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Financial Instruments - Net Effects of Expired Contracts That Met Hedging Criteria (Detail) - Derivative Contract Met Hedging Criteria [Member] - MXN ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Cross-currency swaps [member] | Interest Expense [Member]      
Disclosure of detailed information about hedges [line items]      
Net effects of expired contracts $ (109) $ 199 $ 157
Cross-currency swaps [member] | Foreign exchange [Member]      
Disclosure of detailed information about hedges [line items]      
Net effects of expired contracts 1,212 480 642
Interest rate swaps [member] | Interest Expense [Member]      
Disclosure of detailed information about hedges [line items]      
Net effects of expired contracts (163) 515  
Foreign exchange forward contracts [member] | Foreign exchange [Member]      
Disclosure of detailed information about hedges [line items]      
Net effects of expired contracts (167) (116) (87)
Foreign exchange forward contracts [member] | Cost of Sales [Member]      
Disclosure of detailed information about hedges [line items]      
Net effects of expired contracts 839 (163) 240
Commodity price contracts [Member] | Cost of Sales [Member]      
Disclosure of detailed information about hedges [line items]      
Net effects of expired contracts (129) (391) (258)
Foreign currency option [Member] | Cost of Sales [Member]      
Disclosure of detailed information about hedges [line items]      
Net effects of expired contracts 8 $ (63) $ (8)
Treasury Locks [Member] | Interest Expense [Member]      
Disclosure of detailed information about hedges [line items]      
Net effects of expired contracts $ 153