ATI (ATI) 10-K 24 Feb 23 2022 FY Annual report Financial data

Cover

Cover - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2022	Feb. 03, 2023	Jun. 30, 2022
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2022
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	1-12001
Entity Registrant Name	ATI Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	25-1792394
Entity Address, Address Line One	2021 McKinney Avenue
Entity Address, City or Town	Dallas,
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	75201
City Area Code	800
Local Phone Number	289-7454
Title of 12(b) Security	Common stock, par value $0.10
Trading Symbol	ATI
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		128,611,280
Entity Public Float			$ 3
Documents Incorporated by Reference	Documents Incorporated By Reference Selected portions of the Proxy Statement for the Annual Meeting of Stockholders to be held on May 11, 2023 are incorporated by reference into Part III of this Report.
Amendment Flag	false
Entity Central Index Key	0001018963
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2022
Audit Information [Abstract]
Auditor Name	Ernst & Young LLP
Auditor Location	Pittsburgh, Pennsylvania
Auditor Firm ID	42

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Statement [Abstract]
Sales	$ 3,836	$ 2,799.8	$ 2,982.1
Costs and expenses:
Cost of sales	3,121.8	2,466.6	2,689.3
Gross profit	714.2	333.2	292.8
Selling and administrative expenses	297.5	226.9	201
Impairment of goodwill	0	0	287
Restructuring charges (credits)	(4.8)	(11.3)	1,107.5
Loss on asset sales and sales of businesses, net	134.2	0	0
Operating income (loss)	287.3	117.6	(1,302.7)
Nonoperating retirement benefit income (expense)	(25.4)	37.2	(62.1)
Interest expense, net	(87.4)	(96.9)	(94.4)
Debt extinguishment charge	0	(65.5)	(21.5)
Other income (loss), net	(12.5)	18.2	(1.2)
Income (loss) before income taxes	162	10.6	(1,481.9)
Income tax provision	15.5	26.8	77.7
Net income (loss)	146.5	(16.2)	(1,559.6)
Less: Net income attributable to noncontrolling interests	15.6	22	13
Net income (loss) attributable to ATI	$ 130.9	$ (38.2)	$ (1,572.6)
Basic net income (loss) per common share
Continuing operations attributable to ATI per common share (in dollars per share)	$ 1.03	$ (0.30)	$ (12.43)
Basic net income (loss) attributable to ATI per common share (in dollars per share)	1.03	(0.30)	(12.43)
Diluted net income (loss) per common share
Continuing operations attributable to ATI per common share (in dollars per share)	0.96	(0.30)	(12.43)
Diluted net income (loss) attributable to ATI per common share (in dollars per share)	$ 0.96	$ (0.30)	$ (12.43)

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 146.5	$ (16.2)	$ (1,559.6)
Currency translation adjustment
Unrealized net change arising during the period	(43.5)	(4.6)	32.5
Reclassification adjustment included in net income (loss)	20	0	0
Total	(23.5)	(4.6)	32.5
Derivatives
Net derivatives gain (loss) on hedge transactions	53.8	15.5	(2.8)
Reclassification to net income (loss) of net realized (gain) loss	(42.8)	(11.4)	6
Income taxes on derivative transactions	0	0	0
Total	11	4.1	3.2
Postretirement benefit plans- Actuarial loss
Amortization of net actuarial loss	76.7	89.5	85.3
Net gain (loss) arising during the period	155	155.9	(128.4)
Postretirement benefit plans- Prior Service Cost
Amortization to net income (loss) of net prior service credits	(0.5)	(1.8)	(3.1)
Settlement loss (gain) included in net income (loss)	29.5	(21.9)	0
Income taxes on postretirement benefit plans	0	(15.5)	0
Total	260.7	237.2	(46.2)
Other comprehensive income (loss)	248.2	236.7	(10.5)
Comprehensive income (loss)	394.7	220.5	(1,570.1)
Less: Comprehensive income (loss) attributable to noncontrolling interests	(2.7)	26.8	24.4
Comprehensive income (loss) attributable to ATI	$ 397.4	$ 193.7	$ (1,594.5)

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Assets
Cash and cash equivalents	$ 584	$ 687.7
Accounts receivable, net	579.2	470
Short-term contract assets	64.1	53.9
Inventories, net	1,195.7	1,046.3
Prepaid expenses and other current assets	53.4	48.8
Total Current Assets	2,476.4	2,306.7
Property, plant and equipment, net	1,549.1	1,528.5
Goodwill	227.2	227.9
Other assets	192.9	222.1
Total Assets	4,445.6	4,285.2
Liabilities and Stockholders’ Equity
Accounts payable	553.3	375.5
Short-term contract liabilities	149.1	116.2
Short-term debt and current portion of long-term debt	41.7	131.3
Other current liabilities	219.8	233.4
Total Current Liabilities	963.9	856.4
Long-term debt	1,706.3	1,711.6
Accrued postretirement benefits	184.9	258.1
Pension liabilities	225.6	415.4
Other long-term liabilities	207.7	211
Total Liabilities	3,288.4	3,452.5
ATI Stockholders’ Equity:
Preferred stock, par value $0.10: authorized-50,000,000 shares; issued-none	0	0
Common stock, par value $0.10: authorized-500,000,000 shares; issued- 131,392,262 shares at December 31, 2022 and 127,484,902 shares at December 31, 2021; outstanding-128,273,042 shares at December 31, 2022 and 127,253,045 shares at December 31, 2021	13.1	12.7
Additional paid-in capital	1,668.1	1,596.7
Retained earnings	176.9	72.7
Treasury stock: 3,119,220 shares at December 31, 2022 and 231,857 shares at December 31, 2021	(87)	(4.8)
Accumulated other comprehensive loss, net of tax	(725.2)	(991.7)
Total ATI Stockholders’ Equity	1,045.9	685.6
Noncontrolling interests
Noncontrolling Interests	111.3	147.1
Total Stockholders' Equity	1,157.2	832.7
Total Liabilities and Stockholders' Equity	$ 4,445.6	$ 4,285.2

Consolidated Balance Sheets (PA

Consolidated Balance Sheets (PARENTHETICAL) - $ / shares	Dec. 31, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.10	$ 0.10
Preferred stock, authorized	50,000,000	50,000,000
Preferred stock, issued	0	0
Common stock, par value	$ 0.10	$ 0.10
Common stock, authorized	500,000,000	500,000,000
Common stock, issued	131,392,262	127,484,902
Common stock, oustanding	128,273,042	127,253,045
Treasury Stock	3,119,220	231,857

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Operating Activities:
Net income (loss)	$ 146.5	$ (16.2)	$ (1,559.6)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	142.9	143.9	143.3
Share-based compensation	26	21.1	2.9
Deferred taxes	(0.1)	1	69.9
Impairment of goodwill	0	0	287
Debt extinguishment charge	0	65.5	21.5
Gain from disposal of property, plant and equipment, net	(0.9)	(2.9)	(2.9)
Net loss (gain) on sale of business	141	(13.8)	0
Non-cash restructuring charges	0	0	1,041.5
Change in operating assets and liabilities:
Retirement benefits	(46.7)	(110.7)	(91.9)
Accounts receivable	(128.5)	(126)	208.4
Inventories	(190.8)	(53.9)	158.2
Accounts payable	156.1	88.5	(230.5)
Accrued income taxes	2.5	(2.6)	2.4
Accrued liabilities and other	(23.1)	22.2	116.7
Cash provided by operating activities	224.9	16.1	166.9
Investing Activities:
Purchases of property, plant and equipment	(130.9)	(152.6)	(136.5)
Proceeds from disposal of property, plant and equipment	3.1	20.8	5.9
Proceeds from sale of businesses, net of transaction costs	0.3	53.1	0
Other	0.8	1.4	1.9
Cash used in investing activities	(126.7)	(77.3)	(128.7)
Financing Activities:
Borrowings on long-term debt	0	675.7	391.4
Payments on long-term debt and finance leases	(23.1)	(515.6)	(212.1)
Net borrowings (payments) under credit facilities	(5.6)	21.7	0.2
Purchase of convertible note capped call	0	0	(19.4)
Debt issuance costs	0	(9.5)	(9.1)
Debt extinguishment charge	0	(64.5)	(19.1)
Purchase of treasury stock	(139.9)	0	0
Sale to noncontrolling interests	6.4	0	0
Dividends paid to noncontrolling interests	(34)	0	(7.2)
Shares repurchased for income tax withholding on share-based compensation	(5.7)	(4.8)	(7.8)
Cash provided by (used in) financing activities	(201.9)	103	116.9
Increase (decrease) in cash and cash equivalents	(103.7)	41.8	155.1
Cash and cash equivalents at beginning of year	687.7	645.9	490.8
Cash and cash equivalents at end of year	$ 584	$ 687.7	$ 645.9

Statements of Changes in Consol

Statements of Changes in Consolidated Equity - USD ($) $ in Millions	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests
Beginning balance at Dec. 31, 2019	$ 2,193.2	$ 12.7	$ 1,618	$ 1,679.3	$ (18.2)	$ (1,201.7)	$ 103.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(1,559.6)			(1,572.6)			13
Other comprehensive income (loss)	(10.5)					(21.9)	11.4
Equity component of convertible note	49.8		49.8
Convertible note capped call	(19.4)		(19.4)
Dividends paid to noncontrolling interest	$ (7.2)						(7.2)
Accounting Standards Update [Extensible Enumeration]	Accounting Standards Update 2020-06
Employee Stock Plans	$ (4.9)		(22.9)	(0.2)	18.2
Ending balance at Dec. 31, 2020	641.4	12.7	1,625.5	106.5	0	(1,223.6)	120.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(16.2)			(38.2)			22
Other comprehensive income (loss)	236.7					231.9	4.8
Employee Stock Plans	16.2		21		(4.8)
Ending balance at Dec. 31, 2021	832.7	12.7	1,596.7	72.7	(4.8)	(991.7)	147.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	146.5			130.9			15.6
Other comprehensive income (loss)	248.2					266.5	(18.3)
Purchase of treasury stock	(139.9)				(139.9)
Conversion of convertible notes	82.5	0.3	45.4	(26.7)	63.5
Dividends paid to noncontrolling interest	(34)						(34)
Sales of subsidiary shares to noncontrolling interest	0.9						0.9
Employee Stock Plans	20.3	0.1	26	0	(5.8)
Ending balance at Dec. 31, 2022	$ 1,157.2	$ 13.1	$ 1,668.1	$ 176.9	$ (87)	$ (725.2)	$ 111.3

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Principles of Consolidation and Reporting The consolidated financial statements include the accounts of ATI Inc. and its subsidiaries. The financial results of majority-owned joint ventures are consolidated into the Company’s operating results and financial position, with the minority ownership interest recognized in the consolidated statement of operations as net income attributable to noncontrolling interests, and as equity attributable to the noncontrolling interests within total stockholders’ equity. The results for the Shanghai STAL Precision Stainless Steel Company Limited (STAL) are reported on a one month lag. Investments in which the Company exercises significant influence, but which it does not control (generally a 20% to 50% ownership interest) are accounted for under the equity method of accounting, whereby ATI’s carrying value of the equity method investment on the consolidated balance sheet is the capital investment and any undistributed profit or loss. The investments are classified in other (noncurrent) assets on the consolidated balance sheet. The profit or loss attributable to ATI from equity method investments is included in the consolidated statements of operations as a component of Other (non-operating) income (expense). See Note 7 for further explanation of the Company’s joint ventures. Intercompany accounts and transactions have been eliminated. Unless the context requires otherwise, “ATI” and the “Company” refer to ATI Inc. and its subsidiaries. Risks and Uncertainties and Use of Estimates The preparation of consolidated financial statements in conformity with United States generally accepted accounting principles requires management to make estimates and assumptions that affect reported amounts of assets and liabilities at the date of the financial statements, as well as the reported amounts of income and expenses during the reporting period. Actual results could differ from those estimates. Management believes that the estimates are reasonable. The Company markets its products to a diverse customer base, principally throughout the United States. No single customer accounted for more than 10% of sales for any year presented. The major end markets for ATI’s products are customers in the aerospace & defense, energy, automotive, construction and mining, food equipment and appliances, and medical markets. At December 31, 2022, ATI has approximately 6,700 active employees, of which approximately 15% are located outside the United States. Approximately 35% of ATI’s workforce is covered by various collective bargaining agreements (CBAs), predominantly with the United Steel, Paper and Forestry, Rubber, Manufacturing, Energy, Allied & Industrial Service Workers International Union, AFL-CIO, CLC (USW). The Company’s CBA with the USW involving approximately 1,100 active full- time represented employees located primarily within the Advanced Alloys & Solutions (AA&S) segment operations, as well as a number of inactive employees, expired on February 28, 2021. USW-represented employees continued to work under the terms of the expired CBA until March 30, 2021 when they engaged in a strike. On July 14, 2021, ATI announced that a new four-year labor agreement with the USW was ratified, ending the strike. The Company has no significant CBAs that expire in 2023. Cash and Cash Equivalents Cash equivalents are highly liquid investments that are readily convertible to cash with original maturities of three months or less. Accounts Receivable Accounts receivable are presented net of a reserve for doubtful accounts of $7.7 million and $3.8 million at December 31, 2022 and 2021, respectively. Trade credit is extended based upon evaluations of each customer’s ability to perform its obligations, which are updated periodically. The Company’s accounts receivable reserves are determined based on expected credit losses. Amounts are written-off against the reserve in the period it is determined that the receivable is uncollectible. Inventories Inventories are stated at the lower of cost (first-in, first-out (FIFO) and average cost methods) or net realizable value. Costs include direct material, direct labor and applicable manufacturing and engineering overhead, and other direct costs. The term net realizable value is defined as estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. The Company evaluates product lines on a quarterly basis to identify inventory carrying values that exceed estimated net realizable value. The calculation of a resulting reserve, if any, is recognized as an expense in the period that the need for the reserve is identified. It is the Company’s general policy to write-down to scrap value any inventory that is identified as slow- moving or aged more than twelve months, subject to sales, backlog and anticipated order considerations. In some instances this aging criterion is up to twenty-four months. Inventory valuation reserves also include amounts pertaining to intercompany profit elimination between different subsidiaries. Long-Lived Assets Property, plant and equipment are recorded at cost, including capitalized interest, and include long-lived assets acquired under finance leases. Depreciation is primarily recorded using the straight-line method. Prior to December 2020, property, plant and equipment associated with the Hot-Rolling and Processing Facility (HRPF) in the AA&S segment was being depreciated utilizing the units of production method of depreciation, which the Company believed provided a better matching of costs and revenues. However, based on changed business conditions resulting from the decision to exit production of standard stainless sheet products and the recognition of an impairment charge on the property, plant and equipment associated with the HRPF in December 2020 (see Note 19 for further discussion), depreciation of the remaining carrying value of the HRPF began using the straight-line method in December 2020. The Company periodically reviews estimates of useful life and production capacity assigned to new and in service assets. Significant enhancements, including major maintenance activities that extend the lives of property and equipment, are capitalized. Costs related to repairs and maintenance are charged to expense in the period incurred. The cost and related accumulated depreciation of property and equipment retired or disposed of are removed from the accounts and any related gains or losses are included in income. The Company monitors the recoverability of the carrying value of its long-lived assets. An impairment charge is recognized when an indicator of impairment occurs and the expected net undiscounted future cash flows from an asset’s use (including any proceeds from disposition) are less than the asset’s carrying value and the asset’s carrying value exceeds its fair value. If an impairment loss is recognized, the adjusted carrying value of the long-lived asset is its new cost basis and this new cost basis is depreciated over the remaining useful life of the asset. Assets to be disposed of by sale are stated at the lower of their fair values or carrying amounts and depreciation is no longer recognized. Leases The Company classifies leases as either operating or financing, and records a right-of-use (ROU) asset and a lease liability on the consolidated balance sheets as further discussed below. The lease liability is equal to the present value of the minimum lease payments for the term of the lease, including any optional renewal periods determined to be reasonably certain to be exercised, using the discount rate determined at lease commencement. This discount rate is the rate implicit in the lease, if known; otherwise, the incremental borrowing rate (IBR) for the expected lease term is used. The Company’s IBRs approximate the rate the Company would have to pay to borrow on a collateralized basis over a similar term at lease inception. The ROU asset is equal to the initial measurement of the lease liability plus any lease payments made to the lessor at or before the commencement date and any unamortized initial direct costs incurred by the lessee, less any unamortized lease incentives received. The Company has elected to not separate lease components from non-lease components for all asset classes, and has made an accounting policy election to apply the short-term exception, which does not require the capitalization of leases with terms of 12 months or less. The Company has lease contracts for real property and machinery and equipment, primarily for mobile, office and information technology equipment. At inception of a contract, the Company determines whether the contract is or contains a lease. If the Company has a right to obtain substantially all of the economic benefits from the use of the identified asset and the right to direct the use of the asset, then the contract contains a lease. Several of the Company’s real property lease contracts include options to extend the lease term, and the Company reassesses the likelihood of renewal on at least an annual basis. In addition, several real property leases include variable lease payments, for items such as common area maintenance and utilities, which are expensed as incurred as variable lease expense. There are two types of leases: operating leases and finance leases. Lease classification is determined at lease commencement. A finance lease exists when specific criteria are met that indicate that all the risk and rewards related to the leased assets are transferred to the lessee. All other leases not meeting the finance lease criteria are classified as operating leases. Operating lease expense is recognized on a straight-line basis on the consolidated statement of operations. Finance leases have front-loaded expense recognition which is reported as amortization expense and interest expense on the consolidated statement of operations. ROU assets for operating leases are classified in other long-term assets property, plant and equipment other current liabilities other long-term liabilities short-term debt long-term debt Goodwill Goodwill is reviewed annually for impairment, or more frequently if impairment indicators arise. The review for goodwill impairment requires a comparison of the fair value of each reporting unit that has goodwill associated with its operations with its carrying amount, including goodwill. If this comparison reflects impairment, then the loss would be measured as the excess of the carrying value over the calculated fair value. Generally accepted accounting principles provide the option to qualitatively assess goodwill for impairment before completing a quantitative assessment. Under the qualitative approach, if, after assessing the totality of events or circumstances, including both macroeconomic, industry and market factors, and entity-specific factors, the Company determines it is likely (more likely than not) that the fair value of a reporting unit is greater than its carrying amount, then the quantitative impairment analysis is not required. The quantitative assessment may be performed each year for a reporting unit at the Company’s option without first performing a qualitative assessment. The Company’s quantitative assessment of goodwill for possible impairment includes estimating the fair market value of a reporting unit which has goodwill associated with its operations using discounted cash flow and multiples of cash earnings valuation techniques, plus valuation comparisons to recent public sale transactions of similar businesses, if any. These impairment assessments and valuation methods require the Company to make estimates and assumptions regarding revenue growth, changes in working capital and capital expenditures, selling prices and profitability that drive cash flows, and the weighted average cost of capital. Many of these assumptions are determined by reference to market participants identified by the Company. Although management believes that the estimates and assumptions used were reasonable, actual results could differ from those estimates and assumptions. Other events and changes in circumstances may also require goodwill to be tested for impairment between annual measurement dates. While a decline in stock price and market capitalization is not specifically cited as a goodwill impairment indicator, a company’s stock price and market capitalization should be considered in determining whether it is more likely than not that the fair value of a reporting unit is less that its carrying value. Additionally, a significant decline in a company’s stock price may suggest that an adverse change in the business climate may have caused the fair value of one or more reporting units to fall below carrying value. A sustained decline in market capitalization below book value may be determined to require an interim goodwill impairment review. Environmental Costs that mitigate or prevent future environmental contamination or extend the life, increase the capacity or improve the safety or efficiency of property utilized in current operations are capitalized. Other costs that relate to current operations or an existing condition caused by past operations are expensed. Environmental liabilities are recorded when the Company’s liability is probable and the costs are reasonably estimable, but generally not later than the completion of the feasibility study or the Company’s recommendation of a remedy or commitment to an appropriate plan of action. The accruals are reviewed periodically and, as investigations and remediations proceed, adjustments of the accruals are made to reflect new information as appropriate. Accruals for losses from environmental remediation obligations are not discounted to their present value. The accruals are not reduced by possible recoveries from insurance carriers or other third parties, but do reflect allocations among potentially responsible parties (PRPs) at Federal Superfund sites or similar state-managed sites after an assessment is made of the likelihood that such parties will fulfill their obligations at such sites and after appropriate cost-sharing or other agreements are entered. The measurement of environmental liabilities by the Company is based on currently available facts, present laws and regulations, and current technology. Such estimates take into consideration the Company’s prior experience in site investigation and remediation, the data concerning cleanup costs available from other companies and regulatory authorities, and the professional judgment of the Company’s environmental experts in consultation with outside environmental specialists, when necessary. Foreign Currency Translation Assets and liabilities of international operations are translated into U.S. dollars using year-end exchange rates, while revenues and expenses are translated at average exchange rates during the period. The resulting net translation adjustments are recorded as a component of accumulated other comprehensive income (loss) in stockholders’ equity. Sales Recognition The following is the Company’s accounting policy as it relates to Accounting Standards Codification Topic 606 (ASC 606), Contracts with Revenue from Customers. This guidance provides a five-step analysis of transactions to determine when and how revenue is recognized, and requires an entity to recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The following is the Company’s accounting policy as it relates to the five-step analysis for revenue recognition: 1. Identify the contract : The Company has determined that the contract with the customer is established when the customer purchase order is accepted or acknowledged. Long-term agreements (LTAs), which typically extend multiple years, are used by the Company and certain of its customers for its specialty materials, in the form of mill products, powders, parts and components, to reduce their supply uncertainty. While these LTAs generally define commercial terms including pricing, termination clauses and other contractual requirements, they do not represent the contract with the customer. 2. Identify the performance obligation in the contract : When the Company accepts or acknowledges the customer purchase order, the type of good or service is defined on a line by line basis. Individual performance obligations are established by virtue of the individual line items identified on the sales order acknowledgment at the time of issuance. Generally, the Company’s revenue relates to the sale of goods and contains a single performance obligation for each distinct good. Conversion services that transform customer-owned inventory to a different dimension, product form, and/or changed mechanical properties are classified as “goods”. 3. Determine the transaction price : Pricing is also defined on a sales order acknowledgment on a line item basis and includes an estimate of variable consideration when required by the terms of the individual customer contract. Variable consideration is when the selling price of the good is not known or is subject to adjustment under certain conditions. Types of variable consideration may include volume discounts, customer rebates and surcharges. ATI also provides assurances that goods or services will meet the product specifications contained within the acknowledged customer contract. As such, returns and refunds reserves are estimated based upon past product line history or, at certain locations, on a claim by claim basis. 4. Allocate the transaction price to the performance obligation : Since a customer contract generally contains only one performance obligation, this step of the analysis is generally not applicable to the Company. 5. Recognize revenue when or as the performance obligation is satisfied : Performance obligations generally occur at a point in time and are satisfied when control passes to the customer. For most transactions, control passes at the time of shipment in accordance with agreed upon delivery terms. On occasion, shipping and handling charges occur after the customer obtains control of the good. When this occurs, the shipping and handling services are considered activities to fulfill the promise to transfer the good. Certain customer agreements involving production of parts and components require revenue to be recognized over time due to there being no alternative use for the product without significant economic loss and an enforceable right to payment including a normal profit margin from the customer in the event of contract termination. The Company uses an input method for determining the amount of revenue, and associated standard cost, to recognize over-time revenue, cost and gross margin for these customer agreements. The input methods used for these agreements include costs incurred and labor hours expended, both of which give an accurate representation of the progress made toward complete satisfaction of that particular performance obligation. Contract assets are recognized when ATI’s conditional right to consideration for goods or services have transferred to the customer. A conditional right indicates that additional performance obligations associated with the contract are yet to be satisfied. Contract assets are assessed separately for impairment purposes. If ATI’s right to consideration from the customer is unconditional, this asset is accounted for as a receivable and presented separately from other contract assets. A right is unconditional if nothing other than the passage of time is required before payment of that consideration is due. Performance obligations that are recognized as revenue at a point-in-time and are billed to the customer are recognized as accounts receivable. Payment terms vary from customer to customer depending upon credit worthiness, prior payment history and other credit considerations. Contract costs are the incremental costs of obtaining and fulfilling a contract (i.e., costs that would not have been incurred if the contract had not been obtained) to provide goods and services to customers. Contract costs for ATI largely consist of design and development costs for molds, dies and other tools that ATI will own and that will be used in producing the products under the supply arrangement. Contract costs are classified as non-current assets and amortized to expense on a systematic and rational basis over a period consistent with the transfer to the customer of the goods or services to which the asset relates. Contract liabilities are recognized when ATI has received consideration from a customer to transfer goods or services at a future point in time when the Company performs under the contract. Elements of variable consideration discussed above may be recorded as contract liabilities. In addition, progress billings and advance payments from customers for costs incurred to date are also reported as contract liabilities. Research and Development Research, development and technical service activities are closely interrelated and are directed toward development of new products, improvement of existing products, cost reduction, process improvement and control, quality assurance and control, development of new manufacturing methods, and improvement of existing manufacturing methods. Research and development costs are expensed as incurred. Company funded research and development costs were $16.3 million in 2022, $16.5 million in 2021, and $14.1 million in 2020. Customer funded research and development costs were $1.4 million in 2022, $3.5 million in 2021, and $0.7 million in 2020. Government Assistance The Company enters into agreements with U.S. federal agencies, U.S. state and local governments, and foreign governments that provide financial assistance and incentives supporting both new capital projects to expand and enhance manufacturing capabilities and also to sustain and maintain existing operations. Depending on the nature of the government program, the financial impacts may be recorded as a reduction to cost of sales through direct offset of labor and overhead costs or lower depreciation expense, or as a reduction of selling, general and administrative expenses for property tax abatement or other similar categories. Benefits from government assistance are recognized as the activities are incurred, subject to ongoing assessments of meeting other relevant terms such as employment or expenditure levels. In November 2021, ATI entered into an agreement with the U.S. Department of Transportation under the Aviation Manufacturing Jobs Protection (AMJP) program for a grant of up to $22.2 million. The receipt of the award was primarily conditioned upon the Company committing to not furlough or lay off a defined group of employees in High Performance Materials & Components (HPMC) segment operations during the six-month period of performance between November 2021 and May 2022. The AMJP grant benefit was recognized over the six-month performance period as a reduction to cost of sales in proportion to the compensation expense that the award was intended to defray, with $16.6 million recognized in 2022 operating results. Cash receipts from the AMJP program were $11.0 million in 2022, and this program is now completed. ATI is a party to various U.S. states’ economic development incentive programs that provide economic benefits in the forms of property tax relief or cash payments to offset capital expenditures. These programs generally include requirements for levels of capital spending and/or employment to qualify for the government assistance. For the year ended December 31, 2022, these state-level programs reduced selling, general and administrative expenses by $1.6 million and cash receipts were $2.8 million. Receivables for ongoing programs are $3.7 million as of December 31, 2022. Stock-based Compensation The Company accounts for stock-based compensation transactions, such as nonvested restricted stock or stock units and performance equity awards, using fair value. Compensation expense for an award is estimated at the date of grant and is recognized over the requisite service period. Compensation expense is adjusted for equity awards that do not vest because service or performance conditions are not satisfied. However, compensation expense already recognized on plans which vest based solely on the attainment of market conditions, such as total shareholder return measures, is not adjusted based on the award attainment status at the end of the measurement period. Compensation expense is adjusted for estimated forfeitures over the award measurement period. Income Taxes The provision for, or benefit from, income taxes includes deferred taxes resulting from temporary differences in income for financial and tax purposes using the liability method. Such temporary differences result primarily from differences in the carrying value of assets and liabilities. Future realization of deferred income tax assets requires sufficient taxable income within the carryback and/or carryforward period available under tax law. The Company evaluates on a quarterly basis whether, based on all available evidence, it is probable that the deferred income tax assets are realizable. Valuation allowances are established when it is estimated that it is more likely than not that the tax benefit of the deferred tax asset will not be realized. The evaluation includes the consideration of all available evidence, both positive and negative, regarding the estimated future reversals of existing taxable temporary differences, estimated future taxable income exclusive of reversing temporary differences and carryforwards, historical taxable income in prior carryback periods if carryback is permitted, and potential tax planning strategies which may be employed to prevent an operating loss or tax credit carryforward from expiring unused. The verifiable evidence such as future reversals of existing temporary differences and the ability to carryback are considered before the subjective sources such as estimated future taxable income exclusive of temporary differences and tax planning strategies. It is the Company’s policy to classify interest and penalties recognized on underpayment of income taxes as income tax expense. It is also the Company’s policy to recognize deferred tax amounts stranded in accumulated other comprehensive income (AOCI), which result from tax rate differences on changes in AOCI balances, as an element of income tax expense in the period that the related balance sheet item associated with the AOCI balance ceases to exist. In the case of derivative financial instruments accounted for as hedges, or marketable securities, ATI uses the portfolio method where the stranded deferred tax amount is recognized when all items of a particular category, such as cash flow hedges of a particular risk such as a foreign currency hedge, are settled. In the case of defined benefit pension and other postretirement benefit plans, the stranded deferred tax balance is recognized as an element of income tax expense in the period the benefit plan is extinguished or divested. Net Income Per Common Share Basic and diluted net income per share are calculated by dividing the net income available to common stockholders by the weighted average number of common shares outstanding during the year. Diluted amounts assume the issuance of common stock for all potentially dilutive share equivalents outstanding. The calculations of all diluted income/loss per share figures for a period exclude the potentially dilutive effect of dilutive share equivalents if there is a net loss since the inclusion in the calculation of additional shares in the net loss per share would result in a lower per share loss and therefore be anti-dilutive. New Accounting Pronouncements Adopted In November 2021, the Financial Accounting Standards Board (FASB) issued new accounting guidance related to disclosures about certain types of government assistance. This new guidance requires business entities that account for transactions with a government by analogizing to a grant or contribution accounting model to make certain annual disclosures. It requires disclosure of the nature and significant terms and considerations of the transactions, the accounting policies used and the effects of those transactions on an entity’s financial statements. This new guidance is effective for the Company in fiscal year 2022, with early adoption permitted. The Company adopted this new accounting guidance effective January 1, 2022. The adoption of these changes did not have an impact on the Company’s consolidated financial statements other than the annual disclosure requirements included in the accounting policies discussion above. In August 2020, the FASB issued new accounting guidance related to accounting for convertible instruments. Under this new guidance, embedded conversion features are no longer separated from the host contract for convertible instruments with conversion features that are not required to be accounted for as derivatives, or that do not result in substantial premiums accounted for as paid-in capital. As such, a convertible debt instrument will be accounted for as a single liability measured at its amortized cost, as long as no other features require bifurcation and recognition as derivatives. By removing those separation models, the reported interest rate of convertible debt instruments typically will be closer to the coupon interest rate. The new guidance also addresses how convertible instruments are accounted for in the diluted earnings per share calculation, requiring the if-converted method, and requires enhanced disclosures about the terms of convertible instruments and contracts in an entity’s own equity. This new guidance was effective for the Company in fiscal year 2022, with early adoption permitted. The Company early adopted this new accounting guidance related to accounting for convertible instruments effective January 1, 2021 using the modified transition approach with the cumulative effect recognized as an adjustment to the opening balance of retained earnings. This new guidance was applicable to the Company’s 3.5% Convertible Senior Notes due 2025 (the 2025 Convertible Notes) that were issued in June 2020, for which the embedded conversion option was required to be separately accounted for as a component of stockholders’ equity. Upon adoption on January 1, 2021, long-term debt increased by $45.4 million and stockholders’ equity decreased by the same amount, representing the net impact of two adjustments: (1) the $49.8 million value of the embedded conversion, which is net of allocated offering costs, previously classified in additional paid-in capital in stockholders’ equity, and (2) a $4.4 million increase to retained earnings for the cumulative effect of adoption primarily related to the non-cash interest expense recorded in fiscal year 2020 for the amortization of the portion of the 2025 Convertible Notes allocated to stockholders’ equity. Prospectively, the reported interest expense for the 2025 Convertible Notes no longer included the non-cash interest expense of the equity component as required under prior accounting standards and is closer to the 3.5% cash coupon rate. There was no impact to the Company’s earnings per share calculation as it previously applied the if-converted method to the 2025 Convertible Notes given ATI’s flexibility to settle conversions of the 2025 Convertible Notes in cash, shares of ATI’s common stock or a combination thereof, at ATI’s election. Pending Accounting Pronouncements In September 2022, the FASB issued new accounting guidance related to disclosures about supplier finance programs. Supplier finance programs allow a buyer to offer its suppliers the option for access to payment in advance of an invoice due date, which is paid by a third-party finance provider or intermediary on the basis of invoices that the buyer has confirmed as valid. This new guidance requires a buyer in a supplier finance program to disclose sufficient information about the program to allow a user of financial statements to understand the program’s nature, activity during the period, changes from period to period, and potential magnitude, using both qualitative and quantitative information about its supplier finance programs. This new

Business Segments

Business Segments	12 Months Ended
	Dec. 31, 2022
Segment Reporting [Abstract]
Business Segments	Business Segments The Company operates under two business segments: High Performance Materials & Components (HPMC) and Advanced Alloys & Solutions (AA&S). HPMC is comprised of the Specialty Materials and Forged Products businesses, as well as the ATI Europe distribution operations. Approximately 80% of its revenue is derived from the aerospace & defense markets including nearly 60% of its revenue from products for commercial jet engines. Other major HPMC end markets include medical and energy. HPMC produces a wide range of high performance materials, components, and advanced metallic powder alloys. These are made from nickel-based alloys and superalloys, titanium and titanium-based alloys, and a variety of other specialty materials. Capabilities range from cast/wrought and powder alloy development to final production of highly engineered finished components, including those used for next-generation jet engine forgings and 3D-printed aerospace products. The AA&S segment includes the Specialty Alloys & Components business, the Specialty Rolled Products business, the 60%-owned STAL PRS joint venture, and the Uniti and A&T Stainless 50%-owned joint ventures that are reported in AA&S segment results under the equity method of accounting. See Note 7 for further information on the Company’s joint ventures. AA&S is focused on delivering high-value flat products primarily to the energy, aerospace, and defense markets, which comprise approximately 50% of its revenue. Other important end markets for AA&S include automotive and electronics. AA&S produces nickel-based alloys, titanium and titanium-based alloys, and specialty alloys in a variety of forms including plate, sheet, and strip products. On December 2, 2020, the Company announced a strategic repositioning of its SRP business, which includes exiting production of lower-margin standard stainless sheet products, streamlining the production footprint of the AA&S segment and making certain capital investments to increase its focus on higher-margin products and its aerospace & defense end markets. See Note 19 for further discussion of this strategic realignment and its associated long-lived asset impairments, restructuring and other charges recorded in the fourth quarter of 2020. The measure of segment EBITDA categorically excludes income taxes, depreciation and amortization, corporate expenses, net interest expense, closed operations and other expenses, charges for goodwill and asset impairments, restructuring and other charges, strike related costs, debt extinguishment charges and gains or losses on asset sales and sales of businesses. Management believes segment EBITDA, as defined, provides an appropriate measure of controllable operating results at the business segment level. Intersegment sales are generally recorded at full cost or market. Common services are allocated on the basis of estimated utilization. (In millions) 2022 2021 2020 Total sales: High Performance Materials & Components $ 1,815.7 $ 1,248.3 $ 1,235.4 Advanced Alloys & Solutions 2,433.7 1,762.4 1,947.5 Total sales 4,249.4 3,010.7 3,182.9 Intersegment sales: High Performance Materials & Components 174.5 93.2 70.8 Advanced Alloys & Solutions 238.9 117.7 130.0 Total intersegment sales 413.4 210.9 200.8 Sales to external customers: High Performance Materials & Components 1,641.2 1,155.1 1,164.6 Advanced Alloys & Solutions 2,194.8 1,644.7 1,817.5 Total sales to external customers $ 3,836.0 $ 2,799.8 $ 2,982.1 Total international sales were $1,617.4 million in 2022, $1,264.9 million in 2021, and $1,173.0 million in 2020. Of these amounts, sales by operations in the United States to customers in other countries were $1,217.9 million in 2022, $846.3 million in 2021, and $812.3 million in 2020. (In millions) 2022 2021 2020 EBITDA: High Performance Materials & Components $ 296.0 $ 159.9 $ 129.6 Advanced Alloys & Solutions 327.8 191.7 115.0 Total segment EBITDA 623.8 351.6 244.6 Corporate expenses (62.4) (55.9) (40.9) Closed operations and other expenses (12.1) (4.8) (7.4) Depreciation & amortization (142.9) (143.9) (143.3) Interest expense, net (87.4) (96.9) (94.4) Restructuring and other credits (charges) (See Note 19) (23.7) 10.5 (1,132.1) Strike related costs — (63.2) — Retirement benefit settlement gain (See Note 14) — 64.9 — Impairment of goodwill (See Note 5) — — (287.0) Joint venture restructuring credit (charge) (See Note 7) 0.9 — (2.4) Debt extinguishment charge (See Note 10) — (65.5) (21.5) Gain (loss) on asset sales and sale of business, net (134.2) 13.8 2.5 Income (loss) before income taxes $ 162.0 $ 10.6 $ (1,481.9) Beginning in 2020, the U.S. government enacted various relief packages in response to the COVID-19 pandemic. Results for the fiscal year ended December 31, 2022 include $34 million related to this government sponsored COVID relief in segment EBITDA. HPMC segment results for 2022 include $27 million of benefits from the AMJP Program and employee retention credits, and AA&S segment results for 2022 include $7 million in employee retention credits. Corporate expenses are primarily classified as selling and administrative expenses in the consolidated statement of operations, and consist of salaries and benefits, incentive compensation, facility leases and other costs of ATI’s corporate functions. Corporate expenses in 2022 reflect business transformation initiatives and higher incentive compensation costs compared to the prior year periods. Closed operations and other expenses are primarily presented in selling and administrative expenses in the consolidated statements of operations. These items included costs at closed facilities, including legal matters, environmental, real estate and other facility costs, and changes in foreign currency remeasurement impacts primarily related to ATI’s European Treasury Center operation. Closed operations and other expenses in 2022 primarily relate to unfavorable foreign currency remeasurement impacts primarily related to ATI’s European Treasury Center operation and higher legal costs for closed facilities compared to prior year periods. During the fiscal year ended December 31, 2021, the Company recorded $63.2 million in strike related costs, of which $59.7 million were excluded from AA&S segment EBITDA and $3.5 million were excluded from HPMC segment EBITDA. These items primarily consisted of overhead costs recognized in the period due to below-normal operating rates, higher costs for outside conversion activities, and ongoing benefit costs for striking employees. Gain (loss) on asset sales and sales of businesses, net, for 2022 relate to a $141.0 million loss on the sale of the Company’s Sheffield, UK operations, partially offset by a $6.8 million gain from the sale of assets from the Pico Rivera, CA operations. The $13.8 million net gain on asset sales in 2021 consists of a gain on the sale of the Company’s Flowform Products business. See Note 6 for further explanation regarding the sale of business transactions in 2022 and 2021. The $2.5 million net gain on asset sales in 2020 consists of a gain on the sale of certain oil and gas rights (see Note 9). Certain additional information regarding the Company’s business segments is presented below: (In millions) 2022 2021 2020 Depreciation and amortization: High Performance Materials & Components $ 68.3 $ 75.0 $ 78.1 Advanced Alloys & Solutions 67.4 64.5 62.1 Other 7.2 4.4 3.1 Total depreciation and amortization $ 142.9 $ 143.9 $ 143.3 Capital expenditures: High Performance Materials & Components $ 33.3 $ 40.2 $ 83.1 Advanced Alloys & Solutions 89.6 110.6 45.9 Corporate 8.0 1.8 7.5 Total capital expenditures $ 130.9 $ 152.6 $ 136.5 Identifiable assets: 2022 2021 2020 High Performance Materials & Components $ 1,749.3 $ 1,624.8 $ 1,594.6 Advanced Alloys & Solutions 1,981.1 1,914.0 1,664.0 Corporate: Deferred Taxes 4.7 6.3 5.1 Cash and cash equivalents and other 710.5 740.1 771.2 Total assets $ 4,445.6 $ 4,285.2 $ 4,034.9 ($ in millions) 2022 Percent 2021 Percent 2020 Percent Total assets: United States $ 3,942.7 89 % $ 3,587.0 84 % $ 3,356.8 83 % China 321.1 7 % 406.4 9 % 325.5 8 % United Kingdom 13.4 — % 153.9 4 % 122.4 3 % Other 168.4 4 % 137.9 3 % 230.2 6 % Total Assets $ 4,445.6 100 % $ 4,285.2 100 % $ 4,034.9 100 %

