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Short-term Loans - Summary of Short-term Loans (Detail)
€ in Millions, $ in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2020
TWD ($)
Dec. 31, 2019
TWD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2020
EUR (€)
Dec. 31, 2019
USD ($)
Dec. 31, 2019
EUR (€)
Disclosure of detailed information about borrowings [line items]            
Amount $ 88,559.0 $ 118,522.3 $ 3,153.8      
Loan content     $ 200.0 € 2,398.0 $ 2,370.0 € 1,410.0
Maturity date 2021-02 2020-05        
Bottom of range [member]            
Disclosure of detailed information about borrowings [line items]            
Annual interest rate (0.54%) 0.01% (0.54%) (0.54%) 0.01% 0.01%
Top of range [member]            
Disclosure of detailed information about borrowings [line items]            
Annual interest rate 0.33% 2.22% 0.33% 0.33% 2.22% 2.22%
Unsecured Loans [member]            
Disclosure of detailed information about borrowings [line items]            
Amount $ 88,559.0 $ 118,522.3