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STOCKHOLDERS' EQUITY - Treasury Stock (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Activity in treasury stock      
Balance at the beginning of the period $ 3,001.1    
Balance at the end of the period $ 3,019.6 $ 3,001.1  
Southern copper common shares      
Activity in treasury stock      
Treasury stock balance at the end of the period (in shares) 111,551,617 111,567,617  
Parent Company (Grupo Mexico) common shares      
Activity in treasury stock      
Purchase of shares $ 2,900.0    
TREASURY STOCK: | Southern copper common shares      
Activity in treasury stock      
Balance at the beginning of the period 2,768.7 $ 2,769.0  
Purchase of shares     $ 71.7
Used for corporate purposes (0.4) (0.3) (0.3)
Balance at the end of the period 2,768.3 2,768.7 2,769.0
TREASURY STOCK: | Parent Company (Grupo Mexico) common shares      
Activity in treasury stock      
Balance at the beginning of the period 232.4 218.6  
Other activity, including dividend, interest and foreign currency transaction effect 18.9 13.8 7.3
Balance at the end of the period $ 251.3 $ 232.4 $ 218.6