Restructuring Costs

Restructuring Costs	12 Months Ended
	Dec. 31, 2022
Restructuring and Related Activities [Abstract]
Restructuring and Related Activities Disclosure	Note 19. Restructuring and other charges For the year ended December 31, 2022, restructuring and other charges were $23.7 million, which included a $28.5 million charge for a litigation settlement (see Note 21), partially offset by $4.8 million of restructuring credits for reductions in severance-related reserves related to approximately 110 employees based on changes in planned operating rates and revised workforce estimates. For the year ended December 31, 2021, restructuring and other charges were a net benefit of $10.5 million, which primarily included $11.3 million of reversals of previously-recognized restructuring charges separately classified on the consolidated statement of operations, as well as an $0.8 million charge for inventory valuation reserves classified in cost of sales on the consolidated statement of operations related to the 2020 idling of the Albany, OR primary titanium facility. Restructuring items in 2021 include a $12.0 million reduction in severance-related reserves related to approximately 350 employees based on changes in planned operating rates and revised workforce reduction estimates, partially offset by $0.7 million of other costs related to facility idlings. For the year ended December 31, 2020, the Company recorded restructuring and other charges of $1,132.1 million, predominantly related to the Company’s December 2020 announcement to cease production of standard stainless sheet products. On December 2, 2020, the Company announced a strategic repositioning of its SRP business within the AA&S segment, with a focus of increasing emphasis on the specialty rolled products portion of its product portfolio, which is comprised of titanium-based alloys including aerospace-grade titanium plate products, nickel-based alloys, and stainless products with more differentiated characteristics for specialty applications, including thin-gauge PRS. Restructuring charges recorded on the consolidated statement of operations for the year ended December 31, 2020 were $1,107.5 million, comprised of $1,041.5 million of non-cash asset impairment charges, $60.5 million of employee benefit-related costs, and $5.5 million of other costs related to facility idlings. The December 2, 2020 decision to exit production of standard stainless products represented a significant indicator of impairment in the carrying value of certain long-lived assets. Based on projected cash flows of the Brackenridge, PA operations, including the HRPF, the Company completed a fair value analysis as of the beginning of the fourth quarter of 2020 and recognized a $1,032.6 million impairment charge for this facility based on an estimated fair value of $354 million. This long-lived asset impairment charge was determined using a held in use framework and an income approach, which represents Level 3 unobservable information in the fair value hierarchy. This impairment assessment and valuation method require the Company to make estimates and assumptions regarding future operating results, cash flows, changes in working capital and capital expenditures, selling prices, profitability, and the cost of capital. Many of these assumptions are determined by reference to market participants the Company has identified. For example, the weighted average cost of capital used in the discounted cash flow assessment was 9.3% and the long-term growth rate was 2%. Other long-lived asset impairment charges of $8.9 million were also recognized in 2020 for various AA&S segment operations identified for closure as part of the standard stainless sheet exit decision. Restructuring charges in 2020 also include $60.5 million of employee benefit costs, representing severance, supplemental unemployment and medical benefits for the elimination of approximately 1,400 positions related to the standard stainless exit, as well as for employees impacted by the idling of the Albany, OR primary titanium operations in the fourth quarter of 2020, and workforce right-sizing actions, including both involuntary reductions and voluntary retirement incentive programs implemented throughout 2020 to better match the Company’s cost structure to expected demand, primarily as a result of economic challenges created by the COVID-19 pandemic. Other costs of $5.5 million included in 2020 restructuring charges primarily relate to asset retirement and environmental obligations associated with facility idlings. Other charges for the year ended December 31, 2020 include: • $17.4 million of termination benefits for pension and postretirement medical obligations related to facility closures from the standard stainless exit (see Note 14 for further explanation). These costs are classified within nonoperating retirement benefit expense in the consolidated statements of operations. • $7.2 million of other charges for inventory valuation reserves, classified in cost of sales on the consolidated statement of operations, primarily related to excess raw material and work in process inventory at the idled Albany, OR primary titanium facility. Restructuring reserves for severance cost activity is as follows: Severance and Employee Benefit Costs December 31, 2022 December 31, 2021 December 31, 2020 Beginning of year balance $ 17.7 $ 43.4 $ 4.5 Additions/(Adjustments) (4.8) (12.0) 60.5 Payments (3.1) (13.7) (21.6) End of year balance $ 9.8 $ 17.7 $ 43.4

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2022
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets At December 31, 2022, the Company had $227.2 million of goodwill on its consolidated balance sheet, all of which relates to the HPMC segment. Goodwill decreased in 2022 by $0.7 million as a result of currency translation on goodwill denominated in functional currencies other than the U.S. dollar. The Company performs its annual goodwill impairment evaluations in the fourth quarter of each year. The $227.2 million of goodwill as of December 31, 2022 on the Company’s consolidated balance sheet is comprised of $161.2 million at the Forged Products reporting unit and $66.0 million at the Specialty Materials reporting unit. For the Company’s annual goodwill impairment evaluation in 2022, quantitative goodwill assessments were performed for these two HPMC reporting units with goodwill. This quantitative fair value assessment may include discounted cash flow and multiples of cash earnings valuation techniques, plus valuation comparisons to recent public sale transactions of similar businesses, if any, which represents Level 3 unobservable information in the fair value hierarchy. These impairment assessments and valuation methods require the Company to make estimates and assumptions regarding revenue growth, changes in working capital and capital expenditures, selling prices and profitability that drive cash flows, and the weighted average cost of capital. Many of these assumptions are determined by reference to market participants the Company has identified. For example, the weighted average cost of capital used in the discounted cash flow assessment was 11.7% and the long-term growth rates ranged from 3% to 3.5%. In order to validate the reasonableness of the estimated fair values of the reporting units as of the valuation date, a reconciliation of the aggregate fair values of all reporting units to market capitalization was performed using a reasonable control premium. Although the Company believes that the estimates and assumptions used were reasonable, actual results could differ from those estimates and assumptions. The Specialty Materials reporting unit had a fair value that was significantly in excess of carrying value. The Forged Products reporting unit had a fair value that exceeded carrying value by more than 50% for the 2022 annual assessment, which increased compared to the annual evaluation for 2021. No impairments were determined to exist from the annual goodwill impairment evaluation for the years ended December 31, 2022, 2021 or 2020. During the second quarter of 2020, the Company performed an interim goodwill impairment analysis on the Forged Products reporting unit and its $460.4 million goodwill balance based on assessed potential indicators of impairment, including recent disruptions to the global commercial aerospace market resulting from the COVID-19 pandemic, and the increasing uncertainty of near-term demand requirements of aero-engine and airframe markets based on government responses to the pandemic and ongoing interactions with customers. For the 2020 interim impairment analysis, fair value was determined by a quantitative assessment that used a discounted cash flow technique. As a result of the 2020 interim goodwill impairment evaluation, the Company determined that the fair value of the Forged Products reporting unit was below carrying value, including goodwill, by $287.0 million, primarily due to changes in the timing and amount of expected cash flows resulting from lower projected revenues, profitability and cash flows due to near-term reductions in commercial aerospace market demand. Consequently, during the second quarter of 2020, the Company recorded a $287.0 million charge for the partial impairment of the Forged Products reporting unit goodwill, most of which was assigned from the Company’s 2011 Ladish acquisition that was not deductible for income tax purposes. This goodwill impairment charge was excluded from 2020 HPMC business segment results. No indicators of impairment were observed in 2022, 2021 and 2020 associated with any of the Company’s long-lived assets in the HPMC segment. Accumulated goodwill impairment losses as of December 31, 2022, 2021 and 2020 were $528.0 million. Other intangible assets, which are included in Other assets on the accompanying consolidated balance sheets as of December 31, 2022 and 2021 were as follows: December 31, 2022 December 31, 2021 (in millions) Gross Accumulated Gross Accumulated Technology $ 61.2 $ (35.4) $ 61.2 $ (32.3) Customer relationships 24.8 (11.6) 24.8 (10.6) Trademarks 48.8 (29.3) 48.8 (26.0) Total amortizable intangible assets $ 134.8 $ (76.3) $ 134.8 $ (68.9) Amortization expense related to intangible assets was approximately $8 million for each of the years ended December 31, 2022, 2021 and 2020. For each of the years ending December 31, 2023 through 2027, annual amortization expense is expected to be approximately $7 million.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	12 Months Ended
	Dec. 31, 2022
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	Revenue from Contracts with Customers Disaggregation of Revenue The Company operates in two business segments: High Performance Materials & Components (HPMC) and Advanced Alloys & Solutions (AA&S). Revenue is disaggregated within these two business segments by diversified global markets, primary geographical markets, and diversified products. Comparative information of the Company’s overall revenues (in millions) by global and geographical markets for the fiscal years ended December 31, 2022, 2021 and 2020 is as follows: (in millions) 2022 2021 2020 HPMC AA&S Total HPMC AA&S Total HPMC AA&S Total Diversified Global Markets: Aerospace & Defense: Jet-Engines- Commercial $ 975.7 $ 87.8 $ 1,063.5 $ 480.9 $ 36.3 $ 517.2 $ 542.7 $ 58.2 $ 600.9 Airframes- Commercial 184.1 284.8 468.9 132.8 129.9 262.7 219.8 191.0 410.8 Defense 158.2 183.0 341.2 221.8 131.0 352.8 184.4 163.9 348.3 Total Aerospace & Defense $ 1,318.0 $ 555.6 $ 1,873.6 $ 835.5 $ 297.2 $ 1,132.7 $ 946.9 $ 413.1 $ 1,360.0 Energy: Oil & Gas 35.0 441.7 476.7 42.2 290.1 332.3 37.3 328.5 365.8 Specialty Energy 113.6 163.0 276.6 136.1 123.5 259.6 68.9 184.2 253.1 Total Energy 148.6 604.7 753.3 178.3 413.6 591.9 106.2 512.7 618.9 Automotive 11.2 290.9 302.1 8.7 296.4 305.1 5.5 257.7 263.2 Electronics 2.4 197.6 200.0 1.2 213.9 215.1 0.9 176.8 177.7 Construction/Mining 34.1 142.3 176.4 24.0 98.2 122.2 18.6 123.4 142.0 Medical 73.2 89.9 163.1 60.3 71.2 131.5 47.7 71.4 119.1 Food Equipment & Appliances 0.2 158.3 158.5 0.1 153.0 153.1 — 159.2 159.2 Other 53.5 155.5 209.0 47.0 101.2 148.2 38.8 103.2 142.0 Total $ 1,641.2 $ 2,194.8 $ 3,836.0 $ 1,155.1 $ 1,644.7 $ 2,799.8 $ 1,164.6 $ 1,817.5 $ 2,982.1 (in millions) 2022 2021 2020 HPMC AA&S Total HPMC AA&S Total HPMC AA&S Total Primary Geographical Market: United States $ 742.9 $ 1,475.7 $ 2,218.6 $ 571.3 $ 963.6 $ 1,534.9 $ 641.0 $ 1,168.1 $ 1,809.1 China 59.8 292.0 351.8 49.5 320.9 370.4 31.0 284.5 315.5 United Kingdom 165.7 52.0 217.7 136.7 17.2 153.9 101.9 24.6 126.5 Germany 148.4 52.5 200.9 74.1 47.2 121.3 76.6 48.8 125.4 France 125.7 31.5 157.2 48.7 9.8 58.5 66.5 18.4 84.9 Canada 46.2 41.2 87.4 36.3 39.6 75.9 28.3 40.6 68.9 Rest of World 352.5 249.9 602.4 238.5 246.4 484.9 219.3 232.5 451.8 Total $ 1,641.2 $ 2,194.8 $ 3,836.0 $ 1,155.1 $ 1,644.7 $ 2,799.8 $ 1,164.6 $ 1,817.5 $ 2,982.1 Comparative information of the Company’s major products based on their percentages of sales is included in the following table. The Company no longer reports standard stainless product sales as a separate product category. Prior period information includes these sales within the nickel-based alloys and specialty alloys category. HRPF conversion service sales in the AA&S segment are excluded from this presentation. 2022 2021 2020 HPMC AA&S Total HPMC AA&S Total HPMC AA&S Total Diversified Products: Nickel-based alloys and specialty alloys 49 % 54 % 52 % 43 % 44 % 43 % 38 % 49 % 45 % Precision forgings, castings and components 34 % — % 15 % 38 % — % 16 % 34 % — % 14 % Precision rolled strip — % 25 % 14 % — % 33 % 19 % — % 25 % 15 % Titanium and titanium-based alloys 17 % 7 % 11 % 19 % 6 % 12 % 28 % 11 % 17 % Zirconium and related alloys — % 14 % 8 % — % 17 % 10 % — % 15 % 9 % Total 100 % 100 % 100 % 100 % 100 % 100 % 100 % 100 % 100 % The Company maintains a backlog of confirmed orders totaling $2.9 billion, $2.1 billion and $1.4 billion at December 31, 2022, 2021 and 2020, respectively. Due to the structure of the Company’s LTAs, 80% of this backlog at December 31, 2022 represented booked orders with performance obligations that will be satisfied within the next twelve months. The backlog does not reflect any elements of variable consideration. Accounts Receivable As of December 31, 2022 and 2021, accounts receivable with customers were $586.9 million and $473.8 million, respectively. The following represents the rollforward of accounts receivable - reserve for doubtful accounts for the fiscal years ended December 31, 2022, 2021 and 2020: (in millions) Accounts Receivable - Reserve for Doubtful Accounts Balance as of December 31, 2019 4.6 Expense to increase the reserve 0.2 Write-off of uncollectible accounts (0.5) Balance as of December 31, 2020 4.3 Expense to increase the reserve 0.3 Write-off of uncollectible accounts (0.8) Balance as of December 31, 2021 3.8 Expense to increase the reserve 4.6 Write-off of uncollectible accounts (0.7) Balance as of December 31, 2022 $ 7.7 Contract balances The following represents the rollforward of contract assets and liabilities for the fiscal years ended December 31, 2022, 2021 and 2020: (in millions) Contract Assets Short-term 2022 2021 2020 Balance as of beginning of fiscal year $ 53.9 $ 38.9 $ 38.5 Recognized in current year 105.0 93.8 84.2 Reclassified to accounts receivable (88.0) (76.2) (83.9) Reclassification to/from long-term and contract liability (6.8) (2.6) 0.1 Balance as of period end $ 64.1 $ 53.9 $ 38.9 Long-term (a) 2022 2021 2020 Balance as of beginning of fiscal year $ — $ — $ 0.1 Reclassification to/from short-term — — (0.1) Balance as of period end $ — $ — $ — (in millions) Contract Liabilities Short-term 2022 2021 2020 Balance as of beginning of fiscal year $ 116.2 $ 111.8 $ 78.7 Recognized in current year 183.1 161.5 170.3 Amounts in beginning balance reclassified to revenue (99.8) (85.1) (55.9) Current year amounts reclassified to revenue (72.3) (72.9) (90.1) Divestiture — (0.8) — Other 0.7 0.1 — Reclassification to/from long-term and contract asset 21.2 1.6 8.8 Balance as of period end $ 149.1 $ 116.2 $ 111.8 Long-term (a) 2022 2021 2020 Balance as of beginning of fiscal year $ 84.4 $ 32.0 $ 25.9 Recognized in current year 10.4 56.6 14.9 Reclassification to/from short-term (28.0) (4.2) (8.8) Balance as of period end $ 66.8 $ 84.4 $ 32.0 (a) Long-term contract assets are included in Other long-term assets and long-term contract liabilities are included in Other long-term liabilities on the consolidated balance sheets. Contract costs for obtaining and fulfilling a contract were $7.3 million and $5.2 million as of December 31, 2022 and 2021, respectively, which are reported in other long-term assets on the consolidated balance sheets. Amortization expense for the fiscal years ended December 31, 2022, 2021 and 2020 of these contract costs was $1.0 million, $1.0 million, and $1.4 million, respectively.

Inventories

Inventories	12 Months Ended
	Dec. 31, 2022
Inventory Disclosure [Abstract]
Inventories	Inventories Inventories at December 31, 2022 and 2021 were as follows (in millions): 2022 2021 Raw materials and supplies $ 213.6 $ 160.3 Work-in-process 941.1 829.6 Finished goods 111.9 121.8 1,266.6 1,111.7 Inventory valuation reserves (70.9) (65.4) Total inventories, net $ 1,195.7 $ 1,046.3 Inventories are stated at the lower of cost (FIFO and average cost methods) or net realizable value.

