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Business Combinations - Summary of Goodwill Recognized on Acquisitions (Detail) $ in Thousands, $ in Thousands | Dec. 31, 2019 TWD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 TWD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 TWD ($) | Dec. 31, 2016 TWD ($)
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Disclosure of detailed information about business combination [Line Items] |  |  |  |  |  |
Ending balance of goodwill in respective year | $ 50,198,436 | $ 1,678,316 | $ 49,974,446 | $ 1,670,827 | $ 9,934,494 | $ 10,490,309
SPIL [member] |  |  |  |  |  |
Disclosure of detailed information about business combination [Line Items] |  |  |  |  |  |
Total consideration | 168,440,585 |  |  |  |  |
Add: Non-controlling interests | 3,582,866 |  |  |  |  |
Less: Fair value of identifiable net assets acquired | (132,033,220) |  |  |  |  |
Ending balance of goodwill in respective year | 39,990,231 |  |  |  |  |
AMPI [member] |  |  |  |  |  |
Disclosure of detailed information about business combination [Line Items] |  |  |  |  |  |
Total consideration | 250,000 | 8,358 |  |  |  |
Add: Fair value of investments previously owned | 315,925 | 10,563 |  |  |  |
Add: Non-controlling interests | 416,716 | 13,932 |  |  |  |
Less: Fair value of identifiable net assets acquired | (849,863) | (28,414) |  |  |  |
Ending balance of goodwill in respective year | 132,778 | 4,439 |  |  |  |
ASEEE [member] |  |  |  |  |  |
Disclosure of detailed information about business combination [Line Items] |  |  |  |  |  |
Total consideration | 0 | 0 |  |  |  |
Add: Fair value of investments previously owned | 117,609 | 3,932 |  |  |  |
Add: Non-controlling interests | 105,464 | 3,526 |  |  |  |
Less: Fair value of identifiable net assets acquired | (215,233) | (7,196) |  |  |  |
Ending balance of goodwill in respective year | 7,840 | 262 |  |  |  |
UGPL [Member] |  |  |  |  |  |
Disclosure of detailed information about business combination [Line Items] |  |  |  |  |  |
Total consideration | 313,057 | 10,467 |  |  |  |
Add: Non-controlling interests | 142,494 | 4,764 |  |  |  |
Less: Fair value of identifiable net assets acquired | (331,192) | (11,073) |  |  |  |
Ending balance of goodwill in respective year | $ 124,359 | $ 4,158 |  |  |  |

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- Definition The acquisition-date fair value of equity interest in the acquiree held by the acquirer immediately before the acquisition date in a business combination achieved in stages. [Refer: Business combinations [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 3 -IssueDate 2019-01-01 -Paragraph B64 -Subparagraph p -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=3&code=ifrs-tx-2019-en-r&anchor=para_B64_p_i&doctype=Appendix&subtype=B -URIDate 2019-03-27 + Details
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- Definition The fair value, at acquisition date, of the consideration transferred in a business combination. [Refer: Business combinations [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 3 -IssueDate 2019-01-01 -Paragraph B64 -Subparagraph f -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=3&code=ifrs-tx-2019-en-r&anchor=para_B64_f&doctype=Appendix&subtype=B -URIDate 2019-03-27 + Details
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- Definition The amount of assets representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognised. [Refer: Business combinations [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 3 -IssueDate 2019-01-01 -Paragraph B67 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=3&code=ifrs-tx-2019-en-r&anchor=para_B67_d&doctype=Appendix&subtype=B -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 36 -IssueDate 2019-01-01 -Paragraph 134 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=36&code=ifrs-tx-2019-en-r&anchor=para_134_a&doctype=Standard -URIDate 2019-03-27 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 36 -IssueDate 2019-01-01 -Paragraph 135 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=36&code=ifrs-tx-2019-en-r&anchor=para_135_a&doctype=Standard -URIDate 2019-03-27 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 54 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_54_c&doctype=Standard -URIDate 2019-03-27 + Details
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