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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
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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% |

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