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Commitments and Contingencies - Legal Contingencies (Details) |  |  |  | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Oct. 01, 2021 USD ($) | Apr. 01, 2021 | Aug. 18, 2017 USD ($) | Sep. 30, 2017 USD ($) | Sep. 30, 2022 USD ($) MW | Sep. 30, 2021 USD ($) | Sep. 30, 2022 USD ($) MW | Sep. 30, 2021 USD ($) | Dec. 31, 2022 USD ($) MW | Dec. 31, 2013 USD ($) | Jul. 31, 2021 MW
Ravenswood Retiree Medical Benefits Changes |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Litigation settlement amount |  |  | $ 23,000,000 |  |  |  |  |  |  |  |
Litigation settlement period |  |  |  |  |  |  |  |  | 10 years |  |
Ravenswood retiree legal settlement |  |  |  | $ 5,000,000 |  |  |  |  |  |  |
Gain (loss) related to litigation settlement |  |  |  | 5,500,000 |  |  |  |  |  |  |
Loss contingency accrual |  |  |  | $ 12,500,000 |  |  |  |  |  |  |
Litigation settlement, annual installment |  |  |  |  |  |  |  |  | $ 2,000,000 |  |
Litigation settlement installment period |  |  |  |  |  |  |  |  | 9 years |  |
Loss contingency, accrual, current |  |  |  |  |  |  |  |  | $ 2,000,000 |  |
Other liabilities |  |  |  |  |  |  |  |  | 4,800,000 |  |
Pension Benefit Guarantee Corporation |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Required pension contributions above minimum |  |  |  |  |  |  |  |  |  | $ 17,400,000 |
Pension contributions |  |  |  |  | $ 0 | $ 0 | $ 0 | $ 0 | $ 2,400,000 |  |
Pension contributions, amended term, annual contribution | $ 2,400,000 |  |  |  |  |  |  |  |  |  |
Pension contributions, amended term, total contribution | $ 9,600,000 |  |  |  |  |  |  |  |  |  |
Pension contributions, term | 4 years |  |  |  |  |  |  |  |  |  |
Mt. Holly |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Short-term power agreement, supply percentage |  | 100.00% |  |  |  |  |  |  |  |  |
Power supply agreement, increase production at full capacity, percentage |  | 75.00% |  |  |  |  |  |  |  |  |
Grundartangi - HS, Landsvirkjun |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Underlying, derivative power, available | MW |  |  |  |  |  |  |  |  | 545 |  |
Grundartangi - Landsvirkjun |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Underlying, derivative power, available | MW |  |  |  |  | 25 |  | 25 |  |  |  |
Underlying, derivative power, available, extension | MW |  |  |  |  | 42 |  | 42 |  |  |  | 161
Underlying, derivative power, rate | MW |  |  |  |  | 119 |  | 119 |  |  |  |
Underlying, derivative power, available, requested | MW |  |  |  |  |  |  |  |  |  |  | 182

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- Definition Pursuant to the terms of the settlement agreement with the Pension Benefit Guaranty Corporation, we will make additional contributions (above any minimum required contributions) to our defined benefit pension plans. + References No definition available. + Details
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- Definition Amount of gain (loss) recognized in settlement of litigation and insurance claims. Excludes claims within an insurance entity's normal claims settlement process. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349 + Details
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