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Income Tax - Reconciliation of Accounting Profit and Income Tax Expense (Detail) $ in Millions, $ in Millions | 12 Months Ended
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Dec. 31, 2020 TWD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 TWD ($) | Dec. 31, 2018 TWD ($)
Reconciliation Of Accounting Profit Multiplied By Applicable Tax Rates [Abstract] |  |  |  |
Income before income tax | $ 42,826 | $ 1,525 | $ 41,867 | $ 44,986
Income tax expense calculated at the statutory rate | 8,565 |  | 8,373 | 8,997
Nondeductible income and expenses in determining taxable income | 15 |  | 18 | 227
Unrecognized deductible temporary differences | (5) |  | 3 | 1
Unrecognized loss carryforwards | 4 |  | 7 | 21
Tax-exempt income | (367) |  | (148) | (580)
Additional income tax under Alternative Minimum Tax Act | 0 |  | 0 | 46
Income tax on unappropriated earnings | 8 |  | (20) | (2,070)
Investment credits | (131) |  | (203) | (204)
Change in tax rate | 0 |  | 0 | (38)
Effect of different tax rates of group entities operating in other jurisdictions | 10 |  | (9) | (15)
Income tax adjustments on prior years | 4 |  | (92) | 26
Others | 19 |  | 17 | (6)
Income tax expense recognized in profit or loss | $ 8,122 | $ 289 | $ 7,946 | $ 6,405

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- Definition The amount that represents the difference between the tax expense (income) and the product of the accounting profit multiplied by the applicable tax rate(s) that relates to changes in the tax rate. [Refer: Accounting profit] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2020-01-01 -Paragraph 81 -Subparagraph c -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2020-en-r&anchor=para_81_c_i&doctype=Standard -URIDate 2020-01-01 + Details
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