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Summary of Significant Accounting Policies - Detail Information of Subsidiaries (Detail)
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Jul. 31, 2020
Light Era Development Co., Ltd. ("LED") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Planning and development of real estate      and intelligent buildings, and property      management    
Percentage of Ownership interests 100.00% 100.00%  
Donghwa Telecom Co., Ltd. ("DHT") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products International private leased circuit, IP VPN      service, and IP transit services    
Percentage of Ownership interests 100.00% 100.00%  
Chunghwa Telecom Singapore Pte., Ltd. ("CHTS") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products International private leased circuit, IP VPN      service, and IP transit services    
Percentage of Ownership interests 100.00% 100.00%  
Chunghwa System Integration Co., Ltd. ("CHSI") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Providing system integration services and      telecommunications equipment    
Percentage of Ownership interests 100.00% 100.00%  
Chunghwa Investment Co., Ltd. ("CHI") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Investment    
Percentage of Ownership interests 89.00% 89.00%  
CHYP Multimedia Marketing & Communications Co., Ltd. ("CHYP") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Digital information supply services and      advertisement services    
Percentage of Ownership interests 100.00% 100.00%  
Prime Asia Investments Group Ltd. (B.V.I.) ("Prime Asia") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Investment    
Percentage of Ownership interests 100.00% 100.00%  
Spring House Entertainment Tech. Inc. ("SHE") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Software design services, internet contents      production and play, and motion picture      production and distribution    
Percentage of Ownership interests 56.00% 56.00%  
Chunghwa Telecom Global, Inc. ("CHTG") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products International private leased circuit, internet      services, and transit services    
Percentage of Ownership interests 100.00% 100.00%  
Chunghwa Telecom Vietnam Co., Ltd. ("CHTV") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Intelligent energy saving solutions,      international circuit, and      information and communication      technology (“ICT”) services    
Percentage of Ownership interests 100.00% 100.00%  
Smartfun Digital Co., Ltd. ("SFD") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Providing diversified family education      digital services    
Percentage of Ownership interests 65.00% 65.00%  
Chunghwa Telecom Japan Co., Ltd. ("CHTJ") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products International private leased circuit, IP VPN      service, and IP transit services    
Percentage of Ownership interests 100.00% 100.00%  
Chunghwa Sochamp Technology Inc. ("CHST") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Design, development and production of      Automatic License Plate Recognition      software and hardware    
Percentage of Ownership interests 51.00% 51.00%  
Honghwa International Co., Ltd. ("HHI") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Telecommunications engineering, sales      agent of mobile phone plan application      and other business services, etc.    
Percentage of Ownership interests 100.00% 100.00%  
Chunghwa Leading Photonics Tech Co., Ltd. ("CLPT") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Production and sale of electronic      components and finished products    
Percentage of Ownership interests 75.00% 75.00%  
Chunghwa Telecom (Thailand) Co., Ltd. ("CHTT") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products International private leased circuit, IP VPN      service, ICT and cloud VAS services    
Percentage of Ownership interests 100.00% 100.00%  
CHT Security Co., Ltd. ("CHTSC") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Computing equipment installation,      wholesale of computing and business      machinery equipment and software,      management consulting services,      data processing services, digital      information supply services and      internet identify services    
Percentage of Ownership interests 77.00% 80.00%  
International Integrated Systems, Inc. ("IISI") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products IT solution provider, IT application      consultation, system integration      and package solution    
Percentage of Ownership interests 51.00% 51.00% 51.54%
Chunghwa Telecom Co., Ltd. ("Chunghwa") [Member] | Senao International Co., Ltd. ("SENAO") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Handset and peripherals retailer, sales of      CHT mobile phone plans as an agent    
Percentage of Ownership interests 28.00% 28.00%  
Chunghwa Telecom Co., Ltd. ("Chunghwa") [Member] | CHIEF Telecom Inc. ("CHIEF") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Network integration, internet data center      (“IDC”), communications      integration and cloud application      services    
Percentage of Ownership interests 56.00% 56.00%  
Senao International Co., Ltd. ("SENAO") [Member] | Senao International (Samoa) Holding Ltd. ("SIS") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products International investment    
Percentage of Ownership interests 100.00% 100.00%  
Senao International Co., Ltd. ("SENAO") [Member] | SENYOUNG Insurance Agent Co., Ltd. ("SENYOUNG") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Property and liability insurance agency    
Percentage of Ownership interests 100.00% 100.00%  
Senao International Co., Ltd. ("SENAO") [Member] | Youth Co., Ltd. ("Youth") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Sale of information and communication      technologies products    
Percentage of Ownership interests 96.00% 96.00%  
Senao International Co., Ltd. ("SENAO") [Member] | Aval Technologies Co., Ltd. ("Aval") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Sale of information and communication      technologies products    
Percentage of Ownership interests 100.00% 100.00%  
Chunghwa Precision Test Tech. Co., Ltd. ("CHPT") [Member] | CHPT Japan Co., Ltd. ("CHPT (JP)") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Related services of electronic parts,      machinery processed products      and printed circuit board    
