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Retirement Benefit Plans - Movements in Present Value of Defined Benefit Obligation (Detail) - TWD ($)
$ in Millions
12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Remeasurement:      
Actuarial loss arising from experience adjustments $ 68.3 $ 1,413.8 $ 94.3
Actuarial loss arising from changes in demographic assumptions     277.4
Actuarial (gain) loss arising from changes in financial assumptions 571.3 (160.8) (540.5)
Present value of defined benefit obligation [member]      
Disclosure of defined benefit plans [line items]      
Balance, beginning of year 17,484.0 16,585.5 16,980.3
Current service cost 139.1 134.3 145.3
Interest expense 304.0 120.8 66.7
Remeasurement:      
Actuarial loss arising from experience adjustments 68.3 1,413.8 94.3
Actuarial loss arising from changes in demographic assumptions     277.4
Actuarial (gain) loss arising from changes in financial assumptions 571.3 (160.8) (540.5)
Benefits paid from plan assets (556.5) (585.3) (431.8)
Benefits paid directly by the Company (15.1) (24.3) (6.2)
Balance, end of year $ 17,995.1 $ 17,484.0 $ 16,585.5