Hedging Financial Instruments - Additional Information (Detail) $ in Millions	12 Months Ended
Dec. 31, 2017 TWD ($)
Disclosure Of Detailed Information About Hedging Instruments [Abstract]
Gains (losses) on change in value of forward elements of forward contracts, net of tax	$ 1
Reclassification of gain (loss) arising from forward exchange contracts	$ 2

The amount of reclassification adjustments related to change in value of forward elements of forward contracts, net of tax. Reclassification adjustments are amounts reclassified to profit (loss) in the current period that were recognised in other comprehensive income in the current or previous periods. [Refer: Other comprehensive income]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2019-01-01
-Paragraph 92
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_92&doctype=Standard
-URIDate 2019-03-27

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration