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Other Operating Income and Expenses, Net - Summary of Other Operating Income and Expenses, Net (Detail)
$ in Millions, $ in Millions
 9 Months Ended 12 Months Ended
Sep. 30, 2015
TWD ($)
Dec. 31, 2017
TWD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
TWD ($)
Dec. 31, 2015
TWD ($)
Other Operating Income And Expense Net [Abstract]          
Gain (loss) on disposal or retirement of property, plant and equipment, net   $ (1,097.9) $ (37.0) $ 46.5 $ 433.5
Impairment loss on property, plant and equipment $ (2,286.0)       (2,545.6)
Gain from lease agreement modification         430.0
Others   (267.6)   (16.7) (198.5)
Other operating income and expenses, net   $ (1,365.5) $ (46.0) $ 29.8 $ (1,880.6)