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Lease Arrangements - Maturity Analysis of Lease Payments Receivable Under Operating Subleases (Detail) - TWD ($)
$ in Millions
Jun. 30, 2021
Dec. 31, 2020
Operating Sublease Agreement [Member] | Year 1 [Member]    
Disclosure Of Maturity Analysis Of Operating Lease Receivables Under Subleases [Line Items]    
Maturity analysis of lease payments receivable $ 65.0 $ 144.1