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Related Parties Transactions - Additional Information (Detail)
$ in Millions, $ in Millions
 1 Months Ended 12 Months Ended
Aug. 31, 2011
TWD ($)
Dec. 31, 2020
TWD ($)
Dec. 31, 2019
TWD ($)
Dec. 31, 2018
TWD ($)
Aug. 31, 2011
SGD ($)
Disclosure of transactions between related parties [Line Items]          
Lease contract value   $ 9,597 $ 9,758    
Lease contract value, prepayment amount       $ 1,551  
Interest on lease liabilities   80 85 0  
ST-2 Satellite Ventures Pte., Ltd. ("STS") [Member]          
Disclosure of transactions between related parties [Line Items]          
Lease contract value   999 1,212    
Interest on lease liabilities   $ 9 $ 11    
ST-2 Satellite Ventures Pte., Ltd. ("STS") [Member]          
Disclosure of transactions between related parties [Line Items]          
Lease term 15 years        
Lease contract value $ 6,000       $ 261
Lease contract value, prepayment amount $ 3,068        
Rental expense       394  
Rental expense, offsetting credit of the prepayment       204  
Rental expense, additional accrual       $ 190