Retirement Benefit Plans - Maturity Analysis of Undiscounted Benefit Payments (Detail) $ in Millions	12 Months Ended
Dec. 31, 2018 TWD ($)
Disclosure Of Defined Benefit Plans [Abstract]
2019	$ 2,736
2020	6,089
2021	10,454
2022	12,566
2023 and thereafter	46,894
Total	$ 78,739

Estimated future benefit payments five fiscal years thereafter.

No definition available.

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Namespace Prefix:	cht_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration