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Subsidiaries - Less Than Wholly Owned Subsidiaries of the Company That Have Material Noncontrolling Interests (Detail) $ in Millions, $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2017 TWD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 TWD ($) | Dec. 31, 2015 TWD ($) | Jan. 01, 2018 TWD ($) | Dec. 31, 2017 USD ($)
Disclosure of subsidiaries [Line Items] |  |  |  |  |  |
Profit Allocated to Noncontrolling Interests | $ 1,172 | $ 40 | $ 1,141 | $ 813 |  |
Accumulated Noncontrolling Interests | $ 8,474 |  | $ 6,272 |  | $ 8,470 | $ 286
Senao International Co., Ltd. (SENAO) [Member] |  |  |  |  |  |
Disclosure of subsidiaries [Line Items] |  |  |  |  |  |
Place of Incorporation | Taiwan | Taiwan |  |  |  |
Principal Place of Business | Taiwan | Taiwan |  |  |  |
Proportion of Ownership Interests Held by Noncontrolling Interests | 71.00% | 71.00% | 71.00% |  |  |
Proportion of Voting Rights Held by Noncontrolling Interests | 71.00% | 71.00% | 71.00% |  |  |
Profit Allocated to Noncontrolling Interests | $ 592 |  | $ 690 | 551 |  |
Accumulated Noncontrolling Interests | $ 4,092 |  | $ 4,069 |  |  |
Chunghwa Precision Test Tech. Co., Ltd. (CHPT) [Member] |  |  |  |  |  |
Disclosure of subsidiaries [Line Items] |  |  |  |  |  |
Place of Incorporation | Taiwan | Taiwan |  |  |  |
Principal Place of Business | Taiwan | Taiwan |  |  |  |
Proportion of Ownership Interests Held by Noncontrolling Interests | 62.00% | 62.00% | 59.00% |  |  |
Proportion of Voting Rights Held by Noncontrolling Interests | 62.00% | 62.00% | 59.00% |  |  |
Profit Allocated to Noncontrolling Interests | $ 431 |  | $ 341 | $ 212 |  |
Accumulated Noncontrolling Interests | 3,513 |  | 1,575 |  |  |
Individually immaterial subsidiaries with noncontrolling interests [Member] |  |  |  |  |  |
Disclosure of subsidiaries [Line Items] |  |  |  |  |  |
Accumulated Noncontrolling Interests | $ 869 |  | $ 628 |  |  |

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- Definition The amount of equity in a subsidiary not attributable, directly or indirectly, to a parent. [Refer: Subsidiaries [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 12 -IssueDate 2016-01-13 -Paragraph 12 -Subparagraph f -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=12&date=2016-03-30&anchor=para_12_f&doctype=Standard -URIDate 2016-03-31 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2016-01-13 -Paragraph 54 -Subparagraph q -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_54_q&doctype=Standard -URIDate 2016-03-31 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 10 -IssueDate 2016-01-13 -Paragraph 22 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=10&date=2016-03-30&anchor=para_22&doctype=Standard -URIDate 2016-03-31 + Details
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