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Net Income and Other Comprehensive Income (Loss) - Impairment Loss (Reversal of Impairment Loss) on Financial Instruments and Non-financial Assets (Detail)
$ in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2017
TWD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
TWD ($)
Dec. 31, 2015
TWD ($)
Disclosure Of Impairment Loss And Reversal Of Impairment Loss [Abstract]        
Trade notes and accounts receivable $ 578   $ 943 $ 480
Other receivables 65   (2) 39
Available-for-sale financial assets 0 $ 0 577 107
Inventories 52 2 192 198
Impairment losses 0 0 596 138
Impairment loss on investments accounted for using equity method 0 0 0 8
Investment properties (11) 0 (148) (142)
Impairment loss on intangible assets $ 9 $ 0 $ 0 $ 0