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Segment Information - Main Products and Service Revenues (Detail)
$ in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2021
TWD ($)
Dec. 31, 2021
USD ($)
Dec. 31, 2020
TWD ($)
Dec. 31, 2019
TWD ($)
Disclosure Of Products And Services [Line Items]        
Revenues $ 210,478 $ 7,588 $ 207,609 $ 207,520
Mobile services [Member]        
Disclosure Of Products And Services [Line Items]        
Revenues 58,048   56,724 58,703
Sales of products [Member]        
Disclosure Of Products And Services [Line Items]        
Revenues 42,907   39,391 41,593
Local telephone and domestic long distance telephone services [Member]        
Disclosure Of Products And Services [Line Items]        
Revenues 25,704   26,475 27,929
Broadband access and domestic leased line services [Member]        
Disclosure Of Products And Services [Line Items]        
Revenues 23,012   22,420 22,116
Data communications internet services [Member]        
Disclosure Of Products And Services [Line Items]        
Revenues 22,281   21,447 21,003
International network and leased line services revenue [Member]        
Disclosure Of Products And Services [Line Items]        
Revenues 4,367   3,884 7,066
Others [Member]        
Disclosure Of Products And Services [Line Items]        
Revenues $ 34,159   $ 37,268 $ 29,110