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Equity - Unrealized Gain or Loss on Financial Assets at FVOCI (Detail) - TWD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Statement Of Changes In Equity [Abstract] |  |  |
Beginning balance | $ 735 | $ 538 | $ 883
Unrealized gain or loss for the year |  |  |
Equity instruments | 522 | 197 | (345)
Transferred accumulated gain or loss to unappropriated earnings resulting from the disposal of equity instruments | (17) | 0 | 0
Ending balance | $ 1,240 | $ 735 | $ 538

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- Definition Unrealized gain loss on transferred accumulated changes to unappropriated earnings resulting from the disposal of equity instruments. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
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Period Type: | duration

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- Definition Unrealized gain or loss for the year. + References No definition available. + Details
Name: | cht_UnrealizedGainOrLossForYearAbstract
Namespace Prefix: | cht_
Data Type: | xbrli:stringItemType
Balance Type: | na
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- Definition Unrealized gain (loss) on equity instrument. + 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 Unrealized gain or loss on financial assets at fair value through other comprehensive income. + References No definition available. + Details
Name: | cht_UnrealizedGainOrLossOnFinancialAssetsAtFVOCI
Namespace Prefix: | cht_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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