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Available-for-sale Financial Assets Non Current - Additional Information (Detail) $ in Millions | 12 Months Ended
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Dec. 31, 2017 TWD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 TWD ($) | Dec. 31, 2015 TWD ($)
Disclosure of financial assets [Line Items] |  |  |  |
Impairment loss on available-for-sale financial assets | $ 0 | $ 0 | $ 577,000,000 | $ 107,000,000
Carrying value of non-listed available-for-sale financial assets disposed | 5,000,000 |  | 9,000,000 | 2,000,000
Gains (losses) from disposal of available-for-sale assets | 3,000,000 |  | 1,000,000 | (400,000)
Taiwania Capital Buffalo Fund Co Ltd [Member] |  |  |  |
Disclosure of financial assets [Line Items] |  |  |  |
Amount invested in investment entity | $ 300,000,000 |  |  |
Ownership percentage in investment entity | 12.90% | 12.90% |  |
Domestic listed stocks [Member] |  |  |  |
Disclosure of financial assets [Line Items] |  |  |  |
Impairment loss on available-for-sale financial assets | $ 0 |  | 577,000,000 | 26,000,000
Non-listed stocks [Member] | Ceased operations [Member] |  |  |  |
Disclosure of financial assets [Line Items] |  |  |  |
Impairment loss on available-for-sale financial assets |  |  |  | 77,000,000
Non-listed stocks [Member] | Profit recession or deficit [Member] |  |  |  |
Disclosure of financial assets [Line Items] |  |  |  |
Impairment loss on available-for-sale financial assets | $ 0 |  | $ 0 | $ 4,000,000

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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 The amount of financial assets that are measured at fair value and for which gains (losses) are recognised in profit or loss. A financial asset shall be measured at fair value through profit or loss unless it is measured at amortised cost or at fair value through other comprehensive income. A gain (loss) on a financial asset measured at fair value shall be recognised in profit or loss unless it is part of a hedging relationship, it is an investment in an equity instrument for which the entity has elected to present gains and losses in other comprehensive income or it is a financial asset measured at fair value through other comprehensive income. [Refer: At fair value [member]; Financial assets] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2016-01-13 -Paragraph 8 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2016-03-30&anchor=para_8_a&doctype=Standard -URIDate 2016-03-31 + Details
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- Definition The gains (losses) on available-for-sale financial assets. [Refer: Financial assets available-for-sale] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2018-01-01 -Name IFRS -Number 7 -IssueDate 2016-01-13 -Paragraph 20 -Subparagraph a -Clause ii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2016-03-30&anchor=para_20_a_ii&doctype=Standard -URIDate 2016-03-31 + Details
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