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Investments Accounted for Using Equity Method - Investments in Joint Ventures (Detail) $ in Millions, $ in Millions | 12 Months Ended
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Dec. 31, 2017 TWD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 TWD ($) | Dec. 31, 2015 TWD ($)
Disclosure of joint ventures [Line Items] |  |  |  |
Investments in joint ventures | $ 0 |  | $ 3 |
Percentage of ownership in joint ventures | 0.00% | 0.00% | 0.00% |
Percentage of voting rights in joint ventures | 0.00% | 0.00% | 0.00% |
The Company’s share of loss | $ 419 | $ 14 | $ 515 | $ 897
Huada Digital Corporation ("HDD") [Member] |  |  |  |
Disclosure of joint ventures [Line Items] |  |  |  |
Investments in joint ventures | $ 0 |  | $ 0 |
Percentage of ownership in joint ventures | 0.00% | 0.00% | 50.00% |
Percentage of voting rights in joint ventures | 0.00% | 0.00% | 50.00% |
Chunghwa Benefit One Co., Ltd. ("CBO") [Member] |  |  |  |
Disclosure of joint ventures [Line Items] |  |  |  |
Investments in joint ventures | $ 0 |  | $ 3 |
Percentage of ownership in joint ventures | 0.00% | 0.00% | 50.00% |
Percentage of voting rights in joint ventures | 0.00% | 0.00% | 50.00% |
Joint ventures [Member] |  |  |  |
Disclosure of joint ventures [Line Items] |  |  |  |
The Company’s share of loss | $ (1) |  | $ (42) | (29)
The Company’s share of other comprehensive (loss) income | 0 |  | 0 | 0
The Company’s share of total comprehensive loss | $ (1) |  | $ (42) | $ (29)

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- Definition The amount of investments in joint ventures. [Refer: Joint ventures [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2016-01-13 -Paragraph 10 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=27&date=2016-03-30&anchor=para_10&doctype=Standard -URIDate 2016-03-31 + Details
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- Definition The proportion of ownership interest in a joint venture attributable to the entity. [Refer: Joint ventures [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2016-01-13 -Paragraph 17 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=27&date=2016-03-30&anchor=para_17_b_iii&doctype=Standard -URIDate 2016-03-31 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2016-01-13 -Paragraph 16 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=27&date=2016-03-30&anchor=para_16_b_iii&doctype=Standard -URIDate 2016-03-31 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 12 -IssueDate 2016-01-13 -Paragraph 21 -Subparagraph a -Clause iv -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=12&date=2016-03-30&anchor=para_21_a_iv&doctype=Standard -URIDate 2016-03-31 + Details
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- Definition The proportion of the voting rights in a joint venture held by the entity. [Refer: Joint ventures [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2016-01-13 -Paragraph 17 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=27&date=2016-03-30&anchor=para_17_b_iii&doctype=Standard -URIDate 2016-03-31 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2016-01-13 -Paragraph 16 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=27&date=2016-03-30&anchor=para_16_b_iii&doctype=Standard -URIDate 2016-03-31 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 12 -IssueDate 2016-01-13 -Paragraph 21 -Subparagraph a -Clause iv -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=12&date=2016-03-30&anchor=para_21_a_iv&doctype=Standard -URIDate 2016-03-31 + Details
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- Definition The entity's share of the profit (loss) of associates and joint ventures accounted for using the equity method. [Refer: Associates [member]; Investments accounted for using equity method; Joint ventures [member]; Profit (loss)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 8 -IssueDate 2016-01-13 -Paragraph 23 -Subparagraph g -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=8&date=2016-03-30&anchor=para_23_g&doctype=Standard -URIDate 2016-03-31 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 8 -IssueDate 2016-01-13 -Paragraph 28 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=8&date=2016-03-30&anchor=para_28_e&doctype=Standard -URIDate 2016-03-31 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2016-01-13 -Paragraph 82 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_82_c&doctype=Standard -URIDate 2016-03-31 + Details
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- Definition The entity's share of the total comprehensive income of associates and joint ventures accounted for using the equity method. [Refer: Associates [member]; Joint ventures [member]; Investments accounted for using equity method] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 12 -IssueDate 2016-01-13 -Paragraph B16 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=12&date=2016-03-30&anchor=para_B16_d&doctype=Appendix&seq=2 -URIDate 2016-03-31 + Details
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