Property Plant And Equipment

Property Plant And Equipment	12 Months Ended
	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
Property Plant and Equipment	Property, Plant and Equipment Property, plant and equipment at December 31, 2022 and 2021 was as follows: (In millions) 2022 2021 Land $ 31.5 $ 34.4 Buildings 601.6 575.5 Equipment and leasehold improvements 2,895.5 2,870.2 3,528.6 3,480.1 Accumulated depreciation and amortization (1,979.5) (1,951.6) Total property, plant and equipment, net $ 1,549.1 $ 1,528.5 Construction in progress at December 31, 2022 and 2021 was $262.1 million and $215.3 million, respectively. Capital expenditures on the consolidated statement of cash flows for the year ended December 31, 2022 exclude $38.3 million of incurred but unpaid capital expenditures that were included in property, plant and equipment and accrued at December 31, 2022. Depreciation and amortization for the years ended December 31, 2022, 2021 and 2020 was as follows: (In millions) 2022 2021 2020 Depreciation of property, plant and equipment $ 115.4 $ 117.4 $ 119.5 Software and other amortization 27.5 26.5 23.8 Total depreciation and amortization $ 142.9 $ 143.9 $ 143.3

Divestitures - (Notes)

Divestitures - (Notes)	12 Months Ended
	Dec. 31, 2022
Discontinued Operations and Disposal Groups [Abstract]
Divestitures	Divestitures On May 12, 2022, the Company completed the sale of its Sheffield, UK operations, which included facilities for melting and re-melting, machining and bar mill operations, and was part of the Specialty Materials business in the HPMC segment. A $141.0 million loss on sale of the Sheffield operations is reported in loss on asset sales and sales of businesses, net, on the consolidated statement of operations for 2022, and is excluded from HPMC segment results. The loss includes $55.6 million related to the UK defined benefit pension plan, of which $26.1 million was reported as a net pension asset but which was in a deficit funding position for UK statutory reporting purposes, and $29.5 million in accumulated other comprehensive loss on the consolidated ATI balance sheet. The loss also includes $20.0 million of cumulative translation adjustment foreign exchange losses since ATI’s acquisition of these operations in 1998. The Company received proceeds, net of transaction costs, of $0.3 million in 2022, which is reported as an investing activity on the consolidated statement of cash flows. In 2021, the Sheffield operations had external sales of $36 million, with over 80% of its sales to energy markets, primarily oil & gas, and had a net loss before tax of $9 million. The Company completed the sale of the small Pico Rivera, CA operations, as part of the strategy to exit standard stainless products, on January 31, 2022. The Company received cash proceeds of $6.2 million on the sale of these assets. The Company recognized a $6.8 million pretax gain on sale, including de-recognizing certain lease liabilities, which is reported in loss on asset sales and sales of businesses, net, on the consolidated statement of operations and is excluded from AA&S segment results. On August 13, 2021, the Company completed the sale of its Flowform Products business for $55 million. Located in Billerica, MA, this operation uses flowforming process technologies to produce thin-walled components in net or near-net shapes across multiple alloy systems for use in the aerospace & defense and energy markets. The Company received cash proceeds, net of transaction costs and working capital adjustments, of $53.1 million on the sale of this business during the year ended December 31, 2021, which is reported as an investing activity on the consolidated statement of cash flows. With $12.2 million of goodwill allocated to this operation from ATI’s Forged Products reporting unit, the Company recognized a $13.8 million pretax gain in 2021, which is recorded in other income/expense, net, on the consolidated statement of operations and is excluded from HPMC segment results. This business was historically reported as part of the HPMC segment through the date of sale. Flowform Products’ sales were $26 million in 2020.

Joint Ventures

Joint Ventures	12 Months Ended
	Dec. 31, 2022
Equity Method Investments and Joint Ventures [Abstract]
Joint Ventures	Joint VenturesThe financial results of majority-owned joint ventures are consolidated into the Company’s operating results and financial position, with the minority ownership interest recognized in the consolidated statement of operations as net income attributable to noncontrolling interests, and as equity attributable to the noncontrolling interests within total stockholders’ equity. Investments in which the Company exercises significant influence, but which it does not control (generally a 20% to 50% ownership interest) are accounted for under the equity method of accounting. Stockholders’ equity includes undistributed earnings of investees accounted for under the equity method of accounting of approximately $7.8 million at December 31, 2022. Majority-Owned Joint Ventures STAL: The Company has a 60% interest in the Chinese joint venture known as STAL. The remaining 40% interest in STAL is owned by China Baowu Steel Group Corporation Limited, a state authorized investment company whose equity securities are publicly traded in the People’s Republic of China. STAL is part of ATI’s AA&S segment, and manufactures Precision Rolled Strip ® (PRS) stainless products mainly for the electronics and automotive markets located in Asia. Cash and cash equivalents held by STAL as of December 31, 2022 were $53.5 million. Next Gen Alloys LLC: The Company has a 51% interest in Next Gen Alloys LLC, a joint venture with GE Aviation for the development of a new meltless titanium alloy powder manufacturing technology. Next Gen Alloys LLC funds its development activities through the sale of shares to the two joint venture partners, and in the first quarter of 2022 the Company received $0.9 million from sales of noncontrolling interests to its joint venture partner, which is reported as a financing activity on the consolidated statements of cash flows. Cash and cash equivalents held by this joint venture as of December 31, 2022 were $1.2 million. Equity Method Joint Ventures A&T Stainless: The Company has a 50% interest in A&T Stainless, a joint venture with an affiliate company of Tsingshan Group (Tsingshan) to produce 60-inch wide stainless sheet products for sale in North America. Tsingshan purchased its 50% joint venture interest in A&T Stainless in 2018 for $17.5 million, of which $12.0 million had been received by ATI through December 31, 2021. ATI received the remaining $5.5 million from Tsingshan in the fourth quarter of 2022, which is reported as a financing activity on the consolidated statement of cash flows. The A&T Stainless operations included the Company’s previously-idled direct roll and pickle (DRAP) facility in Midland, PA. ATI provided hot-rolling conversion services to A&T Stainless using the AA&S segment’s Hot-Rolling and Processing Facility. ATI accounts for the A&T Stainless joint venture under the equity method of accounting. In late March 2018, ATI filed for an exclusion from the Section 232 tariffs on behalf of A&T Stainless, which imported semi- finished stainless slab products from Indonesia. In April 2019, the Company learned that this exclusion request was denied by the U.S. Department of Commerce. ATI filed new requests on behalf of A&T Stainless for exclusion from the Section 232 tariffs in October 2019. These requests were denied by the U.S. Department of Commerce in the second quarter of 2020, and the 25% tariff remains in place. Due to repeated tariff exclusion denials, the DRAP facility was idled in an orderly shut down process that was completed in 2020. A&T Stainless recorded a $4.8 million charge in 2020 for contractual termination benefits as a result of the idling decision, of which $1.8 million was reversed in 2022 as a result of revised estimates. In April 2022, ATI and A&T Stainless entered into a settlement agreement with the United States pursuant to which the United States, without admitting liability, agreed to refund a substantial portion of the Section 232 tariffs previously paid by A&T Stainless. As a result of the settlement agreement, A&T Stainless recorded tariff refunds and accrued interest of approximately $19.7 million, which was recognized as income by the joint venture in 2022. ATI’s share of the A&T Stainless results were income of $9.1 million for the fiscal year ended December 31, 2022, which included ATI’s $9.9 million share of the tariff refund and accrued interest, and losses of $0.9 million and $10.6 million for the fiscal years ended December 31, 2021 and 2020, respectively, which is included within other income/expense, net, on the consolidated statements of operations. AA&S segment results in 2022 include equity method recognition of A&T Stainless operating income of $8.2 million, and in 2021 and 2020 include operating losses of $0.9 million and $8.2 million, respectively. ATI’s share of the A&T Stainless credits/charges for termination benefits in 2022 and 2020 were excluded from AA&S segment results. As of December 31, 2022, ATI had net receivables from A&T Stainless for working capital advances and administrative services of $3.2 million, of which $0.4 million was reported in prepaid expenses and other current assets and $2.8 million in other long-term assets on the consolidated balance sheet. As of December 31, 2021, ATI had net receivables from A&T Stainless for working capital advances and administrative services of $2.9 million, of which $0.7 million was reported in prepaid expenses and other current assets and $2.2 million in other long-term assets on the consolidated balance sheet. Sales to A&T Stainless, which are included in ATI’s consolidated statement of operations for the 2020 fiscal year, were $18.4 million. There were no sales to A&T Stainless for the 2022 and 2021 fiscal years. Uniti: ATI has a 50% interest in the industrial titanium joint venture known as Uniti LLC (Uniti), with the remaining 50% interest held by VSMPO, a Russian producer of titanium, aluminum, and specialty steel products. Uniti is accounted for under the equity method of accounting. ATI’s share of Uniti’s income was $4.4 million in 2022, $1.0 million in 2021, and $1.2 million in 2020, which is included in AA&S segment’s operating results, and within other income/expense, net, on the consolidated statements of operations. Sales to Uniti, which are included in ATI’s consolidated statements of operations, were $45.0 million in 2022, $45.8 million in 2021, and $36.7 million in 2020. Accounts receivable from Uniti were $4.5 million and $6.1 million at December 31, 2022 and 2021, respectively. On March 9, 2022, the Company announced the termination of Uniti, LLC. The joint venture is expected to be dissolved in early 2023. No impairments were recorded as a result of the decision to terminate the Uniti joint venture.

Asset Retirement Obligations

Asset Retirement Obligations	12 Months Ended
	Dec. 31, 2022
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligation	Asset Retirement Obligations The Company maintains reserves where a legal obligation exists to perform an asset retirement activity and the fair value of the liability can be reasonably estimated. These asset retirement obligations (AROs) include liabilities where the timing and (or) method of settlement may be conditional on a future event, that may or may not be within the control of the entity. At December 31, 2022, the Company had recognized AROs of $17.8 million related to landfill closures, decommissioning costs, facility leases and conditional AROs associated with manufacturing activities using what may be characterized as potentially hazardous materials. Estimates of AROs are evaluated annually in the fourth quarter, or more frequently if material new information becomes known. Accounting for asset retirement obligations requires significant estimation and in certain cases, the Company has determined that an ARO exists, but the amount of the obligation is not reasonably estimable. The Company may determine that additional AROs are required to be recognized as new information becomes available. Changes in asset retirement obligations for the years ended December 31, 2022 and 2021 were as follows: (In millions) 2022 2021 Balance at beginning of year $ 19.0 $ 24.0 Accretion expense 0.8 0.8 Payments (2.0) (5.6) Divestiture — (0.2) Balance at end of year $ 17.8 $ 19.0

Supplemental Financial Statemen

Supplemental Financial Statement Information	12 Months Ended
	Dec. 31, 2022
Additional Financial Information Disclosure [Abstract]
Supplemental Financial Statement Information	Supplemental Financial Statement Information Cash and cash equivalents at December 31, 2022 and 2021 were as follows: (In millions) 2022 2021 Cash $ 164.9 $ 222.8 Other short-term investments 419.1 464.9 Total cash and cash equivalents $ 584.0 $ 687.7 Other current liabilities included salaries, wages and other employee-related liabilities of $100.8 million and $92.7 million, and accrued interest of $11.8 million and $15.2 million at December 31, 2022 and 2021, respectively. Other income (expense) for the years ended December 31, 2022, 2021, and 2020 was as follows: (in millions) 2022 2021 2020 Rent, royalty income and other income $ 2.3 $ 1.1 $ 0.9 Gains from disposal of property, plant and equipment, net 0.2 2.9 2.9 Net equity income (loss) on joint ventures (See Note 7) 12.6 0.1 (7.0) Gain on sales of businesses, net (See Note 6) — 13.8 — Joint venture restructuring credit (charge) (See Note 7) 0.9 — (2.4) Adjustment to indemnification for conditional ARO costs — — 4.3 Litigation settlement (See Note 21) (28.5) — — Other — 0.3 0.1 Total other income (expense), net $ (12.5) $ 18.2 $ (1.2) Gains from disposal of property, plant and equipment, net for the year ended December 31, 2020 include $2.5 million on sales of certain oil and gas rights in Eddy County, NM. These cash gains are reported as an investing activity on the consolidated statement of cash flows for the year ended December 31, 2020, and are excluded from segment operating results. These oil and gas rights were initially acquired in 1972 along with land purchased by Teledyne, Inc., which later became part of ATI. The land was subsequently sold, with the Company retaining the underlying oil and gas rights that it sold in 2020. In 2020, the Company finalized a settlement agreement for an indemnity claim concerning a conditional ARO with the buyer of a formerly-owned business and as a result, the Company reduced ARO reserves by $4.3 million, which is recorded in other income/expense, net, on the consolidated statements of operations.

Debt

Debt	12 Months Ended
	Dec. 31, 2022
Debt Disclosure [Abstract]
Debt	Debt Debt at December 31, 2022 and 2021 was as follows: (In millions) 2022 2021 ATI Inc. 5.875% Senior Notes due 2027 350.0 350.0 ATI Inc. 5.125% Senior Notes due 2031 350.0 350.0 ATI Inc. 4.875% Notes due 2029 325.0 325.0 ATI Inc. 3.5% Convertible Senior Notes due 2025 291.4 291.4 ATI Inc. 4.75% Convertible Senior Notes due 2022 — 84.2 Allegheny Ludlum 6.95% Debentures due 2025 (a) 150.0 150.0 ABL Term Loan 200.0 200.0 U.S. revolving credit facility — — Foreign credit agreements 19.4 27.4 Finance leases and other 79.4 85.7 Debt issuance costs (17.2) (20.8) Total short-term and long-term debt 1,748.0 1,842.9 Short-term debt and current portion of long-term debt 41.7 131.3 Total long-term debt $ 1,706.3 $ 1,711.6 (a) The payment obligations of these debentures issued by Allegheny Ludlum, LLC are fully and unconditionally guaranteed by ATI. Interest expense was $92.1 million in 2022, $97.6 million in 2021, and $96.1 million in 2020. Interest expense was reduced by $5.1 million, $4.3 million, and $7.7 million, in 2022, 2021, and 2020, respectively, from interest capitalization on capital projects. Interest and commitment fees paid were $92.8 million in 2022, $97.5 million in 2021, and $95.4 million in 2020. Net interest expense includes interest income of $4.7 million in 2022, $0.7 million in 2021, and $1.7 million in 2020. Scheduled principal payments during the next five years are $41.7 million in 2023, $19.9 million in 2024, $457.8 million in 2025, $10.5 million in 2026, and $557.4 million in 2027. See Note 11, Leases, for the portion of these scheduled principal payments that are related to finance leases. Debt Extinguishment Charges In October 2021, ATI recognized a $65.5 million debt extinguishment charge on the redemption of its 5.875% Senior Notes due 2023 (2023 Notes), which included a $64.5 million cash make-whole payment related to the early extinguishment of the 2023 Notes as required by the applicable indenture, and a $1.0 million charge for deferred debt issue costs, as further discussed below. In June 2020, ATI recognized a $21.5 million debt extinguishment charge on the partial redemption of its 4.75% Convertible Senior Notes due 2022 (the 2022 Convertible Notes), which included a $19.1 million cash make-whole payment related to the early extinguishment of the 2022 Convertible Notes partial redemption, as required by the applicable indenture, and a $2.4 million charge for deferred debt issue costs, as further discussed below. 2029 and 2031 Notes On September 14, 2021, ATI issued $325 million aggregate principal amount of 4.875% Senior Notes due 2029 (2029 Notes) and $350 million aggregate principal amount of 5.125% Senior Notes due 2031 (2031 Notes). Interest on the 2029 Notes is payable semi-annually in arrears at a rate of 4.875% per year, and the 2029 Notes will mature on October 1, 2029. Interest on the 2031 Notes is payable semi-annually in arrears at a rate of 5.125% per year, and the 2031 Notes will mature on October 1, 2031. Total combined net proceeds of $665.7 million from both of these issuances were primarily used to fund the full redemption of the $500 million aggregate principal amount outstanding of the 2023 Notes on October 14, 2021, including a make-whole payment and accrued interest, resulting in a $65.5 million debt extinguishment charge. Underwriting fees and other third-party expenses for the issuance of the 2029 and 2031 Notes were $4.7 million each, and are being amortized to interest expense over the 8-year and 10-year terms of the 2029 and 2031 Notes, respectively. The 2029 and 2031 Notes are unsecured and unsubordinated obligations of the Company and equally ranked with all of its existing and future senior unsecured debt. The 2029 and 2031 Notes restrict the Company’s ability to create certain liens, to enter into sale leaseback transactions, guarantee indebtedness and to consolidate or merge all, or substantially all, of its assets. The Company has the option to redeem the 2029 and 2031 Notes, as a whole or in part, at any time or from time to time, on at least 15 days, but not more than 60 days, prior notice to the holders of the Notes at redemption prices specified in the 2029 and 2031 Notes. The 2029 and 2031 Notes are subject to repurchase upon the occurrence of a change in control repurchase event (as defined in the 2029 and 2031 Notes) at a repurchase price in cash equal to 101% of the aggregate principal amount of the Notes repurchased, plus any accrued and unpaid interest on the 2029 or 2031 Notes repurchased, as applicable. 2025 Convertible Notes In 2020, the Company issued $291.4 million aggregate principal amount of 3.5% Convertible Senior Notes due 2025 (2025 Convertible Notes). The Company used a portion of the net proceeds from the offering of the 2025 Convertible Notes to repurchase $203.2 million aggregate principal amount of its outstanding 2022 Convertible Notes, resulting in a $21.5 million debt extinguishment charge. The Company also used $19.4 million of the net proceeds of the offering of the 2025 Convertible Notes to pay the cost of capped call transactions, described below, which was recorded as a reduction to additional paid-in-capital in stockholders’ equity on the consolidated balance sheet. The remainder of the net proceeds from the offering were used for general corporate purposes. As of December 31, 2022 and 2021, the fair value of the 2025 Convertible Notes was $590 million and $379 million, respectively, based on the quoted market price, which is classified in Level 1 of the fair value hierarchy. The 2025 Convertible Notes have a 3.5% cash coupon rate that is payable semi-annually in arrears on each June 15 and December 15, commencing December 15, 2020. Including amortization of deferred issuance costs, the effective interest rate is 4.2% for the years ended December 31, 2022 and 2021 and 8.4% for the year ended December 31, 2020. The effective interest rate is lower in 2022 and 2021 due to the early-adoption of new accounting guidance on January 1, 2021, as described below. Remaining deferred issuance costs were $4.8 million and $6.5 million at December 31, 2022 and 2021, respectively. Interest expense on the 2025 Convertible Notes was as follows: Fiscal year ended December 31, (in millions) 2022 2021 2020 Contractual coupon rate $ 10.2 $ 10.2 $ 5.3 Amortization of debt issuance costs 1.8 1.7 0.7 Total interest expense $ 12.0 $ 11.9 $ 6.0 The Company does not have the right to redeem the 2025 Convertible Notes prior to June 15, 2023. On or after June 15, 2023 and prior to the 41st scheduled trading day immediately preceding the maturity date, the Company may redeem all or any portion of the 2025 Convertible Notes, at its option, at a redemption price equal to 100% of the principal amount thereof, plus any accrued and unpaid interest if the last reported sale price of ATI’s common stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading day period (including the last trading day of such period) ending on the trading day immediately preceding the date on which ATI provides written notice of redemption. The initial conversion rate for the 2025 Convertible Notes is 64.5745 shares of ATI common stock per $1,000 principal amount of the 2025 Convertible Notes, equivalent to an initial conversion price of approximately $15.49 per share (18.8 million shares). Prior to the close of business on the business day immediately preceding March 15, 2025, the 2025 Convertible Notes will be convertible at the option of the holders of 2025 Convertible Notes only upon the satisfaction of specified conditions and during certain periods. Thereafter, until the close of business on the second scheduled trading day immediately preceding the maturity date, the 2025 Convertible Notes will be convertible at the option of holders of 2025 Convertible Notes at any time regardless of these conditions. Conversions of the 2025 Convertible Notes may be settled in cash, shares of ATI’s common stock or a combination thereof, at ATI’s election. As a result of this flexible settlement feature of the 2025 Convertible Notes, the embedded conversion option was required to be separately accounted for as a component of stockholders’ equity. The value of the embedded conversion option was determined to be $51.4 million based on the estimated fair value of comparable senior unsecured debt without the conversion feature, using an income approach of expected present value. During the 2020 fiscal year, the equity component was amortized as additional non-cash interest expense, commonly referred to as phantom yield, over the term of the 2025 Convertible Notes using the effective interest method. As a result, as of December 31, 2020, $49.8 million of the 2025 Convertible Notes was recorded in additional paid-in-capital in stockholders’ equity ($51.4 million of the gross $291.4 million net of $1.6 million of allocated offering costs). Due to the non-cash phantom yield and including debt issue cost amortization, the 2025 Convertible Notes had reported interest expense in 2020 at an 8.4% rate, higher than the 3.5% cash coupon rate. Effective January 1, 2021, ATI early-adopted new accounting guidance as discussed in Note 1 that eliminated the equity component classification of the embedded conversion option, as well as the phantom yield portion of interest expense on a prospective basis. Upon adoption on January 1, 2021, long-term debt increased by $45.4 million representing the $46.8 million equity component of convertible debt as of December 31, 2020, net of reclassified debt issue costs. Holders of the 2025 Convertible Notes may require ATI to repurchase their 2025 Convertible Notes upon the occurrence of certain events that constitute a fundamental change under the indenture governing the 2025 Convertible Notes at a purchase price equal to 100% of the principal amount thereof, plus any accrued and unpaid interest to, but excluding, the fundamental change repurchase date. In connection with certain corporate events or if ATI issues a notice of redemption, it will, under certain circumstances, increase the conversion rate for holders who elect to convert their 2025 Convertible Notes in connection with such corporate event or during the relevant redemption period. In connection with the pricing of the 2025 Convertible Notes, ATI entered into privately negotiated capped call transactions with certain of the initial purchasers or their respective affiliates. The capped call transactions are expected generally to reduce potential dilution to ATI’s common stock upon any conversion of the 2025 Convertible Notes and/or offset any cash payments ATI is required to make in excess of the principal amount of converted 2025 Convertible Notes, as the case may be, with such reduction and/or offset subject to a cap based on the cap price. The cap price of the capped call transactions initially is approximately $19.76 per share, and is subject to adjustments under the terms of the capped call transactions. 2022 Convertible Notes In 2022, $82.5 million of the 2022 Convertible Senior Notes were converted into 5.7 million shares of ATI common stock, with the remaining $1.7 million of outstanding principal balance paid in cash for notes that were not converted at the July 1, 2022 maturity date. The conversion rate for the 2022 Convertible Notes was 69.2042 shares of ATI common stock per $1,000 principal amount of the 2022 Convertible Notes, equivalent to a conversion price of $14.45 per share. As of December 31, 2021, the fair value of the 2022 Convertible Notes was $102 million based on the quoted market price, which is classified in Level 1 of the fair value hierarchy. Interest on the 2022 Convertible Notes at the 4.75% cash coupon rate was payable semi-annually in arrears on each January 1 and July 1. Including amortization of deferred issuance costs, the effective interest rate was 5.4% for the fiscal years ended December 31, 2022, 2021 and 2020. Remaining deferred issuance costs were $0.3 million at December 31, 2021. Interest expense on the 2022 Convertible Notes was as follows: Fiscal year ended December 31, (in millions) 2022 2021 2020 Contractual coupon rate $ 2.0 $ 4.0 $ 8.6 Amortization of debt issuance costs 0.3 0.5 1.0 Total interest expense $ 2.3 $ 4.5 $ 9.6 2023 Notes The 5.875% stated interest rate payable on the 2023 Notes was subject to adjustment in the event of changes in the credit ratings on the 2023 Notes by either Moody’s or Standard & Poor’s. Each notch of credit rating downgrade from the credit ratings in effect when the 2023 Notes were issued in July 2013 increased interest expense by 0.25% on the 2023 Notes, up to a maximum 4 notches by each of the two rating agencies, or a total 2.0% potential interest rate change up to 7.875%. The annual interest rate on the 2023 Notes was at the maximum 7.875% from February 2016 until their redemption in October 2021 as discussed above. Credit Agreements On September 9, 2022, the Company amended and restated its Asset Based Lending (ABL) Credit Facility, which is collateralized by the accounts receivable and inventory of the Company’s operations. As amended, the ABL facility also provides the Company with the option of including certain machinery and equipment as additional collateral for purposes of determining availability under the facility. This amendment and restatement extended the ABL facility through September 2027 and includes an increase of $100 million in the revolving credit facility, to $600 million. The ABL continues to include a letter of credit sub-facility of up to $200 million, a $200 million term loan (ABL Term Loan), and a swing loan facility of up to $60 million. The ABL Term Loan can be prepaid in increments of $25 million if certain minimum liquidity conditions are satisfied. In addition, as amended, the Company has the right to request an increase of up to $300 million in the maximum amount available under the revolving credit facility for the duration of the ABL. The Company has a $50 million floating-for-fixed interest rate swap which converts a portion of the ABL Term Loan to a 4.21% fixed interest rate. The swap matures in June 2024. The ABL, as amended, has interest rates that are consistent with the previous facility, replacing LIBOR with Secured Overnight Financing Rate (SOFR) plus an applicable SOFR adjustment. The ABL Term Loan, as amended, has an interest rate of 2.0% above adjusted SOFR. As amended, the applicable interest rate for revolving credit borrowings under the ABL facility includes interest rate spreads based on available borrowing capacity that range between 1.25% and 1.75% for SOFR-based borrowings and between 0.25% and 0.75% for base rate borrowings. The ABL facility contains a financial covenant whereby the Company must maintain a fixed charge coverage ratio of not less than 1.00:1.00 after an event of default has occurred and is continuing or if the undrawn availability under the ABL revolving credit portion of the facility is less than the greater of (i) 10% of the then applicable maximum loan amount under the revolving credit portion of the ABL and the outstanding ABL Term Loan balance, or (ii) $60.0 million. The Company was in compliance with the fixed charge coverage ratio as of December 31, 2022. Additionally, the Company must demonstrate minimum liquidity specified by the facility during the 90-day period immediately preceding the stated maturity date of its 3.5% Convertible Senior Notes due 2025 and the 6.95% Debentures due 2025 issued by the Company’s wholly owned subsidiary, Allegheny Ludlum LLC. Costs associated with entering into the ABL amendment were $2.4 million, and are being amortized to interest expense over the extended term of the facility ending September 2027, along with $1.7 million of unamortized deferred costs previously recorded for the ABL. The ABL, as amended, also contains customary affirmative and negative covenants for credit facilities of this type, including limitations on the Company’s ability to incur additional indebtedness or liens or to enter into investments, mergers and acquisitions, dispositions of assets and transactions with affiliates, some of which are more restrictive, at any time during the term of the ABL when the Company’s fixed charge coverage ratio is less than 1.00:1.00 and its undrawn availability under the revolving portion of the ABL is less than the greater of (a) $120 million or (b) 20% of the sum of the maximum loan amount under the revolving credit portion of the ABL and the outstanding ABL Term Loan balance. As of December 31, 2022, there were no outstanding borrowings under the revolving portion of the ABL, and $39.8 million was utilized to support the issuance of letters of credit. There were no revolving credit borrowings under the ABL during 2022 or 2021. The Company also has foreign credit facilities, primarily in China, that total $60 million based on December 31, 2022 foreign exchange rates, under which $19.4 million and $27.4 million was drawn as of December 31, 2022 and 2021, respectively. The Company has no off-balance sheet financing relationships as defined in Item 303(a)(4) of SEC Regulation S-K, with variable interest entities, structured finance entities, or any other unconsolidated entities. At December 31, 2022, the Company had not guaranteed any third-party indebtedness.

