Long Term Loans - Summary of Long-term Loans (Detail) - Long-term loans [Member] - TWD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of detailed information about borrowings [Line Items]
Secured loans	$ 1,600	$ 1,600
Secured loans [Member]
Disclosure of detailed information about borrowings [Line Items]
Interest rates of loans	0.92%	0.91%

The amount of loans received from banks that have been secured by collateral. [Refer: Loans received]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2018-01-01
-Paragraph 112
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_112_c&doctype=Standard
-URIDate 2018-03-16

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