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
Dec. 31, 2025
Oct. 10, 2025
Sep. 08, 2025
Feb. 06, 2025
Dec. 31, 2024
Oct. 22, 2024
Debt Instrument [Line Items]            
Total debt $ 7,330       $ 7,148  
Unamortized discounts and issuance costs (77)       (83)  
Total long-term debt $ 7,253       7,065  
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 $ 0       73  
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 $ 0       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 $ 0       556  
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  
6.875% 2029 Senior Notes | Cleveland-Cliffs Inc.            
Debt Instrument [Line Items]            
Stated interest rate 6.875%          
Annual Effective Interest Rate           6.875%
Total debt         900 $ 900
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  
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  
7.500% 2031 Senior Notes | Cleveland-Cliffs Inc.            
Debt Instrument [Line Items]            
Stated interest rate 7.50%     7.50%    
Annual Effective Interest Rate 7.50%          
Total debt $ 850     $ 850 0  
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 $ 1,425       1,425  
7.375% 2033 Senior Notes | Cleveland-Cliffs Inc.            
Debt Instrument [Line Items]            
Stated interest rate 7.375%          
Annual Effective Interest Rate           7.375%
Total debt         900 $ 900
7.625% 2034 Senior Notes | Cleveland-Cliffs Inc.            
Debt Instrument [Line Items]            
Stated interest rate 7.625%   7.625%      
Annual Effective Interest Rate           7.516%
Total debt   $ 275 $ 850   0 $ 1,125
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  
ABL Facility            
Debt Instrument [Line Items]            
Credit facility, amount outstanding 452          
ABL Facility | Cleveland-Cliffs Inc.            
Debt Instrument [Line Items]            
Annual Effective Interest Rate         5.327%  
Credit facility, amount outstanding $ 452       $ 1,560