Number of shares entitled to acquire per stock option.

No definition available.

Name:	cht_NumberOfSharesEntitledToAcquirePerStockOption
Namespace Prefix:	cht_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of treasury stock transfer to specific employees.

+ References

No definition available.

+ Details

Name:	cht_NumberOfTreasuryStockTransferToSpecificEmployees
Namespace Prefix:	cht_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Options granted vesting percentage.

+ References

No definition available.

+ Details

Name:	cht_OptionsGrantedVestingPercentage
Namespace Prefix:	cht_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Reserve for employee subscription.

+ References

No definition available.

+ Details

Name:	cht_ReserveForEmployeeSubscription
Namespace Prefix:	cht_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The description of the maximum term of options granted for a type of share-based payment arrangement that existed at any time during the period. An entity with substantially similar types of share-based payment arrangements may aggregate this information. [Refer: Share-based payment arrangements [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2016-01-13
-Paragraph 45
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2016-03-30&anchor=para_45_a&doctype=Standard
-URIDate 2016-03-31

+ Details

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

- Definition

The description of the vesting requirements for a type of share-based payment arrangement that existed at any time during the period. An entity with substantially similar types of share-based payment arrangements may aggregate this information. [Refer: Share-based payment arrangements [member]]

+ References

+ Details

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

- 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_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The exercise price of outstanding share options.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2016-01-13
-Paragraph 45
-Subparagraph d
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2016-03-30&anchor=para_45_d&doctype=Standard
-URIDate 2016-03-31

+ Details

Name:	ifrs-full_ExercisePriceOfOutstandingShareOptions
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of expense from share-based payment transactions with employees.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2016-01-13
-Paragraph 112
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_112_c&doctype=Standard
-URIDate 2016-03-31

+ Details

Name:	ifrs-full_ExpenseFromSharebasedPaymentTransactionsWithEmployees
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The increase (decrease) in the number of ordinary shares issued. [Refer: Ordinary shares [member]]

+ References

+ Details

Name:	ifrs-full_IncreaseDecreaseInNumberOfOrdinarySharesIssued
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	ifrs-full_SignificantInvestmentsInSubsidiariesAxis=cht_SenaoInternationalCoLtdMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	cht_GrantDateAxis=cht_StockOptionGrantedInMayAndNovemberMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_TypesOfSharebasedPaymentArrangementsAxis=cht_SharebasedPaymentArrangementTrancheOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_TypesOfSharebasedPaymentArrangementsAxis=cht_SharebasedPaymentArrangementTrancheTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_TypesOfSharebasedPaymentArrangementsAxis=cht_SharebasedPaymentArrangementTrancheThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_SignificantInvestmentsInSubsidiariesAxis=cht_CHIEFTelecomIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	cht_GrantDateAxis=cht_TwentyTwoOctoberTwoThousandFifteenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	cht_GrantDateAxis=cht_NineteenDecemberTwoThousandSeventeenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_SignificantInvestmentsInSubsidiariesAxis=cht_ChunghwaPrecisionTestTechCoLtdMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Share-based Payments Arrangement - Additional Information (Detail) $ in Millions						12 Months Ended
	Dec. 19, 2017 TWD ($) shares	Feb. 08, 2017 shares	Dec. 08, 2015 shares	Oct. 22, 2015 TWD ($) shares	May 07, 2013 shares	Dec. 31, 2017 TWD ($) shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 TWD ($)	Dec. 31, 2015 TWD ($)	Jul. 31, 2017 TWD ($)	Jun. 30, 2017 TWD ($)	Jul. 31, 2016 TWD ($)	Jun. 30, 2016 TWD ($)	Jul. 31, 2015 TWD ($)
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Compensation costs						$ 22,000,000	$ 1	$ 17,000,000	$ 36,000,000
Senao International Co., Ltd. (SENAO) [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Number of common share each option is eligible \| shares					1
Option expire period					six years
Compensation costs						4,000,000		13,000,000	35,000,000
Exercise Price						70.70		76.10	81.40	$ 70.70	$ 76.10	$ 76.10	$ 81.40	$ 84.30
Senao International Co., Ltd. (SENAO) [Member] \| Stock Option Granted in May and November 2017 [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Compensation costs						$ 9,000,000
Number of treasury stock transfer to its specific employees \| shares						3,342,000	3,342,000
Senao International Co., Ltd. (SENAO) [Member] \| 2 years after grant date [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Vesting period					two years
Vesting percentage					50.00%
Senao International Co., Ltd. (SENAO) [Member] \| 3 years after grant date [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Vesting period					three years
Vesting percentage					25.00%
Senao International Co., Ltd. (SENAO) [Member] \| 4 years after grant date [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Vesting period					four years
Vesting percentage					25.00%
CHIEF Telecom Inc. (CHIEF) [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Number of common share each option is eligible \| shares	1,000			1,000
Exercise Price	$ 147.00			$ 43.00								$ 34.40	$ 43.00
CHIEF Telecom Inc. (CHIEF) [Member] \| Granted on October 22, 2015 [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Option expire period						five years	five years
Vesting period						two years	two years
Compensation costs						$ 3,000,000		4,000,000	$ 1,000,000
Exercise Price						$ 34.40		34.40
CHIEF Telecom Inc. (CHIEF) [Member] \| Granted on December 19, 2017 [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Option expire period						five years	five years
Vesting period						two years	two years
Compensation costs						$ 100,000
Exercise Price						147.00
Chunghwa Precision Test Tech. Co., Ltd. (CHPT) [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Compensation costs						$ 6,000,000		$ 16,000
Shares issued \| shares		2,000,000	2,787,000
Reserve for employee subscription \| shares		300,000	418,000