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Income Taxes - Summary of Analysis of Temporary Differences Giving Rise to Net Deferred Tax Liability (Detail) - MXN ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Net deferred tax assets $ 66,303,077 $ 88,074,856 $ 86,613,327 $ 104,573,985
Deferred tax expense in net profit for the year 12,292,014 (3,894,383) 1,994,063  
Provisions [member]        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Net deferred tax assets 19,312,081 17,964,305    
Deferred tax expense in net profit for the year 4,458,848 (257,070) 1,841,705  
Deferred revenues [member]        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Net deferred tax assets 6,748,101 5,820,260    
Deferred tax expense in net profit for the year 897,762 (1,077,259) 3,632,051  
Tax losses carry forward [member]        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Net deferred tax assets 25,121,933 26,630,407    
Deferred tax expense in net profit for the year 2,236,244 (9,873) (5,833,660)  
Property, plant and equipment [member]        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Net deferred tax assets (39,459,549) (11,962,544)    
Deferred tax expense in net profit for the year 3,524,761 (461,594) 453,493  
Inventories [member]        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Net deferred tax assets (537,404) 1,787,065    
Deferred tax expense in net profit for the year (2,393,979) (291,531) 81,270  
Licenses and rights of use [member]        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Net deferred tax assets (5,177,924) (3,399,931)    
Deferred tax expense in net profit for the year 344,729 432,403 961,402  
Employee benefits [member]        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Net deferred tax assets 45,467,827 41,743,744    
Deferred tax expense in net profit for the year 422,473 (1,019,042) 1,128,209  
Other [member]        
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]        
Net deferred tax assets 14,828,012 9,491,550    
Deferred tax expense in net profit for the year $ 2,801,176 $ (1,210,417) $ (270,407)