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Financial Instruments - Fair Value of Financial Instruments Not Measured at Fair Value but for which Fair Value is Disclosed (Detail) - TWD ($)
$ in Millions
Jun. 30, 2021
Dec. 31, 2020
Disclosure of detailed information about financial instruments [line items]    
Financial assets $ 1,075,496.6 $ 958,471.8
Financial liabilities 921,708.0 748,224.6
Financial assets at amortised cost, class [member] | Corporate bonds [member]    
Disclosure of detailed information about financial instruments [line items]    
Financial assets 4,336.6 10,970.2
Financial liabilities at amortised cost [member] | Bonds payable including long-term liabilities-current portion) [member]    
Disclosure of detailed information about financial instruments [line items]    
Financial liabilities 410,464.9 256,705.1
Not measured at fair value but for which the fair value is disclosed [member] | Level 2 [member] | Financial assets at amortised cost, class [member] | Corporate bonds [member]    
Disclosure of detailed information about financial instruments [line items]    
Financial assets, at fair value 4,373.9 11,053.6
Not measured at fair value but for which the fair value is disclosed [member] | Level 2 [member] | Financial liabilities at amortised cost [member] | Bonds payable including long-term liabilities-current portion) [member]    
Disclosure of detailed information about financial instruments [line items]    
Financial liabilities, at fair value $ 407,330.0 $ 257,551.2