Percentage of Ownership interests 100.00% 100.00%  
Chunghwa Precision Test Tech. Co., Ltd. ("CHPT") [Member] | Chunghwa Precision Test Tech. International Ltd. ("CHPT (International)") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Wholesale and retail of electronic      materials, and investment    
Percentage of Ownership interests 100.00% 100.00%  
Chunghwa Precision Test Tech. Co., Ltd. ("CHPT") [Member] | Chunghwa Precision Test Tech. USA Corporation ("CHPT (US)") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Design and after-sale services of      semiconductor testing components      and printed circuit board    
Percentage of Ownership interests 100.00% 100.00%  
Youth Co., Ltd. ("Youth") [Member] | ISPOT Co., Ltd. ("ISPOT") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Sale of information and communication      technologies products    
Percentage of Ownership interests 100.00% 100.00%  
Youth Co., Ltd. ("Youth") [Member] | Youyi Co., Ltd. ("Youyi") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Maintenance of information and      communication technologies      products    
Percentage of Ownership interests 100.00% 100.00%  
Aval Technologies Co., Ltd. ("Aval") [Member] | Wiin Technology Co., Ltd. ("Wiin") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Sale of information and communication      technologies products    
Percentage of Ownership interests 100.00% 100.00%  
SENYOUNG Insurance Agent Co., Ltd. ("SENYOUNG") [Member] | Senaolife Insurance Agent Co., Ltd. ("Senaolife") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Life insurance services    
Percentage of Ownership interests 100.00% 100.00%  
CHIEF Telecom Inc. ("CHIEF") [Member] | Unigate Telecom Inc. ("Unigate") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Telecommunications and internet service    
Percentage of Ownership interests 100.00% 100.00%  
CHIEF Telecom Inc. ("CHIEF") [Member] | Chief International Corp. ("CIC") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Telecommunications and internet service    
Percentage of Ownership interests 100.00% 100.00%  
CHIEF Telecom Inc. ("CHIEF") [Member] | Shanghai Chief Telecom Co., Ltd. ("SCT") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Telecommunications and internet service    
Percentage of Ownership interests 49.00% 49.00%  
Chunghwa Investment Co., Ltd. ("CHI") [Member] | Chunghwa Precision Test Tech. Co., Ltd. ("CHPT") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Production and sale of semiconductor      testing components and printed      circuit board    
Percentage of Ownership interests 34.00% 34.00%  
Senao International (Samoa) Holding Ltd. ("SIS") [Member] | Senao International HK Limited ("SIHK") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products International investment    
Percentage of Ownership interests 100.00% 100.00%  
Senao International HK Limited ("SIHK") [Member] | Senao Trading (Fujian) Co., Ltd. ("STF") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Sale of information and communication      technologies products    
Percentage of Ownership interests 0.00% 100.00%  
Prime Asia Investments Group Ltd. (B.V.I.) ("Prime Asia") [Member] | Chunghwa Hsingta Co., Ltd. ("CHC") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Investment    
Percentage of Ownership interests 100.00% 100.00%  
Chunghwa Precision Test Tech. International Ltd. ("CHPT (International)") [Member] | Su Zhou Precision Test Tech. Ltd. ("SZPT") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Assembly processed of circuit board,      design of printed circuit board and      related consultation service    
Percentage of Ownership interests 100.00% 100.00%  
Chunghwa Precision Test Tech. International Ltd. ("CHPT (International)") [Member] | Shanghai Taihua Electronic Technology Limited ("STET") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Design of printed circuit board and related      consultation service    
Percentage of Ownership interests 100.00% 100.00%  
Chunghwa Hsingta Co., Ltd. ("CHC") [Member] | Chunghwa Telecom (China) Co., Ltd. ("CTC") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Integrated information and communication      solution services for enterprise clients,      and intelligent energy network service    
Percentage of Ownership interests 100.00% 100.00%  
International Integrated Systems, Inc. ("IISI") [Member] | Unitronics Technology Corp. ("UTC") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Development and maintenance of      information system    
Percentage of Ownership interests 99.96% 99.96%  
International Integrated Systems, Inc. ("IISI") [Member] | IISI Investment Co., Ltd. ("IICL") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Investment    
Percentage of Ownership interests 100.00% 100.00%  
International Integrated Systems, Inc. ("IISI") [Member] | Infoexplorer International Co., Ltd.("IESA") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Investment    
Percentage of Ownership interests 100.00% 100.00%  
Infoexplorer International Co., Ltd.("IESA") [Member] | International Integrated Systems (Hong Kong) Limited ("IEHK") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Investment and technical consulting service    
Percentage of Ownership interests 100.00% 100.00%  
IISI Investment Co., Ltd. ("IICL") [Member] | Leading Tech Co., Ltd. ("LTCL") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Investment    
Percentage of Ownership interests 100.00% 100.00%  
Leading Tech Co., Ltd. ("LTCL") [Member] | Leading Systems Co., Ltd. ("LSCL") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Investment    
Percentage of Ownership interests 100.00% 100.00%  
Leading Systems Co., Ltd. ("LSCL") [Member] | International Integrated Systems Inc. (Shanghai) ("IISS") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Development and maintenance of      information system    
Percentage of Ownership interests 0.00% 100.00%  
International Integrated Systems Inc. (Shanghai) ("IISS") [Member] | Huiyu Shanghai Management Consultancy Co., Ltd. ("HSMC") [Member]      
Disclosure of subsidiaries [Line Items]      
Main Businesses and Products Development and maintenance of      information system    
Percentage of Ownership interests 0.00% 0.00%