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Income Tax - Information About Unused Loss Carryforwards (Detail) $ in Millions, $ in Millions | Dec. 31, 2018 TWD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 TWD ($)
--- | --- | --- | ---
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Remaining creditable amount | $ 3,554 | $ 116 | $ 2,730
Unused tax losses [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Remaining creditable amount | 277 |  |
Unused tax losses [Member] | 2019 [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Remaining creditable amount | 136 |  |
Unused tax losses [Member] | 2020 [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Remaining creditable amount | 41 |  |
Unused tax losses [Member] | 2021 [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Remaining creditable amount | 22 |  |
Unused tax losses [Member] | 2022 [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Remaining creditable amount | 11 |  |
Unused tax losses [Member] | 2023 [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Remaining creditable amount | 9 |  |
Unused tax losses [Member] | 2024 [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Remaining creditable amount | 2 |  |
Unused tax losses [Member] | 2025 [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Remaining creditable amount | 33 |  |
Unused tax losses [Member] | 2026 [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Remaining creditable amount | 12 |  |
Unused tax losses [Member] | 2027 [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Remaining creditable amount | 3 |  |
Unused tax losses [Member] | 2028 [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Remaining creditable amount | $ 8 |  |

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- Definition The amounts of income taxes recoverable in future periods in respect of: (a) deductible temporary differences; (b) the carryforward of unused tax losses; and (c) the carryforward of unused tax credits. [Refer: Temporary differences [member]; Unused tax credits [member]; Unused tax losses [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2018-01-01 -Paragraph 81 -Subparagraph g -Clause i -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2018-03-01&anchor=para_81_g_i&doctype=Standard -URIDate 2018-03-16 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 54 -Subparagraph o -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_54_o&doctype=Standard -URIDate 2018-03-16 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 56 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_56&doctype=Standard -URIDate 2018-03-16 + Details
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