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Net Income and Other Comprehensive Income (Loss) - Reclassification Adjustments of Other Comprehensive Income (Loss) (Detail) $ in Millions, $ in Millions | 12 Months Ended
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Dec. 31, 2018 TWD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 TWD ($) | Dec. 31, 2016 TWD ($)
Unrealized gain or loss on available-for-sale financial assets |  |  |  |
Arising during the year |  |  | $ 605 | $ (721)
Reclassification adjustments |  |  |  |
Upon disposal |  |  | 0 | 0
Upon impairment |  |  | 0 | 577
Unrealized gain or loss on available-for- sale financial assets | $ 0 | $ 0 | 605 | (144)
Cash flow hedges |  |  |  |
Gain arising during the year |  |  | 3 | 15
Reclassification adjustments included in profit or loss |  |  | (2) | (1)
Adjusted against the carrying amount of hedged items |  |  | (2) | (15)
Cash flow hedges | $ 0 | $ 0 | $ (1) | $ (1)

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- Definition The amounts removed from equity and included in the initial cost or other carrying amount of a non-financial asset (liability) whose acquisition or incurrence was a hedged, highly probable forecast transaction, before tax. [Refer: Carrying amount [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2021-01-01 -Name IFRS -Number 7 -IssueDate 2018-01-01 -Paragraph 23 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-02&anchor=para_23_e&doctype=Standard&book=b -URIDate 2018-03-16 + Details
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- Definition The gains (losses) recognised in other comprehensive income on cash flow hedges, before tax. [Refer: Cash flow hedges [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 91 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_91_b&doctype=Standard -URIDate 2018-03-16 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2021-01-01 -Name IFRS -Number 7 -IssueDate 2018-01-01 -Paragraph 23 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-02&anchor=para_23_c&doctype=Standard&book=b -URIDate 2018-03-16 + Details
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- Definition The gains (losses) recognised in other comprehensive income on remeasuring available-for-sale financial assets, before tax. [Refer: Financial assets available-for-sale] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2021-01-01 -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 91 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-02&anchor=para_91_b&doctype=Standard&book=b_pdf -URIDate 2018-03-16 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2021-01-01 -Name IFRS -Number 7 -IssueDate 2018-01-01 -Paragraph 20 -Subparagraph a -Clause ii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-02&anchor=para_20_a_ii&doctype=Standard&book=b -URIDate 2018-03-16 + Details
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- Definition The amount of impairment loss recognised in other comprehensive income. Impairment loss on a revalued asset is recognised in other comprehensive income to the extent that the impairment loss does not exceed the amount in the revaluation surplus for that same asset. [Refer: Impairment loss; Revaluation surplus; Other comprehensive income] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 36 -IssueDate 2018-01-01 -Paragraph 126 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2018-03-01&anchor=para_126_c&doctype=Standard -URIDate 2018-03-16 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 36 -IssueDate 2018-01-01 -Paragraph 129 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2018-03-01&anchor=para_129_a&doctype=Standard -URIDate 2018-03-16 + Details
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- Definition The amount of other comprehensive income, before tax, related to available-for-sale financial assets. [Refer: Financial assets available-for-sale; Other comprehensive income, before tax] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2021-01-01 -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 91 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-02&anchor=para_91_b&doctype=Standard&book=b_pdf -URIDate 2018-03-16 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2021-01-01 -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 7 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-02&anchor=para_7&doctype=Standard&book=b_pdf -URIDate 2018-03-16 + Details
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- Definition The amount of other comprehensive income, before tax, related to cash flow hedges. [Refer: Cash flow hedges [member]; Other comprehensive income, before tax] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 91 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_91_b&doctype=Standard -URIDate 2018-03-16 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 7 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_7&doctype=Standard -URIDate 2018-03-16 + Details
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- Definition The amount of reclassification adjustments related to cash flow hedges, before tax. Reclassification adjustments are amounts reclassified to profit (loss) in the current period that were recognised in other comprehensive income in the current or previous periods. [Refer: Cash flow hedges [member]; Other comprehensive income] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 92 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_92&doctype=Standard -URIDate 2018-03-16 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2021-01-01 -Name IFRS -Number 7 -IssueDate 2018-01-01 -Paragraph 23 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-02&anchor=para_23_d&doctype=Standard&book=b -URIDate 2018-03-16 + Details
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