Retirement Benefit Plans - Additional Information (Detail)	12 Months Ended
Dec. 31, 2018
Disclosure of Defined Retirement Plans
Percentage of monthly salaries and wages contributed to employees' individual pension accounts	6.00%
Top of range [Member]
Disclosure of Defined Retirement Plans
Defined benefit plan contribution, percentage	15.00%

Percentage of salaries and wages contributed to employees defined contribution plans.

No definition available.

Name:	cht_PercentageOfSalariesAndWagesContributedToEmployeesDefinedContributionPlans
Namespace Prefix:	cht_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant