Entity Number Of Employees Covered By USW Collective Bargaining Agreements That Expired February 28 2021

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Strike Related Costs

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount of gain (loss) on sale or disposal of oil and gas property or timber property.

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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Business Segments - Additional Information (Details)	3 Months Ended		9 Months Ended
Business Segments - Additional Information (Details)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) segment	Sep. 30, 2020 USD ($)	Feb. 28, 2021 employee	Dec. 31, 2020 USD ($)
Restructuring Cost and Reserve [Line Items]
Number of business segments \| segment			2
Strike related costs	$ 22,900,000	$ 0	$ 63,200,000	$ 0
Impairment of goodwill	0	0	0	(287,000,000)
Debt extinguishment charge	0	$ 0	0	(21,500,000)
Gain on the sale of oil and gas rights				$ 2,500,000
Entity number of employees covered by USW Collective Bargaining Agreements that expired February 28 2021 \| employee					1,100
Allegheny Technologies 3.5% Convertible Senior Notes due 2025 \| Convertible Debt
Restructuring Cost and Reserve [Line Items]
Debt, Gross	291,400,000		291,400,000			$ 291,400,000
High Performance Materials & Components \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Strike related costs	1,400,000		3,500,000
Advanced Alloys & Solutions [Member] \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Strike related costs	$ 21,500,000		$ 59,700,000