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Share-based Payments Arrangement - Additional Information (Detail) $ in Millions |  |  |  |  |  | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 19, 2017 TWD ($) shares | Feb. 08, 2017 shares | Dec. 08, 2015 shares | Oct. 22, 2015 TWD ($) shares | May 07, 2013 shares | Dec. 31, 2017 TWD ($) shares | Dec. 31, 2017 USD ($) shares | Dec. 31, 2016 TWD ($) | Dec. 31, 2015 TWD ($) | Jul. 31, 2017 TWD ($) | Jun. 30, 2017 TWD ($) | Jul. 31, 2016 TWD ($) | Jun. 30, 2016 TWD ($) | Jul. 31, 2015 TWD ($)
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Compensation costs |  |  |  |  |  | $ 22,000,000 | $ 1 | $ 17,000,000 | $ 36,000,000 |  |  |  |  |
Senao International Co., Ltd. (SENAO) [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of common share each option is eligible | shares |  |  |  |  | 1 |  |  |  |  |  |  |  |  |
Option expire period |  |  |  |  | six years |  |  |  |  |  |  |  |  |
Compensation costs |  |  |  |  |  | 4,000,000 |  | 13,000,000 | 35,000,000 |  |  |  |  |
Exercise Price |  |  |  |  |  | 70.70 |  | 76.10 | 81.40 | $ 70.70 | $ 76.10 | $ 76.10 | $ 81.40 | $ 84.30
Senao International Co., Ltd. (SENAO) [Member] | Stock Option Granted in May and November 2017 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Compensation costs |  |  |  |  |  | $ 9,000,000 |  |  |  |  |  |  |  |
Number of treasury stock transfer to its specific employees | shares |  |  |  |  |  | 3,342,000 | 3,342,000 |  |  |  |  |  |  |
Senao International Co., Ltd. (SENAO) [Member] | 2 years after grant date [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Vesting period |  |  |  |  | two years |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  |  | 50.00% |  |  |  |  |  |  |  |  |
Senao International Co., Ltd. (SENAO) [Member] | 3 years after grant date [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Vesting period |  |  |  |  | three years |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  |  | 25.00% |  |  |  |  |  |  |  |  |
Senao International Co., Ltd. (SENAO) [Member] | 4 years after grant date [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Vesting period |  |  |  |  | four years |  |  |  |  |  |  |  |  |
Vesting percentage |  |  |  |  | 25.00% |  |  |  |  |  |  |  |  |
CHIEF Telecom Inc. (CHIEF) [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of common share each option is eligible | shares | 1,000 |  |  | 1,000 |  |  |  |  |  |  |  |  |  |
Exercise Price | $ 147.00 |  |  | $ 43.00 |  |  |  |  |  |  |  | $ 34.40 | $ 43.00 |
CHIEF Telecom Inc. (CHIEF) [Member] | Granted on October 22, 2015 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Option expire period |  |  |  |  |  | five years | five years |  |  |  |  |  |  |
Vesting period |  |  |  |  |  | two years | two years |  |  |  |  |  |  |
Compensation costs |  |  |  |  |  | $ 3,000,000 |  | 4,000,000 | $ 1,000,000 |  |  |  |  |
Exercise Price |  |  |  |  |  | $ 34.40 |  | 34.40 |  |  |  |  |  |
CHIEF Telecom Inc. (CHIEF) [Member] | Granted on December 19, 2017 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Option expire period |  |  |  |  |  | five years | five years |  |  |  |  |  |  |
Vesting period |  |  |  |  |  | two years | two years |  |  |  |  |  |  |
Compensation costs |  |  |  |  |  | $ 100,000 |  |  |  |  |  |  |  |
Exercise Price |  |  |  |  |  | 147.00 |  |  |  |  |  |  |  |
Chunghwa Precision Test Tech. Co., Ltd. (CHPT) [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Compensation costs |  |  |  |  |  | $ 6,000,000 |  | $ 16,000 |  |  |  |  |  |
Shares issued | shares |  | 2,000,000 | 2,787,000 |  |  |  |  |  |  |  |  |  |  |
Reserve for employee subscription | shares |  | 300,000 | 418,000 |  |  |  |  |  |  |  |  |  |  |

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- Definition The description of the maximum term of options granted for a type of share-based payment arrangement that existed at any time during the period. An entity with substantially similar types of share-based payment arrangements may aggregate this information. [Refer: Share-based payment arrangements [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2016-01-13 -Paragraph 45 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2016-03-30&anchor=para_45_a&doctype=Standard -URIDate 2016-03-31 + Details
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- Definition The description of the vesting requirements for a type of share-based payment arrangement that existed at any time during the period. An entity with substantially similar types of share-based payment arrangements may aggregate this information. [Refer: Share-based payment arrangements [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2016-01-13 -Paragraph 45 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2016-03-30&anchor=para_45_a&doctype=Standard -URIDate 2016-03-31 + Details
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