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Pensions and Post-Employment Benefits - Summary of Actuarial (Gains) Losses (Detail) - MXN ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Gain (loss) on remeasurement, net defined benefit liability (asset) [abstract]      
Actuarial (gains) losses due to experience $ 121 $ (511) $ (105)
Actuarial (gains) losses due to demographic assumptions (46) (231) (153)
Actuarial (gains) losses due financial assumptions (78) 4,761 1,006
Total $ (3) $ 4,019 $ 748