Contents of Significant Accounts - Leases - Additional Information (Detail) - TWD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Disclosures Of Leases [Abstract]
Addition to right of use assets	$ 567	$ 264

The amount of additions to right-of-use assets. [Refer: Right-of-use assets]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 16
-IssueDate 2020-01-01
-Paragraph 53
-Subparagraph h
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=16&code=ifrs-tx-2020-en-r&anchor=para_53_h&doctype=Standard
-URIDate 2020-01-01

Name:	ifrs-full_AdditionsToRightofuseAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration