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Related Parties Transactions - Additional Information (Detail)
$ in Millions, $ in Millions
 1 Months Ended 12 Months Ended
Aug. 31, 2011
TWD ($)
Dec. 31, 2019
TWD ($)
Dec. 31, 2018
TWD ($)
Dec. 31, 2017
TWD ($)
Jan. 01, 2019
TWD ($)
Aug. 31, 2011
SGD ($)
Disclosure of transactions between related parties [Line Items]            
Lease contract value   $ 9,758     $ 10,340  
Lease contract value, prepayment amount     $ 1,551      
Interest on lease liabilities   85 0 $ 0    
ST-2 Satellite Ventures Pte., Ltd. ("STS") [Member]            
Disclosure of transactions between related parties [Line Items]            
Lease contract value   1,212        
Interest on lease liabilities   $ 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     394 392    
Rental expense, offsetting credit of the prepayment     204 204    
Rental expense, additional accrual     $ 190 $ 188