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v3.22.4

Per Share Information (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | Feb. 02, 2022
Earnings Per Share Reconciliation [Abstract] |  |  |  |
Net income (loss) | $ 130.9 | $ (38.2) | $ (1,572.6) |
Numerator for diluted net income (loss) per common share - Income (loss) attributable to ATI after assumed conversions | $ 144.4 | $ (38.2) | $ (1,572.6) |
Denominator for basic net income (loss) per common share - weighted average shares (shares) | 127.5 | 127.1 | 126.5 |
Effect of dilutive securities: Share-based compensation | 2.1 | 0.0 | 0.0 |
Denominator for diluted net income (loss) per common share—adjusted weighted average shares and assumed conversions | 151.2 | 127.1 | 126.5 |
Basic income (loss) attributable to ATI per common share (in dollars per share) | $ 1.03 | $ (0.30) | $ (12.43) |
Diluted income (loss) attributable to ATI per common share (in dollars per share) | $ 0.96 | $ (0.30) | $ (12.43) |
Anti-dilutive securities excluded from computation of earnings per share amount | 0.0 | 25.6 | 22.8 |
Authorized amount |  |  |  | $ 150.0
Purchase of treasury stock | $ (139.9) | $ 0.0 | $ 0.0 |
Treasury stock, shares, acquired | 5.2 |  |  |
ATI Convertible Senior Notes, 4.75%, Due 2022 [Member] |  |  |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  | 4.75% |  |
Earnings Per Share Reconciliation [Abstract] |  |  |  |
Effect of dilutive securities: Convertible Senior Notes | $ 2.2 | $ 0.0 | $ 0.0 |
Effect of dilutive securities: Convertible Senior Notes | 2.8 | 0.0 | 0.0 |
Debt instrument interest rate stated percentage |  | 4.75% |  |
ATI Convertible Senior Notes, 3.5%, Due 2025 [Member] |  |  |  |
Earnings Per Share Reconciliation [Abstract] |  |  |  |
Effect of dilutive securities: Convertible Senior Notes | $ 11.3 | $ 0.0 | $ 0.0 |
Effect of dilutive securities: Convertible Senior Notes | 18.8 | 0.0 | 0.0 |
Convertible Debt [Member] | ATI Convertible Senior Notes, 4.75%, Due 2022 [Member] |  |  |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  | 4.75% |  |
Earnings Per Share Reconciliation [Abstract] |  |  |  |
Debt instrument interest rate stated percentage |  | 4.75% |  |
Convertible Debt [Member] | ATI Convertible Senior Notes, 3.5%, Due 2025 [Member] |  |  |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 3.50% | 3.50% |  |
Earnings Per Share Reconciliation [Abstract] |  |  |  |
Debt instrument interest rate stated percentage | 3.50% | 3.50% |  |

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