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Retirement Benefit Plans - Summary of Sensitivity Analysis (Detail) - TWD ($)
$ in Millions
12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Disclosure of sensitivity analysis for actuarial assumptions [Line Items]    
The expected contributions to the plan for the next year $ 1,224 $ 1,355
Bottom of range [Member]    
Disclosure of sensitivity analysis for actuarial assumptions [Line Items]    
The average duration of the defined benefit obligations 6 years 6 years 1 month 6 days
Top of range [Member]    
Disclosure of sensitivity analysis for actuarial assumptions [Line Items]    
The average duration of the defined benefit obligations 10 years 10 years