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Retirement Benefit Plans - Additional Information (Detail)	12 Months Ended
	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%

X

- Definition

Defined benefit plans employer contribution percentage.

+ References

No definition available.

+ Details

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

X

- Definition

Disclosure Of Defined Contribution Plan [line items]

+ References

No definition available.

+ Details

Name:	cht_DisclosureOfDefinedContributionPlanLineItems
Namespace Prefix:	cht_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- 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

X

- Details

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