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Derivatives, Hedging Programs and Other Financial Instruments, Material Derivative Positions (Details) mmlbs in Millions | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2018 EUR (€) MMBTU MWH mmlbs
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Aluminum | Designated as Hedging Instrument | Purchase |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative non-monetary notional amount |  |  |  |  | 138.3
Aluminum | Designated as Hedging Instrument | Sales |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative non-monetary notional amount |  |  |  |  | 2.1
Midwest premium swap contracts | Designated as Hedging Instrument | Purchase |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative non-monetary notional amount |  |  |  |  | 105.9
Alloy Metal Hedge | Designated as Hedging Instrument | Purchase |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative non-monetary notional amount |  |  |  |  | 9.9
Natural Gas | Designated as Hedging Instrument | Purchase |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative non-monetary notional amount | MMBTU |  |  |  |  | 4,130,000
Electricity | Designated as Hedging Instrument | Purchase |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative non-monetary notional amount | MWH |  |  |  |  | 219,600
Foreign Exchange Contract | Designated as Hedging Instrument | Purchase |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative notional amount | € |  |  |  |  | € 33,064
Scenario, Forecast | Natural Gas |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage | 63.00% | 67.00% | 68.00% | 70.00% |
Scenario, Forecast | Electricity |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage | 9.00% | 54.00% | 54.00% | 53.00% |

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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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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + 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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- Definition The percentage of expected requirements covered by the aggregate notional amount of derivative contracts expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract as a percentage of expected need. + References No definition available. + Details
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