Quarterly report [Sections 13 or 15(d)]

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
Mar. 31, 2026
Dec. 31, 2025
Debt Instrument [Line Items]    
Long-term Debt, Gross $ 7,837 $ 7,330
Unamortized discounts and issuance costs (74) (77)
Long-term Debt 7,763 7,253
ABL Facility    
Debt Instrument [Line Items]    
Long-term Line of Credit $ 959  
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. | 6.875% 2029 Senior Notes [Member]    
Debt Instrument [Line Items]    
Stated interest rate 6.875%  
Annual Effective Interest Rate 6.875%  
Long-term Debt, Gross $ 900 900
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. | 7.500% 2031 Senior Notes [Member]    
Debt Instrument [Line Items]    
Stated interest rate 7.50%  
Annual Effective Interest Rate 7.50%  
Long-term Debt, Gross $ 850 850
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 1,425
Cleveland-Cliffs Inc. | 7.375% 2033 Senior Notes [Member]    
Debt Instrument [Line Items]    
Stated interest rate 7.375%  
Annual Effective Interest Rate 7.375%  
Long-term Debt, Gross $ 900 900
Cleveland-Cliffs Inc. | 7.625% 2034 Senior Notes [Member]    
Debt Instrument [Line Items]    
Stated interest rate 7.625%  
Annual Effective Interest Rate 7.516%  
Long-term Debt, Gross $ 1,125 1,125
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 5.305%  
Long-term Line of Credit $ 959 $ 452