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Retirement Benefit Plans - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2017
Disclosure Of Defined Contribution Plan [line items] |
Percentage of monthly salaries and wages contributed to employees' individual pension accounts | 6.00%
Top of range [Member] |
Disclosure Of Defined Contribution Plan [line items] |
Defined benefit plan contribution, percentage | 15.00%

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- Definition Defined benefit plans employer contribution percentage. + References No definition available. + Details
Name: | cht_DefinedBenefitPlansEmployerContributionPercentage
Namespace Prefix: | cht_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Disclosure Of Defined Contribution Plan [line items] + References No definition available. + Details
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Namespace Prefix: | cht_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Percentage of salaries and wages contributed to employees defined contribution plans. + References No definition available. + Details
Name: | cht_PercentageOfSalariesAndWagesContributedToEmployeesDefinedContributionPlans
Namespace Prefix: | cht_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Details
Name: | ifrs-full_RangeAxis=ifrs-full_TopOfRangeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |