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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
	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)

X

- 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

X

- 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

X

- Details

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

X

- Details

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

X

- Details

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

X

- Details

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