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Financial Assets at Fair Value through Other Comprehensive Income Noncurrent - Additional Information (Detail) - TWD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Noncurrent Financial Assets At Fair Value Through Other Comprehensive Income [Abstract]
fair value amount	$ 568
Investment settlement fuds	270
Unrealized gain on investments in equity instruments at fair value through other comprehensive income	17
Dividends received	$ 246	$ 296	$ 396

X

- Definition

Settlement funds of disposed of investment.

+ References

No definition available.

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- Definition

The amount of dividends received.

+ References

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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]]

+ References

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- References

No definition available.

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- Definition

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]

+ References

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