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DEBT AND CREDIT FACILITIES - Schedule Of Long-Term Debt (Details) - USD ($) $ in Millions | Sep. 30, 2024 | Aug. 16, 2024 | Mar. 18, 2024 | Dec. 31, 2023
--- | --- | --- | --- | ---
Debt Instrument [Line Items] |  |  |  |
Long-term Debt, Gross | $ 3,835 |  |  | $ 3,192
Unamortized discounts and issuance costs | (61) |  |  | (55)
Long-term Debt | 3,774 |  |  | 3,137
ABL Facility |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Long-term Line of Credit | $ 47 |  |  |
Cleveland-Cliffs Inc. | 6.750% 2026 Senior Secured Notes |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Stated interest rate | 6.75% |  |  |
Annual Effective Interest Rate | 6.99% |  |  |
Long-term Debt, Gross | $ 0 |  |  | 829
Cleveland-Cliffs Inc. | 7.000% 2027 Senior Notes |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Stated interest rate | 7.00% |  |  |
Annual Effective Interest Rate | 9.24% |  |  |
Long-term Debt, Gross | $ 73 |  |  | 73
Cleveland-Cliffs Inc. | 5.875% 2027 Senior Notes |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Stated interest rate | 5.875% |  |  |
Annual Effective Interest Rate | 6.49% |  |  |
Long-term Debt, Gross | $ 556 |  |  | 556
Cleveland-Cliffs Inc. | 4.625% 2029 Senior Notes |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Stated interest rate | 4.625% |  |  |
Annual Effective Interest Rate | 4.625% |  |  |
Long-term Debt, Gross | $ 368 |  |  | 368
Cleveland-Cliffs Inc. | 6.750% 2030 Senior Notes |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Stated interest rate | 6.75% |  |  |
Annual Effective Interest Rate | 6.75% |  |  |
Long-term Debt, Gross | $ 750 |  |  | 750
Cleveland-Cliffs Inc. | 4.875% 2031 Senior Notes |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Stated interest rate | 4.875% |  |  |
Annual Effective Interest Rate | 4.875% |  |  |
Long-term Debt, Gross | $ 325 |  |  | 325
Cleveland-Cliffs Inc. | 7.000% 2032 Senior Notes |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Stated interest rate | 7.00% |  |  |
Annual Effective Interest Rate | 7.054% |  |  |
Long-term Debt, Gross | $ 1,425 | $ 600 | $ 825 | 0
Cleveland-Cliffs Inc. | 6.250% 2040 Senior Notes |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Stated interest rate | 6.25% |  |  |
Annual Effective Interest Rate | 6.34% |  |  |
Long-term Debt, Gross | $ 235 |  |  | 235
Cleveland-Cliffs Inc. | ABL Facility |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Annual Effective Interest Rate | 8.25% |  |  |
Long-term Line of Credit | $ 47 |  |  | 0
Cleveland-Cliffs Inc. | ABL Facility | Minimum |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage on Incremental Borrowings | 5.63% |  |  |
Cleveland-Cliffs Inc. | ABL Facility | Maximum |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage on Incremental Borrowings | 8.25% |  |  |
AK Steel | 7.000% 2027 AK Senior Notes |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Stated interest rate | 7.00% |  |  |
Annual Effective Interest Rate | 9.24% |  |  |
Long-term Debt, Gross | $ 56 |  |  | $ 56

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