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Short-term Loans - Summary of Short-term Loans (Detail)
€ in Millions, $ in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2019
TWD ($)
Dec. 31, 2018
TWD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2019
EUR (€)
Dec. 31, 2018
USD ($)
Dec. 31, 2018
EUR (€)
Disclosure of detailed information about borrowings [line items]            
Amount $ 118,522.3 $ 88,754.7 $ 3,962.6      
Original loan content     $ 2,370.0 € 1,410.0 $ 2,610.0 € 242.0
Maturity date 2020-05 2019-01        
Bottom of range [member]            
Disclosure of detailed information about borrowings [line items]            
Annual interest rate 0.01% 0.01% 0.01% 0.01% 0.01% 0.01%
Top of range [member]            
Disclosure of detailed information about borrowings [line items]            
Annual interest rate 2.22% 3.22% 2.22% 2.22% 3.22% 3.22%
Unsecured Loans [member]            
Disclosure of detailed information about borrowings [line items]            
Amount $ 118,522.3 $ 88,754.7