb in Millions | 9 Months Ended
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Sep. 30, 2021 EUR (€) mmlb MMBTU MWh
Purchase | Aluminum |
Derivative [Line Items] |
Derivative non-monetary notional amount | 97.8
Purchase | Aluminum | Minimum |
Derivative [Line Items] |
Derivative maturity period | 2021-10
Purchase | Aluminum | Maximum |
Derivative [Line Items] |
Derivative maturity period | 2023-12
Purchase | Midwest premium swap contracts |
Derivative [Line Items] |
Derivative non-monetary notional amount | 81.1
Purchase | Midwest premium swap contracts | Minimum |
Derivative [Line Items] |
Derivative maturity period | 2021-10
Purchase | Midwest premium swap contracts | Maximum |
Derivative [Line Items] |
Derivative maturity period | 2023-12
Purchase | Alloying Metals |
Derivative [Line Items] |
Derivative non-monetary notional amount | 9.4
Purchase | Alloying Metals | Minimum |
Derivative [Line Items] |
Derivative maturity period | 2021-10
Purchase | Alloying Metals | Maximum |
Derivative [Line Items] |
Derivative maturity period | 2022-12
Purchase | Natural Gas |
Derivative [Line Items] |
Derivative non-monetary notional amount | MMBTU | 5,220,000
Purchase | Natural Gas | Minimum |
Derivative [Line Items] |
Derivative maturity period | 2021-10
Purchase | Natural Gas | Maximum |
Derivative [Line Items] |
Derivative maturity period | 2024-12
Purchase | Foreign Exchange Contract |
Derivative [Line Items] |
Derivative notional amount | € | € 208,080
Purchase | Foreign Exchange Contract | Minimum |
Derivative [Line Items] |
Derivative maturity period | 2021-12
Purchase | Foreign Exchange Contract | Maximum |
Derivative [Line Items] |
Derivative maturity period | 2023-03
Purchase | Electricity |
Derivative [Line Items] |
Derivative non-monetary notional amount | MWh | 285,270
Purchase | Electricity | Minimum |
Derivative [Line Items] |
Derivative maturity period | 2021-10
Purchase | Electricity | Maximum |
Derivative [Line Items] |
Derivative maturity period | 2022-12
Sales | Aluminum |
Derivative [Line Items] |
Derivative non-monetary notional amount | 0.8
Sales | Aluminum | Minimum |
Derivative [Line Items] |
Derivative maturity period | 2021-10
Sales | Aluminum | Maximum |
Derivative [Line Items] |
Derivative maturity period | 2021-12
Sales | Alloying Metals |
Derivative [Line Items] |
Derivative non-monetary notional amount | 1.8
Sales | Alloying Metals | Minimum |
Derivative [Line Items] |
Derivative maturity period | 2021-10
Sales | Alloying Metals | Maximum |
Derivative [Line Items] |
Derivative maturity period | 2021-12

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