Annual report [Section 13 and 15(d), not S-K Item 405]

DEBT AND CREDIT FACILITIES - Schedule Of Long-Term Debt (Details)

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DEBT AND CREDIT FACILITIES - Schedule Of Long-Term Debt (Details) - USD ($)
$ in Millions
12 Months Ended
Aug. 16, 2024
Apr. 03, 2024
Mar. 18, 2024
Dec. 31, 2024
Oct. 22, 2024
Dec. 31, 2023
Debt Instrument [Line Items]            
Total debt       $ 7,148   $ 3,192
Unamortized discounts and issuance costs       (83)   (55)
Total long-term debt       $ 7,065   3,137
6.750% 2026 Senior Secured Notes | Cleveland-Cliffs Inc.            
Debt Instrument [Line Items]            
Stated interest rate       6.75%    
Annual Effective Interest Rate       6.99%    
Total debt       $ 0   829
Extinguishment of Debt, Amount   $ 189 $ 640      
7.000% 2027 Senior Notes | Cleveland-Cliffs Inc.            
Debt Instrument [Line Items]            
Stated interest rate       7.00%    
Annual Effective Interest Rate       9.24%    
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%    
7.000% 2027 AK Senior Notes | AK Steel            
Debt Instrument [Line Items]            
Stated interest rate       7.00%    
Annual Effective Interest Rate       9.24%    
Total debt       $ 56   56
5.875% 2027 Senior Notes | Cleveland-Cliffs Inc.            
Debt Instrument [Line Items]            
Stated interest rate       5.875%    
Annual Effective Interest Rate       6.49%    
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%    
Annual Effective Interest Rate       4.625%    
Total debt       $ 368   368
6.750% 2030 Senior Notes | Cleveland-Cliffs Inc.            
Debt Instrument [Line Items]            
Stated interest rate       6.75%    
Annual Effective 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%    
4.875% 2031 Senior Notes | Cleveland-Cliffs Inc.            
Debt Instrument [Line Items]            
Stated interest rate       4.875%    
Annual Effective Interest Rate       4.875%    
Total debt       $ 325   325
6.250% 2040 Senior Notes | Cleveland-Cliffs Inc.            
Debt Instrument [Line Items]            
Stated interest rate       6.25%    
Annual Effective Interest Rate       6.34%    
Total debt       $ 235   $ 235
6.250% 2040 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period One            
Debt Instrument [Line Items]            
Redemption price, percentage       100.00%    
ABL Facility            
Debt Instrument [Line Items]            
Credit facility, amount outstanding       $ 1,560    
ABL Facility | Cleveland-Cliffs Inc.            
Debt Instrument [Line Items]            
Annual Effective Interest Rate           5.829%
Credit facility, amount outstanding       $ 1,560   $ 0
6.875% 2029 Senior Notes | Cleveland-Cliffs Inc.            
Debt Instrument [Line Items]            
Annual Effective Interest Rate         6.875%  
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%    
7.000% 2032 Senior Notes | Cleveland-Cliffs Inc.            
Debt Instrument [Line Items]            
Stated interest rate       7.00%    
Annual Effective Interest Rate       7.054%    
Total debt $ 600   $ 825 $ 1,425   0
DebtInstrumentIssuePriceAsAPercentageOfFaceAmount 99.25%          
7.000% 2032 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 [Line Items]            
Annual Effective Interest Rate         7.375%  
Total debt         $ 900 $ 0
7.375% 2033 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period One            
Debt Instrument [Line Items]            
Redemption price, percentage       100.00%