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Retirement Benefit Plans - Maturity Analysis of Undiscounted Benefit Payments (Detail) $ in Millions | 12 Months Ended
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Dec. 31, 2020 TWD ($)
Disclosure Of Defined Benefit Plans [Abstract] |
2021 | $ 3,285
2022 | 7,056
2023 | 10,669
2024 | 11,799
2025 and thereafter | 39,497
Total | $ 72,306

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- Definition Estimated future benefit payments. + References No definition available. + Details
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Namespace Prefix: | cht_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Estimated future benefit payments five fiscal years thereafter. + References No definition available. + Details
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Namespace Prefix: | cht_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Estimated future benefit payments next twelve months. + References No definition available. + Details
Name: | cht_EstimatedFutureBenefitPaymentsNextTwelveMonths
Namespace Prefix: | cht_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Estimated future benefit payments year four. + References No definition available. + Details
Name: | cht_EstimatedFutureBenefitPaymentsYearFour
Namespace Prefix: | cht_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Estimated future benefit payments year three. + References No definition available. + Details
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Namespace Prefix: | cht_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Estimated future benefit payments year two. + References No definition available. + Details
Name: | cht_EstimatedFutureBenefitPaymentsYearTwo
Namespace Prefix: | cht_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
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Namespace Prefix: | ifrs-full_
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Balance Type: | na
Period Type: | duration