Leases (Notes)

Leases (Notes)	12 Months Ended
	Dec. 31, 2022
Leases [Abstract]
Leases	Leases The following represents the components of lease cost and other information for both operating and financing leases for the years ending December 31, 2022, 2021 and 2020: ($ in millions) Year ended December 31, 2022 December 31, 2021 December 31, 2020 Lease Cost Finance Lease Cost: Amortization of right of use asset $ 8.9 $ 7.1 $ 3.5 Interest on lease liabilities 4.1 3.1 1.0 Operating lease cost 16.4 22.7 20.8 Short-term lease cost 2.9 1.6 1.9 Variable lease cost 1.0 0.9 0.9 Sublease income — (0.3) (0.1) Total lease cost $ 33.3 $ 35.1 $ 28.0 Other information Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from finance leases $ 4.1 $ 3.0 $ 1.0 Operating cash flows from operating leases $ 17.4 $ 20.0 $ 21.7 Financing cash flows from finance leases $ 20.9 $ 14.3 $ 6.2 Right of use assets obtained in exchange for new finance lease liabilities $ 15.3 $ 58.9 $ 42.3 Right of use assets obtained in exchange for new operating lease liabilities $ 18.0 $ 4.8 $ 12.4 Weighted average remaining lease term - finance leases 4 years 5 years 4 years Weighted average remaining lease term - operating leases 6 years 5 years 6 years Weighted average discount rate - finance leases 5.6 % 5.2 % 6.2 % Weighted average discount rate - operating leases 6.8 % 6.5 % 6.9 % The following table reconciles future minimum undiscounted rental commitments for operating leases to the operating lease liabilities recorded on the consolidated balance sheet as of December 31, 2022 (in millions): December 31, 2022 2023 $ 15.5 2024 12.7 2025 10.3 2026 8.0 2027 6.6 2028 and thereafter 16.5 Total undiscounted lease payments $ 69.6 Present value adjustment (14.4) Operating lease liabilities $ 55.2 The following table reconciles future minimum undiscounted rental commitments for finance leases to the finance lease liabilities recorded on the consolidated balance sheet as of December 31, 2022 (in millions): December 31, 2022 2023 $ 26.2 2024 22.4 2025 17.9 2026 11.0 2027 7.8 2028 and thereafter 3.0 Total undiscounted lease payments $ 88.3 Present value adjustment (9.5) Finance lease liabilities $ 78.8
Leases	Leases The following represents the components of lease cost and other information for both operating and financing leases for the years ending December 31, 2022, 2021 and 2020: ($ in millions) Year ended December 31, 2022 December 31, 2021 December 31, 2020 Lease Cost Finance Lease Cost: Amortization of right of use asset $ 8.9 $ 7.1 $ 3.5 Interest on lease liabilities 4.1 3.1 1.0 Operating lease cost 16.4 22.7 20.8 Short-term lease cost 2.9 1.6 1.9 Variable lease cost 1.0 0.9 0.9 Sublease income — (0.3) (0.1) Total lease cost $ 33.3 $ 35.1 $ 28.0 Other information Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from finance leases $ 4.1 $ 3.0 $ 1.0 Operating cash flows from operating leases $ 17.4 $ 20.0 $ 21.7 Financing cash flows from finance leases $ 20.9 $ 14.3 $ 6.2 Right of use assets obtained in exchange for new finance lease liabilities $ 15.3 $ 58.9 $ 42.3 Right of use assets obtained in exchange for new operating lease liabilities $ 18.0 $ 4.8 $ 12.4 Weighted average remaining lease term - finance leases 4 years 5 years 4 years Weighted average remaining lease term - operating leases 6 years 5 years 6 years Weighted average discount rate - finance leases 5.6 % 5.2 % 6.2 % Weighted average discount rate - operating leases 6.8 % 6.5 % 6.9 % The following table reconciles future minimum undiscounted rental commitments for operating leases to the operating lease liabilities recorded on the consolidated balance sheet as of December 31, 2022 (in millions): December 31, 2022 2023 $ 15.5 2024 12.7 2025 10.3 2026 8.0 2027 6.6 2028 and thereafter 16.5 Total undiscounted lease payments $ 69.6 Present value adjustment (14.4) Operating lease liabilities $ 55.2 The following table reconciles future minimum undiscounted rental commitments for finance leases to the finance lease liabilities recorded on the consolidated balance sheet as of December 31, 2022 (in millions): December 31, 2022 2023 $ 26.2 2024 22.4 2025 17.9 2026 11.0 2027 7.8 2028 and thereafter 3.0 Total undiscounted lease payments $ 88.3 Present value adjustment (9.5) Finance lease liabilities $ 78.8

Derivative Financial Instrument

Derivative Financial Instruments and Hedging	12 Months Ended
	Dec. 31, 2022
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments and Hedging	Derivative Financial Instruments and Hedging As part of its risk management strategy, the Company, from time-to-time, utilizes derivative financial instruments to manage its exposure to changes in raw material prices, energy costs, foreign currencies, and interest rates. In accordance with applicable accounting standards, the Company accounts for most of these contracts as hedges. The Company sometimes uses futures and swap contracts to manage exposure to changes in prices for forecasted purchases of raw materials, such as nickel, and natural gas. Under these contracts, which are generally accounted for as cash flow hedges, the price of the item being hedged is fixed at the time that the contract is entered into and the Company is obligated to make or receive a payment equal to the net change between this fixed price and the market price at the date the contract matures. The majority of ATI’s products are sold utilizing raw material surcharges and index mechanisms. However, as of December 31, 2022, the Company had entered into financial hedging arrangements primarily at the request of its customers, related to firm orders, for an aggregate notional amount of approximately 6 million pounds of nickel with hedge dates through 2024. The aggregate notional amount hedged is approximately 8% of a single year’s estimated nickel raw material purchase requirements. These derivative instruments are used to hedge the variability of a selling price that is based on the London Metals Exchange (LME) index for nickel, as well as to hedge the variability of the purchase cost of nickel based on this LME index. Any gain or loss associated with these hedging arrangements is included in sales or cost of sales, depending on whether the underlying risk being hedged was the variable selling price or the variable raw material cost, respectively. At December 31, 2022, the outstanding financial derivatives used to hedge the Company’s exposure to energy cost volatility included natural gas cost hedges. At December 31, 2022, the company hedged approximately 70% of the Company’s annual forecasted domestic requirements for natural gas for 2023 and approximately 25% for 2024. While the majority of the Company’s direct export sales are transacted in U.S. dollars, foreign currency exchange contracts are used, from time-to-time, to limit transactional exposure to changes in currency exchange rates for those transactions denominated in a non-U.S. currency. The Company sometimes purchases foreign currency forward contracts that permit it to sell specified amounts of foreign currencies expected to be received from its export sales for pre-established U.S. dollar amounts at specified dates. The forward contracts are denominated in the same foreign currencies in which export sales are denominated. These contracts are designated as hedges of the variability in cash flows of a portion of the forecasted future export sales transactions which otherwise would expose the Company to foreign currency risk, primarily euros. In addition, the Company may also hedge forecasted capital expenditures and designate cash balances held in foreign currencies as hedges of forecasted foreign currency transactions. At December 31, 2022, the Company had no significant outstanding foreign currency forward contracts. The Company may enter into derivative interest rate contracts to maintain a reasonable balance between fixed- and floating-rate debt. The Company has a $50 million floating-for-fixed interest rate swap that matures in June 2024 which converts half of the ABL Term Loan to a 4.21% fixed rate. The Company designated the interest rate swap as a cash flow hedge of the Company’s exposure to the variability of the payment of interest on a portion of its ABL Term Loan borrowings. The ineffective portion at hedge inception, determined from the fair value of the swap immediately prior to amendment in July 2019, was amortized to interest expense over the initial ABL Term Loan swap maturity date of January 12, 2021. There are no credit risk-related contingent features in the Company’s derivative contracts, and the contracts contained no provisions under which the Company has posted, or would be required to post, collateral. The counterparties to the Company’s derivative contracts were substantial and creditworthy commercial banks that are recognized market makers. The Company controls its credit exposure by diversifying across multiple counterparties and by monitoring credit ratings and credit default swap spreads of its counterparties. The Company also enters into master netting agreements with counterparties when possible. The fair values of the Company’s derivative financial instruments are presented below, representing the gross amounts recognized which are not offset by counterparty or by type of item hedged. All fair values for these derivatives were measured using Level 2 information as defined by the accounting standard hierarchy, which includes quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and inputs derived principally from or corroborated by observable market data. (In millions) December 31, December 31, Asset derivatives Balance sheet location Derivatives designated as hedging instruments: Interest rate swap Prepaid expenses and other current assets $ 1.4 $ — Natural gas contracts Prepaid expenses and other current assets 2.4 2.0 Nickel and other raw material contracts Prepaid expenses and other current assets 12.5 5.0 Interest rate swap Other assets 0.5 — Natural gas contracts Other assets 0.7 0.5 Nickel and other raw material contracts Other assets 0.5 0.1 Total derivatives designated as hedging instruments 18.0 7.6 Total asset derivatives $ 18.0 $ 7.6 Liability derivatives Balance sheet location Derivatives designated as hedging instruments: Interest rate swap Other current liabilities $ — $ 0.9 Natural gas contracts Other current liabilities 2.0 0.7 Nickel and other raw material contracts Other current liabilities 2.1 0.2 Interest rate swap Other long-term liabilities — 0.7 Natural gas contracts Other long-term liabilities 0.5 0.2 Total derivatives designated as hedging instruments 4.6 2.7 Total liability derivatives $ 4.6 $ 2.7 Assuming market prices remain constant with those at December 31, 2022, a pre-tax gain of $12.2 million is expected to be recognized over the next 12 months. For derivative financial instruments that are designated as cash flow hedges, the gain or loss on the derivative is reported as a component of other comprehensive income (OCI) and reclassified into earnings in the same period or periods during which the hedged item affects earnings. For derivative financial instruments that are designated as fair value hedges, changes in the fair value of these derivatives are recognized in current period results and are reported as changes within accrued liabilities and other on the consolidated statements of cash flows. There were no outstanding fair value hedges as of December 31, 2022 or 2021. The Company did not use net investment hedges for the periods presented. The effects of derivative instruments in the tables below are presented net of related income taxes, excluding any impacts of changes to income tax valuation allowances affecting results of operations or other comprehensive income, when applicable. Activity with regard to derivatives designated as cash flow hedges for the years ended December 31, 2022 and 2021 were as follows (in millions): Derivatives in Cash Flow Hedging Relationships Amount of Gain (Loss) Amount of Gain (Loss) 2022 2021 2022 2021 Nickel and other raw material contracts $ 27.1 $ 6.2 $ 20.5 $ 5.4 Natural gas contracts 10.9 5.2 11.5 4.0 Foreign exchange contracts 0.7 0.2 0.7 0.1 Interest rate swap 2.3 0.1 (0.1) (0.8) Total $ 41.0 $ 11.7 $ 32.6 $ 8.7 (a) The gains (losses) reclassified from accumulated OCI into income related to the derivatives, with the exception of the interest rate swap, are presented in sales and cost of sales in the same period or periods in which the hedged item affects earnings. The gains (losses) reclassified from accumulated OCI into income on the interest rate swap are presented in interest expense in the same period as the interest expense on the ABL Term Loan is recognized in earnings. The disclosures of gains or losses presented above for nickel and other raw material contracts and foreign currency contracts do not take into account the anticipated underlying transactions. Since these derivative contracts represent hedges, the net effect of any gain or loss on results of operations may be fully or partially offset.

