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Retirement Benefit Plans - Fair Value of Plan Assets by Major Categories (Detail) - TWD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Disclosure of fair value of plan assets [abstract]    
Cash $ 1,569.7 $ 1,351.8
Equity instruments 6,245.6 4,998.9
Debt instruments 2,936.2 2,387.2
Fair value of plan assets $ 10,751.5 $ 8,737.9