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STOCKHOLDERS' EQUITY - Treasury Stock (Details) - USD ($)
$ in Millions
 12 Months Ended 60 Months Ended 120 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2017
Activity in treasury stock              
Balance at the beginning of the period $ 2,987.6            
Purchase of shares   $ 71.7 $ 1,004.4 $ 682.8 $ 281.4 $ 878.1 $ 2,918.4
Balance at the end of the period $ 3,001.1 $ 2,987.6         $ 3,001.1
Southern copper common shares              
Activity in treasury stock              
Treasury stock balance at the end of the period (in shares) 111,567,617 111,579,617         111,567,617
Parent Company (Grupo Mexico) common shares              
Activity in treasury stock              
Treasury stock balance at the end of the period (in shares) 108,450,672 115,667,784         108,450,672
TREASURY STOCK: | Southern copper common shares              
Activity in treasury stock              
Balance at the beginning of the period $ 2,769.0 $ 2,697.6          
Purchase of shares   71.7 1,004.4        
Used for corporate purposes (0.3) (0.3) (0.3)        
Balance at the end of the period 2,768.7 2,769.0 2,697.6       $ 2,768.7
TREASURY STOCK: | Parent Company (Grupo Mexico) common shares              
Activity in treasury stock              
Balance at the beginning of the period 218.6 211.3          
Other activity, including dividend, interest and foreign currency transaction effect 13.8 7.3 4.2        
Balance at the end of the period $ 232.4 $ 218.6 $ 211.3       $ 232.4