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Retirement Benefit Plans - Pension Costs Recognized in Profit and Loss for Defined Benefit Plans (Detail) - TWD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Disclosure Of Defined Plan [line items]      
Defined benefit plans pension costs recognized in profit and loss $ 835 $ 935 $ 1,048
Operating costs [Member]      
Disclosure Of Defined Plan [line items]      
Defined benefit plans pension costs recognized in profit and loss 416 488 565
Marketing expenses [Member]      
Disclosure Of Defined Plan [line items]      
Defined benefit plans pension costs recognized in profit and loss 314 334 360
General and administrative expenses [Member]      
Disclosure Of Defined Plan [line items]      
Defined benefit plans pension costs recognized in profit and loss 73 78 86
Research and development expenses [Member]      
Disclosure Of Defined Plan [line items]      
Defined benefit plans pension costs recognized in profit and loss $ 32 $ 35 $ 37