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Financial Instruments - Financing Facilities (Detail) - TWD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Unsecured loans [Member] |  |
Disclosure of detailed information about financial instruments [Line Items] |  |
Unsecured bank loan facility, amount used | $ 7,068 | $ 121
Bank loan facility, amount unused | 59,277 | 46,109
Unsecured bank loan facility | 66,345 | 46,230
Secured loans [Member] |  |
Disclosure of detailed information about financial instruments [Line Items] |  |
Bank loan facility, amount unused | 20 | 1,340
Secured bank loan facility, amount used | 1,600 | 1,600
Secured bank loan facility | $ 1,620 | $ 2,940

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- Definition Secured bank loan facility. + References No definition available. + Details
Name: | cht_SecuredBankLoanFacility
Namespace Prefix: | cht_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Unsecured bank loan facility. + References No definition available. + Details
Name: | cht_UnsecuredBankLoanFacility
Namespace Prefix: | cht_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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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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Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The amount of loans received from banks that have been secured by collateral. [Refer: Loans received] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 112 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_112_c&doctype=Standard -URIDate 2020-01-01 + Details
Name: | ifrs-full_SecuredBankLoansReceived
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The amount of undrawn borrowing facilities that may be available for future operating activities and to settle capital commitments. [Refer: Capital commitments] + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Name IAS -Number 7 -IssueDate 2020-01-01 -Paragraph 50 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=7&code=ifrs-tx-2020-en-r&anchor=para_50_a&doctype=Standard -URIDate 2020-01-01 + Details
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Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The amount of loans received from banks that have not been secured by collateral. [Refer: Loans received] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 112 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_112_c&doctype=Standard -URIDate 2020-01-01 + Details
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Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | ifrs-full_ClassesOfFinancialLiabilitiesAxis=cht_SecuredLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |