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Bonds Payable - Summary of Bonds Payable (Detail)
$ in Millions, $ in Millions
Dec. 31, 2020
TWD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2019
TWD ($)
Bonds payable [line items]      
Less: Current portion $ (2,600.0)   $ (31,800.0)
Noncurrent bonds payable 254,105.1 $ 9,049.3 25,100.0
Cost [member] | Taiwan [member]      
Bonds payable [line items]      
Unsecured bonds 173,197.0   $ 56,900.0
Cost [member] | Overseas [member]      
Bonds payable [line items]      
Unsecured bonds 84,291.0    
Discounts on bonds payable [member]      
Bonds payable [line items]      
Discounts on bonds payable $ (782.9)