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Financial Instruments - Hedging reserve rollforward (Detail) - MXN ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Disclosure of detailed information about hedged items [line items] |  |  |
Taxes due to changes in reserves during the period | $ 871 | $ (391) | $ (293)
Hedging reserve [member] |  |  |
Disclosure of detailed information about hedged items [line items] |  |  |
Balances at beginning of the period | 431 |  |
Balances at the end of the period | 2,890 | $ 431 |
Hedging reserve [member] | Foreign currency risk [member] | Purchase of stock [member] |  |  |
Disclosure of detailed information about hedged items [line items] |  |  |
Fair value changes | 82 |  |
Hedging reserve [member] | Foreign currency risk [member] | Other stock [member] |  |  |
Disclosure of detailed information about hedged items [line items] |  |  |
Fair value changes | (626) |  |
Hedging reserve [member] | Interest rate risk [member] |  |  |
Disclosure of detailed information about hedged items [line items] |  |  |
Fair value changes | 2,991 |  |
Taxes due to changes in reserves during the period | $ 12 |  |

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- Definition The gains (losses) recognised in other comprehensive income on cash flow hedges, net of tax. [Refer: Cash flow hedges [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2020-01-01 -Paragraph 24C -Subparagraph b -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2020-en-r&anchor=para_24C_b_i&doctype=Standard -URIDate 2020-01-01 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2020-01-01 -Paragraph 24E -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2020-en-r&anchor=para_24E_a&doctype=Standard -URIDate 2020-01-01 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 91 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_91_a&doctype=Standard -URIDate 2020-01-01 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2021-01-01 -Name IFRS -Number 7 -IssueDate 2020-01-01 -Paragraph 23 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2017-en-b&anchor=para_23_c&doctype=Standard&book=b -URIDate 2020-01-01 + Details
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- Definition The amount of income tax relating to amounts recognised in other comprehensive income in relation to cash flow hedges. [Refer: Cash flow hedges [member]; Other comprehensive income] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2020-01-01 -Paragraph 81 -Subparagraph ab -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2020-en-r&anchor=para_81_ab&doctype=Standard -URIDate 2020-01-01 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 90 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_90&doctype=Standard -URIDate 2020-01-01 + Details
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- Definition A component of equity representing the accumulated portion of gain (loss) on a hedging instrument that is determined to be an effective hedge for cash flow hedges. [Refer: Cash flow hedges [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 78 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_78_e&doctype=Standard -URIDate 2020-01-01 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 9 -IssueDate 2020-01-01 -Paragraph 6.5.11 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=9&code=ifrs-tx-2020-en-r&anchor=para_6.5.11&doctype=Standard -URIDate 2020-01-01 + Details
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