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Other Expense (Income), Net - Summary of Other Non-Operating Income and Expense (Details) - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2018 | Mar. 31, 2017
Other Income and Expenses [Abstract] |  |
Non-service related net periodic benefit cost | $ 28 | $ 38
Interest income | (6) | (4)
Foreign currency gains, net | (3) | (5)
Other, net | (2) | 4
Total | (20) | 316
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |
Gain on disposition of assets | $ (3) | 349
Alcoa Corporation |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |
Gain on disposition of assets |  | 351
Cash received on sale of operations |  | $ 888

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