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Related Parties Transactions - Details of Transactions Between the Company and Other Related Parties (Detail)
$ in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2017
TWD ($)
Dec. 31, 2016
TWD ($)
Dec. 31, 2015
TWD ($)
Dec. 31, 2017
USD ($)
Disclosure of transactions between related parties [Line Items]        
Revenues $ 410 $ 348 $ 423  
Operating Costs and Expenses 1,270 1,496 1,530  
Non-operating Income and Expenses 32 37 36  
Receivables 49 14   $ 2
Payables 684 762   $ 23
Customers' deposits 6 11    
Acquisition of property, plant and equipment 390 320 325  
Prepaid rents - current 204 204    
Prepaid rents - noncurrent 1,551 1,755    
Prepaid rents 1,755 1,959    
Associates [Member]        
Disclosure of transactions between related parties [Line Items]        
Revenues 344 292 333  
Operating Costs and Expenses 1,197 1,405 1,451  
Non-operating Income and Expenses 32 37 36  
Receivables 43 9    
Payables 680 757    
Customers' deposits 6 10    
Acquisition of property, plant and equipment 390 313 314  
Joint ventures [Member]        
Disclosure of transactions between related parties [Line Items]        
Revenues 1 7 9  
Operating Costs and Expenses 2 17 17  
Receivables 0 0    
Payables 0 1    
Customers' deposits 0 1    
Acquisition of property, plant and equipment 0 7 11  
Others [Member]        
Disclosure of transactions between related parties [Line Items]        
Revenues 65 49 81  
Operating Costs and Expenses 71 74 62  
Non-operating Income and Expenses 0 0 $ 0  
Receivables 6 5    
Payables $ 4 $ 4