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Investment Properties - Key Assumptions and Fair Values of Investment Properties (Detail) $ in Millions, $ in Millions | Dec. 31, 2020 TWD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 TWD ($)
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Disclosure of detailed information about investment property [Line Items] |  |  |
Investment properties | $ 9,621 | $ 343 | $ 8,169
Bottom of Range [Member] |  |  |
Disclosure of detailed information about investment property [Line Items] |  |  |
Overall capital interest rate | 0.93% | 0.93% | 1.03%
Profit margin ratio | 12.00% | 12.00% | 12.00%
Capitalization rate | 0.73% | 0.73% | 0.79%
Top of Range [Member] |  |  |
Disclosure of detailed information about investment property [Line Items] |  |  |
Overall capital interest rate | 3.03% | 3.03% | 4.04%
Profit margin ratio | 20.00% | 20.00% | 20.00%
Capitalization rate | 2.20% | 2.20% | 1.74%
At fair value [Member] |  |  |
Disclosure of detailed information about investment property [Line Items] |  |  |
Investment properties | $ 22,644 |  | $ 18,701

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- Definition The amount of property (land or a building - or part of a building - or both) held (by the owner or by the lessee as a right-of-use asset) to earn rentals or for capital appreciation or both, rather than for: (a) use in the production or supply of goods or services or for administrative purposes; or (b) sale in the ordinary course of business. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 40 -IssueDate 2020-01-01 -Paragraph 76 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=40&code=ifrs-tx-2020-en-r&anchor=para_76&doctype=Standard -URIDate 2020-01-01 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 40 -IssueDate 2020-01-01 -Paragraph 79 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=40&code=ifrs-tx-2020-en-r&anchor=para_79_d&doctype=Standard -URIDate 2020-01-01 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 54 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_54_b&doctype=Standard -URIDate 2020-01-01 + Details
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