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Supplemental Financial Statement Information - Schedule of Other Income, Net (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020
Other Income and Expenses [Abstract] |  |  |  |
Rent and royalty income | $ 0.2 | $ 0.2 | $ 0.5 | $ 0.5
Gains from disposal of property, plant and equipment, net | 1.2 | 0.0 | 2.4 | 2.5
Net equity (loss) gain on joint ventures | 0.0 | (1.9) | 0.0 | (5.6)
Adjustment to indemnification for conditional ARO costs | 0.0 | 4.3 | 0.0 | 4.3
Other Nonoperating Income (Expense), Other | 0.0 | 0.3 | 0.0 | 0.3
Other income (expense), net | 1.4 | 0.5 | 2.9 | (0.4)
Gain on the sale of oil and gas rights |  |  |  | 2.5
Allegheny & Tsingshan Stainless | Employee Severance [Member] |  |  |  |
Other Income and Expenses [Abstract] |  |  |  |
Net equity (loss) gain on joint ventures | $ 0.0 | $ (2.4) | $ 0.0 | $ (2.4)

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