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STOCKHOLDERS' EQUITY - Treasury Stock (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Activity in treasury stock      
Balance at the beginning of the period $ 3,048.9    
Purchase of shares 2,900.0    
Balance at the end of the period $ 3,063.5 $ 3,048.9  
Southern Copper common shares      
Activity in treasury stock      
Treasury stock balance at the end of the period (in shares) 111,522,817 111,537,217  
TREASURY STOCK: | Southern Copper common shares      
Activity in treasury stock      
Balance at the beginning of the period $ 2,767.9 $ 2,768.3  
Used for corporate purposes (0.4) (0.4) $ (0.4)
Balance at the end of the period 2,767.5 2,767.9 2,768.3
TREASURY STOCK: | Parent Company (Grupo Mexico) common shares      
Activity in treasury stock      
Balance at the beginning of the period 281.0 251.3  
Other activity, including dividend, interest and foreign currency transaction effect 15.0 29.7 18.9
Balance at the end of the period $ 296.0 $ 281.0 $ 251.3