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Operating Segments Information - Summary of Geographical Information (Detail)
$ in Thousands, $ in Thousands
 12 Months Ended
Dec. 31, 2018
USD ($)
Dec. 31, 2018
TWD ($)
Dec. 31, 2017
TWD ($)
Dec. 31, 2016
TWD ($)
Dec. 31, 2018
TWD ($)
Disclosure of geographical areas [line items]          
Operating revenue $ 12,123,242 $ 371,092,421 $ 290,441,208 $ 274,884,107  
Noncurrent assets, excluding financial instruments, post-employment benefit assets and deferred tax assets 10,280,594   163,752,501   $ 314,689,000
United States [Member]          
Disclosure of geographical areas [line items]          
Operating revenue 7,539,731 230,791,164 196,462,345 180,745,837  
Taiwan [member]          
Disclosure of geographical areas [line items]          
Operating revenue 1,490,715 45,630,792 35,413,647 38,868,679  
Noncurrent assets, excluding financial instruments, post-employment benefit assets and deferred tax assets 7,512,071   93,350,839   229,944,505
Asia [Member]          
Disclosure of geographical areas [line items]          
Operating revenue 1,830,484 56,031,108 30,201,332 29,896,304  
Europe [Member]          
Disclosure of geographical areas [line items]          
Operating revenue 1,203,668 36,844,258 26,445,240 23,275,732  
Other geographical areas [member]          
Disclosure of geographical areas [line items]          
Operating revenue 58,644 $ 1,795,099 1,918,644 $ 2,097,555  
Noncurrent assets, excluding financial instruments, post-employment benefit assets and deferred tax assets 839,146   25,025,498   25,686,256
China [member]          
Disclosure of geographical areas [line items]          
Noncurrent assets, excluding financial instruments, post-employment benefit assets and deferred tax assets $ 1,929,377   $ 45,376,164   $ 59,058,239