XML 186 R172.htm IDEA: XBRL DOCUMENT v3.8.0.1
Income Tax - Information About Unused Loss Carryforwards (Detail)
$ in Millions, $ in Millions
Dec. 31, 2017
TWD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
TWD ($)
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]      
Remaining creditable amount $ 2,730 $ 92 $ 2,322
Unused tax losses [Member]      
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]      
Remaining creditable amount 387    
Unused tax losses [Member] | 2018 [Member]      
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]      
Remaining creditable amount 126    
Unused tax losses [Member] | 2019 [Member]      
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]      
Remaining creditable amount 138    
Unused tax losses [Member] | 2020 [Member]      
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]      
Remaining creditable amount 45    
Unused tax losses [Member] | 2021 [Member]      
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]      
Remaining creditable amount 20    
Unused tax losses [Member] | 2022 [Member]      
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]      
Remaining creditable amount 12    
Unused tax losses [Member] | 2023 [Member]      
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]      
Remaining creditable amount 1    
Unused tax losses [Member] | 2024 [Member]      
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]      
Remaining creditable amount 4    
Unused tax losses [Member] | 2025 [Member]      
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]      
Remaining creditable amount 28    
Unused tax losses [Member] | 2026 [Member]      
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]      
Remaining creditable amount 10    
Unused tax losses [Member] | 2027 [Member]      
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]      
Remaining creditable amount $ 3