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Contents of Significant Accounts - Leases - Additional Information (Detail) - TWD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023
Disclosures Of Leases [Abstract] |  |
Addition to right of use assets | $ 1,683 | $ 206

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- Definition The amount of additions to right-of-use assets. [Refer: Right-of-use assets] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 16 -IssueDate 2024-01-01 -Paragraph 53 -Subparagraph h -URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=16&code=ifrs-tx-2024-en-r&anchor=para_53_h&doctype=Standard -URIDate 2024-03-27 + Details
Name: | ifrs-full_AdditionsToRightofuseAssets
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Disclosures of leases + References No definition available. + Details
Name: | umc_DisclosuresOfLeasesAbstract
Namespace Prefix: | umc_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration