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Application of New and Amended International Financial Reporting Standards - Additional Information (Detail) $ in Millions, $ in Millions |  | 12 Months Ended |
--- | --- | --- | ---
Jan. 01, 2018 TWD ($) | Dec. 31, 2018 TWD ($) | Dec. 31, 2017 TWD ($) | Dec. 31, 2016 TWD ($) | Dec. 31, 2018 USD ($)
Disclosure Of Initial Application Of Standards Or Interpretations [Line Items] |  |  |  |  |
NONCONTROLLING INTERESTS |  | $ 9,857 | $ 8,474 |  | $ 322
Unappropriated earnings |  | 66,626 | 54,633 |  | 2,177
Tax obligation |  | 8,271 | 7,996 | $ 6,736 |
Deferred income tax liabilities |  | $ 1,992 | $ 1,430 |  | $ 65
Remeasured FVOCI [Member] |  |  |  |  |
Disclosure Of Initial Application Of Standards Or Interpretations [Line Items] |  |  |  |  |
Total effect on assets | $ 1,842 |  |  |  |
Total effect on equity | 1,843 |  |  |  |
NONCONTROLLING INTERESTS | (1) |  |  |  |
Reclassification of Impairment [Member] |  |  |  |  |
Disclosure Of Initial Application Of Standards Or Interpretations [Line Items] |  |  |  |  |
Total effect on assets | 1,516 |  |  |  |
Unappropriated earnings | 1,516 |  |  |  |
Increase (Decrease) Due to Application of IFRS 9 [Member] |  |  |  |  |
Disclosure Of Initial Application Of Standards Or Interpretations [Line Items] |  |  |  |  |
Unrealized gain or loss on available-for-sale financial assets | 4 |  |  |  |
NONCONTROLLING INTERESTS | (3) |  |  |  |
Deferred income tax liabilities | (1) |  |  |  |
Increase (Decrease) Due to Application of IFRS 9 [Member] | Classification of assets as held for sale [member] |  |  |  |  |
Disclosure Of Initial Application Of Standards Or Interpretations [Line Items] |  |  |  |  |
Tax obligation | 0 |  |  |  |
Total retained earnings [Member] |  |  |  |  |
Disclosure Of Initial Application Of Standards Or Interpretations [Line Items] |  |  |  |  |
Unrealized gain or loss on available-for-sale financial assets | 6 |  |  |  |
Other Equity [Member] |  |  |  |  |
Disclosure Of Initial Application Of Standards Or Interpretations [Line Items] |  |  |  |  |
Unrealized gain or loss on available-for-sale financial assets | $ 556 |  |  |  |

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