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Application of New and Amended International Financial Reporting Standards - Schedule of Anticipated Significant Impact on Assets, Liabilities and Equity of Retrospective Application of IFRS 9 (Detail) $ in Millions, $ in Millions | Jan. 01, 2018 TWD ($) | Dec. 31, 2017 TWD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 TWD ($)
--- | --- | --- | --- | ---
Impact on assets, liabilities and equity |  |  |  |
Financial assets at fair value through profit or loss - noncurrent | $ 54 | $ 0 |  |
Financial assets at fair value through other comprehensive income - noncurrent | 7,539 | 0 |  |
Available-for-sale financial assets - noncurrent | 0 | 5,751 | $ 194 | $ 4,764
Total effect on liabilities (deferred income tax liabilities) | 1,429 | 1,430 |  |
Unrealized gain or loss on available-for-sale financial assets | 0 | 558 |  |
Unrealized gain or loss on financial assets at fair value through other comprehensive income | 883 | 0 |  |
Unappropriated earnings | 56,155 | 54,633 | 1,843 | 55,657
Noncontrolling interests | 8,470 | $ 8,474 | $ 286 | $ 6,272
Increase decrease due to application of IFRS 9 [Member] |  |  |  |
Impact on assets, liabilities and equity |  |  |  |
Financial assets at fair value through profit or loss - noncurrent | 54 |  |  |
Financial assets at fair value through other comprehensive income - noncurrent | 7,539 |  |  |
Available-for-sale financial assets - noncurrent | (5,751) |  |  |
Total effect on assets | 1,842 |  |  |
Total effect on liabilities (deferred income tax liabilities) | (1) |  |  |
Unrealized gain or loss on available-for-sale financial assets | (558) |  |  |
Unrealized gain or loss on financial assets at fair value through other comprehensive income | 883 |  |  |
Unappropriated earnings | 1,522 |  |  |
Noncontrolling interests | (4) |  |  |
Total effect on equity | $ 1,843 |  |  |

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