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Net Income and Other Comprehensive Income (Loss) - Other Income (Detail) $ in Millions, $ in Millions | 12 Months Ended
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Dec. 31, 2017 TWD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 TWD ($) | Dec. 31, 2015 TWD ($)
Analysis Of Income And Expense [Abstract] |  |  |  |
Dividend income | $ 328 | $ 11 | $ 391 | $ 218
Rental income | 61 |  | 41 | 38
Income from Piping Fund | 0 |  | 202 | 202
Others | 447 |  | 438 | 192
Other income | $ 836 | $ 28 | $ 1,072 | $ 650

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- Definition The amount of dividends recognised as income. Dividends are distributions of profits to holders of equity investments in proportion to their holdings of a particular class of capital. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2018-01-01 -Name IAS -Number 18 -IssueDate 2016-01-13 -Paragraph 35 -Subparagraph b -Clause v -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=18&date=2016-03-30&anchor=para_35_b_v&doctype=Standard -URIDate 2016-03-31 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2016-01-13 -Paragraph 112 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_112_c&doctype=Standard -URIDate 2016-03-31 + Details
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