Equity - Unrealized Gain or Loss on Financial Assets at FVOCI (Detail) - TWD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Effect of retrospective application of IFRS 9		$ 883
Unrealized gain or loss for the year
Equity instruments	$ (345)
Ending balance	538
IFRS 9 [Member]
Beginning balance	$ 883

The increase (decrease) in financial assets arising from a change in measurement attribute on the entity's transition to IFRS 9. [Refer: Financial assets]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2018-01-01
-Paragraph 42L
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2018-03-01&anchor=para_42L_b&doctype=Standard
-URIDate 2018-03-16

Name:	ifrs-full_IncreaseDecreaseInFinancialAssetsArisingFromChangeInMeasurementAttributeFirstApplicationOfIFRS9
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant