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Fair Value Information - Schedule of Reconciliations for Financial Assets (Detail) - Level 3 [Member] - TWD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Disclosure Of Fair Value Measurement Of Assets [Line Items] |  |  |  |
Foreign currency denominated monetary assets | $ 5,116 | $ 5,478 | $ 4,550 | $ 4,468
Acquisition |  | 300 | 290 |
Recognized in profit or loss under “Other gains and losses” | (101) | (39) | (26) |
Recognized in other comprehensive income under “Unrealized gain or loss on financial assets at fair value through other comprehensive income” | (263) | 676 | (175) |
Proceeds from return of investees |  |  | (7) |
Proceed from return of investments |  | (9) |  |
Reclassified from investments accounted for using equity method | 2 |  |  |
Measured at Fair Value Through Profit or Loss [Member] |  |  |  |
Disclosure Of Fair Value Measurement Of Assets [Line Items] |  |  |  |
Foreign currency denominated monetary assets | 677 | 778 | 517 | 543
Acquisition |  | 300 |  |
Recognized in profit or loss under “Other gains and losses” | (101) | (39) | (26) |
Unrealized loss | (101) | (39) | (26) |
FVOCI [Member] |  |  |  |
Disclosure Of Fair Value Measurement Of Assets [Line Items] |  |  |  |
Foreign currency denominated monetary assets | 4,439 | 4,700 | 4,033 | $ 3,925
Acquisition |  | 0 | 290 |
Recognized in other comprehensive income under “Unrealized gain or loss on financial assets at fair value through other comprehensive income” | (263) | 676 | (175) |
Proceeds from return of investees |  |  | $ (7) |
Proceed from return of investments |  | $ (9) |  |
Reclassified from investments accounted for using equity method | $ 2 |  |  |

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- Definition The amount of assets that are: (a) cash; (b) an equity instrument of another entity; (c) a contractual right: (i) to receive cash or another financial asset from another entity; or (ii) to exchange financial assets or financial liabilities with another entity under conditions that are potentially favourable to the entity; or (d) a contract that will, or may be, settled in the entity’s own equity instruments and is: (i) a non-derivative for which the entity is, or may be, obliged to receive a variable number of the entity’s own equity instruments; or (ii) a derivative that will, or may be, settled other than by the exchange of a fixed amount of cash or another financial asset for a fixed number of the entity’s own equity instruments. For this purpose the entity’s own equity instruments do not include puttable financial instruments classified as equity instruments in accordance with paragraphs 16A-16B of IAS 32, instruments that impose on the entity an obligation to deliver to another party a pro rata share of the net assets of the entity only on liquidation and are classified as equity instruments in accordance with paragraphs 16C-16D of IAS 32, or instruments that are contracts for the future receipt or delivery of the entity’s own equity instruments. [Refer: Financial instruments, class [member]; Financial liabilities] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2020-01-01 -Paragraph 25 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2020-en-r&anchor=para_25&doctype=Standard -URIDate 2020-01-01 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2020-01-01 -Paragraph 35H -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2020-en-r&anchor=para_35H&doctype=Standard -URIDate 2020-01-01 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2020-01-01 -Paragraph 35I -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2020-en-r&anchor=para_35I&doctype=Standard -URIDate 2020-01-01 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2020-01-01 -Paragraph 35M -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2020-en-r&anchor=para_35M&doctype=Standard -URIDate 2020-01-01 Reference 5: http://www.xbrl.org/2003/role/exampleRef -Name IFRS -Number 7 -IssueDate 2020-01-01 -Paragraph 35N -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2020-en-r&anchor=para_35N&doctype=Standard -URIDate 2020-01-01 + Details
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