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Financial Instruments - Net Effects of Expired Contracts That Met Hedging Criteria (Detail) - Derivative Contract Met Hedging Criteria [Member] - MXN ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Cross-currency swaps [member] | Interest Expense [Member] |  |  |
Disclosure of detailed information about hedges [line items] |  |  |
Net effects of expired contracts | $ (109) | $ 199 | $ 157
Cross-currency swaps [member] | Foreign exchange [Member] |  |  |
Disclosure of detailed information about hedges [line items] |  |  |
Net effects of expired contracts | 1,212 | 480 | 642
Interest rate swaps [member] | Interest Expense [Member] |  |  |
Disclosure of detailed information about hedges [line items] |  |  |
Net effects of expired contracts | (163) | 515 |
Foreign exchange forward contracts [member] | Foreign exchange [Member] |  |  |
Disclosure of detailed information about hedges [line items] |  |  |
Net effects of expired contracts | (167) | (116) | (87)
Foreign exchange forward contracts [member] | Cost of Sales [Member] |  |  |
Disclosure of detailed information about hedges [line items] |  |  |
Net effects of expired contracts | 839 | (163) | 240
Commodity price contracts [Member] | Cost of Sales [Member] |  |  |
Disclosure of detailed information about hedges [line items] |  |  |
Net effects of expired contracts | (129) | (391) | (258)
Foreign currency option [Member] | Cost of Sales [Member] |  |  |
Disclosure of detailed information about hedges [line items] |  |  |
Net effects of expired contracts | 8 | $ (63) | $ (8)
Treasury Locks [Member] | Interest Expense [Member] |  |  |
Disclosure of detailed information about hedges [line items] |  |  |
Net effects of expired contracts | $ 153 |  |

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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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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
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- Details
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- Details
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Data Type: | na
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- Details
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- Details
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- Details
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- Details
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- Details
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- Details
Name: | ifrs-full_HedgingInstrumentsAxis=fmx_CommodityContract1Member
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- Details
Name: | ifrs-full_HedgingInstrumentsAxis=ifrs-full_OptionContractMember
Namespace Prefix: |
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- Details
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