Fair Value Of Financial Instrum

Fair Value Of Financial Instruments	12 Months Ended
	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Fair Value Of Financial Instruments	Fair Value of Financial Instruments The estimated fair value of financial instruments at December 31, 2022 was as follows: Fair Value Measurements at Reporting Date Using (In millions) Total Total Quoted Prices in Significant Cash and cash equivalents $ 584.0 $ 584.0 $ 584.0 $ — Derivative financial instruments: Assets 18.0 18.0 — 18.0 Liabilities 4.6 4.6 — 4.6 Debt (a) 1,765.2 1,964.5 1,665.7 298.8 The estimated fair value of financial instruments at December 31, 2021 was as follows: Fair Value Measurements at Reporting Date Using (In millions) Total Total Quoted Prices in Significant Cash and cash equivalents $ 687.7 $ 687.7 $ 687.7 $ — Derivative financial instruments: Assets 7.6 7.6 — 7.6 Liabilities 2.7 2.7 — 2.7 Debt (a) 1,863.7 2,003.2 1,690.1 313.1 (a) The total carrying amount for debt excludes debt issuance costs related to the recognized debt liability which is presented in the consolidated balance sheets as a direct reduction from the carrying amount of the debt liability. In accordance with accounting standards, fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date. Accounting standards established three levels of a fair value hierarchy that prioritizes the inputs used to measure fair value. This hierarchy requires entities to maximize the use of observable inputs and minimize the use of unobservable inputs. The three levels of inputs used to measure fair value are as follows: Level 1 – Quoted prices in active markets for identical assets or liabilities. Level 2 – Observable inputs other than quoted prices included in Level 1, such as quoted prices for similar assets and liabilities in active markets; quoted prices for identical or similar assets and liabilities in markets that are not active; or other inputs that are observable or can be corroborated by observable market data. Level 3 – Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets and liabilities. This includes certain pricing models, discounted cash flow methodologies and similar techniques that use significant unobservable inputs. The availability of observable market data is monitored to assess the appropriate classification of financial instruments within the fair value hierarchy. Changes in economic conditions or model-based valuation techniques may require the transfer of financial instruments from one fair value level to another. In such instances, the transfer is reported at the beginning of the reporting period. The following methods and assumptions were used by the Company in estimating the fair value of its financial instruments: Cash and cash equivalents: Fair values were determined using Level 1 information. Derivative financial instruments: Fair values for derivatives were measured using exchange-traded prices for the hedged items. The fair value was determined using Level 2 information, including consideration of counterparty risk and the Company’s credit risk. Short-term and long-term debt: The fair values of the 2022 Convertible Notes (prior to conversion in the second quarter of 2022), the 2025 Convertible Notes, the Allegheny Ludlum 6.95% Debentures due 2025, the 2027 Notes, the 2029 Notes and the 2031 Notes were determined using Level 1 information. The fair values of other short-term and long-term debt were determined using Level 2 information.

Retirement Benefits

Retirement Benefits	12 Months Ended
	Dec. 31, 2022
Retirement Benefits [Abstract]
Retirement Benefits	Retirement Benefits The Company has defined contribution retirement plans or defined benefit pension plans covering substantially all employees. Company contributions to defined contribution retirement plans are generally based on a percentage of eligible pay or based on hours worked. Benefits under the defined benefit pension plans are generally based on years of service and/or final average pay. The Company also sponsors several postretirement plans covering certain collectively-bargained salaried and hourly employees. The plans provide health care and life insurance benefits for eligible retirees. In most retiree health care plans, Company contributions towards premiums are capped based on the cost as of a certain date, thereby creating a defined contribution. ATI instituted several initiatives over a multi-year period as part of its retirement benefit liability reduction strategy. Future benefit accruals for all participants in the U.S. defined benefit pension plans other than those subject to a CBA were frozen at the end of 2014, and subsequently CBAs were negotiated to close these plans to new entrants. As a result of these actions, the Company has now completely closed all defined benefit pension plans to new entrants, and has substantially limited the number of employees still accruing benefit service to less than 900 participants, or approximately 7% of the population in the U.S. qualified defined benefit pension plans. Additionally, all of ATI’s remaining collectively-bargained, capped defined benefit retiree health care plans are closed to new entrants. These liability management actions have transitioned ATI’s retirement benefit and other postretirement benefit programs largely to a defined contribution structure. Since 2013, five annuity buyouts of retired participants and two voluntary cash out programs of deferred participants during this period have helped to reduce the total participants in ATI’s U.S. qualified defined benefit pension plans by more than 60%. Costs for defined contribution retirement plans were $31.1 million in 2022, $20.4 million in 2021, and $29.9 million in 2020. Company contributions to these defined contribution plans are funded with cash. From June 1, 2020 in response to the economic challenges created by the COVID-19 pandemic, the Company reduced its qualified non-elective contribution percentage and suspended all Company match contributions for salaried participants in the ATI 401(k) Savings Plan, and deferred the funding of Company contributions to this plan, until mid-2021. In 2022, the Company implemented certain plan design changes to the ATI 401(k) Savings Plan which decreased the qualified non-elective contribution percentage and increased the Company match contribution percentage. Other postretirement benefit costs for a defined contribution plan under the terms of a CBA were $1.0 million and $0.7 million for the years ended December 31, 2022 and 2020, respectively. There were no costs for this plan in 2021. The components of pension and other postretirement benefit expense for the Company’s defined benefit plans included the following: Pension Benefits Other Postretirement Benefits (In millions) 2022 2021 2020 2022 2021 2020 Service cost—benefits earned during the year $ 11.9 $ 15.1 $ 12.7 $ 1.1 $ 1.5 $ 2.3 Interest cost on benefits earned in prior years 69.7 68.4 86.3 7.7 8.0 10.7 Expected return on plan assets (128.2) (136.4) (134.5) — — — Amortization of prior service cost (credit) 0.4 0.6 0.7 (0.9) (2.4) (3.8) Amortization of net actuarial loss 63.5 75.6 74.5 13.2 13.9 10.8 Settlement loss (gain) 29.5 — — — (64.9) — Curtailment gain — — — — — (0.2) Termination benefits — — 10.9 — — 6.7 Total retirement benefit expense (income) $ 46.8 $ 23.3 $ 50.6 $ 21.1 $ (43.9) $ 26.5 On May 12, 2022, the Company completed the sale of its Sheffield, UK operations (see Note 6). As a result of this sale, ATI recognized a $29.5 million settlement loss, which is recorded in loss on asset sales and sales of businesses, net, on the consolidated statement of operations, related to the amount in accumulated other comprehensive loss for the UK defined benefit pension plan that transferred as part of the sale. Pension liabilities and assets for this UK defined benefit pension plan that were removed as a result of this divestiture are included below in the tables of changes in benefit obligations and changes in plan assets, respectively. On July 14, 2021, ATI announced that a new four-year labor agreement with the USW was ratified (see Note 1 for further discussion). As a result of this new CBA, ATI recognized a $64.9 million pretax settlement gain, which is recorded in nonoperating retirement benefit income/expense on the consolidated statement of operations, related to a plan termination that eliminated certain postretirement medical benefit liabilities, comprised of $43.0 million of long-term postretirement benefit liabilities as of July 2021 and $21.9 million of amounts recorded in accumulated other comprehensive income at that date. Discrete tax effects related to this event were $15.5 million of income tax expense (see Note 17 for further discussion). In 2020, the Company recorded a $17.4 million termination benefits charge for pension and postretirement medical obligations, net of a $0.2 million curtailment gain, related to facility closures in the AA&S segment resulting from the Company’s strategic shift to exit lower-margin standard stainless products. See Note 19 for further explanation. Actuarial assumptions used to develop the components of defined benefit pension expense and other postretirement benefit expense were as follows: Pension Benefits Other Postretirement Benefits 2022 2021 2020 2022 2021 2020 Discount rate 2.95 % 2.60 % 3.40 % 2.80 % 2.45 % 3.25 % Rate of increase in future compensation levels 2.00% - 3.00% 1.00 % 1.00 % — — — Weighted average expected long-term rate of return on assets 6.43 % 6.71 % 7.16 % — % — % — % Actuarial assumptions used for the valuation of defined benefit pension and other postretirement benefit obligations at the end of the respective periods were as follows: Pension Benefits Other Postretirement Benefits 2022 2021 2022 2021 Discount rate 5.55 % 2.95 % 5.45 % 2.80 % Rate of increase in future compensation levels 3.00 % 2.00% - 3.00% — — A reconciliation of the funded status for the Company’s defined benefit pension and other postretirement benefit plans at December 31, 2022 and 2021 was as follows: Pension Benefits Other Postretirement Benefits (In millions) 2022 2021 2022 2021 Change in benefit obligations: Benefit obligation at beginning of year $ 2,517.0 $ 2,720.1 $ 287.3 $ 357.6 Service cost 11.9 15.1 1.1 1.5 Interest cost 69.7 68.4 7.7 8.0 Benefits paid (155.6) (235.0) (29.7) (28.9) Subsidy received — — 0.3 0.4 Divestiture (75.8) — — — Effect of currency rates (3.2) (1.3) — — Net actuarial (gains) losses – discount rate change (556.8) (104.0) (48.2) (9.0) – other 11.1 53.7 (5.8) 0.7 Settlement gain — — — (43.0) Benefit obligation at end of year $ 1,818.3 $ 2,517.0 $ 212.7 $ 287.3 Actuarial effects of changes in discount rates are separately identified in the preceding table. Net actuarial (gains) losses – other for 2021 is primarily comprised of revisions to estimates for mortality, termination rates, retirement rates, forms of benefit payment elected, and other demographic assumptions based on an updated study of plan experience. Pension Benefits Other Postretirement Benefits (In millions) 2022 2021 2022 2021 Change in plan assets: Fair value of plan assets at beginning of year $ 2,120.9 $ 2,046.4 $ — $ — Actual returns on plan assets and plan expenses (317.0) 233.8 — — Employer contributions 57.4 77.3 — — Divestiture (101.8) — — — Effect of currency rates (4.4) (1.6) — — Benefits paid (155.6) (235.0) — — Fair value of plan assets at end of year $ 1,599.5 $ 2,120.9 $ — $ — Pension benefit payments in 2021 include $70 million for the annuity buyout of smaller pension balances in a U.S. defined benefit pension plan. This action was part of ATI’s retirement benefit liability management strategy to reduce the overall size of the pension obligation and to lower administrative costs. Assets (liabilities) recognized in the consolidated balance sheets: Pension Benefits Other Postretirement Benefits 2022 2021 2022 2021 Noncurrent assets $ 12.5 $ 25.0 $ — $ — Current liabilities (5.7) (5.7) (27.8) (29.2) Noncurrent liabilities (225.6) (415.4) (184.9) (258.1) Total amount recognized $ (218.8) $ (396.1) $ (212.7) $ (287.3) Changes to accumulated other comprehensive loss related to pension and other postretirement benefit plans in 2022 and 2021 were as follows: Pension Benefits Other Postretirement Benefits (In millions) 2022 2021 2022 2021 Beginning of year accumulated other comprehensive loss $ (1,376.5) $ (1,600.3) $ (121.2) $ (119.1) Amortization of net actuarial loss 63.5 75.6 13.2 13.9 Amortization of prior service cost (credit) 0.4 0.6 (0.9) (2.4) Settlement loss (gain) 29.5 — — (21.9) Remeasurements 101.9 147.6 53.1 8.3 End of year accumulated other comprehensive loss $ (1,181.2) $ (1,376.5) $ (55.8) $ (121.2) Net change in accumulated other comprehensive loss $ 195.3 $ 223.8 $ 65.4 $ (2.1) Amounts included in accumulated other comprehensive loss at December 31, 2022 and 2021 were as follows: Pension Benefits Other Postretirement Benefits (In millions) 2022 2021 2022 2021 Prior service (cost) credit $ (8.8) $ (9.9) $ 2.5 $ 3.4 Net actuarial loss (1,172.4) (1,366.6) (58.3) (124.6) Accumulated other comprehensive loss (1,181.2) (1,376.5) (55.8) (121.2) Deferred tax effect 473.1 507.6 27.8 42.4 Accumulated other comprehensive loss, net of tax $ (708.1) $ (868.9) $ (28.0) $ (78.8) Amounts in accumulated other comprehensive loss presented above do not include any effects of deferred tax asset valuation allowances. See Note 15 for further discussion on deferred tax asset valuation allowances. Retirement benefit expense for 2023 for defined benefit plans is estimated to be approximately $74 million, comprised of $58 million for pension expense and $16 million of expense for other postretirement benefits. The net actuarial loss is recognized in the consolidated statement of operations using a corridor method. Because all of ATI’s pension plans are inactive, cumulative gains and losses in excess of 10% of the greater of the projected benefit obligation or the market value of plan assets are amortized over the expected average remaining future lifetime of participants, which is approximately 17 years on a weighted average basis. Prior service cost (credit) amortization is recognized in level amounts over the expected service of the active membership as of the amendment effective date. Amounts in accumulated other comprehensive loss that are expected to be recognized as components of net periodic benefit cost in 2023 are: (In millions) Pension Other Total Amortization of prior service cost (credit) $ 0.4 $ (0.9) $ (0.5) Amortization of net actuarial loss 57.7 6.0 63.7 Amortization of accumulated other comprehensive loss $ 58.1 $ 5.1 $ 63.2 The accumulated benefit obligation for all defined benefit pension plans was $1,716.8 million and $2,398.0 million at December 31, 2022 and 2021, respectively. Additional information for pension plans with accumulated benefit obligations and projected benefit obligations in excess of plan assets: Pension Benefits (In millions) 2022 2021 Projected benefit obligation $ 1,727.3 $ 2,417.0 Accumulated benefit obligation $ 1,716.8 $ 2,398.0 Fair value of plan assets $ 1,496.0 $ 1,995.9 Cash contributions to ATI’s U.S. qualified defined benefit pension plans were $50 million in 2022, $67 million in 2021 and $130 million in 2020. The Company funds the U.S. defined benefit pension plans in accordance with the Employee Retirement Income Security Act of 1974, as amended, and the Internal Revenue Code. As a result of the American Rescue Plan Act (ARPA) enacted in March 2021, the rules governing pension funding calculations changed, and minimum funding requirements were reduced. As a result of these ARPA changes, ATI’s prior contributions have generated a credit balance that may be utilized to offset future minimum required contributions. The Company has no required cash contributions to its U.S. qualified defined benefit pension plans in 2023, and made a voluntary cash contribution of approximately $50 million to these plans in early 2023. In addition, for 2023, the Company expects approximately $6 million of payments for U.S. nonqualified pension benefits. The following table summarizes expected benefit payments from the Company’s various pension and other postretirement defined benefit plans through 2032, and also includes estimated Medicare Part D subsidies projected to be received during this period based on currently available information. Pension benefit payments for the U.S. qualified defined benefit pension plans are made from pension plan assets. (In millions) Pension Other Medicare Part 2023 $ 157.5 $ 27.8 $ — 2024 155.0 26.0 — 2025 152.3 24.0 — 2026 149.6 22.1 — 2027 146.8 20.4 — 2028-2032 684.0 77.5 — The annual assumed rate of increase in the per capita cost of covered benefits (the health care cost trend rate) for health care plans was 7.8% in 2023 and is assumed to gradually decrease to 4.0% in the year 2048 and remain at that level thereafter. Assumed health care cost trend rates can have a significant effect on the amounts reported for the health care plans, however, the Company’s contributions for most of its retiree health plans are capped based on a fixed premium amount, which limits the impact of future health care cost increases. The fair values of the Company’s pension plan assets are determined using net asset value (NAV) as a practical expedient, or by information categorized in the fair value hierarchy level based on the inputs used to determine fair value, as further discussed in Note 13. The fair values at December 31, 2022 were as follows: (In millions) Quoted Prices in Significant Significant Asset category Total NAV (Level 1) (Level 2) (Level 3) Equity securities: U.S. equities $ 363.1 $ 202.6 $ 160.5 $ — $ — International equities 299.7 284.8 14.9 — — Fixed income and cash equivalents 455.4 330.8 13.8 110.8 — Private equity 224.3 224.3 — — — Alternative investments- hedge funds, real estate and other 257.0 257.0 — — — Total assets $ 1,599.5 $ 1,299.5 $ 189.2 $ 110.8 $ — The fair values of the Company’s pension plan assets at December 31, 2021 were as follows: (In millions) Quoted Prices in Significant Significant Asset category Total NAV (Level 1) (Level 2) (Level 3) Equity securities: U.S. equities $ 509.8 $ 281.4 $ 228.4 $ — $ — International equities 408.8 396.6 12.2 — — Fixed income and cash equivalents 707.7 482.3 24.5 200.9 — Private equity 176.7 176.7 — — — Alternative investments- hedge funds, real estate and other 317.9 317.9 — — — Total assets $ 2,120.9 $ 1,654.9 $ 265.1 $ 200.9 $ — A financial instrument’s categorization within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement. Investments in U.S. and International equities, and Fixed Income are predominantly held in common/collective trust funds and registered investment companies. Some of these investments are publicly traded securities and are classified as Level 1, while others are public investment vehicles valued using the NAV provided by the administrator of the fund. The NAV is based on the value of the underlying assets owned by the fund, minus its liabilities, and then divided by the number of shares outstanding. These investments are not classified in the fair value hierarchy. In addition, some fixed income instruments are investments in debt instruments that are valued using external pricing vendors and are classified within Level 2 of the fair value hierarchy. Floating interest rate global debt instruments are both domestic and foreign and include first lien debt, second lien debt and structured finance obligations, among others. These instruments are valued using NAV and are not classified in the fair value hierarchy. Private equity investments include both Direct Funds and Fund-of-Funds. Direct Funds are investments in Limited Partnership (LP) interests. Fund-of-Funds are investments in private equity funds that invest in other private equity funds or LPs. Fair value of these investments is determined utilizing net asset values, and are not classified in the fair value hierarchy. Alternative investments include hedge fund and real estate investments that are made as a limited partner in funds managed by a general partner. Fair value of these investments is determined utilizing net asset values, and are not classified in the fair value hierarchy. For certain investments which have formal financial valuations reported on a one-quarter lag, fair value is determined utilizing net asset values adjusted for subsequent cash flows, estimated financial performance and other significant events. For 2023, the weighted average expected long-term rate of return on defined benefit pension assets is 6.57%. In developing expected long-term rate of return assumptions, the Company evaluated input from its third party pension plan asset managers and actuaries, including reviews of their asset class return expectations and long-term inflation assumptions. An expected long-term rate of return is based on expected asset allocations within ranges for each investment category and projected annual compound returns. The Company’s actual, weighted average returns on pension assets for the last five years have been (14.5)% for 2022, 12.4% for 2021, 15.2% for 2020, 15.1% for 2019, and (4.8)% for 2018. The plan assets for the ATI Pension Plan, the Company’s primary U.S. qualified defined benefit pension plan, represent nearly 95% of ATI’s total pension plan assets at December 31, 2022. The ATI Pension Plan invests in a diversified portfolio consisting of an array of asset classes that attempts to maximize returns while minimizing volatility. These asset classes include U.S. domestic equities, non-U.S. developed market equities, emerging market equities, hedge funds, private equity, traditional fixed income consisting of long government/credit and alternative credit, and real estate. The Company continually monitors the investment results of these asset classes and its fund managers, and explores other potential asset classes for possible future investment. The target asset allocations for ATI Pension Plan for 2023, by major investment category, are: Asset category Target asset allocation range Equities 30% - 70% Fixed income and cash equivalents 15% - 40% Private equity 0% - 30% Alternative investments- hedge funds, real estate and other 10% - 30% As of December 31, 2022, the Company’s pension plans had outstanding commitments to invest up to $45 million in global debt securities, $125 million in private equity investments and $29 million in real estate investments. These commitments are expected to be satisfied through the reallocation of pension trust assets while maintaining investments within the target asset allocation ranges. The Company contributes to several multiemployer defined benefit pension plans under collective bargaining agreements that cover certain of its union-represented employees. The risks of participating in such plans are different from the risks of single-employer plans, in the following respects: a. Assets contributed to a multiemployer plan by one employer may be used to provide benefits to employees of other participating employers. b. If a participating employer ceases to contribute to the plan, the unfunded obligations of the plan may be borne by the remaining participating employers. c. If the Company ceases to have an obligation to contribute to the multiemployer plan in which it had been a contributing employer, it may be required to pay to the plan an amount based on the underfunded status of the plan and on the history of the Company’s participation in the plan prior to the cessation of its obligation to contribute. The amount that an employer that has ceased to have an obligation to contribute to a multiemployer plan is required to pay to the plan is referred to as a withdrawal liability. A subsidiary of the Company participates in the Steelworkers Western Independent Shops Pension Plan (WISPP) for union-represented employees of the primary titanium operations in Albany, OR, which is funded on an hours-worked basis. Manufacturing operations at this facility have been idled throughout 2021 and most of 2022, with a limited number of employees that participate in the WISPP remaining active in maintenance and other functions. It is at least reasonably possible that significant reductions in, or the elimination of hours-worked contributions due to changes in operating rates at this facility could result in a withdrawal liability assessment in a future period. A complete withdrawal liability is estimated to be approximately $27 million on an undiscounted basis, based on information for the plan year ended September 30, 2021, which is the most recent information available from the Plan Administrator. If this complete withdrawal liability was incurred, ATI estimates that payments of the obligation would be required on a straight-line basis over a 15-year period. The Company’s participation in multiemployer plans for the years ended December 31, 2022, 2021 and 2020 is reported in the following table. Pension FIP / RP Status in millions Expiration Dates EIN / Pension Company Contributions Surcharge Pension Fund 2022 2021 2022 2021 2020 Steelworkers Western Independent Shops Pension Plan 90-0169564 Green Green N/A $ 0.1 $ 0.1 $ 0.7 No 2/28/2025 Boilermakers-Blacksmiths National Pension Trust 48-6168020 Green Yellow Yes 2.3 2.0 2.1 No 9/30/2026 IAM National Pension Fund 51-6031295 Red Red Yes 1.9 1.9 2.0 Yes Various between 2023-2028 (4) Total contributions $ 4.3 $ 4.0 $ 4.8 (1) The most recent Pension Protection Act Zone Status is based on information provided to ATI and other participating employers by each plan, as certified by the plan’s actuary. A plan in the “deep red” zone had been determined to be in “critical and declining status”, based on criteria established by the Internal Revenue Code (Code), and is in critical status (as defined by the “red” zone) and is projected to become insolvent (run out of money to pay benefits) within 15 years (or within 20 years if a special rule applies). A plan in the “red” zone had been determined to be in “critical status”, based on criteria established by the Code, and is generally less than 65% funded. A plan in the “yellow” zone has been determined to be in “endangered status”, based on criteria established under the Code, and is generally less than 80% funded. A plan in the “green” zone has been determined to be neither in “critical status” nor in “endangered status”, and is generally at least 80% funded. Additionally, a plan may voluntarily place itself into a rehabilitation plan. In April 2019, the Company received notification from the IAM National Pension Fund (IAM Fund) that its’ actuary certified the IAM Fund as “endangered status” for the plan year beginning January 1, 2019, and that the IAM Fund was voluntarily placing itself in “red” zone status and implementing a rehabilitation plan. In April 2020, 2021 and 2022, the Company received notification from the IAM Fund that it was certified by its actuary as being in “red” zone status for the plan years beginning January 1, 2020 and 2021. A contribution surcharge was imposed as of June 1, 2019 in addition to the contribution rate specified in the applicable collective bargaining agreements. The contribution surcharge remains in effect, and ends when an employer begins contributing under a collective bargaining agreement that includes terms consistent with the rehabilitation plan. In April 2019, the Company received notifications from the Boilermakers-Blacksmiths National Pension Trust (Blacksmiths Trust) that it was certified by its actuary as being in “red” zone status for the plan year beginning January 1, 2019. A rehabilitation plan has been adopted for the Blacksmiths Trust, and the Company and the Blacksmiths union agreed to adopt the rehabilitation plan in 2019 prior to a contribution surcharge being imposed. In April 2020 and 2021, the funding status improved for the Blacksmiths Trust as it was certified by its actuary as being in the “yellow” zone for the plan years beginning January 1, 2020 and 2021. In April 2022, the funding status further improved to being in the "green" zone for the plan year beginning January 1, 2022. (2) The “FIP / RP Status Pending / Implemented” column indicates whether a Funding Improvement Plan, as required under the Code by plans in the “yellow” zone, or a Rehabilitation Plan, as required under the Code to be adopted by plans in the “red” or “deep red” zones, is pending or has been implemented as of the end of the plan year that ended in 2022. (3) The “Surcharge Imposed” column indicates whether ATI’s contribution rate for 2022 included an amount in addition to the contribution rate specified in the applicable collective bargaining agreement, as imposed by a plan in “critical status” or “critical and declining status”, in accordance with the requirements of the Code. (4) The Company is party to five separate bargaining agreements that require contributions to this plan. Expiration dates of these collective bargaining agreements range between November 13, 2023 and July 14, 2028.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2022
Equity [Abstract]
Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) The changes in AOCI by component, net of tax, for the fiscal years ended December 31, 2022, 2021 and 2020 were as follows (in millions): Post- Currency Derivatives Deferred Tax Asset Valuation Allowance Total Balance, December 31, 2019 $ (1,083.1) $ (76.6) $ (0.5) $ (41.5) $ (1,201.7) OCI before reclassifications (99.3) 21.1 (2.0) — (80.2) Amounts reclassified from AOCI (a) 62.5 (b) — (d) 4.6 (e) (8.8) 58.3 Net current-period OCI (36.8) 21.1 2.6 (8.8) (21.9) Balance, December 31, 2020 (1,119.9) (55.5) 2.1 (50.3) (1,223.6) OCI before reclassifications 118.3 (9.4) 11.7 — 120.6 Amounts reclassified from AOCI (a) 53.9 (b) — (d) (8.7) (e) 66.1 111.3 Net current-period OCI 172.2 (9.4) 3.0 66.1 231.9 Balance, December 31, 2021 (947.7) (64.9) 5.1 15.8 (991.7) OCI before reclassifications 117.9 (25.2) 41.0 — 133.7 Amounts reclassified from AOCI (a) 93.7 (c) 20.0 (d) (32.6) (e) 51.7 132.8 Net current-period OCI 211.6 (5.2) 8.4 51.7 266.5 Balance, December 31, 2022 $ (736.1) $ (70.1) 13.5 $ 67.5 $ (725.2) Attributable to noncontrolling interests: Balance, December 31, 2019 $ — $ 9.8 $ — $ — $ 9.8 OCI before reclassifications — 11.4 — — 11.4 Amounts reclassified from AOCI — (b) — — — — Net current-period OCI — 11.4 — — 11.4 Balance, December 31, 2020 — 21.2 — — 21.2 OCI before reclassifications — 4.8 — — 4.8 Amounts reclassified from AOCI — (b) — — — — Net current-period OCI — 4.8 — — 4.8 Balance, December 31, 2021 — 26.0 — — 26.0 OCI before reclassifications — (18.3) — — (18.3) Amounts reclassified from AOCI — (b) — — — — Net current-period OCI — (18.3) — — (18.3) Balance, December 31, 2022 $ — $ 7.7 $ — $ — $ 7.7 (a) Amounts were included in net periodic benefit cost for pension and other postretirement benefit plans (see Note 14) and/or loss on asset sales and sales of businesses, net, as part of the loss on sale of the Sheffield, UK operations (see Note 6). (b) No amounts were reclassified to earnings. (c) Amounts were included in loss on asset sales and sales of businesses, net, as part of the loss on sale of the Sheffield, UK operations (see Note 6). (d) Amounts related to derivatives are included in sales, cost of goods sold or interest expense in the period or periods the hedged item affects earnings (see Note 12). (e) Represents the net change in deferred tax asset valuation allowances on changes in AOCI balances between the balance sheet dates. The 2021 income tax provision includes $6.4 million of tax expense for the recognition of a stranded deferred tax balance arising from deferred tax valuation allowances that was associated with certain postretirement medical benefits due to plan termination (see Notes 14 and 17). Other comprehensive income (loss) amounts (OCI) reported above by category are net of applicable income tax expense (benefit) for each year presented. Income tax expense (benefit) on OCI items is recorded as a change in a deferred tax asset or liability. Amounts recognized in OCI include the impact of any deferred tax asset valuation allowances, when applicable. Foreign currency translation adjustments, including those pertaining to noncontrolling interests, are generally not adjusted for income taxes as they relate to indefinite investments in non-U.S. subsidiaries. Reclassifications out of AOCI for the fiscal years ended December 31, 2022, 2021 and 2020 were as follows: Amount reclassified from AOCI (d) Fiscal year ended Details about AOCI Components (In millions) December 31, 2022 December 31, 2021 December 31, 2020 Affected line item in the Postretirement benefit plans Prior service credit $ 0.5 (a) $ 1.8 (a) $ 3.1 (a) Actuarial losses (76.7) (a) (89.5) (a) (85.3) (a) Settlement gain (loss) (29.5) (b) 21.9 (a) — (105.7) (d) (65.8) (d) (82.2) (d) Total before tax (12.0) (11.9) (19.7) Tax benefit (e) $ (93.7) $ (53.9) $ (62.5) Net of tax Currency translation adjustment (20.0) (b,d) — (d) — (d) Derivatives Nickel and other raw material contracts $ 26.9 (c) $ 7.1 (c) $ (0.8) (c) Natural gas contracts 15.1 (c) 5.3 (c) (3.7) (c) Foreign exchange contracts 0.9 (c) 0.1 (c) (0.1) (c) Interest rate swap (0.1) (c) (1.1) (c) (1.4) (c) 42.8 (d) 11.4 (d) (6.0) (d) Total before tax 10.2 2.7 (1.4) Tax provision (benefit) (e) $ 32.6 $ 8.7 $ (4.6) Net of tax (a) Amounts are included in nonoperating retirement benefit expense (see Note 14). (b) Amounts in 2022 were included in loss on asset sales and sales of businesses, net, as part of the loss on sale of the Sheffield, UK operations (see Note 6). (c) Amounts related to derivatives, with the exception of the interest rate swap, are included in sales or cost of goods sold in the period or periods the hedged item affects earnings. Amounts related to the interest rate swap are included in interest expense in the same period as the interest expense on the ABL Term Loan is recognized in earnings (see Note 12). (d) For pretax items, positive amounts are income and negative amounts are expense in terms of the impact to net income. Tax effects are presented in conformity with ATI’s presentation in the consolidated statements of operations. (e) These amounts exclude the impact of any deferred tax asset valuation allowances, when applicable, including recognition of stranded balances (see Note 17 for further explanation).

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2022
Equity [Abstract]
Stockholders' Equity	Stockholders’ Equity Preferred Stock Authorized preferred stock may be issued in one or more series, with designations, powers and preferences as shall be designated by the Board of Directors. At December 31, 2022, there were no shares of preferred stock issued. Dividends Under the ABL facility, there is no limit on dividend declarations or payments provided that the undrawn availability, after giving effect to a particular dividend payment, is at least the greater of $120 million and 20% of the total facility size, after giving effect to any repayment of term loans, and no event of default under the ABL facility has occurred and is continuing or would result from paying the dividend. In addition, there is no limit on dividend declarations or payments if the undrawn availability is less than the greater of $120 million and 20% of the total facility size, after giving effect to any repayment of term loans, but more than the greater of $75 million and 12.5% of the total facility size, after giving effect to any repayment of term loans, if (i) no event of default has occurred and is continuing or would result from paying the dividend, (ii) the Company demonstrates to the administrative agent that, prior to and after giving effect to the payment of the dividend (A) the undrawn availability, as measured both at the time of the dividend payment and as an average for the 60 consecutive day period immediately preceding the dividend payment, is at least the greater of $75 million and 12.5% of the total facility size, after giving effect to any repayment of term loans, and (B) the Company maintains a fixed charge coverage ratio of at least 1.00:1.00, as calculated in accordance with the terms of the ABL facility. Share-based Compensation In May 2022, the Company’s stockholders approved the ATI Inc. 2022 Incentive Plan (the “2022 Incentive Plan”). Following adoption, all new share-based compensation awards are being made under the 2022 Incentive Plan. Shares previously remaining available for grant under prior incentive plans, or which become available for award due to the forfeiture or cancellation of prior awards under those prior plans, are available for award under the 2022 Incentive Plan. Outstanding grants previously made under prior incentive plans remain in effect in accordance with relevant terms. Awards earned under the Company’s share-based incentive compensation programs are generally paid with shares held in treasury, if sufficient treasury shares are held, and any additional required share payments are made with newly issued shares. At December 31, 2022, 4.6 million shares of common stock were available for future awards under the 2022 Incentive Plan. The general terms of each arrangement granted under the 2022 Incentive Plan, and predecessor plans, the method of estimating fair value for each arrangement, and award activity is reported below. The Company’s share-based incentive compensation program consists of both service-based and performance/market-based awards. These awards convey participants the right to receive shares of ATI common stock if the service conditions, and performance or market requirements, of the awards are attained. Service-based awards: Restricted share units (RSUs) are rights to receive shares of Company stock when the award vests. The RSUs generally vest over three years based on employment service, with one-third of the award vesting on each of the first, second and third anniversaries of the grant date. RSU awards to non-employee directors vest in one year. No dividends are accumulated or paid on the RSUs. The fair value of the RSU award is measured based on the stock price at the grant date. Compensation expense related to RSU awards was $13.4 million in 2022, $14.3 million in 2021, and $9.6 million in 2020. Approximately $8.2 million of unrecognized fair value compensation expense relating to restricted stock units is expected to be recognized through 2025, with $6.3 million expected to be recognized in 2023, including estimates of service period forfeitures. Activity under the Company’s RSU awards for the years ended December 31, 2022, 2021, and 2020 was as follows: (Shares in thousands, $ in millions) 2022 2021 2020 Number of Weighted Number of Weighted Number of Weighted Nonvested, beginning of year 1,409 $ 25.6 929 $ 17.9 756 $ 19.6 Granted 831 14.8 1,033 17.5 647 10.1 Vested (634) (12.3) (505) (8.9) (450) (11.2) Forfeited (127) (2.1) (48) (0.9) (24) (0.6) Nonvested, end of year 1,479 $ 26.0 1,409 $ 25.6 929 $ 17.9 Performance condition awards: The Company awarded performance share units (PSUs) with performance requirements through fiscal year 2020. These PSU award opportunities, the last of which vested at the conclusion of its applicable three-year performance period on December 31, 2022, were determined at a target number of units, and the number of shares awarded was based on attainment of two ATI financial performance metrics. PSU awards through 2020 are accounted for as performance condition plans with service vesting requirements, with compensation expense during the performance period recognized based on estimates of attaining the performance criteria, including estimated forfeitures. The metrics for PSU awards granted through 2018 measured (1) net income attributable to ATI and (2) return on invested capital, over a three-year performance period. The metrics for PSU awards granted in 2019 and 2020 measured (1) net income attributable to ATI and (2) return on capital employed, over a three-year performance period with a threshold attainment of 25% and a maximum attainment of 200% of the target financial performance metrics and target share units, measured over the applicable three-year performance period. For certain senior executives, the number of PSUs to be awarded based on the performance criteria was modified up or down by up to 20% based on the Company’s relative total shareholder return (TSR) over the performance measurement period (“TSR Modifier”), but not above the maximum number of PSUs to be vested. The TSR Modifier measured the return of the Company’s stock price (including assumed dividend reinvestment, if any) at the end of the performance period as compared to the stock prices (including assumed dividend reinvestment, if any) of a group of industry peers. The fair value of the PSU award was measured based on the stock price at the grant date, including the effect of the TSR Modifier. The fair value of the TSR Modifier was determined by using Monte Carlo simulations of stock price correlation, projected dividend yields and other variables over a three-year time horizon matching the TSR performance measurement period. Expense recognition varied with the level of performance achieved. Market condition awards: The Company awarded PSUs with market requirements in 2021 and 2022. The 2021 and 2022 PSU award opportunities are determined at a target number of share units, and the number of shares awarded is based on TSR, representing the measured return of the Company’s stock price (including assumed dividend reinvestment, if any) at the end of the three year period as compared to the stock prices (including assumed dividend reinvestment, if any) of a group of industry peers. The 2021 and 2022 PSU awards are accounted for as a market condition plan with service vesting requirements, with expense recognized over the service period without regard to the level of TSR attainment or shares awarded. The actual number of shares awarded at the end of the measurement period may range from a minimum of zero to a maximum of two times target. TSR is determined over eight distinct quarterly periods as measured from January 1 of the grant year of the award through the end of each quarterly period starting with the first quarter ending in the second year following the grant of the award; earned payouts from each TSR measurement period are averaged to determine the final payout at the conclusion of the three-year period. The fair value for this award was determined by using Monte Carlo simulations of stock price correlation, projected dividend yields and other variables over the three-year time horizon matching the TSR measurement period. In 2022, the Company awarded a new one-time grant of PSUs with market requirements, called the Breakout Performance Award (BPA). The BPA has a target number of share units, and the number of shares awarded is based on the absolute return on the Company’s stock during a four-year measurement period. The service vesting requirements of the BPA award are four years for one half of the award and five years for the remaining half. The BPA award is accounted for as a market condition plan with service vesting requirements, with expense recognized over the service periods without regard to the level of absolute return attainment or shares awarded. The actual number of BPA shares awarded at the end of the measurement period may range from a minimum of zero to a maximum of three times target. The fair value for this award was determined by using Monte Carlo simulations of stock price correlation, projected dividend yields and other variables over the four-year time horizon matching the BPA measurement period. At December 31, 2022, a maximum of 5.2 million shares have been reserved for issuance for all PSU awards. The Company recognized $12.6 million and $6.8 million of compensation expense in 2022 and 2021, respectively, for all PSU awards, and compensation income of $6.7 million in 2020 due to decreased financial performance attainment estimates, which required reversal of previously-recognized expense. Forfeited share units in 2020, 2021 and 2022 were 50,050, 71,801 and 159,298, respectively, with a weighted average grant date fair value of $1.4 million, $1.7 million and $3.4 million, respectively. The fair value of each PSU award, the target share units awarded and projected future compensation expense to be recognized for these awards, including actual and estimated forfeitures at December 31, 2022 was as follows: (Shares in thousands, $ in millions) PSU Award Performance Period Award Fair Value December 31, 2022 Unrecognized Compensation Expense Compensation Expense Expected to be Recognized in the next 12 months Target Share Units 2020-2022 $ 13.5 $ — $ — 674 2021-2023 $ 9.3 3.1 3.1 459 2022-2024 $ 11.0 8.9 3.9 494 2022-2025 BPA $ 18.5 12.1 3.3 811 Total $ 24.1 $ 10.3

