Annual report pursuant to Section 13 and 15(d)

CAPITAL STOCK - Narrative (Details)

v3.20.4
CAPITAL STOCK - Narrative (Details)
$ / shares in Units, $ in Millions
 12 Months Ended
Dec. 09, 2020
shares
Mar. 13, 2020
USD ($)
Dec. 31, 2020
USD ($)
shareMultiple
$ / shares
shares
Dec. 31, 2019
USD ($)
shares
Dec. 31, 2018
USD ($)
Apr. 24, 2019
USD ($)
Nov. 26, 2018
USD ($)
Class of Stock [Line Items]              
Common shares, par value | $ / shares     $ 0.125        
Temporary Equity, Shares Issued     583,273        
Temporary Equity, Shares Outstanding     583,273        
Stock Repurchase Program, Authorized Amount | $           $ 100 $ 200
Repurchase of common shares | $     $ 0 $ 253 $ 48    
Preferred Stock, Share Multiple | shareMultiple     100        
AK Steel [Member]              
Class of Stock [Line Items]              
Business Acquisition, Shares Exchange Ratio   0.400          
Common Stock [Member]              
Class of Stock [Line Items]              
Common shares, par value | $ / shares     $ 0.125        
Stock Repurchased During Period, Shares       24,000,000      
Common Stock [Member] | AK Steel [Member]              
Class of Stock [Line Items]              
Business Acquisition, Shares Exchange Ratio     0.400        
Stock Issued During Period, Shares, Acquisitions     127,000,000        
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned | $   $ 618          
Common Stock [Member] | ArcelorMittal USA [Member]              
Class of Stock [Line Items]              
Stock Issued During Period, Shares, Acquisitions 78,186,671   78,000,000        
Series A Preferred Stock              
Class of Stock [Line Items]              
Preferred Stock, Shares Authorized     3,000,000        
Preferred Stock, Shares Issued     0        
Preferred Stock, Shares Outstanding     0        
Series B Preferred Stock              
Class of Stock [Line Items]              
Preferred Stock, Shares Authorized     4,000,000        
Temporary Equity, Shares Issued     583,273        
Temporary Equity, Shares Outstanding     583,273        
Series B Preferred Stock | ArcelorMittal USA [Member]              
Class of Stock [Line Items]              
Stock Issued During Period, Shares, Acquisitions 583,273   583,273        
Series B Redeemable Preferred Stock              
Class of Stock [Line Items]              
Preferred Stock, Dividend Rate, Percentage, Daily Compounding Rate     10.00%        
Preferred Stock, Dividend Rate, Percentage     2.00%