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Summary of Significant Accounting Policies - Detail Information of Subsidiaries (Parenthetical) (Detail)
Dec. 31, 2020
Sep. 30, 2020
Jul. 31, 2020
Jul. 01, 2020
Apr. 30, 2020
Dec. 31, 2019
Nov. 30, 2019
Oct. 31, 2019
Sep. 30, 2019
Spring House Entertainment Tech. Inc. ("SHE") [Member]                  
Disclosure of subsidiaries [Line Items]                  
Percentage of Ownership interests 56.00%         56.00%      
Percentage of Ownership           19.72%      
International Integrated Systems, Inc. ("IISI") [Member]                  
Disclosure of subsidiaries [Line Items]                  
Percentage of Ownership interests 51.00% 51.20% 51.54%     0.00%      
Percentage of additional ownership interest obtained       20.38%          
Chunghwa Telecom Co., Ltd. and Chunghwa Investment Co., Ltd. [Member] | Senao International Co., Ltd. (SENAO) [Member]                  
Disclosure of subsidiaries [Line Items]                  
Percentage of Ownership interests 28.18%         28.18%      
Chunghwa Telecom Co., Ltd. and Chunghwa Investment Co., Ltd. [Member] | CHIEF Telecom Inc. ("CHIEF") [Member]                  
Disclosure of subsidiaries [Line Items]                  
Percentage of Ownership interests 59.08%         59.75%      
Youth Co., Ltd. ("Youth") [Member] | Senao International Co., Ltd. (SENAO) [Member] | Bottom of Range [Member]                  
Disclosure of subsidiaries [Line Items]                  
Percentage of Ownership interests         92.89%        
Youth Co., Ltd. ("Youth") [Member] | Senao International Co., Ltd. (SENAO) [Member] | Top of Range [Member]                  
Disclosure of subsidiaries [Line Items]                  
Percentage of Ownership interests         95.79%        
Aval Technologies Co., Ltd. ("Aval") [Member] | Wiin Technology Co., Ltd. ("Wiin") [Member]                  
Disclosure of subsidiaries [Line Items]                  
Percentage of Ownership interests                 100.00%
SENYOUNG Insurance Agent Co., Ltd. ("SENYOUNG") [Member] | Senaolife Insurance Agent Co., Ltd. [Member]                  
Disclosure of subsidiaries [Line Items]                  
Percentage of Ownership interests 100.00%         100.00% 100.00%    
Light Era Development Co., Ltd. ("LED") [Member] | Taoyuan Asia Silicon Valley Innovation Co., Ltd [Member]                  
Disclosure of subsidiaries [Line Items]                  
Percentage of Ownership interests 0.00%         0.00%      
Chunghwa Investment Co., Ltd. ("CHI") [Member] | Chunghwa Precision Test Tech. Co., Ltd. ("CHPT") [Member]                  
Disclosure of subsidiaries [Line Items]                  
Percentage of Ownership interests 34.25%         34.25%      
Chunghwa Investment Co., Ltd. ("CHI") [Member] | Chunghwa Precision Test Tech. Co., Ltd. ("CHPT") [Member] | Bottom of Range [Member]                  
Disclosure of subsidiaries [Line Items]                  
Percentage of Ownership interests 50.00%                
Chunghwa Precision Test Tech. International Ltd. ("CHPT (International)") [Member] | Su Zhou Precision Test Tech. Ltd. ("SZPT") [Member]                  
Disclosure of subsidiaries [Line Items]                  
Percentage of Ownership interests 100.00%         100.00%   100.00%