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STOCKHOLDERS' EQUITY: - Treasury Stock (Details) - USD ($)
$ in Millions
 6 Months Ended 114 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Activity in treasury stock      
Balance at the beginning of the period $ 2,987.6    
Cost of purchase of shares     $ 2.9
Balance at the end of the period $ 2,991.6 $ 2,967.0 $ 2,991.6
Southern copper common shares      
Activity in treasury stock      
Treasury stock balance at the end of the period (in shares) 111,568,817 110,877,016 111,568,817
Southern copper common shares | Directors' Stock Award Plan      
Share Based Compensation Plan, share distributions      
Share Based Compensation Plan, share distributions during the period 10,800 12,000  
Parent Company (Grupo Mexico) common shares      
Activity in treasury stock      
Treasury stock balance at the end of the period (in shares) 111,939,269 116,923,605 111,939,269
Parent Company (Grupo Mexico) common shares | Employee Stock Purchase Plan      
Share Based Compensation Plan, share distributions      
Share Based Compensation Plan, share distributions during the period 300,000 600,000  
TREASURY STOCK: | Southern copper common shares      
Activity in treasury stock      
Balance at the beginning of the period $ 2,769.0 $ 2,697.6  
Cost of purchase of shares   53.7  
Used for corporate purposes (0.3) (0.3)  
Balance at the end of the period 2,768.7 2,751.0 $ 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 4.3 4.7  
Balance at the end of the period $ 222.9 $ 216.0 $ 222.9