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v3.23.3

Debt Schedule of Debt (Details) - USD ($) | 9 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Sep. 30, 2023 | Dec. 31, 2022 | Aug. 11, 2023
Debt Instrument [Line Items] |  |  |
Debt Issuance Costs, Net | $ (20,700,000) | $ (17,200,000) |
Debt | 2,185,200,000 | 1,748,000,000 |
Short-term debt and current portion of long-term debt | 37,500,000 | 41,700,000 |
Long-term debt | 2,147,700,000 | 1,706,300,000 |
ATI Inc. 5.875% Notes due 2027 |  |  |
Debt Instrument [Line Items] |  |  |
Debt, Gross | $ 350,000,000.0 | $ 350,000,000.0 |
Debt Instrument, Issuer | ATI Inc. | ATI Inc. |
Interest rate | 5.875% | 5.875% |
Debt Instrument, Maturity Date | Dec. 01, 2027 | Dec. 01, 2027 |
ATI Inc. 3.5% Convertible Senior Notes due 2025 | Convertible Debt |  |  |
Debt Instrument [Line Items] |  |  |
Debt, Gross | $ 291,400,000 | $ 291,400,000 |
Debt Issuance Costs, Net | $ (3,400,000) | $ (4,800,000) |
Debt Instrument, Issuer | ATI Inc. | ATI Inc. |
Interest rate | 3.50% | 3.50% |
Debt Instrument, Maturity Date | Jun. 15, 2025 | Jun. 15, 2025 |
Allegheny Ludlum 6.95% Debentures due 2025 (a) |  |  |
Debt Instrument [Line Items] |  |  |
Debt, Gross | $ 150,000,000.0 | $ 150,000,000.0 |
Debt Instrument, Issuer | Allegheny Ludlum | Allegheny Ludlum |
Interest rate | 6.95% | 6.95% |
Debt Instrument, Maturity Date | Dec. 15, 2025 | Dec. 15, 2025 |
Foreign credit facilities |  |  |
Debt Instrument [Line Items] |  |  |
Short-term Debt | $ 11,200,000 | $ 19,400,000 |
Finance leases and other |  |  |
Debt Instrument [Line Items] |  |  |
Debt, Gross | 103,300,000 | 79,400,000 |
ATI 2031 Notes |  |  |
Debt Instrument [Line Items] |  |  |
Debt, Gross | $ 350,000,000.0 | $ 350,000,000.0 |
Debt Instrument, Issuer | ATI Inc. | ATI Inc. |
Interest rate | 5.125% | 5.125% |
Debt Instrument, Maturity Date | Oct. 01, 2031 | Oct. 01, 2031 |
ATI 2029 Notes |  |  |
Debt Instrument [Line Items] |  |  |
Debt, Gross | $ 325,000,000.0 | $ 325,000,000.0 |
Debt Instrument, Issuer | ATI Inc. | ATI Inc. |
Interest rate | 4.875% | 4.875% |
Debt Instrument, Maturity Date | Oct. 01, 2029 | Oct. 01, 2029 |
Domestic Bank Group $600 million asset-based credit facility |  |  |
Debt Instrument [Line Items] |  |  |
Short-term Debt | $ 0 | $ 0 |
2027 Term Loan |  |  |
Debt Instrument [Line Items] |  |  |
Debt, Gross | $ 200,000,000.0 | $ 200,000,000.0 |
Debt Instrument, Issuer | ATI Inc. | ATI Inc. |
Interest rate | 4.21% |  |
Debt Instrument, Maturity Date | Sep. 09, 2027 | Sep. 09, 2027 |
ATI 2030 Notes |  |  |
Debt Instrument [Line Items] |  |  |
Debt, Gross | $ 425,000,000.0 | $ 0 |
Debt Issuance Costs, Net |  |  | $ (6,200,000)
Debt Instrument, Issuer | ATI Inc. |  |
Interest rate | 7.25% |  |
Debt Instrument, Maturity Date | Aug. 15, 2030 |  |

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