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Contents of Significant Accounts - Share-Based Payment - Additional Information (Detail)
$ / shares in Units, shares in Millions, Right in Millions, $ in Millions
 1 Months Ended 12 Months Ended
Dec. 05, 2023
$ / shares
shares
Dec. 05, 2022
$ / shares
shares
May 27, 2022
shares
Jun. 30, 2021
Jun. 09, 2021
$ / shares
shares
Sep. 30, 2020
Sep. 01, 2020
$ / shares
shares
Jun. 10, 2020
shares
Jun. 30, 2021
Right
Sep. 30, 2020
Right
Dec. 31, 2023
TWD ($)
Dec. 31, 2022
TWD ($)
Dec. 31, 2021
TWD ($)
Dec. 31, 2020
Restricted Stock Plan For Employees [Member]                            
Disclosure of terms and conditions of share-based payment arrangement [line items]                            
Compensation expenses | $                     $ 1,025 $ 1,352 $ 1,520  
Compensation plan description                     UMC is authorized to issue restricted stocks in one tranche or in installments, under the custody of trust institution, within two years from the date of receiving the effective declaration from the competent authority.     UMC is authorized to issue restricted stocks in one tranche or in installments, under the custody of trust institution, within one year from the date of receiving the effective declaration from the competent authority.
Eligibility terms to vested restricted stocks                     Beginning from the end of two years since the date of grant, those employees who fulfill both service period and performance conditions set by UMC are gradually eligible to the vested restricted stocks at certain percentage and time frame.      
Maximum shares to be issued under compensation plan | shares | shares     50         233            
Shares of restricted stock for employees issued | shares | shares 27 23     1   200              
Life of plan 4 years 4 years     4 years   4 years              
Grant date quoted market price per share | $ / shares | $ / shares $ 48.9 $ 44.4     $ 53   $ 21.8              
Stock Appreciation Right Plan For Employees [Member]                            
Disclosure of terms and conditions of share-based payment arrangement [line items]                            
Compensation expenses | $                     $ 105 210 $ 271  
Stock Appreciation Right Plan For Employees Description                     One unit of stock appreciation right to employees represents a right to the intrinsic value of one common share of UMC.      
Life of plan       4 years   4 years                
Liabilities for stock appreciation right recognized                     $ 207 $ 340    
Unit of cash-settled stock appreciation right | Right                 1 26