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Financial Instruments - Net Effect of Expired Contracts That Did Not Meet Hedging Criteria (Detail) - Derivative Contract Not Met Hedging Criteria [member] - Market value gain (loss) on financial instruments [member] - MXN ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Cross-currency swaps [member] |  |  |
Disclosure of detailed information about hedges [line items] |  |  |
Net effects of expired contracts | $ 212 | $ 293 | $ 186
Embedded Derivative [Member] |  |  |
Disclosure of detailed information about hedges [line items] |  |  |
Net effects of expired contracts |  | $ (4) |

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- Definition The gain (loss) attributable to expired derivative contracts recognized in profit or loss during the period. + References No definition available. + Details
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Namespace Prefix: | fmx_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table. + References No definition available. + Details
Name: | ifrs-full_DisclosureOfHedgeAccountingLineItems
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | ifrs-full_ClassesOfFinancialInstrumentsAxis=fmx_DerivativeContractNotMetHedgingCriteriaMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | ifrs-full_HedgingInstrumentsAxis=ifrs-full_CurrencySwapContractMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | fmx_IfrsIncomeStatementLocationAxis=fmx_UnrealisedGainLossesOnDerivativeFinancialInstrumentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | ifrs-full_HedgingInstrumentsAxis=fmx_EmbeddedDerivativeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |