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Financial Assets at Fair Value Through Other Comprehensive Income - Summary of Financial Assets at Fair Value through Other Comprehensive Income (Detail)
$ in Millions, $ in Millions
Dec. 31, 2020
TWD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2019
TWD ($)
Disclosure of financial assets [line items]      
Current $ 122,448.5   $ 127,396.6
Non current 4,514.9 $ 160.8 4,124.3
Investment in equity and debt instruments at FVTOCI 126,963.4   131,520.9
Debt securities [member]      
Disclosure of financial assets [line items]      
Investments in debt instruments at FVTOCI 122,398.5   127,396.6
Debt securities [member] | Corporate bonds [member]      
Disclosure of financial assets [line items]      
Investments in debt instruments at FVTOCI 56,593.6   51,790.0
Debt securities [member] | Agency bonds/Agency mortgage-backed securities [member]      
Disclosure of financial assets [line items]      
Investments in debt instruments at FVTOCI 43,977.1   51,966.5
Debt securities [member] | Government bonds [member]      
Disclosure of financial assets [line items]      
Investments in debt instruments at FVTOCI 13,459.5   12,824.2
Debt securities [member] | Asset-backed securities [Member]      
Disclosure of financial assets [line items]      
Investments in debt instruments at FVTOCI 8,368.3   10,815.9
Equity instruments [member]      
Disclosure of financial assets [line items]      
Investment in equity instruments at FVTOCI 4,564.9   4,124.3
Equity instruments [member] | Non-publicly traded stocks [member]      
Disclosure of financial assets [line items]      
Investment in equity instruments at FVTOCI 4,514.9   $ 4,124.3
Equity instruments [member] | Publicly traded stocks [member]      
Disclosure of financial assets [line items]      
Investment in equity instruments at FVTOCI $ 50.0