Financial Assets at Fair Value through Other Comprehensive Income Noncurrent - Additional Information (Detail) - TWD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Noncurrent Financial Assets At Fair Value Through Other Comprehensive Income [Abstract]
Dividends received	$ 296	$ 396

The amount of dividends received.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 12
-IssueDate 2019-01-01
-Paragraph B12
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=12&code=ifrs-tx-2019-en-r&anchor=para_B12_a&doctype=Appendix&subtype=B
-URIDate 2019-03-27

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