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Derivatives, Hedging Programs and Other Financial Instruments, Notional Quantity Table (Details) mmlbs in Millions | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 mmlbs MMBTU
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Not Designated as Hedging Instrument | Aluminum | Purchase |  |  |  |
Derivative [Line Items] |  |  |  |
Derivative Notional Amount (Non-Monetary) |  |  |  | 139.1
Not Designated as Hedging Instrument | Aluminum | Sale |  |  |  |
Derivative [Line Items] |  |  |  |
Derivative Notional Amount (Non-Monetary) |  |  |  | 0.9
Not Designated as Hedging Instrument | Midwest premium swap contracts | Purchase |  |  |  |
Derivative [Line Items] |  |  |  |
Derivative Notional Amount (Non-Monetary) |  |  |  | 100.1
Not Designated as Hedging Instrument | Natural Gas Member | Purchase |  |  |  |
Derivative [Line Items] |  |  |  |
Derivative Notional Amount (Non-Monetary) | MMBTU |  |  |  | 4,040,000
Not Designated as Hedging Instrument | Electricity | Purchase |  |  |  |
Derivative [Line Items] |  |  |  |
Derivative Notional Amount (Non-Monetary) | MMBTU |  |  |  | 219,600
Designated as Hedging Instrument | Alloy Metal Hedge | Purchase |  |  |  |
Derivative [Line Items] |  |  |  |
Derivative Notional Amount (Non-Monetary) |  |  |  | 9.0
Scenario, Forecast | Natural Gas Member |  |  |  |
Derivative [Line Items] |  |  |  |
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage |  |  | 66.00% |
Scenario, Forecast | Electricity |  |  |  |
Derivative [Line Items] |  |  |  |
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage | 9.00% | 55.00% | 54.00% |

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- Definition Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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