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Financial Instruments - Additional Information (Detail) - TWD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Foreign currency risk [Member]
Disclosure of detailed information about financial instruments [Line Items]
Sensitivity rate	5.00%	5.00%	5.00%
Interest rate risk [member]
Disclosure of detailed information about financial instruments [Line Items]
Sensitivity rate	0.25%	0.25%	0.25%
Increase decrease in pre-tax income due to sensitivity analysis	$ 19	$ 15	$ 19
Equity price risk [Member]
Disclosure of detailed information about financial instruments [Line Items]
Sensitivity rate	5.00%	5.00%	5.00%
Equity price risk [Member] | Pre-tax profit [Member]
Disclosure of detailed information about financial instruments [Line Items]
Increase decrease in pretax income of financial assets at FVTPL, FVOCI	$ 34	$ 39	$ 26
Equity price risk [Member] | Pre-tax other comprehensive income [Member]
Disclosure of detailed information about financial instruments [Line Items]
Increase decrease in pretax income of financial assets at FVTPL, FVOCI	$ 360	$ 358	$ 347

X

- Definition

Increase decrease pre-tax profit and pre-tax other comprehensive income of financial assets at FVTOCI.

+ References

No definition available.

+ Details

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X

- Definition

Risk exposure associated with instruments sharing characteristic, percentage change in risk.

+ References

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+ Details

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- 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

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- Definition

The amount of risk exposure associated with financial instruments with a shared characteristic that identifies a concentration of risks. [Refer: Financial instruments, class [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2020-01-01
-Paragraph B8
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2020-en-r&anchor=para_B8_c&doctype=Appendix&subtype=B
-URIDate 2020-01-01

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