Annual report pursuant to Section 13 and 15(d)

DEBT AND CREDIT FACILITIES - Debt Issuances and Terms (Details)

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DEBT AND CREDIT FACILITIES - Debt Issuances and Terms (Details)
$ in Millions
12 Months Ended
Dec. 31, 2023
USD ($)
day
Apr. 14, 2023
USD ($)
Dec. 31, 2022
USD ($)
Debt Instrument [Line Items]      
Total debt $ 3,192   $ 4,306
6.750% 2026 Senior Secured Notes | Cleveland-Cliffs Inc.      
Debt Instrument [Line Items]      
Stated interest rate 6.75%    
Repurchase price if triggering event occurs 101.00%    
Total debt $ 829   829
6.750% 2026 Senior Secured Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period One      
Debt Instrument [Line Items]      
Redemption price, percentage 103.375%    
6.750% 2026 Senior Secured Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period Two      
Debt Instrument [Line Items]      
Redemption price, percentage 101.688%    
6.750% 2030 Senior Notes | Cleveland-Cliffs Inc.      
Debt Instrument [Line Items]      
Stated interest rate 6.75%    
Repurchase price if triggering event occurs 101.00%    
Total debt $ 750 $ 750 0
6.750% 2030 Senior Notes | Cleveland-Cliffs Inc. | Minimum      
Debt Instrument [Line Items]      
Redemption notice period | day 10    
6.750% 2030 Senior Notes | Cleveland-Cliffs Inc. | Maximum      
Debt Instrument [Line Items]      
Redemption notice period | day 60    
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 102.333%    
7.000% 2027 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period Two      
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 101.958%    
5.875% 2027 Senior Notes | Cleveland-Cliffs Inc. | Debt Instrument, Redemption, Period Two      
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 One, Upon Equity Issuance      
Debt Instrument [Line Items]      
Redemption price, percentage 104.625%    
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 | US Treasury (UST) Interest Rate      
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 One      
Debt Instrument [Line Items]      
Redemption price, percentage 102.333%    
7.000% 2027 AK Senior Notes | AK Steel | Debt Instrument, Redemption, Period Two      
Debt Instrument [Line Items]      
Redemption price, percentage 101.167%