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Provisions - Movements in Provisions (Detail) - TWD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Disclosure of other provisions [Line Items] |  |  |
Beginning balance | $ 185 | $ 248 | $ 272
Additional provisions recognized | 155 | 121 | 112
Used / forfeited during the year | (73) | (184) | (136)
Ending balance | 267 | 185 | 248
Warranties [Member] |  |  |
Disclosure of other provisions [Line Items] |  |  |
Beginning balance | 111 | 213 | 212
Additional provisions recognized | 79 | 81 | 100
Used / forfeited during the year | (58) | (183) | (99)
Ending balance | 132 | 111 | 213
Trade-in rights [Member] |  |  |
Disclosure of other provisions [Line Items] |  |  |
Beginning balance | 31 | 0 | 0
Additional provisions recognized | 69 | 31 | 0
Used / forfeited during the year | (13) | 0 | 0
Ending balance | 87 | 31 | 0
Employee benefits [Member] |  |  |
Disclosure of other provisions [Line Items] |  |  |
Beginning balance | 38 | 30 | 55
Additional provisions recognized | 7 | 9 | 12
Used / forfeited during the year | (2) | (1) | (37)
Ending balance | 43 | 38 | 30
Others [Member] |  |  |
Disclosure of other provisions [Line Items] |  |  |
Beginning balance | 5 | 5 | 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
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Namespace Prefix: | cht_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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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 the amount recognised when: (a) the entity has a present obligation (legal or constructive) as a result of a past event; (b) it is probable (ie more likely than not) that an outflow of resources embodying economic benefits will be required to settle the obligation; and (c) a reliable estimate can be made of the amount of the obligation. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2016-01-13 -Paragraph 54 -Subparagraph l -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_54_l&doctype=Standard -URIDate 2016-03-31 + 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=cht_TradeInRightsProvisionMember
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
Name: | ifrs-full_ClassesOfProvisionsAxis=ifrs-full_MiscellaneousOtherProvisionsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |