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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, 2021
Dec. 31, 2020
Dec. 31, 2019
Disclosure of fair value of plan assets [line items]      
Balance, beginning of year $ 5,066.2 $ 4,301.6 $ 4,011.3
Interest income 19.5 37.2 51.4
Remeasurement:      
Return on plan assets (excluding amounts included in net interest expense) 73.3 139.2 124.4
Contributions from employer 821.4 987.2 458.6
Benefits paid from plan assets (431.8) (399.0) (344.1)
Balance, end of year $ 5,548.6 $ 5,066.2 $ 4,301.6