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Net Income and Other Comprehensive Income (Loss) - Other Income and Expenses (Detail)
$ in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2018
TWD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
TWD ($)
Dec. 31, 2016
TWD ($)
Analysis Of Income And Expense [Abstract]        
Gain or loss on disposal of property, plant and equipment $ 142 $ 5 $ (107) $ (48)
Reversal of impairment loss on investment properties 19 1 11 148
Loss on disposal of intangible assets 0 0 0 0
Impairment loss on intangible assets (51) (2) (9) 0
Impairment loss on property, plant and equipment 0 0 0 (596)
Other income and expenses $ 110 $ 4 $ (105) $ (496)