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Revenue - Additional Information (Detail) $ in Millions, $ in Millions | 12 Months Ended
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Dec. 31, 2018 TWD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 TWD ($) | Dec. 31, 2016 TWD ($)
Revenue From Contract With Customer Line Item |  |  |  |
Amortization of incremental costs of obtaining contracts | $ 1,941 | $ 63 | $ 0 | $ 0
Telecommunications Business [Member] |  |  |  |
Revenue From Contract With Customer Line Item |  |  |  |
Transaction price allocated to performance obligations | $ 38,909 |  |  |
Remaining performance obligations, timing of satisfaction | The Company expects to recognize revenue when service is provided over contract terms in the next 36 months, $24,388 million, $11,581 million and $2,940 million for 2019, 2020 and 2021, respectively. | The Company expects to recognize revenue when service is provided over contract terms in the next 36 months, $24,388 million, $11,581 million and $2,940 million for 2019, 2020 and 2021, respectively. |  |
Telecommunications Business [Member] | Not later than one year [member] |  |  |  |
Revenue From Contract With Customer Line Item |  |  |  |
Transaction price allocated to performance obligations | $ 24,388 |  |  |
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 | 11,581 |  |  |
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 | 2,940 |  |  |
Project Business [Member] |  |  |  |
Revenue From Contract With Customer Line Item |  |  |  |
Transaction price allocated to performance obligations | $ 20,990 |  |  |
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 $3,656 million, $12,893 million and $4,441 million in 2019, 2020 and 2021, respectively | The Company recognizes revenues when the project business contract is completed and accepted by customers. The Company expects to recognize such revenue of $3,656 million, $12,893 million and $4,441 million in 2019, 2020 and 2021, respectively |  |
Project Business [Member] | Not later than one year [member] |  |  |  |
Revenue From Contract With Customer Line Item |  |  |  |
Transaction price allocated to performance obligations | $ 3,656 |  |  |
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 | 12,893 |  |  |
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 | $ 4,441 |  |  |

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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 2018-01-01 -Paragraph 128 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=15&date=2018-03-01&anchor=para_128_b&doctype=Standard -URIDate 2018-03-16 + Details
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- Definition The explanation of when the entity expects to recognise the transaction price allocated to the remaining performance obligations as revenue. [Refer: Revenue; Transaction price allocated to remaining performance obligations] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 15 -IssueDate 2018-01-01 -Paragraph 120 -Subparagraph b -Clause ii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=15&date=2018-03-01&anchor=para_120_b_ii&doctype=Standard -URIDate 2018-03-16 + 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 2018-01-01 -Paragraph 120 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=15&date=2018-03-01&anchor=para_120_a&doctype=Standard -URIDate 2018-03-16 + Details
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