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Acquisitions and Divestitures - 2014 Acquisitions (Details) - Firth Rixson - USD ($) | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2018 | Nov. 30, 2014
Business Acquisition [Line Items] |  |  |  |  |  |
Contingent consideration liability | $ 0 |  | $ 0 |  | $ 0 |
Contingent consideration arrangements, change in amount of contingent consideration, liability | $ 81,000,000 | $ 56,000,000 | $ (81,000,000) | $ (56,000,000) |  |
Maximum |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |
Contingent consideration liability |  |  |  |  |  | $ 150,000,000

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