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ACCOUNTING POLICIES (Impairment) (Details) - USD ($)
$ in Millions
 9 Months Ended 12 Months Ended
Sep. 30, 2022
Dec. 31, 2024
Dec. 31, 2022
Dec. 31, 2023
Disclosure of impairment loss and reversal of impairment loss [line items]        
Discount rate used in current estimate of value in use   12.38%    
Usiminas Control Group        
Disclosure of impairment loss and reversal of impairment loss [line items]        
Impairment charge $ 120.4      
Total for all cash-generating units        
Disclosure of impairment loss and reversal of impairment loss [line items]        
Growth rate used to extrapolate cash flow projections   2.19%    
Discount rate used in current estimate of value in use   12.40%   12.10%
Argentina | Total for all individual assets or cash-generating units        
Disclosure of impairment loss and reversal of impairment loss [line items]        
Recoverable amount of asset or cash-generating unit   $ 1,700.0    
Percentage increase in discount rate, resulting in impairment charges   0.50%    
Percentage decrease in operating income, resulting in impairment charges   5.00%    
Argentina | Total for all subsidiaries        
Disclosure of impairment loss and reversal of impairment loss [line items]        
Discount rate used in current estimate of value in use   14.00%    
Brazil | Total for all subsidiaries        
Disclosure of impairment loss and reversal of impairment loss [line items]        
Discount rate used in current estimate of value in use   10.30%    
Impairment charge     $ 99.0