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Property, Plant and Equipment - Additional Information (Detail) - TWD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Bottom of range [member]      
Disclosure of detailed information about property, plant and equipment [line items]      
Operating lease term 1 year 1 year  
Top of range [member]      
Disclosure of detailed information about property, plant and equipment [line items]      
Operating lease term 5 years 5 years  
Main plants [member]      
Disclosure of detailed information about property, plant and equipment [line items]      
Estimated useful lives for property, plant and equipment 20 years 20 years 20 years
Mechanical and electrical power equipment [member]      
Disclosure of detailed information about property, plant and equipment [line items]      
Estimated useful lives for property, plant and equipment 10 years 10 years 10 years
Clean rooms [member]      
Disclosure of detailed information about property, plant and equipment [line items]      
Estimated useful lives for property, plant and equipment 10 years 10 years 10 years
Machinery and equipment      
Disclosure of detailed information about property, plant and equipment [line items]      
Reversal of impairment   $ 301.4  
Impairment loss recognized     $ 423.5