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Significant Events After the Reporting Period - Additional Information (Detail) - TWD ($) $ in Millions	1 Months Ended	12 Months Ended
	Feb. 28, 2021	Dec. 31, 2020
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Investments at fair value		$ 568
Unrealized gain on investments in equity instruments at fair value through other comprehensive income		$ 17
Disposal of China Airlines, Ltd. [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Investments at fair value	$ 2,635
Unrealized gain on investments in equity instruments at fair value through other comprehensive income	$ 94

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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.

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No definition available.

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- Definition

The amount investment funds contribute to the fair value of defined benefit plan assets. [Refer: Plan assets, at fair value; Defined benefit plans [member]; Investment funds [member]]

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The amount of other comprehensive income, net of tax, related to gains (losses) from changes in the fair value of investments in equity instruments that the entity has designated at fair value through other comprehensive income. [Refer: Other comprehensive income]

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