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Contents of Significant Accounts - Bonds Payable (Detail) $ in Thousands, $ in Thousands | Dec. 31, 2024 TWD ($) | Dec. 31, 2024 USD ($) | Dec. 31, 2023 TWD ($)
--- | --- | --- | ---
Disclosure of detailed information about bonds [Line Items] |  |  |
Bonds payable | $ 30,051,568 |  | $ 38,359,352
Less: Current or exchangeable portion due within one year | (5,466,589) |  | (13,779,701)
Net | 24,584,979 | $ 749,771 | 24,579,651
Less: Discounts on bonds payable [member] |  |  |
Disclosure of detailed information about bonds [Line Items] |  |  |
Bonds payable | (305,805) |  | (498,021)
Unsecured domestic bonds payable [member] | Cost [member] |  |  |
Disclosure of detailed information about bonds [Line Items] |  |  |
Bonds payable | 24,600,000 |  | 33,100,000
Unsecured exchangeable bonds payable [member] | Cost [member] |  |  |
Disclosure of detailed information about bonds [Line Items] |  |  |
Bonds payable | $ 5,757,373 |  | $ 5,757,373

X
- Definition The amount of current bonds issued and the current portion of non-current bonds issued. [Refer: Bonds issued] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2024-01-01 -Paragraph 112 -Subparagraph c -URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2024-en-r&anchor=para_112_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: | instant

X
- Definition The non-current portion of non-current bonds issued. [Refer: Bonds issued] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2024-01-01 -Paragraph 112 -Subparagraph c -URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2024-en-r&anchor=para_112_c&doctype=Standard -URIDate 2024-03-27 + Details
Name: | ifrs-full_NoncurrentPortionOfNoncurrentBondsIssued
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Bonds payable. + References No definition available. + Details
Name: | umc_BondsPayable
Namespace Prefix: | umc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Disclosure of detailed information about bonds. + References No definition available. + Details
Name: | umc_DisclosureOfDetailedInformationAboutBondsLineItems
Namespace Prefix: | umc_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_BorrowingsByNameAxis=umc_UnsecuredDomesticBondsPayableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
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Namespace Prefix: |
Data Type: | na
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X
- Details
Name: | ifrs-full_BorrowingsByNameAxis=umc_UnsecuredExchangeableBondsPayableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |