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Retirement Benefit Plans - Maturity Analysis of Undiscounted Benefit Payments (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017 TWD ($)
Disclosure Of Defined Benefit Plans [Abstract]
2018	$ 2,042
2019	4,716
2020	8,088
2021	11,201
2022 and thereafter	48,310
Total	$ 74,357

X

- Definition

Estimated future benefit payments.

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No definition available.

+ Details

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Namespace Prefix:	cht_
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Balance Type:	debit
Period Type:	duration

X

- Definition

Estimated future benefit payments Five Fiscal Years Thereafter

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No definition available.

+ Details

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Namespace Prefix:	cht_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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X

- Definition

Estimated future benefit payments next twelve months

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No definition available.

+ Details

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

X

- Definition

Estimated future benefit payments Year Four

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No definition available.

+ Details

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

X

- Definition

Estimated future benefit payments Year Three

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No definition available.

+ Details

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

X

- Definition

Estimated future benefit payments Year Two

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No definition available.

+ Details

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

X

- References

No definition available.

+ Details

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