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Net Income and Other Comprehensive Income (Loss) - Other Gains and Losses (Detail) $ in Millions, $ in Millions | 12 Months Ended
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Dec. 31, 2019 TWD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 TWD ($) | Dec. 31, 2017 TWD ($)
Analysis Of Income And Expense [Abstract] |  |  |  |
Foreign currency exchange gain or loss, net | $ 16 |  | $ 37 | $ (88)
Gain or loss on disposal of investments accounted for using equity method | 151 | $ 5 | 0 | 0
Gain on disposal of financial instruments | 4 | 0 | 6 | 3
Valuation gain or loss on financial assets and liabilities at fair value through profit or loss, net | (38) | (1) | (21) | 1
Others | (49) |  | (68) | (48)
Other gains and losses | $ 84 | $ 3 | $ (46) | $ (132)

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- Definition Gain (loss) on disposal of investments accounted for using equity method, net. + References No definition available. + Details
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- Definition Gain losses on disposal of financial instruments. + References No definition available. + Details
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- Definition Gains losses on financial assets and liabilities at fair value through profit or loss. + References No definition available. + Details
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- Definition The amount of exchange differences recognised in profit or loss that arise from foreign currency transactions, excluding those arising on financial instruments measured at fair value through profit or loss in accordance with IFRS 9. [Refer: At fair value [member]; Financial instruments, class [member]] + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Name IAS -Number 7 -IssueDate 2019-01-01 -Section A Statement of cash flows for an entity other than a financial institution -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=7&code=ifrs-tx-2019-en-r&doctype=Illustrative%20Examples&dita_xref=IAS07_IE_A_TI -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 21 -IssueDate 2019-01-01 -Paragraph 52 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=21&code=ifrs-tx-2019-en-r&anchor=para_52_a&doctype=Standard -URIDate 2019-03-27 + Details
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