Hedging Derivative Financial Instruments - Summary of Hedging Derivative Financial Instruments (Detail) - Cash flow hedges [member] - TWD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Detailed Information About Hedging Instruments [Line Items]
Cash flow hedge-forward exchange contracts, financial liabilities	$ 0	$ 1
Forward exchange contracts [Member]
Disclosure Of Detailed Information About Hedging Instruments [Line Items]
Cash flow hedge-forward exchange contracts, financial liabilities		$ 1

The amount of financial liabilities classified as derivative instruments. [Refer: Financial assets; Derivatives [member]]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2018-01-01
-Paragraph 55
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_55&doctype=Standard
-URIDate 2018-03-16

Name:	ifrs-full_DerivativeFinancialLiabilities
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant