Annual report pursuant to Section 13 and 15(d)

GOODWILL AND INTANGIBLE ASSETS AND LIABILITIES - Goodwill (Details)

v3.20.4
GOODWILL AND INTANGIBLE ASSETS AND LIABILITIES - Goodwill (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Mar. 13, 2020
Dec. 31, 2019
Goodwill [Line Items]      
Goodwill $ 1,406   $ 2
ArcelorMittal USA [Member]      
Goodwill [Line Items]      
Goodwill 1,230    
AK Steel [Member]      
Goodwill [Line Items]      
Goodwill 174 $ 141  
Steelmaking [Member]      
Goodwill [Line Items]      
Goodwill 1,232   2
Steelmaking [Member] | ArcelorMittal USA [Member]      
Goodwill [Line Items]      
Goodwill, Period Increase (Decrease) 1,230    
Other businesses      
Goodwill [Line Items]      
Goodwill 174   $ 0
Other businesses | AK Steel [Member]      
Goodwill [Line Items]      
Goodwill, Period Increase (Decrease) $ 174