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Financial Instruments - Detailed Information About In Maturity Analysis For Lease Liabilities (Detail) - TWD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Disclosure of detailed information about financial instruments [line items]    
Lease liabilities $ 15,067.9 $ 10,947.7
5-10 years [member]    
Disclosure of detailed information about financial instruments [line items]    
Lease liabilities 7,402.0 5,581.1
10-15 years [member]    
Disclosure of detailed information about financial instruments [line items]    
Lease liabilities 5,253.9 3,691.3
15-20 years [member]    
Disclosure of detailed information about financial instruments [line items]    
Lease liabilities 2,255.2 1,600.9
More than 20 years [member]    
Disclosure of detailed information about financial instruments [line items]    
Lease liabilities $ 156.8 $ 74.4