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Hedging Derivative Financial Instruments - Loss (Gain) Arising from Hedging Derivative Financial Instruments that have been Reclassified from Equity to Initial Cost of the Property, Plant and Equipment (Detail) - TWD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Disclosure Of Detailed Information About Hedging Instruments [Abstract] |  |  |
Construction in progress and equipment to be accepted | $ (2) | $ (15) | $ (18)

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- Definition Loss (gain) arising from the hedging derivative financial instruments that have been reclassified from equity to initial cost of property plant and equipment. + 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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- References No definition available. + Details
Name: | ifrs-full_DisclosureOfDetailedInformationAboutHedgingInstrumentsAbstract
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration