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Employee Benefits - Summary of Changes in the Balance of the Defined Benefit Obligation for Post-employment (Detail) - MXN ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of net defined benefit liability (asset) [line items]      
Current service cost $ 408 $ 359 $ 343
Pension and retirement plans [member]      
Disclosure of net defined benefit liability (asset) [line items]      
Initial balance 5,702    
Ending balance 7,370 5,702  
Pension and retirement plans [member] | Present value of defined benefit obligation [member]      
Disclosure of net defined benefit liability (asset) [line items]      
Initial balance 5,702 5,308 5,270
Current service cost 341 245 233
Past service cost 10 45 3
Interest expense 491 369 353
Effect on curtailment (2) (61) (120)
Remeasurements of the net defined benefit obligation 263 (67) (154)
Foreign exchange loss (gain) (79) 150 39
Benefits paid (550) (287) (316)
Acquisitions 1,194    
Ending balance 7,370 5,702 5,308
Seniority premiums [member] | Present value of defined benefit obligation [member]      
Disclosure of net defined benefit liability (asset) [line items]      
Initial balance 663 610 563
Current service cost 106 93 88
Interest expense 49 41 38
Settlement (1)    
Effect on curtailment     (9)
Remeasurements of the net defined benefit obligation 28 (43) (34)
Benefits paid (68) (55) (45)
Acquisitions 6 17 9
Ending balance 783 663 610
Postretirement medical services [member]      
Disclosure of net defined benefit liability (asset) [line items]      
Initial balance 460    
Ending balance 524 460  
Postretirement medical services [member] | Present value of defined benefit obligation [member]      
Disclosure of net defined benefit liability (asset) [line items]      
Initial balance 460 404 338
Current service cost 24 22 16
Interest expense 34 27 26
Remeasurements of the net defined benefit obligation 32 30 44
Benefits paid (26) (23) (20)
Ending balance $ 524 460 404
Post-employment [member] | Present value of defined benefit obligation [member]      
Disclosure of net defined benefit liability (asset) [line items]      
Initial balance   135 194
Current service cost     5
Certain liability cost     73
Reclassification to certain liability cost   $ (135)  
Foreign exchange loss (gain)     (137)
Ending balance     $ 135