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Investments Accounted For Using Equity Method - Additional Information (Detail) |  | 1 Months Ended | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Jul. 01, 2020 TWD ($) | Sep. 30, 2020 | Apr. 30, 2019 TWD ($) | Jun. 30, 2018 TWD ($) | Jan. 31, 2018 TWD ($) | Dec. 31, 2020 TWD ($) NumberofSeat | Dec. 31, 2019 TWD ($) | Jun. 30, 2020 | Jan. 31, 2020 | Nov. 30, 2019 TWD ($) | Feb. 28, 2019 | Oct. 31, 2018
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Investments in associates |  |  |  |  |  | $ 6,685,000,000 | $ 7,139,000,000 |  |  |  |  |
Investment in joint venture |  |  |  |  |  | $ 10,000,000 | $ 0 |  |  |  |  |
KingwayTek Technology Co., Ltd. ("KWT") [Member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership in associates |  |  |  |  |  | 22.72% | 22.52% |  |  |  |  |
Gain on disposal of investment |  |  | $ 151,000,000 |  |  |  |  |  |  |  |  |
Taiwan International Ports Logistics Corporation ("TIPL") [Member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership in associates |  |  |  |  |  | 27.00% | 27.00% |  |  |  |  |
Investments in associates |  |  |  |  |  | $ 56,000,000 | $ 51,000,000 |  |  |  |  |
Click Force Co., Ltd. ("CF") [Member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership in associates |  |  |  |  |  | 49.00% | 49.00% |  |  |  |  |
Investments in associates |  |  |  |  |  | $ 33,000,000 | $ 37,000,000 |  |  |  |  |
Alliance Digital Tech Co., Ltd. ("ADT") [Member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest in associates |  |  |  |  |  | 14.00% |  |  |  |  |  |
Percentage of ownership in associates |  |  |  |  |  | 14.00% | 14.00% |  |  |  |  |
Investments in associates |  |  |  |  |  | $ 3,000,000 | $ 3,000,000 |  |  |  |  |
MeWorks LIMITED (HK) ("MeWorks") [Member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership in associates |  |  |  |  |  | 0.00% | 20.00% |  |  |  |  |
Investments in associates |  |  |  |  |  | $ 0 | $ 0 |  |  |  |  |
Next Commercial Bank Co., Ltd. (“NCB”) [Member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership in associates |  |  |  |  |  | 41.90% | 41.90% |  |  | 41.90% | 41.90% |
Investments in associates |  |  |  |  |  | $ 3,777,000,000 | $ 4,074,000,000 |  |  | $ 4,190,000,000 |  |
International Integrated Systems, Inc. ("IISI") [Member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership in associates |  |  |  |  |  | 0.00% | 31.47% | 31.16% |  |  |  |
Investments in associates |  |  |  |  |  | $ 0 | $ 335,000,000 |  |  |  |  |
International Integrated Systems, Inc. ("IISI") [Member] | Subsequent Events [Member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Investment percentage of ownership interest |  |  |  |  |  |  |  |  | 20.58% |  |  |
Gain on disposal of investment | $ 1,000,000 |  |  |  |  |  |  |  |  |  |  |
UUPON Inc. ("UUPON") [Member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest in associates |  |  |  |  |  | 5.36% |  |  |  |  |  |
Percentage of ownership in associates |  |  |  |  |  | 0.00% | 22.00% |  |  |  |  |
Investments in associates |  |  |  |  |  | $ 0 |  |  |  |  |  |
Gain on disposal of investment |  |  |  |  |  | 15,000,000 |  |  |  |  |  |
Reduction percentage of capital to offset accumulated deficit |  | 95.44% |  |  |  |  |  |  |  |  |  |
Chunghwa SEA Holdings (“CHT SEA”) [Member] | Joint ventures [Member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Investment in joint venture |  |  |  |  |  | $ 10,000,000 | $ 0 |  |  |  |  |
Percentage of ownership in joint venture |  |  |  |  |  | 51.00% | 0.00% |  |  |  |  |
HopeTech Technologies Limited [Member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Proceeds From Capital Reduction |  |  |  |  | $ 19,000,000 |  |  |  |  |  |  |
Proceeds from disposal of shares |  |  |  | $ 3,000,000 |  |  |  |  |  |  |  |
Losses on disposals recognized |  |  |  | $ 100,000 |  |  |  |  |  |  |  |
Chunghwa PChome Fund I Co., Ltd. ("CPFI") [Member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership in associates |  |  |  |  |  |  |  |  |  |  |  | 50.00%
No of seats allotted | NumberofSeat |  |  |  |  |  | 2 |  |  |  |  |  |
Number of seats available for board of directors | NumberofSeat |  |  |  |  |  | 5 |  |  |  |  |  |
Cornerstone Ventures Co., Ltd. ("CVC") [Member] |  |  |  |  |  |  |  |  |  |  |  |
Disclosure Of Significant Investments In Associates And Joint Ventures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership in associates |  |  |  |  |  |  |  |  |  |  |  | 49.00%
No of seats allotted | NumberofSeat |  |  |  |  |  | 2 |  |  |  |  |  |
Number of seats available for board of directors | NumberofSeat |  |  |  |  |  | 5 |  |  |  |  |  |

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