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Income Taxes - Summary of Composition of Income Tax Expense (Detail)
$ in Thousands, $ in Millions
 12 Months Ended
Dec. 31, 2020
MXN ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2019
MXN ($)
Dec. 31, 2018
MXN ($)
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Income tax expense $ 16,366,152 $ 820 $ 51,033,533 $ 46,477,079
Mexico [member]        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Current year income tax 13,407,948   26,295,431 28,572,414
Deferred income tax (9,334,246)   208,658 (2,688,727)
Foreign [member]        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Current year income tax 15,250,218   20,843,720 19,898,728
Deferred income tax $ (2,957,768)   $ 3,685,724 $ 694,664