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Hedging Financial Instruments - Summary of Hedging Transaction and Reclassification Affected Comprehensive Income (Details) - Forecast Purchases - forward Exchange Contract [Member] - Cash flow hedges [member] - TWD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018
Disclosure Of Reclassification Of Financial Assets [Line Items] |  |
Hedging Gain or Loss Recognized in OCI | $ (1) | $ 2
Amount of Hedge Ineffectiveness Recognized in Profit or Loss | 0 | 0
Line item in which hedge ineffectiveness is included | 0 | 0
Amount Reclassified to P/L and the Adjusted Line Item | (2) | (4)
Due to Hedged Future Cash Flows No Longer Expected to Occur | $ 0 | $ 0

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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 gain (loss) on hedge ineffectiveness. Hedge ineffectiveness is the extent to which the changes in the fair value or the cash flows of the hedging instrument are greater or less than those on the hedged item. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2019-01-01 -Paragraph 24C -Subparagraph a -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2019-en-r&anchor=para_24C_a_i&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The gain (loss) recognised in other comprehensive income on hedge ineffectiveness. [Refer: Gain (loss) on hedge ineffectiveness] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2019-01-01 -Paragraph 24C -Subparagraph a -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2019-en-r&anchor=para_24C_a_i&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The gain (loss) recognised in profit or loss on hedge ineffectiveness. [Refer: Gain (loss) on hedge ineffectiveness] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2019-01-01 -Paragraph 24C -Subparagraph a -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2019-en-r&anchor=para_24C_a_i&doctype=Standard -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2019-01-01 -Paragraph 24C -Subparagraph b -Clause ii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2019-en-r&anchor=para_24C_b_ii&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The amount of reclassification adjustments on cash flow hedges for which the hedged future cash flows are no longer expected to occur, net of tax. [Refer: Reclassification adjustments on cash flow hedges, net of tax] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2019-01-01 -Paragraph 24C -Subparagraph b -Clause iv -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2019-en-r&anchor=para_24C_b_iv&doctype=Standard -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2019-01-01 -Paragraph 24E -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2019-en-r&anchor=para_24E_a&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The amount of financial assets reclassified out of the at fair value through profit or loss category. [Refer: Financial assets at fair value through profit or loss] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2021-01-01 -Name IFRS -Number 7 -IssueDate 2019-01-01 -Paragraph 12A -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2017-en-b&anchor=para_12A_a&doctype=Standard&book=b -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2021-01-01 -Name IFRS -Number 7 -IssueDate 2019-01-01 -Paragraph 12 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2017-en-b&anchor=para_12&doctype=Standard&book=b -URIDate 2019-03-27 + Details
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