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Other Operating Income and Expenses, Net - Summary of Other Operating Income and Expenses, Net (Detail)
$ in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2018
TWD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
TWD ($)
Dec. 31, 2016
TWD ($)
Other Operating Income And Expense Net [abstract]        
Gain (loss) on disposal or retirement of property, plant and equipment, net $ (1,005.6) $ (32.9) $ (1,097.9) $ 46.5
Impairment loss on property, plant and equipment (423.5) (13.8)    
Others (672.4)   (267.6) (16.7)
Other operating income and expenses, net $ (2,101.5) $ (68.7) $ (1,365.5) $ 29.8