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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, 2018 TWD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 TWD ($) | Dec. 31, 2016 TWD ($)
Analysis Of Income And Expense [Abstract] |  |  |  |
Net foreign currency exchange gains or losses | $ 37 |  | $ (88) | $ 181
Gain on disposal of financial instruments | 6 | $ 0 | 3 | 0
Gain or loss on disposal of investments accounted for using equity method | 0 | 0 | 0 | (2)
Valuation gain or loss on financial assets and liabilities at fair value through profit or loss, net | (21) | (1) | 1 | (1)
Impairment loss on available-for-sale financial assets | 0 | 0 | 0 | (577)
Others | (68) |  | (48) | (49)
Other gains and losses | $ (46) | $ (2) | $ (132) | $ (448)

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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 Impairment loss (reversal of impairment loss) recognised in profit or loss available-for-sale financial assets. + References No definition available. + Details
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- Definition Miscellaneous other gains (losses). + References No definition available. + Details
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- References No definition available. + Details
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- Definition The net gain arising from foreign exchange differences. [Refer: Foreign exchange gain (loss)] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 21 -IssueDate 2018-01-01 -Paragraph 52 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=21&date=2018-03-01&anchor=para_52_a&doctype=Standard -URIDate 2018-03-16 + Details
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- Definition The gains (losses) that the entity does not separately disclose in the same statement or note. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 102 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_102&doctype=Standard -URIDate 2018-03-16 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 103 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_103&doctype=Standard -URIDate 2018-03-16 + Details
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