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Property, Plant and Equipment - Summary of maturity analysis of operating lease payments receivable (Detail) - Operating Lease Agreement [Member] - TWD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Disclosure Of Maturity Analysis Of Operating Lease Receivables [Line Items]    
Operating Lease Payment Receivables $ 166.1 $ 52.4
Year 1 [member]    
Disclosure Of Maturity Analysis Of Operating Lease Receivables [Line Items]    
Operating Lease Payment Receivables 149.1 18.4
Year 2 [Member]    
Disclosure Of Maturity Analysis Of Operating Lease Receivables [Line Items]    
Operating Lease Payment Receivables $ 17.0 17.0
Year 3 [member]    
Disclosure Of Maturity Analysis Of Operating Lease Receivables [Line Items]    
Operating Lease Payment Receivables   $ 17.0