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Environmental Trust Funds (Tables)
 12 Months Ended
Dec. 31, 2017
Text block1 [abstract]  
Schedule of Environmental Trust Funds
     UNITED STATES DOLLAR  
     2017      2016  

Balance at beginning of the year

      44.5        35.0  

Contributions from continuing operations

      8.6        7.5  

Interest earned

      0.5        1.0  

Translation adjustment

      1.9        1.0  
  

 

 

     

 

 

  

Balance at end of the year

      55.5        44.5