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Fair Value Information - Financial Instruments Measured at Fair Value on a Recurring Basis (Detail) - TWD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
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Disclosure of fair value measurement of assets and liabilities [Line Items] |  |
Amount invested in investment entity |  | $ 5,751
Measured at FVTPL Held for trading | $ 1 | 1
Fair value on a recurring basis [Member] |  |
Disclosure of fair value measurement of assets and liabilities [Line Items] |  |
Amount invested in investment entity |  | 3,125
Measured at FVTPL Held for trading | 1 | 1
Cash flow hedge-forward exchange contracts, financial liabilities |  | 1
Hedging financial assets | 1 |
Equity investment | 6,933 |
Fair value on a recurring basis [Member] | Non-listed stocks [Member] |  |
Disclosure of fair value measurement of assets and liabilities [Line Items] |  |
Non-listed stocks | 517 |
Fair value on a recurring basis [Member] | Level 1 [Member] |  |
Disclosure of fair value measurement of assets and liabilities [Line Items] |  |
Amount invested in investment entity |  | 3,125
Equity investment | 2,900 |
Fair value on a recurring basis [Member] | Level 2 [Member] |  |
Disclosure of fair value measurement of assets and liabilities [Line Items] |  |
Measured at FVTPL Held for trading | 1 | 1
Cash flow hedge-forward exchange contracts, financial liabilities |  | $ 1
Hedging financial assets | 1 |
Fair value on a recurring basis [Member] | Level 3 [Member] |  |
Disclosure of fair value measurement of assets and liabilities [Line Items] |  |
Equity investment | 4,033 |
Fair value on a recurring basis [Member] | Level 3 [Member] | Non-listed stocks [Member] |  |
Disclosure of fair value measurement of assets and liabilities [Line Items] |  |
Non-listed stocks | $ 517 |

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- Definition The amount of derivative financial assets held for hedging. [Refer: Derivative financial assets] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 55 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_55&doctype=Standard -URIDate 2018-03-16 + Details
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- Definition The amount of financial liabilities classified as derivative instruments. [Refer: Financial assets; Derivatives [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 55 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_55&doctype=Standard -URIDate 2018-03-16 + Details
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- Definition The amount of investments in equity instruments that the entity has designated at fair value through other comprehensive income. [Refer: At fair value [member]; Other comprehensive income] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2018-01-01 -Paragraph 11A -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2018-03-01&anchor=para_11A_c&doctype=Standard -URIDate 2018-03-16 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2018-01-01 -Paragraph 8 -Subparagraph h -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2018-03-01&anchor=para_8_h&doctype=Standard -URIDate 2018-03-16 + 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 2018-01-01 -Paragraph 8 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2018-03-01&anchor=para_8_a&doctype=Standard -URIDate 2018-03-16 + Details
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- Definition The amount of non-derivative financial assets that are designated as available for sale or are not classified as (a) loans and receivables; (b) held-to-maturity investments; or (c) financial assets at fair value through profit or loss. [Refer: Derivative financial assets; Financial assets at fair value through profit or loss; Held-to-maturity investments] + 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 8 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-02&anchor=para_8_d&doctype=Standard&book=b -URIDate 2018-03-16 + Details
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- Definition The amount of financial liabilities at fair value through profit or loss that meet the definition of held for trading. A financial liability is classified as held for trading if: (a) it is acquired or incurred principally for the purpose of selling or repurchasing it in the near term; (b) on initial recognition it is part of a portfolio of identified financial instruments that are managed together and for which there is evidence of a recent actual pattern of short-term profit-taking; or (c) it is a derivative (except for a derivative that is a financial guarantee contract or a designated and effective hedging instrument). [Refer: Financial liabilities at fair value through profit or loss] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2018-01-01 -Paragraph 8 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2018-03-01&anchor=para_8_e&doctype=Standard -URIDate 2018-03-16 + Details
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