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Employee Benefits - Summary of Changes in the Balance of Plan Assets (Detail) - Plan assets [member] - MXN ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of net defined benefit liability (asset) [line items]      
Initial balance $ 2,378 $ 2,228 $ 2,158
Actual return on trust assets 213 40 65
Foreign exchange loss (gain) 86 4 7
Life annuities 65 107 61
Benefits paid (136) (1) (63)
Acquisitions 698    
Ending balance $ 3,304 $ 2,378 $ 2,228