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Revenue - Summary of Revenue Recognized (Detail) - TWD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Revenue [Abstract] |  |  |
Telecommunications business | $ 5,492 | $ 6,186 | $ 7,157
Project business | 6,092 | 3,973 | 627
Others | 512 | 404 | 324
Contracts with customers revenue recognized | $ 12,096 | $ 10,563 | $ 8,108

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- Definition Contracts with customers revenue recognized. + References No definition available. + Details
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Namespace Prefix: | cht_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Revenue from others services. + References No definition available. + Details
Name: | cht_RevenueFromOtherServices
Namespace Prefix: | cht_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Revenue from project business. + References No definition available. + Details
Name: | cht_RevenueFromProjectBusiness
Namespace Prefix: | cht_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Revenue from telecommunications business. + References No definition available. + Details
Name: | cht_RevenueFromTelecommunicationsBusiness
Namespace Prefix: | cht_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- References No definition available. + Details
Name: | ifrs-full_RevenueAbstract
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration