Available-for-sale Financial Assets Non Current - Summary of Available-for-sale Financial Assets Non Current(Detail) - TWD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Disclosure of financial assets [Line Items]
Available-for-sale financial assets, non current	$ 5,751	$ 4,764
Domestic listed stocks [Member]
Disclosure of financial assets [Line Items]
Available-for-sale financial assets, non current	3,125	2,521
Domestic non-listed stocks [Member]
Disclosure of financial assets [Line Items]
Available-for-sale financial assets, non current	2,332	1,949
Foreign non-listed stocks [Member]
Disclosure of financial assets [Line Items]
Available-for-sale financial assets, non current	$ 294	$ 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 2018-01-01
-Name IFRS
-Number 7
-IssueDate 2016-01-13
-Paragraph 8
-Subparagraph d
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2016-03-30&anchor=para_8_d&doctype=Standard
-URIDate 2016-03-31

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