Percentage of ownership interest in subsidiary.

No definition available.

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- Definition

The discount rate applied to cash flow projections for a cash-generating unit (group of units). [Refer: Cash-generating units [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 36
-IssueDate 2016-01-13
-Paragraph 134
-Subparagraph d
-Clause v
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2016-03-30&anchor=para_134_d_v&doctype=Standard
-URIDate 2016-03-31

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 36
-IssueDate 2016-01-13
-Paragraph 134
-Subparagraph e
-Clause v
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2016-03-30&anchor=para_134_e_v&doctype=Standard
-URIDate 2016-03-31

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- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

+ References

No definition available.

+ Details

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- Definition

The amount recognised as a reduction of the carrying amount of an asset or cash-generating unit to its recoverable amount. [Refer: Carrying amount [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 36
-IssueDate 2016-01-13
-Paragraph 130
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2016-03-30&anchor=para_130_b&doctype=Standard
-URIDate 2016-03-31

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 36
-IssueDate 2016-01-13
-Paragraph 130
-Subparagraph d
-Clause ii
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2016-03-30&anchor=para_130_d_ii&doctype=Standard
-URIDate 2016-03-31

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- Definition

The profit (loss) of the combined entity as though the acquisition date for all business combinations that occurred during the year had been as of the beginning of the annual reporting period. [Refer: Business combinations [member]; Profit (loss)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 3
-IssueDate 2016-01-13
-Paragraph B64
-Subparagraph q
-Clause ii
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=3&date=2016-03-30&anchor=para_B64_q_ii&doctype=Appendix&seq=2
-URIDate 2016-03-31

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- Definition

The revenue of the combined entity as though the acquisition date for all business combinations that occurred during the year had been as of the beginning of the annual reporting period. [Refer: Business combinations [member]; Revenue]

+ References

+ Details

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Balance Type:	credit
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- Details

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- Details

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- Details

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- Details

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- Details

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Subsidiaries - Additional Information (Detail) - TWD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2018	Jan. 01, 2015	Dec. 31, 2014
Disclosure of subsidiaries [Line Items]
Pro-forma revenue			$ 232,187
Pro-forma net income			$ 42,774
CHIEF Telecom Inc. (CHIEF) [Member]
Disclosure of subsidiaries [Line Items]
Equity ownership percentage	67.00%	69.00%
Chunghwa Investment Co., Ltd. (CHI) [Member] \| Chunghwa Precision Test Tech. Co., Ltd. (CHPT) [Member]
Disclosure of subsidiaries [Line Items]
Equity ownership percentage	38.30%		38.30%
Senao International Co., Ltd. (SENAO) [Member]
Disclosure of subsidiaries [Line Items]
Equity ownership percentage			29.31%		28.18%
Senao International Co., Ltd. (SENAO) [Member] \| Youth Co., Ltd. (Youth) [Member]
Disclosure of subsidiaries [Line Items]
Equity ownership percentage			89.48%			70.00%
Discount rate applied to cash flow projections	14.80%	14.60%	16.30%
Impairment loss	$ 9	$ 0	$ 0
Chunghwa Telecom Co., Ltd. [Member] \| Senao International Co., Ltd. (SENAO) [Member]
Disclosure of subsidiaries [Line Items]
Equity ownership percentage	28.93%	29.00%
Chunghwa Telecom Co., Ltd. [Member] \| CHIEF Telecom Inc. (CHIEF) [Member]
Disclosure of subsidiaries [Line Items]
Equity ownership percentage	70.43%			69.31%