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v3.20.1

Provisions - Movements in Provisions (Detail) - TWD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Jan. 01, 2018
Disclosure of other provisions [Line Items] |  |  |  |
Beginning balance | $ 207 | $ 267 | $ 185 |
Effect of retrospective application of IFRS 15 |  |  |  | $ (87)
Beginning balance as adjusted |  |  |  | 180
Additional provisions recognized | 184 | 192 | 155 |
Used / forfeited during the year | (87) | (165) | (73) |
Ending balance | 304 | 207 | 267 |
Warranties [Member] |  |  |  |
Disclosure of other provisions [Line Items] |  |  |  |
Beginning balance | 132 | 132 | 111 |
Effect of retrospective application of IFRS 15 |  |  |  | 0
Beginning balance as adjusted |  |  |  | 132
Additional provisions recognized | 127 | 164 | 79 |
Used / forfeited during the year | (86) | (164) | (58) |
Ending balance | 173 | 132 | 132 |
Onerous Contracts [Member] |  |  |  |
Disclosure of other provisions [Line Items] |  |  |  |
Beginning balance | 19 | 0 | 0 |
Effect of retrospective application of IFRS 15 |  |  |  | 0
Beginning balance as adjusted |  |  |  | 0
Additional provisions recognized | 48 | 19 | 0 |
Used / forfeited during the year | 0 | 0 | 0 |
Ending balance | 67 | 19 | 0 |
Employee benefits [Member] |  |  |  |
Disclosure of other provisions [Line Items] |  |  |  |
Beginning balance | 51 | 43 | 38 |
Effect of retrospective application of IFRS 15 |  |  |  | 0
Beginning balance as adjusted |  |  |  | 43
Additional provisions recognized | 9 | 9 | 7 |
Used / forfeited during the year | (1) | (1) | (2) |
Ending balance | 59 | 51 | 43 |
Trade-in rights [Member] |  |  |  |
Disclosure of other provisions [Line Items] |  |  |  |
Beginning balance | 0 | 87 | 31 |
Effect of retrospective application of IFRS 15 |  |  |  | (87)
Beginning balance as adjusted |  |  |  | 0
Additional provisions recognized | 0 | 0 | 69 |
Used / forfeited during the year | 0 | 0 | (13) |
Ending balance | 0 | 0 | 87 |
Others [Member] |  |  |  |
Disclosure of other provisions [Line Items] |  |  |  |
Beginning balance | 5 | 5 | 5 |
Effect of retrospective application of IFRS 15 |  |  |  | 0
Beginning balance as adjusted |  |  |  | $ 5
Additional provisions recognized | 0 | 0 | 0 |
Used / forfeited during the year | 0 | 0 | 0 |
Ending balance | $ 5 | $ 5 | $ 5 |

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- Definition Additional provision recognized. + References No definition available. + Details
Name: | cht_AdditionalProvisionRecognized
Namespace Prefix: | cht_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Increase​ decrease ​in provision due to retrospective application of IFRS 15. + References No definition available. + Details
Name: | cht_IncreaseDecreaseInProvisionDueToRetrospectiveApplicationOfIFRS15
Namespace Prefix: | cht_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Provisions as adjusted. + References No definition available. + Details
Name: | cht_ProvisionsAsAdjusted
Namespace Prefix: | cht_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Provisions used. + References No definition available. + Details
Name: | cht_ProvisionsUsed
Namespace Prefix: | cht_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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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
Name: | ifrs-full_DisclosureOfOtherProvisionsLineItems
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The amount of liabilities of uncertain timing or amount. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 54 -Subparagraph l -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_54_l&doctype=Standard -URIDate 2019-03-27 + Details
Name: | ifrs-full_Provisions
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | ifrs-full_ClassesOfProvisionsAxis=ifrs-full_WarrantyProvisionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | ifrs-full_ClassesOfProvisionsAxis=ifrs-full_OnerousContractsProvisionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | ifrs-full_ClassesOfProvisionsAxis=cht_EmploymentBenefitsProvisionMember
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: |

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- Details
Name: | ifrs-full_ClassesOfProvisionsAxis=ifrs-full_MiscellaneousOtherProvisionsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |