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Financial Instruments - Detailed Information About In Maturity Analysis For Lease Liabilities (Detail) - TWD ($)
$ in Millions
Jun. 30, 2021
Dec. 31, 2020
Disclosure of detailed information about financial instruments [line items]    
Lease liabilities $ 15,437.5 $ 15,067.9
5-10 years [member]    
Disclosure of detailed information about financial instruments [line items]    
Lease liabilities 7,658.6 7,402.0
10-15 years [member]    
Disclosure of detailed information about financial instruments [line items]    
Lease liabilities 5,300.3 5,253.9
15-20 years [member]    
Disclosure of detailed information about financial instruments [line items]    
Lease liabilities 2,290.8 2,255.2
More than 20 years [member]    
Disclosure of detailed information about financial instruments [line items]    
Lease liabilities $ 187.8 $ 156.8