Inventories - Additional Information (Detail) - TWD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Classes of current inventories [abstract]
Write down of inventories	$ 1,259.5		$ 1,542.8
Reversal of write down of inventories		$ 840.9

The amount recognised as a reduction in the amount of inventories recognised as an expense due to the reversal of any write-down of inventories resulting from an increase in net realisable value. [Refer: Inventories; Inventory write-down]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 2
-IssueDate 2018-01-01
-Paragraph 36
-Subparagraph f
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=2&date=2018-03-01&anchor=para_36_f&doctype=Standard
-URIDate 2018-03-16

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2018-01-01
-Paragraph 98
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_98_a&doctype=Standard
-URIDate 2018-03-16

Name:	ifrs-full_ReversalOfInventoryWritedown
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration