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Income Tax - Major Components of Income Tax Expense (Detail) $ in Millions, $ in Millions | 12 Months Ended
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Dec. 31, 2018 TWD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 TWD ($) | Dec. 31, 2016 TWD ($)
Current tax |  |  |  |
Current tax expenses recognized for the year | $ 8,271 |  | $ 7,996 | $ 6,736
Income tax on unappropriated earnings | (2,070) |  | (60) | (346)
Income tax adjustments on prior years | 7 |  | (2) | (22)
Others | 8 |  | 10 | 15
Current tax | 6,216 |  | 7,944 | 6,383
Deferred tax |  |  |  |
Deferred tax expense recognized for the year | 208 |  | (101) | 1,404
Income tax adjustments on prior years | 19 |  | 6 | 0
Change in tax rate | (38) |  | 0 | 0
Deferred tax | 189 |  | (95) | 1,404
Income tax expense recognized in profit or loss | $ 6,405 | $ 210 | $ 7,849 | $ 7,787

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