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Subsidiaries - Additional Information (Detail) | Dec. 31, 2019 | Dec. 31, 2018
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Chunghwa Investment Co., Ltd. (CHI) [Member] | Chunghwa Precision Test Tech. Co., Ltd. (CHPT) [Member] |  |
Disclosure of subsidiaries [Line Items] |  |
Equity ownership percentage | 34.25% | 34.25%
Chunghwa Telecom Co., Ltd. and Chunghwa Investment Co., Ltd. (CHI) [Member] | CHIEF Telecom Inc. (CHIEF) [Member] |  |
Disclosure of subsidiaries [Line Items] |  |
Equity ownership percentage | 59.75% | 60.23%
Chunghwa Telecom Co., Ltd. and Chunghwa Investment Co., Ltd. (CHI) [Member] | Senao International Co., Ltd. (SENAO) [Member] |  |
Disclosure of subsidiaries [Line Items] |  |
Equity ownership percentage | 28.18% | 28.18%
Senao International Co., Ltd. (SENAO) [Member] | Youth Co., Ltd. (Youth) [Member] |  |
Disclosure of subsidiaries [Line Items] |  |
Equity ownership percentage | 93.00% | 93.00%

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