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Investment Properties - Key Assumptions and Fair Values of Investment Properties (Detail) $ in Millions, $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 TWD ($) | Dec. 31, 2016 TWD ($) | Dec. 31, 2017 USD ($)
Disclosure of detailed information about investment property [Line Items] |  |  |
Investment properties | $ 8,048 | $ 8,115 | $ 272
Discount rate | 1.04% | 1.04% |
Bottom of range [Member] |  |  |
Disclosure of detailed information about investment property [Line Items] |  |  |
Overall capital interest rate | 1.46% | 1.46% |
Profit margin ratio | 12.00% | 10.00% |
Capitalization rate | 0.47% | 0.43% |
Top of range [Member] |  |  |
Disclosure of detailed information about investment property [Line Items] |  |  |
Overall capital interest rate | 2.20% | 2.20% |
Profit margin ratio | 20.00% | 20.00% |
Capitalization rate | 1.69% | 1.78% |
At fair value [Member] |  |  |
Disclosure of detailed information about investment property [Line Items] |  |  |
Investment properties | $ 17,728 | $ 17,778 |

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- Definition Expiry date 2019-01-01: The amount of property (land or a building - or part of a building - or both) held (by the owner or by the lessee under a finance lease) to earn rentals or for capital appreciation or both, rather than for: (a) use in the production or supply of goods or services or for administrative purposes; or (b) sale in the ordinary course of business. Effective 2019-01-01: The amount of property (land or a building - or part of a building - or both) held (by the owner or by the lessee as a right-of-use asset) to earn rentals or for capital appreciation or both, rather than for: (a) use in the production or supply of goods or services or for administrative purposes; or (b) sale in the ordinary course of business. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 40 -IssueDate 2016-01-13 -Paragraph 76 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=40&date=2016-03-30&anchor=para_76&doctype=Standard -URIDate 2016-03-31 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 40 -IssueDate 2016-01-13 -Paragraph 79 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=40&date=2016-03-30&anchor=para_79_d&doctype=Standard -URIDate 2016-03-31 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2016-01-13 -Paragraph 54 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_54_b&doctype=Standard -URIDate 2016-03-31 + Details
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