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Net Income and Other Comprehensive Income (Loss) - Additional Information (Detail) $ in Millions, $ in Millions | 12 Months Ended
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Dec. 31, 2019 TWD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 TWD ($) | Dec. 31, 2017 TWD ($)
Employee benefits expense [Line Items] |  |  |  |
Non-listed available-for-sale financial assets, carrying amount |  |  |  | $ 5
Gain on disposal of financial instruments | $ 4 | $ 0 | $ 6 | $ 3
Employees' compensation payables | 1,126 |  |  |
Remuneration to directors payables | $ 35 |  |  |
Bottom of Range [Member] |  |  |  |
Employee benefits expense [Line Items] |  |  |  |
Employees' compensation distribution rate | 1.70% | 1.70% |  |
Top of Range [Member] |  |  |  |
Employee benefits expense [Line Items] |  |  |  |
Employees' compensation distribution rate | 4.30% | 4.30% |  |
Directors' remuneration distribution rate | 0.17% | 0.17% |  |

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