Financial Instruments at Fair Value Through Profit or Loss - Summary of Financial Instruments at Fair Value through Profit or Loss (Detail) $ in Millions, $ in Millions	Dec. 31, 2017 TWD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 TWD ($)
Disclosure Of Financial Instruments [Abstract]
Financial assets at fair value through profit or loss	$ 0	$ 0	$ 0
Financial liabilities held for trading, Derivatives (not designated for hedge), Forward exchange contracts	$ 1	$ 0	$ 1

The amount of current financial assets measured at fair value through profit or loss classified as held for trading. [Refer: Financial assets at fair value through profit or loss, classified as held for trading]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2018-01-01
-Name IFRS
-Number 7
-IssueDate 2016-01-13
-Paragraph 8
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2016-03-30&anchor=para_8_a&doctype=Standard
-URIDate 2016-03-31

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