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Post-Employment and Other Non-current Employee Benefits - Summary of Changes in Balance of Trust Assets (Detail) - Trust assets [member] - MXN ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Pension and retirement plans [member]      
Disclosure Of Trust Assets [Line Items]      
Balance at beginning of year $ 910 $ 864 $ 872
Actual return on trust assets 113 15 26
Foreign exchange gain 86 4 2
Life annuities 21 28 27
Benefits paid (136) (1) (63)
Acquisitions 698    
Balance at end of year 1,692 910 864
Seniority premium plan [member]      
Disclosure Of Trust Assets [Line Items]      
Balance at beginning of year 102 101 92
Actual return on trust assets 7 1 9
Balance at end of year $ 109 $ 102 $ 101