Income Tax - Current Tax Assets and Liabilities (Detail) $ in Millions, $ in Millions	Jan. 01, 2018 TWD ($)	Dec. 31, 2017 TWD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 TWD ($)
Major Components Of Tax Expense Income [Abstract]
Tax refund receivable (included in other current assets - other)		$ 2		$ 5
Income tax payable	$ 10,901	$ 8,674	$ 293	$ 6,522

The current amount of current tax liabilities. [Refer: Current tax liabilities]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2016-01-13
-Paragraph 54
-Subparagraph n
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_54_n&doctype=Standard
-URIDate 2016-03-31

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant