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Income Taxes - Summary of Reconciliation of Statutory Income Tax Rate in Mexico to Consolidated Effective Income Tax Rate Recognized (Detail) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Statutory income tax rate in Mexico | 30.00% | 30.00% | 30.00%
Impact of non-deductibleand non-taxable items: |  |  |
Tax inflation effects | 6.10% | 3.50% | 7.30%
Derivatives | (0.70%) | (0.10%) | 0.40%
Employee benefits | 3.00% | 1.80% | 1.30%
Other | (2.40%) | 1.80% | 6.30%
Dividends received from associates Equity | (0.90%) | (0.40%) | (0.80%)
Foreign subsidiaries and other non-deductible items, net | (1.50%) | 5.50% | 1.50%
Effective tax rate | 24.30% | 42.10% | 46.00%
Mexico [member] |  |  |
Impact of non-deductibleand non-taxable items: |  |  |
Effective tax rate | 36.00% | 37.00% | 45.30%
Brazil [member] |  |  |
Impact of non-deductibleand non-taxable items: |  |  |
Tax recoveries in Brazil | (9.30%) |  |

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