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Significant Events After the Reporting Periods - Additional Information (Detail) - Line of credit [member] - TWD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Mar. 31, 2020
Dec. 31, 2019
Bottom of range [member]    
Disclosure of events after reporting period [Line Items]    
Line of credit term   seven years
Top of range [member]    
Disclosure of events after reporting period [Line Items]    
Line of credit term   ten years
MOEA [member]    
Disclosure of events after reporting period [Line Items]    
Borrowings line of credit $ 12,144  
Increase decrease in line of credit $ 3,584