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Retirement Benefit Plans - Fair Value of Plan Assets by Major Categories (Detail) - TWD ($)
$ in Millions
Dec. 31, 2021
Dec. 31, 2020
Disclosure of fair value of plan assets [abstract]    
Cash $ 1,001.0 $ 632.8
Equity instruments 2,951.8 2,926.7
Debt instruments 1,595.8 1,506.7
Fair value of plan assets $ 5,548.6 $ 5,066.2