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Contingencies (Details) - Tax contingent liability [Member]
MXN in Millions, $ in Millions
Dec. 31, 2017
USD ($)
Dec. 31, 2017
MXN
Nov. 30, 2010
USD ($)
Nov. 30, 2010
MXN
Disclosure of contingent liabilities [line items]        
Amount of tax deduction disallowed by Mexican tax authorities | $     $ 10.0  
Amount of tax deduction disallowed by Mexican tax authorities that would be applied against available tax losses | $     4.3  
Amount of tax deduction disallowed by Mexican tax authorities, subsequently reversed | $     $ 4.8  
Portion of disputed tax deduction remaining relating to transactions with certain suppliers | $ $ 5.2      
Portion of disputed tax deduction remaining relating to value added taxes | $ 0.9      
Value of bond that may be required to secure value added tax portion | $ $ 0.9      
Mexican Peso [Member]        
Disclosure of contingent liabilities [line items]        
Amount of tax deduction disallowed by Mexican tax authorities | MXN       MXN 196.8
Amount of tax deduction disallowed by Mexican tax authorities that would be applied against available tax losses | MXN       84.4
Amount of tax deduction disallowed by Mexican tax authorities, subsequently reversed | MXN       MXN 94.6
Portion of disputed tax deduction remaining relating to transactions with certain suppliers | MXN   MXN 102.2    
Portion of disputed tax deduction remaining relating to value added taxes | MXN   17.8    
Value of bond that may be required to secure value added tax portion | MXN   MXN 17.8