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Revenue - 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 ($) | Dec. 31, 2017 TWD ($)
Revenue From Contract With Customer Line Item |  |  |  |
Amortization of incremental costs of obtaining contracts | $ 1,173 | $ 39 | $ 1,941 | $ 0
Telecommunications Business [Member] |  |  |  |
Revenue From Contract With Customer Line Item |  |  |  |
Transaction price allocated to performance obligations | $ 35,634 |  |  |
Remaining performance obligations, timing of satisfaction | The Company expects to recognize such revenue of $20,336 million, $11,971 million and $3,327 million in 2020, 2021 and 2022, respectively. | The Company expects to recognize such revenue of $20,336 million, $11,971 million and $3,327 million in 2020, 2021 and 2022, respectively. |  |
Telecommunications Business [Member] | Year 1 [Member] |  |  |  |
Revenue From Contract With Customer Line Item |  |  |  |
Transaction price allocated to performance obligations | $ 20,336 |  |  |
Telecommunications Business [Member] | Later than one year and not later than two years [member] |  |  |  |
Revenue From Contract With Customer Line Item |  |  |  |
Transaction price allocated to performance obligations | 11,971 |  |  |
Telecommunications Business [Member] | Later than two years and not later than three years [member] |  |  |  |
Revenue From Contract With Customer Line Item |  |  |  |
Transaction price allocated to performance obligations | 3,327 |  |  |
Project Business [Member] |  |  |  |
Revenue From Contract With Customer Line Item |  |  |  |
Transaction price allocated to performance obligations | $ 23,159 |  |  |
Remaining performance obligations, timing of satisfaction | The Company recognizes revenues when the project business contract is completed and accepted by customers. The Company expects to recognize such revenue of $14,183 million, $5,373 million and $3,603 million in 2020, 2021 and 2022, respectively | The Company recognizes revenues when the project business contract is completed and accepted by customers. The Company expects to recognize such revenue of $14,183 million, $5,373 million and $3,603 million in 2020, 2021 and 2022, respectively |  |
Project Business [Member] | Year 1 [Member] |  |  |  |
Revenue From Contract With Customer Line Item |  |  |  |
Transaction price allocated to performance obligations | $ 14,183 |  |  |
Project Business [Member] | Later than one year and not later than two years [member] |  |  |  |
Revenue From Contract With Customer Line Item |  |  |  |
Transaction price allocated to performance obligations | 5,373 |  |  |
Project Business [Member] | Later than two years and not later than three years [member] |  |  |  |
Revenue From Contract With Customer Line Item |  |  |  |
Transaction price allocated to performance obligations | $ 3,603 |  |  |

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- Definition The amount of amortisation for assets recognised from the costs incurred to obtain or fulfil contracts with customers. [Refer: Assets recognised from costs to obtain or fulfil contracts with customers; Amortisation expense] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 15 -IssueDate 2019-01-01 -Paragraph 128 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=15&code=ifrs-tx-2019-en-r&anchor=para_128_b&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The amount of the transaction price allocated to the performance obligations that are unsatisfied (or partially unsatisfied) as of the end of the reporting period. The transaction price is the amount of consideration to which an entity expects to be entitled in exchange for transferring promised goods or services to a customer, excluding amounts collected on behalf of third parties (for example, some sales taxes). [Refer: Performance obligations [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 15 -IssueDate 2019-01-01 -Paragraph 120 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=15&code=ifrs-tx-2019-en-r&anchor=para_120_a&doctype=Standard -URIDate 2019-03-27 + Details
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