Hedging Derivative Financial Instruments - Additional Information (Detail) - TWD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure Of Detailed Information About Hedging Instruments [Abstract]
Gain (loss) arising from changes in fair value of the hedged items recognized in other comprehensive income	$ (1)	$ (1)	$ 1
Reclassification of gain (loss) arising from forward exchange contracts	$ 2	$ 1	$ (1)

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
-Note Effective 2018-01-01
-Name IAS
-Number 1
-IssueDate 2016-01-13
-Paragraph 92
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_92&doctype=Standard
-URIDate 2016-03-31

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Period Type:	duration