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DEBT AND CREDIT FACILITIES - Debt Issuances and Terms (Details) $ in Millions | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Dec. 31, 2024 USD ($) Days day | Oct. 22, 2024 USD ($) | Aug. 16, 2024 USD ($) | Mar. 18, 2024 USD ($) | Dec. 31, 2023 USD ($)
Debt Instrument [Line Items] |  |  |  |  |
Total debt | $ 7,148 |  |  |  | $ 3,192
6.750% 2026 Senior Secured Notes | Cleveland-Cliffs Inc. |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Stated interest rate | 6.75% |  |  |  |
Total debt | $ 0 |  |  |  | 829
6.750% 2030 Senior Notes | Cleveland-Cliffs Inc. |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Stated interest rate | 6.75% |  |  |  |
Total debt | $ 750 |  |  |  | 750
6.750% 2030 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period One |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 100.00% |  |  |  |
6.750% 2030 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period Two |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 103.375% |  |  |  |
6.750% 2030 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period One, Upon Equity Issuance |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 106.75% |  |  |  |
Restricted Amount (percent of original aggregate principal) | 35.00% |  |  |  |
6.750% 2030 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period Three |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 101.688% |  |  |  |
7.000% 2027 Senior Notes | Cleveland-Cliffs Inc. |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Stated interest rate | 7.00% |  |  |  |
Total debt | $ 73 |  |  |  | 73
7.000% 2027 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period One |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 101.167% |  |  |  |
5.875% 2027 Senior Notes | Cleveland-Cliffs Inc. |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Stated interest rate | 5.875% |  |  |  |
Total debt | $ 556 |  |  |  | 556
5.875% 2027 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period One |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 100.979% |  |  |  |
4.625% 2029 Senior Notes | Cleveland-Cliffs Inc. |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Stated interest rate | 4.625% |  |  |  |
Total debt | $ 368 |  |  |  | 368
4.625% 2029 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period Two |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 102.313% |  |  |  |
4.625% 2029 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period Three |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 101.156% |  |  |  |
4.875% 2031 Senior Notes | Cleveland-Cliffs Inc. |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Stated interest rate | 4.875% |  |  |  |
Total debt | $ 325 |  |  |  | 325
4.875% 2031 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period Two |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 102.438% |  |  |  |
4.875% 2031 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period One, Upon Equity Issuance |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 104.875% |  |  |  |
4.875% 2031 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period Three |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 101.625% |  |  |  |
4.875% 2031 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period Four |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 100.813% |  |  |  |
6.250% 2040 Senior Notes | Cleveland-Cliffs Inc. |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Stated interest rate | 6.25% |  |  |  |
Total debt | $ 235 |  |  |  | 235
6.250% 2040 Senior Notes | Cleveland-Cliffs Inc. | Minimum |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption notice period | day | 30 |  |  |  |
6.250% 2040 Senior Notes | Cleveland-Cliffs Inc. | Maximum |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption notice period | day | 60 |  |  |  |
6.250% 2040 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period One |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 100.00% |  |  |  |
6.250% 2040 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period Two |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 0.40% |  |  |  |
Unsecured Debt | Cleveland-Cliffs Inc. |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Repurchase price if triggering event occurs | 101.00% |  |  |  |
7.000% 2027 AK Senior Notes | AK Steel |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Stated interest rate | 7.00% |  |  |  |
Total debt | $ 56 |  |  |  | 56
7.000% 2027 AK Senior Notes | AK Steel | Debt Instrument, Redemption, Period Two |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 101.167% |  |  |  |
7.000% 2032 Senior Notes | Cleveland-Cliffs Inc. |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Stated interest rate | 7.00% |  |  |  |
Repurchase price if triggering event occurs | 101.00% |  |  |  |
Total debt | $ 1,425 |  | $ 600 | $ 825 | 0
7.000% 2032 Senior Notes | Cleveland-Cliffs Inc. | Minimum |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption notice period | Days | 10 |  |  |  |
7.000% 2032 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period One |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 100.00% |  |  |  |
7.000% 2032 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period Two |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 103.50% |  |  |  |
7.000% 2032 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period One, Upon Equity Issuance |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 107.00% |  |  |  |
Restricted Amount (percent of original aggregate principal) | 35.00% |  |  |  |
7.000% 2032 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period Three |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 101.75% |  |  |  |
6.875% 2029 Senior Notes | Cleveland-Cliffs Inc. |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Repurchase price if triggering event occurs | 10100.00% |  |  |  |
Total debt |  | $ 900 |  |  | 0
6.875% 2029 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period One |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 100.00% |  |  |  |
6.875% 2029 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period Two |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 103.438% |  |  |  |
6.875% 2029 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period One, Upon Equity Issuance |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 106.875% |  |  |  |
Restricted Amount (percent of original aggregate principal) | 35.00% |  |  |  |
7.375% 2033 Senior Notes | Cleveland-Cliffs Inc. |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Repurchase price if triggering event occurs | 10100.00% |  |  |  |
Total debt |  | $ 900 |  |  | $ 0
7.375% 2033 Senior Notes | Cleveland-Cliffs Inc. | Minimum |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption notice period | Days | 10 |  |  |  |
7.375% 2033 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period One |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 100.00% |  |  |  |
7.375% 2033 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period Two |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 103.688% |  |  |  |
7.375% 2033 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period One, Upon Equity Issuance |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Redemption price, percentage | 107.375% |  |  |  |
Restricted Amount (percent of original aggregate principal) | 35.00% |  |  |  |

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