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Income Tax - Items for Which No Deferred Income Tax Assets Have Been Recognized (Detail) - TWD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |
Loss carryforwards | $ 89 | $ 101
Deductible temporary differences | 1 | 1
2020 [Member] |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |
Loss carryforwards | 23 | 41
2021 [Member] |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |
Loss carryforwards | 13 | 12
2022 [Member] |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |
Loss carryforwards | 10 | 10
2023 [Member] |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |
Loss carryforwards | 8 | 9
2024 [Member] |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |
Loss carryforwards | 8 | 2
2025 [Member] |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |
Loss carryforwards | 15 | 15
2026 [Member] |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |
Loss carryforwards | 8 | 8
2027 [Member] |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |
Loss carryforwards | 3 | 3
2028 [Member] |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |
Loss carryforwards | 1 | 1
2029 [Member] |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |
Loss carryforwards | $ 0 | $ 0

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- Definition The amount of deductible temporary differences for which no deferred tax asset is recognised in the statement of financial position. [Refer: Temporary differences [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2019-01-01 -Paragraph 81 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2019-en-r&anchor=para_81_e&doctype=Standard -URIDate 2019-03-27 + Details
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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 of unused tax losses for which no deferred tax asset is recognised in the statement of financial position. [Refer: Unused tax losses [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2019-01-01 -Paragraph 81 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2019-en-r&anchor=para_81_e&doctype=Standard -URIDate 2019-03-27 + Details
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