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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
Jun. 30, 2021
Dec. 31, 2020
Disclosure Of Maturity Analysis Of Operating Lease Receivables [Line Items]    
Operating Lease Payment Receivables $ 30.5 $ 166.1
Year 1 [member]    
Disclosure Of Maturity Analysis Of Operating Lease Receivables [Line Items]    
Operating Lease Payment Receivables 22.0 149.1
Year 2 [Member]    
Disclosure Of Maturity Analysis Of Operating Lease Receivables [Line Items]    
Operating Lease Payment Receivables $ 8.5 $ 17.0