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Business Combinations, Goodwill and Intangible Assets - Schedule of Preliminary Purchase Consideration (Details) - USD ($) $ in Millions |  | 3 Months Ended
--- | --- | ---
Mar. 31, 2021 | Mar. 31, 2021
Business Acquisition [Line Items] |  |
Cash paid at acquisition close on March 31, 2021 |  | $ 617.5
Alcoa Warrick LLC [Member] |  |
Business Acquisition [Line Items] |  |
Contract purchase price | $ 670.0 |
Preliminary working capital adjustment | 31.0 |
Initial outstanding indebtedness – Other postretirement benefits liabilities | (83.5) |
Cash paid at acquisition close on March 31, 2021 | 617.5 |
Estimate of post-close adjustments | (12.7) |
Total preliminary purchase consideration to allocate | $ 604.8 |

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