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Contents of Significant Accounts - Summary of Income Recognized in Profit or Loss from Equity Instruments Designated as Fair Value Through Other Comprehensive Income (Detail) - TWD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Dividend Income [Abstract]
Held at end of period	$ 888,826	$ 1,052,336
Derecognized during the period	0	142,535
Total	$ 888,826	$ 1,194,871

X

- Definition

The amount of dividends related to investments in equity instruments that the entity has designated at fair value through other comprehensive income, derecognised during the reporting period. [Refer: Investments in equity instruments designated at fair value through other comprehensive income [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2024-01-01
-Paragraph 11A
-Subparagraph d
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2024-en-r&anchor=para_11A_d&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

X

- Definition

The amount of dividends related to investments in equity instruments that the entity has designated at fair value through other comprehensive income, held at the end of the reporting period. [Refer: Investments in equity instruments designated at fair value through other comprehensive income [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2024-01-01
-Paragraph 11A
-Subparagraph d
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2024-en-r&anchor=para_11A_d&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

X

- Definition

Dividend income.

+ References

No definition available.

+ Details

Name:	umc_DividendIncomeAbstract
Namespace Prefix:	umc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The amount of dividends related to investments in equity instruments that the entity has designated at fair value through other comprehensive income, held at the end of the reporting period and derecognised during the reporting period.

+ References

No definition available.

+ Details

Name:	umc_DividendsRecognisedForInvestmentsInEquityInstrumentsDesignatedAsMeasuredAtFairValueThroughOtherComprehensiveIncomeHeldAtEndOfReportingPeriodAndDerecognisedDuringPeriod
Namespace Prefix:	umc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant