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Long-Term Bank Loans - Summary of Loans and Bonds Payable (Detail)
$ in Millions, $ in Millions
 6 Months Ended 12 Months Ended
Jun. 30, 2021
TWD ($)
Dec. 31, 2020
TWD ($)
Jun. 30, 2021
USD ($)
Disclosure of detailed information about borrowings [line items]      
Long-term bank loans $ 3,171.3 $ 1,967.6 $ 113.6
Long-term bank loans [member]      
Disclosure of detailed information about borrowings [line items]      
Unsecured loans 3,210.0 2,000.0  
Less: Discounts on government grants (38.7) (32.4)  
Long-term bank loans $ 3,171.3 $ 1,967.6  
Annual interest rate   0.40%  
Maturity date March 2026 September 2025  
Long-term bank loans [member] | Bottom of range [member]      
Disclosure of detailed information about borrowings [line items]      
Annual interest rate 0.40%   0.40%
Long-term bank loans [member] | Top of range [member]      
Disclosure of detailed information about borrowings [line items]      
Annual interest rate 0.60%   0.60%