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Lease Arrangements - Additional Information (Details) - TWD ($)
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Disclosure Of Quantitative Information About Rightofuse Assets [Line Items]    
Sublease $ 0 $ 0
Impairment of right-of-use assets $ 0 $ 0
Taiwan [Member] | Bottom of Range [Member] | Handsets Base Stations [Member]    
Disclosure Of Quantitative Information About Rightofuse Assets [Line Items]    
Lease Term 1 year  
Taiwan [Member] | Bottom of Range [Member] | Offices, Server rooms and Stores [Member]    
Disclosure Of Quantitative Information About Rightofuse Assets [Line Items]    
Lease Term 1 year  
Taiwan [Member] | Top of Range [Member] | Handsets Base Stations [Member]    
Disclosure Of Quantitative Information About Rightofuse Assets [Line Items]    
Lease Term 20 years  
Taiwan [Member] | Top of Range [Member] | Offices, Server rooms and Stores [Member]    
Disclosure Of Quantitative Information About Rightofuse Assets [Line Items]    
Lease Term 30 years