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Net Income and Other Comprehensive Income (Loss) - Additional Information (Detail)
$ in Millions
 12 Months Ended
Dec. 31, 2018
TWD ($)
Employee benefits expense [Line Items]  
Employees' compensation payables $ 1,404
Remuneration to directors payables $ 38
Bottom of Range [Member]  
Employee benefits expense [Line Items]  
Employees' compensation distribution rate 1.70%
Top of Range [Member]  
Employee benefits expense [Line Items]  
Employees' compensation distribution rate 4.30%
Directors' remuneration distribution rate 0.17%