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Commitments and Contingencies (Details) € in Thousands |  |  |  | 3 Months Ended | 9 Months Ended |  |  |  |  |  |  |  |  |
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Sep. 30, 2025 USD ($) claim | Sep. 30, 2025 BRL (R$) | Jun. 30, 2025 USD ($) | Jun. 30, 2025 BRL (R$) | Mar. 22, 2022 USD ($) | Sep. 30, 2025 USD ($) claim | Sep. 30, 2025 USD ($) case claim | Sep. 30, 2025 BRL (R$) claim | Jan. 17, 2025 company | Dec. 31, 2024 USD ($) | Jul. 19, 2024 EUR (€) | Nov. 30, 2022 USD ($) | Feb. 25, 2022 EUR (€) | Oct. 14, 2021 EUR (€) | Dec. 30, 2020 USD ($) | Jan. 27, 2020 party
Commitments and Contingencies |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number Of Potentially Related Parties |  |  |  |  |  |  |  |  | 30 |  |  |  |  |  |  |
Reserve for loss contingencies | $ 28,800,000 |  |  |  |  | $ 28,800,000 | $ 28,800,000 |  |  |  |  |  |  |  |  |
Penalties | 6,000,000 |  |  |  |  | 6,000,000 | 6,000,000 | R$ 32,000,000 |  |  |  |  |  |  |  |
Current Portion of Environmental Liabilities | 10,622,000 |  |  |  |  | 10,622,000 | 10,622,000 |  |  | $ 11,815,000 |  |  |  |  |  |
Environmental liabilities | 42,147,000 |  |  |  |  | 42,147,000 | 42,147,000 |  |  | 46,585,000 |  |  |  |  |  |
Total environmental liabilities | 52,769,000 |  |  |  |  | 52,769,000 | 52,769,000 |  |  | 58,400,000 |  |  |  |  |  |
BRAZIL |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies, Unpaid Service Taxes |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,000,000 |
Loss Contingencies, Overall Liability | $ 6,900,000 |  |  |  |  | $ 6,900,000 | 6,900,000 |  |  |  |  |  |  |  |  |
Loss Contingency Accrual, Provision |  |  |  |  |  |  | $ 0 |  |  |  |  |  |  |  |  |
Kentucky Department of Environmental Protection |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Current Portion of Environmental Liabilities |  |  |  |  |  |  |  |  |  | 200,000 |  |  |  |  |  |
Proposed civil penalty |  |  |  |  |  |  |  |  |  | $ 800,000 |  | $ 800,000 |  |  |  |
Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of pending claims | claim | 17,000 |  |  |  |  | 17,000 | 17,000 | 17,000 |  |  |  |  |  |  |  |
Number of claims dismissed to date by stipulation or summary judgment prior to trial | case |  |  |  |  |  |  | 28,500 |  |  |  |  |  |  |  |  |
Loss Contingency Accrual, Provision |  |  |  |  |  |  | $ 0 |  |  |  |  |  |  |  |  |
Alleged Violation of Environmental Permit in Ijmuiden, Netherland | Amsterdam Public Prosecutor’s Office |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingency, Amount Seeking From Other Party | € |  |  |  |  |  |  |  |  |  |  |  |  |  | € 100 |  |
Loss Contingency, Fine Issued By Court | € |  |  |  |  |  |  |  |  |  |  | € 25 |  | € 5 |  |  |
Unfavorable Regulatory Action |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingency Accrual, Provision |  |  |  |  |  | $ 27,200,000 |  |  |  |  |  |  |  |  |  |
Limit and Reduce the Accumulation of Customer-Owned Slag |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss contingency, damages sought, value |  |  | $ 12,000,000 | R$ 66,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Limit and Reduce the Accumulation of Customer-Owned Slag | Pending Litigation | Volta Redonda vs. CSN and Enviri |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss contingency, damages sought, value | $ 81,000,000 | R$ 431,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Limit and Reduce the Accumulation of Customer-Owned Slag | CSN |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss contingency, damages sought, value |  |  | $ 50,000,000 | R$ 264,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Violations of the Federal Emergency Planning and Community Right-to-Know Act | Pending Litigation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss contingency, damages sought, value |  |  |  |  | $ 3,000,000.0 |  |  |  |  |  |  |  |  |  |  |
Loss contingency reserves | $ 600,000 |  |  |  |  | $ 600,000 | $ 600,000 |  |  |  |  |  |  |  |  |

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