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Summary of Significant Accounting Policies - Detail Information of Subsidiaries (Parenthetical) (Detail) | Dec. 31, 2019 | Nov. 30, 2019 | Oct. 31, 2019 | Sep. 30, 2019 | Dec. 31, 2018 | Mar. 31, 2018
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Spring House Entertainment Tech. Inc. (SHE) [Member] |  |  |  |  |  |
Disclosure of subsidiaries [Line Items] |  |  |  |  |  |
Percentage of Ownership | 56.00% |  |  |  | 56.00% |
Percentage of Ownership | 19.72% |  |  |  |  |
Chunghwa Telecom Co., Ltd. and Chunghwa Investment Co., Ltd. [Member] | Senao International Co., Ltd. (SENAO) [Member] |  |  |  |  |  |
Disclosure of subsidiaries [Line Items] |  |  |  |  |  |
Percentage of Ownership | 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 | 59.75% |  |  |  | 60.23% |
Youth Co., Ltd. (Youth) [Member] | Senao International Co., Ltd. (SENAO) [Member] | Bottom of Range [Member] |  |  |  |  |  |
Disclosure of subsidiaries [Line Items] |  |  |  |  |  |
Percentage of Ownership |  |  |  |  | 89.00% |
Youth Co., Ltd. (Youth) [Member] | Senao International Co., Ltd. (SENAO) [Member] | Top of Range [Member] |  |  |  |  |  |
Disclosure of subsidiaries [Line Items] |  |  |  |  |  |
Percentage of Ownership |  |  |  |  | 93.00% |
Aval Technologies Co., Ltd. (Aval) [Member] | Wiin Technology Co., Ltd. (“Wiin”) [Member] |  |  |  |  |  |
Disclosure of subsidiaries [Line Items] |  |  |  |  |  |
Percentage of Ownership |  |  |  | 100.00% |  |
SENYOUNG Insurance Agent Co., Ltd. [Member] | Senaolife Insurance Agent Co., Ltd. [Member] |  |  |  |  |  |
Disclosure of subsidiaries [Line Items] |  |  |  |  |  |
Percentage of Ownership | 100.00% | 100.00% |  |  | 0.00% |
Light Era Development Co., Ltd. (LED) [Member] | Taoyuan Asia Silicon Valley Innovation Co., Ltd [Member] |  |  |  |  |  |
Disclosure of subsidiaries [Line Items] |  |  |  |  |  |
Percentage of Ownership | 0.00% |  |  |  | 60.00% | 60.00%
Chunghwa Investment Co., Ltd. (CHI) [Member] | Chunghwa Precision Test Tech. Co., Ltd. (CHPT) [Member] |  |  |  |  |  |
Disclosure of subsidiaries [Line Items] |  |  |  |  |  |
Percentage of Ownership | 34.25% |  |  |  | 34.25% |
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 | 100.00% |  | 100.00% |  | 0.00% |

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