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Net Income - Impairment Loss (Reversal of Impairment Loss) on Financial Instruments and Non-financial Assets (Detail) $ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020 TWD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 TWD ($)	Dec. 31, 2018 TWD ($)
Disclosure Of Impairment Loss And Reversal Of Impairment Loss [Abstract]
Contract assets	$ 1		$ (2)	$ 19
Trade notes and accounts receivable	49		(54)	805
Other receivables	(5)		(69)	96
Inventories	1,161	$ 41	475	365
Property, plant and equipment	0		93	0
Investment properties	(27)	(1)	(57)	(19)
Intangible assets	9	0	9	51
Other assets	$ 0	$ 0	$ 44	$ 0

X

- Definition

Impairment loss on other assets.

+ References

No definition available.

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- Definition

Impairment loss (reversal of impairment loss) recognised in profit or loss other receivables.

+ References

No definition available.

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- Definition

Impairment loss (reversal) on receivables or contract assets arising from contracts with customers.

+ References

No definition available.

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- Definition

The amount of impairment loss recognised in profit or loss for intangible assets and goodwill. [Refer: Impairment loss recognised in profit or loss; Intangible assets and goodwill]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition

The amount of impairment loss or reversal of impairment loss recognised in profit or loss for trade receivables. [Refer: Impairment loss recognised in profit or loss; Reversal of impairment loss recognised in profit or loss; Trade receivables]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition

The amount of expense recognised related to the write-down of inventories to net realisable value. [Refer: Inventories]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

The amount of reversal of impairment loss recognised in profit or loss for investment property. [Refer: Reversal of impairment loss recognised in profit or loss; Investment property]

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- Definition

The amount recognised resulting from the write-down of property, plant and equipment to its recoverable amount or reversals of those write-downs. [Refer: Property, plant and equipment]

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