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Fair Value of Financial Instruments (Details) - USD ($) $ in Millions | Mar. 31, 2023 | Dec. 31, 2022
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Carrying Value Reported Amount Fair Value Disclosure |  |
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] |  |
Cash and cash equivalents | $ 196.2 | $ 584.0
Derivative financial instruments, Assets | 3.7 | 18.0
Derivative Financial Instruments, liabilities | 6.5 | 4.6
Debt | 1,743.3 | 1,765.2
Estimate Of Fair Value Fair Value Disclosure |  |
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] |  |
Cash and cash equivalents | 196.2 | 584.0
Derivative financial instruments, Assets | 3.7 | 18.0
Derivative Financial Instruments, liabilities | 6.5 | 4.6
Debt | 2,138.4 | 1,964.5
Estimate Of Fair Value Fair Value Disclosure | Fair Value Inputs Level 1 |  |
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] |  |
Cash and cash equivalents | 196.2 | 584.0
Derivative financial instruments, Assets | 0.0 | 0.0
Derivative Financial Instruments, liabilities | 0.0 | 0.0
Debt | 1,861.5 | 1,665.7
Estimate Of Fair Value Fair Value Disclosure | Fair Value Inputs Level 2 |  |
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] |  |
Cash and cash equivalents | 0.0 | 0.0
Derivative financial instruments, Assets | 3.7 | 18.0
Derivative Financial Instruments, liabilities | 6.5 | 4.6
Debt | 276.9 | 298.8
Convertible Debt | ATI Inc. 3.5% Convertible Senior Notes due 2025 | Estimate Of Fair Value Fair Value Disclosure | Fair Value Inputs Level 1 |  |
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] |  |
Debt | $ 753.0 | $ 590.0

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- Definition Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References No definition available. + Details
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- Definition Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 55 -Paragraph 69C -URI https://asc.fasb.org/extlink&oid=123466577&loc=SL123495737-112612 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 55 -Paragraph 69B -URI https://asc.fasb.org/extlink&oid=123466577&loc=SL123495735-112612 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI https://asc.fasb.org/extlink&oid=123594938&loc=d3e13433-108611 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1D -Subparagraph (c) -URI https://asc.fasb.org/extlink&oid=123466505&loc=SL123495340-112611 + Details
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- Definition Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 10 -URI https://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 22 -URI https://asc.fasb.org/extlink&oid=99393222&loc=SL20226052-175313 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI https://asc.fasb.org/extlink&oid=123594938&loc=d3e13433-108611 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (c) -URI https://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 + Details
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