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Net Income - Other Income and Expenses (Detail) $ in Millions, $ in Millions | 12 Months Ended
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Dec. 31, 2020 TWD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 TWD ($) | Dec. 31, 2018 TWD ($)
Analysis Of Income And Expense [Abstract] |  |  |  |
Gain (loss) on disposal of property, plant and equipment | $ 1,428 | $ 51 | $ (38) | $ 142
Impairment loss on property, plant and equipment | 0 | 0 | (93) | 0
Gain on disposal of investment properties | 151 | 5 | 0 | 0
Reversal of impairment loss on investment properties | 27 | 1 | 57 | 19
Loss on disposal of intangible assets | (2) | 0 | 0 | 0
Impairment loss on intangible assets | (9) | 0 | (9) | (51)
Impairment loss on other assets | 0 | 0 | (44) | 0
Other income and expenses | $ 1,595 | $ 57 | $ (127) | $ 110

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- Definition The gains (losses) on disposals of property, plant and equipment. [Refer: Property, plant and equipment] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 98 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_98_c&doctype=Standard -URIDate 2020-01-01 + Details
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