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Contents of Significant Accounts - Summary of Details on Derecognition of Such Investments (Detail) - TWD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Disposed and Derecognized Investments Designated as Fair Value Through Other Comprehensive Income [Abstract] |  |  |
Fair value on the date of disposal | $ 0 | $ 3,035,999 | $ 0
Cumulative gains (losses) reclassified to retained earnings due to derecognition | $ 0 | $ (1,628,388) | $ 0

X
- Definition The cumulative gain (loss) on disposal 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 2024-01-01 -Paragraph 11B -Subparagraph c -URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2024-en-r&anchor=para_11B_c&doctype=Standard -URIDate 2024-03-27 + Details
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Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Disposed and derecognized investments designated as fair value through other comprehensive income. + References No definition available. + Details
Name: | umc_DisposedAndDerecognizedInvestmentsDesignatedAsFairValueThroughOtherComprehensiveIncomeAbstract
Namespace Prefix: | umc_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Fair value of investments measured at fair value through other comprehensive income at date of disposal. + References No definition available. + Details
Name: | umc_FairValueOfInvestmentsMeasuredAtFairValueThroughOtherComprehensiveIncomeAtDateOfDisposal
Namespace Prefix: | umc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration