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Retirement Benefit Plans - Movements in Fair Value of Plan Assets (Detail) - Fair value of plan assets [member] - TWD ($)
$ in Millions
12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Disclosure of fair value of plan assets [line items]      
Balance, beginning of year $ 8,737.9 $ 8,162.9 $ 5,548.6
Interest income 120.1 161.7 46.5
Remeasurement:      
Return on plan assets (excluding amounts included in net interest expense) 774.6 16.2 429.9
Contributions from employer 1,798.0 953.6 2,723.2
Benefits paid from plan assets (679.1) (556.5) (585.3)
Balance, end of year $ 10,751.5 $ 8,737.9 $ 8,162.9