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Employee Benefits - Trust Assets (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Mexican subsidiaries [member]
Variable return:
Plan asset investment for related parties, percentage	10.00%
Federal government instruments of the respective countries [member] | Bottom of range [member]
Variable return:
Fund assets, percentage	30.00%
Level 1 [member]
Variable return:
Trust assets fixed and variable return percentage	100.00%	100.00%
Level 1 [member] | Traded Securities [member]
Fixed return:
Trust assets fixed return percentage	27.00%	9.00%
Level 1 [member] | Bank instruments [member]
Fixed return:
Trust assets fixed return percentage	9.00%	23.00%
Level 1 [member] | Federal government instruments of the respective countries [member]
Fixed return:
Trust assets fixed return percentage	29.00%	33.00%
Level 1 [member] | Publicly traded shares [member]
Variable return:
Trust assets variable return percentage	35.00%	35.00%

X

- Definition

Fixed return.

+ References

No definition available.

+ Details

Name:	fmx_FixedReturnAbstract
Namespace Prefix:	fmx_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Percentage of fund assets.

+ References

No definition available.

+ Details

Name:	fmx_PercentageOfFundAssets
Namespace Prefix:	fmx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Percentage of plan asset investment for related parties.

+ References

No definition available.

+ Details

Name:	fmx_PercentageOfPlanAssetInvestmentForRelatedParties
Namespace Prefix:	fmx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Trust assets fixed and variable return percentage.

+ References

No definition available.

+ Details

Name:	fmx_TrustAssetsFixedAndVariableReturnPercentage
Namespace Prefix:	fmx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Trust assets fixed return percentage.

+ References

No definition available.

+ Details

Name:	fmx_TrustAssetsFixedReturnPercentage
Namespace Prefix:	fmx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Trust assets variable return percentage.

+ References

No definition available.

+ Details

Name:	fmx_TrustAssetsVariableReturnPercentage
Namespace Prefix:	fmx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Variable return.

+ References

No definition available.

+ Details

Name:	fmx_VariableReturnAbstract
Namespace Prefix:	fmx_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	ifrs-full_CategoriesOfRelatedPartiesAxis=ifrs-full_SubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_ClassesOfFinancialAssetsAxis=fmx_FederalGovernmentInstrumentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_RangeAxis=ifrs-full_BottomOfRangeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_LevelsOfFairValueHierarchyAxis=ifrs-full_Level1OfFairValueHierarchyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_ClassesOfFinancialAssetsAxis=fmx_TradedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_ClassesOfFinancialAssetsAxis=fmx_BankInstrumentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_ClassesOfFinancialAssetsAxis=fmx_PubliclyTradedSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: