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Hedging Derivative Financial Instruments - Outstanding Forward Exchange Contracts (Detail) - Forward exchange contracts [Member] - Cash flow hedges [Member] € in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017 TWD ($)	Dec. 31, 2016 TWD ($)	Dec. 31, 2017 EUR (€)	Dec. 31, 2016 EUR (€)
Disclosure of detailed information about hedging instruments [Line Items]
Currency	EUR/NT$	EUR/NT$
Maturity Period	2018.03-06	2017.03
Contract Amount	$ 142	$ 102	€ 4	€ 3

X

- Definition

Derivative contract, cross currency.

+ References

No definition available.

+ Details

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Namespace Prefix:	cht_
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Balance Type:	na
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X

- Definition

Description of derivative financial instruments maturity period.

+ References

No definition available.

+ Details

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Namespace Prefix:	cht_
Data Type:	xbrli:stringItemType
Balance Type:	na
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X

- 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

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X

- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ Details

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Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

X

- Details

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X

- Details

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