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Summary of Significant Accounting Policies - Detail Information of Subsidiaries (Detail) | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Dec. 31, 2020 | Sep. 30, 2020 | Jul. 31, 2020 | Dec. 31, 2019 | Nov. 30, 2019 | Oct. 31, 2019
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 | 80.00% |  |  | 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% | 51.20% | 51.54% | 0.00% |  |
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% |  |  | 57.00% |  |
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% |  |  | 93.00% |  |
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% | 100.00% |
Light Era Development Co., Ltd. ("LED") [Member] | Taoyuan Asia Silicon Valley Innovation Co., Ltd. ("TASVI") [Member] |  |  |  |  |  |
Disclosure of subsidiaries [Line Items] |  |  |  |  |  |
Main Businesses and Products | Development of real estate |  |  |  |  |
Percentage of Ownership interests | 0.00% |  |  | 0.00% |  |
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% |  |  | 0.00% |  |
Senao International HK Limited ("SIHK") [Member] | Senao International Trading (Shanghai) Co., Ltd. ("SITS") [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% |  |
Senao International HK Limited ("SIHK") [Member] | Senao International Trading (Jiangsu) Co., Ltd. ("SITJ") [Member] |  |  |  |  |  |
Disclosure of subsidiaries [Line Items] |  |  |  |  |  |
Main Businesses and Products | Sale of information and communication technologies products |  |  |  |  |
Percentage of Ownership interests | 0.00% |  |  | 0.00% |  |
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% |  | 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% |  |  | 0.00% |  |
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% |  |  | 0.00% |  |
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% |  |  | 0.00% |  |
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% |  |  | 0.00% |  |
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% |  |  | 0.00% |  |
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% |  |  | 0.00% |  |
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 | 100.00% |  |  | 0.00% |  |
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% |  |

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