Available-for-sale Financial Assets Non Current - Summary of Available-for-sale Financial Assets Non Current (Detail) $ in Millions	Dec. 31, 2017 TWD ($)
Disclosure Of Financial Assets [Line Items]
Available-for-sale financial assets, non current	$ 5,751
Domestic listed stocks [Member]
Disclosure Of Financial Assets [Line Items]
Available-for-sale financial assets, non current	3,125
Domestic non-listed stocks [Member]
Disclosure Of Financial Assets [Line Items]
Available-for-sale financial assets, non current	2,332
Foreign non-listed stocks [Member]
Disclosure Of Financial Assets [Line Items]
Available-for-sale financial assets, non current	$ 294

The amount of non-derivative financial assets that are designated as available for sale or are not classified as (a) loans and receivables; (b) held-to-maturity investments; or (c) financial assets at fair value through profit or loss. [Refer: Derivative financial assets; Financial assets at fair value through profit or loss; Held-to-maturity investments]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2021-01-01
-Name IFRS
-Number 7
-IssueDate 2018-01-01
-Paragraph 8
-Subparagraph d
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-02&anchor=para_8_d&doctype=Standard&book=b
-URIDate 2018-03-16

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