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v3.21.1

Significant Contingent Liabilities and Unrecognized Commitments - Additional Information (Detail) - TWD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 | Aug. 15, 1996
Commitments And Contingencies [Line Items] |  |
Unused letters of credit | $ 10 |
Top of Range [Member] | Next Commercial Bank Co Ltd [Member] |  |
Commitments And Contingencies [Line Items] |  |
Ownership interest in associates | 25.00% |
Piping Fund [Member] |  |
Commitments And Contingencies [Line Items] |  |
Commitment amount |  | $ 2,000
Commitment to contribute to a Piping Fund, amount contributed |  | $ 1,000
Commitment to contribute to a Piping Fund, remaining amount | $ 1,000 |
Land and buildings [Member] |  |
Commitments And Contingencies [Line Items] |  |
Commitments for acquisitions of property, plant and equipment | 119 |
Telecommunications equipment [Member] |  |
Commitments And Contingencies [Line Items] |  |
Commitments for acquisitions of property, plant and equipment | $ 26,815 |

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- Definition The amount of contractual commitments for the acquisition of property, plant and equipment. [Refer: Property, plant and equipment] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 16 -IssueDate 2020-01-01 -Paragraph 74 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=16&code=ifrs-tx-2020-en-r&anchor=para_74_c&doctype=Standard -URIDate 2020-01-01 + Details
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- Definition The proportion of ownership interest in an associate attributable to the entity. [Refer: Associates [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2020-01-01 -Paragraph 17 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=27&code=ifrs-tx-2020-en-r&anchor=para_17_b_iii&doctype=Standard -URIDate 2020-01-01 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2020-01-01 -Paragraph 16 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=27&code=ifrs-tx-2020-en-r&anchor=para_16_b_iii&doctype=Standard -URIDate 2020-01-01 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 12 -IssueDate 2020-01-01 -Paragraph 21 -Subparagraph a -Clause iv -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=12&code=ifrs-tx-2020-en-r&anchor=para_21_a_iv&doctype=Standard -URIDate 2020-01-01 + Details
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