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Income Tax - Unused Loss Carryforwards and Deductible Temporary Differences for Which No Deferred Income Tax Assets Have Been Recognized (Detail) - TWD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]    
Loss carryforwards $ 73 $ 47
Deductible temporary differences 16 10
2024 [Member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]    
Loss carryforwards 0 1
2025 [Member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]    
Loss carryforwards 17 15
Investment credits - research and development expenditures 0 8
2026 [Member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]    
Loss carryforwards 10 8
2027 [Member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]    
Loss carryforwards 3 3
2028 [Member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]    
Loss carryforwards 1 1
2029 [Member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]    
Loss carryforwards 2 1
2030 [Member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]    
Loss carryforwards 1 0
2031 [Member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]    
Loss carryforwards 1 0
2032 [Member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]    
Loss carryforwards 6 5
2033 [Member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]    
Loss carryforwards 20 13
2034 [Member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]    
Loss carryforwards $ 12 $ 0