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Income Taxes - Reconciliation of U.S. Federal Statutory Rate to Arconic's Effective Tax Rate (Details) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Income Tax Disclosure [Abstract] |  |  |  |  |
U.S. federal statutory rate |  |  | 21.00% | 35.00% | 35.00%
Taxes on foreign operations |  |  | 4.00% | (8.80%) | (11.50%)
U.S. State and local taxes |  |  | 1.50% | 0.70% | (0.40%)
Federal benefit of state tax |  |  | (0.003) | 0.037 | 0.004
Permanent differences on restructuring and other charges and asset disposals |  |  | (16.90%) | (167.40%) | (107.80%)
Non-deductible acquisition costs |  |  | 0.00% | 0.30% | 8.40%
Statutory tax rate and law changes |  |  | 6.50% | 52.50% | (15.70%)
Tax holidays |  |  | (1.60%) | (3.00%) | (0.80%)
Changes in valuation allowances |  |  | 0.90% | 137.90% | 426.80%
Impairment of goodwill |  |  | 0.00% | 53.50% | 0.00%
Company-owned life insurance/split-dollar net premiums |  |  | (0.00%) | (0.00%) | 23.00%
Changes in uncertain tax positions |  |  | 12.80% | 10.10% | 2.10%
Prior year tax adjustments |  |  | (2.60%) | (0.90%) | (1.70%)
Other |  |  | 0.70% | 2.10% | (1.30%)
Effective tax rate |  |  | 26.00% | 115.70% | 356.50%
Tax cuts and jobs act of 2017, incomplete accounting, provisional income tax expense (benefit) | $ 272 | $ 272 | $ 59 |  |

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