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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, 2018 TWD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 TWD ($) | Dec. 31, 2016 TWD ($)
Analysis Of Income And Expense [Abstract] |  |  |  |
Dividend income | $ 396 | $ 13 | $ 328 | $ 391
Rental income | 70 |  | 61 | 41
Income from Piping Fund | 2 |  | 0 | 202
Others | 232 |  | 447 | 438
Other income | $ 700 | $ 23 | $ 836 | $ 1,072

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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/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 112 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_112_c&doctype=Standard -URIDate 2018-03-16 + Details
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