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Financial Instruments - Financing Facilities (Detail) - TWD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Unsecured loans [Member] |  |
Disclosure of detailed information about financial instruments [Line Items] |  |
Unsecured bank loan facility, amount used | $ 90 | $ 118
Bank loan facility, amount unused | 45,749 | 46,219
Unsecured bank loan facility | 45,839 | 46,337
Secured loans [Member] |  |
Disclosure of detailed information about financial instruments [Line Items] |  |
Secured loans | 1,600 | 1,620
Bank loan facility, amount unused | 1,910 | 200
Secured bank loan facility | $ 3,510 | $ 1,820

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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 2016-01-13 -Paragraph 112 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_112_c&doctype=Standard -URIDate 2016-03-31 + 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 2016-01-13 -Paragraph 50 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=7&date=2016-03-30&anchor=para_50_a&doctype=Standard -URIDate 2016-03-31 + 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 2016-01-13 -Paragraph 112 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_112_c&doctype=Standard -URIDate 2016-03-31 + 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
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |