Financial Instruments - Disclosure of Treasury Lock contracts (Detail) - Treasury Lock contracts [Member] - Less than 1 year [member] $ in Millions	Dec. 31, 2019 MXN ($)
Disclosure of detailed information about hedges [line items]
Notional	$ 10,365
Fair Value Asset	$ 102

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.

No definition available.

+ Details

Name:	ifrs-full_DisclosureOfHedgeAccountingLineItems
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of a hedging instrument, recognised as an asset. [Refer: Hedging instruments [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2019-01-01
-Paragraph 24A
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2019-en-r&anchor=para_24A_a&doctype=Standard
-URIDate 2019-03-27

+ Details

Name:	ifrs-full_HedgingInstrumentAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The nominal or face amount of a financial instrument, used to calculate payments made on that instrument.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2019-01-01
-Paragraph 112
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_112_c&doctype=Standard
-URIDate 2019-03-27

+ Details

Name:	ifrs-full_NotionalAmount
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	ifrs-full_TypesOfHedgesAxis=fmx_TreasuryLockContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_MaturityAxis=ifrs-full_NotLaterThanOneYearMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: