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Inventories - Additional Information (Detail) $ in Millions, $ in Millions | 12 Months Ended
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Dec. 31, 2020 TWD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 TWD ($) | Dec. 31, 2018 TWD ($)
Classes Of Inventories [Abstract] |  |  |  |
Operating costs related to inventories | $ 53,847 |  | $ 49,258 | $ 48,649
Valuation loss on inventories recognized as operating costs | 1,161 | $ 41 | 475 | $ 365
Inventory to be recovered longer than twelve months | $ 2,076 |  | $ 2,076 |

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- Definition The amount of expense recognised related to the write-down of inventories to net realisable value. [Refer: Inventories] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 2 -IssueDate 2020-01-01 -Paragraph 36 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=2&code=ifrs-tx-2020-en-r&anchor=para_36_e&doctype=Standard -URIDate 2020-01-01 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 98 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_98_a&doctype=Standard -URIDate 2020-01-01 + Details
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