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Retirement Benefit Plans - Additional Information (Detail) - TWD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2021
Disclosure of defined benefit plans [line items]        
Employer contribution percentage, defined contribution plans 6.00%      
Defined contribution plans expense $ 2,809.5 $ 2,609.7 $ 2,568.9  
Employer contribution percentage, defined benefit plans 2.00%      
Defined benefit plans contribution in the next year $ 229.9      
Weighted average duration of the defined benefit obligation 9 years      
Future salary increase rate (2021) 3.00% 3.00%    
Forecast [Member]        
Disclosure of defined benefit plans [line items]        
Future salary increase rate (2021)       20.00%
Actuarial assumption of discount rates [member]        
Disclosure of defined benefit plans [line items]        
Amount of increase in defined benefit obligation $ 694.7 $ 725.0    
Actuarial assumption of expected rates of salary increases [member]        
Disclosure of defined benefit plans [line items]        
Percentage of increase in salary rate 0.50%      
Amount of increase in defined benefit obligation $ 836.0 $ 706.5    
Maximum [Member] | Actuarial assumption of discount rates [member]        
Disclosure of defined benefit plans [line items]        
Percentage after decrease in discount rate 0.50%      
Minimum [Member] | Actuarial assumption of discount rates [member]        
Disclosure of defined benefit plans [line items]        
Percentage after decrease in discount rate 0.00%