Equity - Appropriations of Earnings (Detail) - TWD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Special reserve	$ 0		$ 0
Cash dividends per share	$ 4.796	$ 4.9419	$ 5.4852
Total retained earnings [Member]
Special reserve	$ 0	$ 5	$ 0
Reversal of special reserve	5
Cash dividends	$ 37,205	$ 38,336	$ 42,551

The amount of dividends proposed or declared after the reporting period but before financial statements are authorised for issue. Such dividends are not recognised as a liability at the end of the reporting period because no obligation exists at that time.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2016-01-13
-Paragraph 137
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_137_a&doctype=Standard
-URIDate 2016-03-31

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 10
-IssueDate 2016-01-13
-Paragraph 13
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=10&date=2016-03-30&anchor=para_13&doctype=Standard
-URIDate 2016-03-31

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration