Quarterly report pursuant to Section 13 or 15(d)

CAPITAL STOCK - Narrative (Details)

v3.21.2
CAPITAL STOCK - Narrative (Details)
$ / shares in Units, $ in Millions
3 Months Ended 6 Months Ended
Mar. 11, 2021
USD ($)
Dec. 09, 2020
shares
Apr. 24, 2020
USD ($)
Mar. 13, 2020
USD ($)
shares
Jun. 30, 2021
USD ($)
$ / shares
shares
Jun. 30, 2020
USD ($)
Jun. 30, 2021
USD ($)
$ / shares
shares
Jun. 30, 2020
USD ($)
Apr. 29, 2021
shares
Mar. 31, 2021
shares
Feb. 11, 2021
$ / shares
shares
Dec. 31, 2020
shares
Class of Stock [Line Items]                        
Common shares, issued (in shares)         506,832,537   506,832,537       20,000,000 506,832,537
Debt Extinguished | $     $ 736   $ 421 $ 748 $ 1,278 $ 1,488        
Common shares, par value (in dollars per share) | $ / shares         $ 0.125   $ 0.125          
Series B Participating Redeemable Preferred Stock, issued (in shares)         583,273   583,273         583,273
Series B Participating Redeemable Preferred Stock, outstanding (in shares)         583,273   583,273         583,273
Common shares, authorized (in shares)         1,200,000,000   1,200,000,000   1,200,000,000 600,000,000   600,000,000
9.875% 2025 Senior Secured Notes                        
Class of Stock [Line Items]                        
Debt Extinguished | $ $ 322       $ 25   $ 347          
Arcelor Mittal                        
Class of Stock [Line Items]                        
Common shares sold (in shares)                     40,000,000  
Cleveland-Cliffs Inc. | 9.875% 2025 Senior Secured Notes                        
Class of Stock [Line Items]                        
Stated interest rate         9.875%   9.875%         9.875%
AK Steel                        
Class of Stock [Line Items]                        
Exchange ratio       0.400                
Fair value of Cliffs common shares issued for AK Steel outstanding common stock | $       $ 618                
Common Stock                        
Class of Stock [Line Items]                        
Share price (in dollars per share) | $ / shares                     $ 16.12  
Common Stock | ArcelorMittal USA                        
Class of Stock [Line Items]                        
Stock issued during period, shares, acquisitions (in shares)   78,186,671                    
Common Stock | AK Steel                        
Class of Stock [Line Items]                        
Stock issued during period, shares, acquisitions (in shares)       127,000,000                
Exchange ratio             0.400          
Series B Preferred Stock                        
Class of Stock [Line Items]                        
Preferred stock authorized (in shares)         4,000,000   4,000,000          
Series B Participating Redeemable Preferred Stock, issued (in shares)         583,273   583,273          
Series B Participating Redeemable Preferred Stock, outstanding (in shares)         583,273   583,273          
Series B Preferred Stock | ArcelorMittal USA                        
Class of Stock [Line Items]                        
Stock issued during period, shares, acquisitions (in shares)   583,273         583,273          
Series A Preferred Stock                        
Class of Stock [Line Items]                        
Preferred stock authorized (in shares)         3,000,000   3,000,000          
Preferred stock outstanding (in shares)         0   0          
Preferred stock issued (in shares)         0   0