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Income (loss) before income taxes for the Company’s U.S. and non-U.S. operations was as follows: (In millions) 2022 2021 2020 U.S. $ 230.6 $ (42.1) $ (1,505.4) Non-U.S. (68.6) 52.7 23.5 Income (loss) before income taxes $ 162.0 $ 10.6 $ (1,481.9) The income tax provision (benefit) was as follows: (In millions) 2022 2021 2020 Current: Federal $ 5.0 $ 0.7 $ 0.6 State 3.7 (0.3) (1.1) Foreign 10.0 9.4 6.7 Total 18.7 9.8 6.2 Deferred: Federal (3.3) 18.6 26.6 State 0.2 (0.9) 47.1 Foreign (0.1) (0.7) (2.2) Total (3.2) 17.0 71.5 Income tax provision $ 15.5 $ 26.8 $ 77.7 The following is a reconciliation of income taxes computed at the statutory U.S. Federal income tax rate to the actual effective income tax provision (benefit): (In millions) 2022 2021 2020 Taxes computed at the federal rate $ 34.0 $ 2.2 $ (311.2) Goodwill — 2.6 50.4 State and local income taxes, net of federal tax benefit 2.9 0.4 (0.2) Valuation allowance (50.0) 17.6 335.5 Repatriation of foreign earnings (GILTI ) — 2.0 0.2 Divestiture 29.1 — — Recognition of stranded deferred tax balance — 3.9 — Foreign earnings taxed at different rate 3.2 3.0 1.7 Withholding taxes 2.6 3.4 2.1 Preferential tax rate (4.9) (6.2) (4.6) Other (1.4) (2.1) 3.8 Income tax provision $ 15.5 $ 26.8 $ 77.7 The Company’s income tax expense has been impacted by the effects of valuation allowances on federal and state deferred tax assets for years 2020 through 2022. The Company recognizes deferred tax assets to the extent it believes these deferred tax assets are more likely than not to be realized. Valuation allowances are established when it is estimated that it is more likely than not the tax benefit of the deferred tax asset will not be realized. In making such determination, the Company considers all available evidence, both positive and negative, regarding the estimated future reversals of existing taxable temporary differences, estimated future taxable income exclusive of reversing temporary differences and carryforwards, historical taxable income in prior carryback periods if carryback is permitted, and potential tax planning strategies which may be employed to prevent an operating loss or tax credit carryforward from expiring unused. The verifiable evidence such as future reversals of existing temporary differences and the ability to carryback are considered before the subjective sources such as estimated future taxable income exclusive of temporary differences and tax planning strategies. In situations where a three-year cumulative loss position exists, the ability to consider projections of future results as positive evidence to assess the realizability of deferred tax assets is subjective. If the Company determines that it would not be able to realize its deferred tax assets in the future in excess of their recorded net amount, an adjustment to the deferred tax asset valuation allowance would result. In 2020, ATI’s U.S. operations returned to a three-year cumulative loss position, limiting the ability to utilize future projections as verifiable sources of income when analyzing the need for a valuation allowance. The consolidated income tax provision for fiscal year 2020 included a $335.5 million increase to the deferred tax asset valuation allowance based on an analysis of the expected more likely than not realization of deferred tax assets and liabilities within applicable expiration periods, primarily on U.S. federal and state tax attributes. In 2021, ATI incurred tax expense associated with the valuation allowance due to the postretirement medical benefit settlement gain along with the U.S. operations plus permanent adjustments (goodwill and Global Intangible Low-Taxed Income (GILTI)) being a loss. The overall balance of the valuation allowance decreased in total mainly due to the overall change in AOCI associated with the Company’s retirement benefit plans. In 2022, ATI recorded a tax benefit associated with the valuation allowance due to the current year income for the U.S. operations. As a result of the current year income, ATI utilized net operating loss carryovers which in turn resulted in a release of the corresponding valuation allowance on the operating loss deferred tax assets. The provision for income taxes for the year ended December 31, 2022, is mainly attributable to the Company’s foreign operations and state income tax expense associated with states that limit net operating loss utilization. On May 12, 2022, the Company sold its Sheffield, UK operations which resulted in a pre-tax loss of $141.0 million (see Note 6 for further explanation) for which the benefit was disallowed for tax purposes, resulting in a $29.1 million tax expense impact as shown in the effective tax rate reconciliation table above. The provision for income taxes for the year ended December 31, 2021 is mainly attributable to the $15.5 million in discrete tax effects related to the postretirement medical benefits settlement gain discussed in Note 14, in accordance with ATI’s accounting policy for recognizing deferred tax amounts stranded in accumulated other comprehensive income (loss) (AOCI). This $15.5 million is presented within two lines in the above table, $11.6 million within valuation allowance and $3.9 million on the recognition of stranded deferred tax balance line which represents the difference between current and historical tax rates in AOCI. The $11.6 million has two components: $5.2 million of additional required valuation allowance on ATI’s net deferred tax assets following the reduction of deferred tax liabilities in AOCI associated with the recognition of the AOCI portion of the retirement benefit settlement gain of $21.9 million, and $6.4 million of “trapped” valuation allowances remaining in AOCI from prior periods that are now recognized upon extinguishment of the retirement benefit plan (see Notes 14 and 15). In 2021, the Company allocated $12.2 million of the goodwill from ATI’s Forged Products reporting unit to the sale of Flowform Products (see Note 6 for further explanation) which was non-deductible for tax purposes, resulting in a $2.6 million expense included as a reconciling item in the table above. In 2020, the Company recorded a $287.0 million pre-tax charge for goodwill impairment (see Note 5 for additional information) which included a portion that was non-deductible for tax purposes, resulting in a $50.4 million expense included as a reconciling item in the table above. The Company also maintained valuation allowances on deferred tax amounts recorded in AOCI in 2022, 2021 and 2020 of $67.5 million, $15.8 million, and $50.3 million, respectively, which are not reflected in the preceding table reconciling amounts recognized in the income tax provision (benefit) recorded in the statement of operations (see Note 15). Additionally, the Tax Cuts and Jobs Act (Tax Act) requires a current year inclusion in U.S. federal taxable income of certain earnings of controlled foreign corporations, commonly referred to as GILTI. In 2022, due to the loss on the sale of the Sheffield operations, there is no current year inclusion. In 2021, GILTI represents an unfavorable tax rate item of $2.0 million which is primarily related to the Company’s income associated with the PRS joint venture operations in China. The impact in 2020 related to GILTI is minimal due to the global COVID-19 pandemic. The Company has elected to recognize GILTI liabilities as an element of income tax expense in the period incurred. In the fourth quarter of 2021, the Company was granted a preferential tax rate related to the PRS joint venture operations in China for tax years 2021 through 2023. The preferential tax rate is 15%, compared to the statutory rate of 25%. The Company must re-apply for the High Tech-New Enterprise status every three years to be eligible for the preferential rate. This same preferential tax rate was in effect for tax years 2018 through 2020. Deferred income taxes result from temporary differences in the recognition of income and expense for financial and income tax reporting purposes, and differences between the fair value of assets acquired in business combinations accounted for as purchases for financial reporting purposes and their corresponding tax bases. Deferred income taxes represent future tax benefits or costs to be recognized when those temporary differences reverse. The categories of assets and liabilities that have resulted in differences in the timing of the recognition of income and expense at December 31, 2022 and 2021 were as follows: (In millions) 2022 2021 Deferred income tax assets Net operating loss tax carryovers $ 184.1 $ 298.7 Pensions 51.7 94.3 Postretirement benefits other than pensions 51.5 69.8 Tax credits 42.0 40.2 Other items 95.6 103.9 Gross deferred income tax assets 424.9 606.9 Valuation allowance for deferred tax assets (266.9) (431.0) Total deferred income tax assets 158.0 175.9 Deferred income tax liabilities Bases of property, plant and equipment 122.2 114.0 Inventory valuation 17.1 32.5 Bases of amortizable intangible assets 9.0 18.0 Other items 23.0 24.7 Total deferred tax liabilities 171.3 189.2 Net deferred tax liability $ (13.3) $ (13.3) Changes in the valuation allowance for deferred tax assets in 2022 in the above table compared to 2021 include the following: • $50 million of valuation allowance recorded as income tax benefit and included in the reconciliation of the current year income tax provision; • reductions in the valuation allowance related to the benefit in AOCI of $51.7 million (as discussed in Note 15); • $13.6 million removal of valuation allowance associated with the sale of the Sheffield operations. • $43.4 million related to the presentation of state taxes and certain adjustments that have a direct valuation allowance offset, resulting in no net tax expense or benefit. Due to the change in future tax rates in Pennsylvania, the Company recorded an overall decrease in deferred tax assets and liabilities which resulted in an offsetting removal of the valuation allowance. As part of the Tax Act in 2017, a limitation on deductible interest expense was created, which limits deductible interest expense to 30% of adjusted taxable income, as defined in the Tax Act, for various periods. The Company is not limited in its deductible interest expense for 2022 and is utilizing part of the carryover amount associated with the 2021 disallowance of interest expense. A deferred tax asset associated with the carryover limitation is within the “other items” asset category above at December 31, 2022 and December 31, 2021. The following summarizes the carryforward periods for the tax attributes related to NOLs and credits by jurisdiction. ($ in millions, U.S. and U.K. NOL amounts are pre-tax and all other items are after-tax) Jurisdiction Attribute Amount Expiration Period Amount expiring within 5 years Amount expiring in 5-20 years U.S. NOL $439 20 years $— $439 U.S. NOL $129 Indefinite $— $— U.S. Foreign Tax Credit $22 10 years $22 $— U.S. Research and Development Credit $7 20 years $— $7 State NOL $85 Various $16 $69 State NOL $1 Indefinite $— $— State Credits $10 Various $4 $6 U.K. NOL $3 Indefinite $— $— Poland Economic Zone Credit $5 7 years $5 $— Income taxes paid and amounts received as refunds were as follows: (In millions) 2022 2021 2020 Income taxes paid $ 18.9 $ 14.2 $ 7.8 Income tax refunds received (0.4) (0.6) (2.5) Income taxes paid, net $ 18.5 $ 13.6 $ 5.3 In general, the Company is responsible for filing consolidated U.S. federal, foreign and combined, unitary or separate state income tax returns. The Company is responsible for paying the taxes relating to such returns, including any subsequent adjustments resulting from the redetermination of such tax liability by the applicable taxing authorities. Deferred taxes of $5.3 million have been recorded for foreign withholding taxes on earnings expected to be repatriated to the U.S. The Company does not intend to distribute previously taxed earnings resulting from the one-time transition tax under the Tax Act, and has not recorded any deferred taxes related to such amounts. The remaining excess of the amount for financial reporting over the tax basis of investments in foreign subsidiaries is indefinitely reinvested, and the determination of any deferred tax liability on this amount is not practicable. Uncertain tax positions are recorded using a two-step process based on (1) determining whether it is more-likely-than-not the tax positions will be sustained on the basis of the technical merits of the position and (2) for those positions that meet the more-likely-than-not recognition threshold, the Company records the largest amount of the tax benefit that is more than 50 percent likely to be realized upon ultimate settlement with the related tax authority. The changes in the liability for unrecognized income tax benefits for the years ended December 31, 2022, 2021 and 2020 were as follows: (In millions) 2022 2021 2020 Balance at beginning of year $ 14.2 $ 15.2 $ 14.4 Decreases in prior period tax positions (3.3) — — Increases in current period tax positions — 0.3 2.7 Expiration of the statute of limitations (1.8) (1.3) (1.9) Balance at end of year $ 9.1 $ 14.2 $ 15.2 For years ended December 31, 2022, 2021 and 2020, the liability includes $7.8 million, $12.3 million and $13.0 million, respectively, of unrecognized tax benefits that are classified within deferred income taxes as a reduction of NOL carryforwards and other tax attributes. The total estimated unrecognized tax benefit that, if recognized, would affect ATI’s effective tax rate is approximately $1 million. At this time, the Company believes that it is reasonably possible that approximately $1.4 million of the estimated unrecognized tax benefits as of December 31, 2022 will be recognized within the next twelve months based on the expiration of statutory review periods. The Company recognizes accrued interest and penalties related to uncertain tax positions as income tax expense. The amounts accrued for interest and penalty charges for the years ended December 31, 2022, 2021 and 2020 were not significant. At December 31, 2022 and 2021, the accrued liabilities for interest and penalties related to unrecognized tax benefits were $1.4 million and $1.9 million, respectively. The Company, and/or one of its subsidiaries, files income tax returns in the U.S. federal jurisdiction and in various state and foreign jurisdictions. A summary of tax years that remain subject to examination, by major tax jurisdiction, is as follows: Jurisdiction Earliest Year Open to U.S. Federal 2020 States: Pennsylvania 2019 Foreign: China 2019 Poland 2016 United Kingdom 2020

Per Share Information

Per Share Information	12 Months Ended
	Dec. 31, 2022
Earnings Per Share [Abstract]
Per Share Information	Per Share Information The following table sets forth the computation of basic and diluted net income (loss) per common share: (In millions, except per share amounts) For the Years Ended December 31, 2022 2021 2020 Numerator: Numerator for basic net income (loss) per common share - Net income (loss) attributable to ATI $ 130.9 $ (38.2) $ (1,572.6) Effect of dilutive securities: 4.75% Convertible Senior Notes due 2022 2.2 — — 3.5% Convertible Senior Notes due 2025 11.3 — — Numerator for diluted net income (loss) per common share - Net income (loss) attributable to ATI after assumed conversions $ 144.4 $ (38.2) $ (1,572.6) Denominator: Denominator for basic net income (loss) per common share—weighted average shares 127.5 127.1 126.5 Effect of dilutive securities: Share-based compensation 2.1 — — 4.75% Convertible Senior Notes due 2022 2.8 — — 3.5% Convertible Senior Notes due 2025 18.8 — — Denominator for diluted net income (loss) per common share—adjusted weighted average shares and assumed conversions 151.2 127.1 126.5 Basic net income (loss) attributable to ATI per common share $ 1.03 $ (0.30) $ (12.43) Diluted net income (loss) attributable to ATI per common share $ 0.96 $ (0.30) $ (12.43) Common stock that would be issuable upon the assumed conversion of the 2025 Convertible Notes, and the 2022 Convertible Notes prior to their maturity, and other option equivalents and contingently issuable shares are excluded from the computation of contingently issuable shares, and therefore, from the denominator for diluted earnings per share, if the effect of inclusion is anti-dilutive. The 2022 Convertible Notes were converted as of June 30, 2022 (see Note 10 for further explanation). There were no anti-dilutive shares for 2022. There were 25.6 million and 22.8 million anti-dilutive shares for 2021 and 2020, respectively. On February 2, 2022, the Company’s Board of Directors authorized the repurchase of up to $150 million of ATI stock. Repurchases under the program may be made in the open market or in privately negotiated transactions, with the amount and timing of repurchases depending on market conditions and corporate needs. Open market repurchases are structured to occur within the pricing and volume requirements of SEC Rule 10b-18. The stock repurchase program does not obligate the Company to repurchase any specific number of shares and it may be modified, suspended, or terminated at any time by the

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Future minimum rental commitments under leases are disclosed in Note 11. Commitments for expenditures on property, plant and equipment at December 31, 2022 were approximately $39.9 million. The Company is subject to various domestic and international environmental laws and regulations that govern the discharge of pollutants and disposal of wastes, and which may require that it investigate and remediate the effects of the release or disposal of materials at sites associated with past and present operations. The Company could incur substantial cleanup costs, fines, and civil or criminal sanctions, third party property damage or personal injury claims as a result of violations or liabilities under these laws or noncompliance with environmental permits required at its facilities. The Company is currently involved in the investigation and remediation of a number of its current and former sites, as well as third party sites. Environmental liabilities are recorded when the Company’s liability is probable and the costs are reasonably estimable. In many cases, however, the Company is not able to determine whether it is liable or, if liability is probable, to reasonably estimate the loss or range of loss. Estimates of the Company’s liability remain subject to additional uncertainties, including the nature and extent of site contamination, available remediation alternatives, the extent of corrective actions that may be required, and the number, participation, and financial condition of other potentially responsible parties (PRPs). The Company adjusts its accruals to reflect new information as appropriate. Future adjustments could have a material adverse effect on the Company’s consolidated results of operations in a given period, but the Company cannot reliably predict the amounts of such future adjustments. At December 31, 2022, the Company’s reserves for environmental remediation obligations totaled approximately $13 million, of which $5 million was included in other current liabilities Based on currently available information, it is reasonably possible that the costs for active matters may exceed the Company’s recorded reserves by as much as $15 million. Future investigation or remediation activities may result in the discovery of additional hazardous materials, potentially higher levels of contamination than discovered during prior investigation, and may impact costs associated with the success or lack thereof in remedial solutions. Therefore, future developments, administrative actions or liabilities relating to environmental matters could have a material adverse effect on the Company’s consolidated financial condition or results of operations. The timing of expenditures depends on a number of factors that vary by site. The Company expects that it will expend present accruals over many years and that remediation of all sites with which it has been identified will be completed within thirty years. A number of other lawsuits, claims and proceedings have been or may be asserted against the Company relating to the conduct of its currently and formerly owned businesses, including those pertaining to product liability, environmental, health and safety matters and occupational disease (including as each relates to alleged asbestos exposure), as well as patent infringement, commercial, government contracting, construction, employment, employee and retiree benefits, taxes, environmental, and stockholder and corporate governance matters. While the outcome of litigation cannot be predicted with certainty, and some of these lawsuits, claims or proceedings may be determined adversely to the Company, management does not believe that the disposition of any such pending matters is likely to have a material adverse effect on the Company’s financial condition or liquidity, although the resolution in any reporting period of one or more of these matters could have a material adverse effect on the Company’s consolidated results of operations for that period. ATI Titanium LLC (ATI Titanium), a subsidiary of ATI Inc., was party to a lawsuit captioned US Magnesium, LLC v. ATI Titanium LLC (Case No. 2:17-cv-00923-DB) and filed in federal district court in Salt Lake City, UT, pertaining to a Supply and Operating Agreement between US Magnesium LLC (USM) and ATI Titanium entered into in 2006 (the Supply Agreement). In 2016, ATI Titanium notified USM that it would suspend performance under the Supply Agreement in reliance on certain terms and conditions included in the Supply Agreement. USM subsequently filed a claim challenging ATI Titanium’s right to suspend performance under the Supply Agreement. ATI Titanium and USM reached a litigation settlement in 2022 for $28.5 million, which is reported within other (nonoperating) expense on the consolidated statement of operations and was paid in the year ended December 31, 2022.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies - Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation and Reporting The consolidated financial statements include the accounts of ATI Inc. and its subsidiaries. The financial results of majority-owned joint ventures are consolidated into the Company’s operating results and financial position, with the minority ownership interest recognized in the consolidated statement of operations as net income attributable to noncontrolling interests, and as equity attributable to the noncontrolling interests within total stockholders’ equity. The results for the Shanghai STAL Precision Stainless Steel Company Limited (STAL) are reported on a one month lag. Investments in which the Company exercises significant influence, but which it does not control (generally a 20% to 50% ownership interest) are accounted for under the equity method of accounting, whereby ATI’s carrying value of the equity method investment on the consolidated balance sheet is the capital investment and any undistributed profit or loss. The investments are classified in other (noncurrent) assets on the consolidated balance sheet. The profit or loss attributable to ATI from equity method investments is included in the consolidated statements of operations as a component of Other (non-operating) income (expense). See Note 7 for further explanation of the Company’s joint ventures. Intercompany accounts and transactions have been eliminated. Unless the context requires otherwise, “ATI” and the “Company” refer to ATI Inc. and its subsidiaries.
Use of Estimates	Risks and Uncertainties and Use of EstimatesThe preparation of consolidated financial statements in conformity with United States generally accepted accounting principles requires management to make estimates and assumptions that affect reported amounts of assets and liabilities at the date of the financial statements, as well as the reported amounts of income and expenses during the reporting period. Actual results could differ from those estimates. Management believes that the estimates are reasonable.
Concentration Risks	The Company markets its products to a diverse customer base, principally throughout the United States. No single customer accounted for more than 10% of sales for any year presented. The major end markets for ATI’s products are customers in the aerospace & defense, energy, automotive, construction and mining, food equipment and appliances, and medical markets.
Cash Equivalents and Investments	Cash and Cash Equivalents Cash equivalents are highly liquid investments that are readily convertible to cash with original maturities of three months or less.
Accounts Receivable	Accounts Receivable Accounts receivable are presented net of a reserve for doubtful accounts of $7.7 million and $3.8 million at December 31, 2022 and 2021, respectively. Trade credit is extended based upon evaluations of each customer’s ability to perform its obligations, which are updated periodically. The Company’s accounts receivable reserves are determined based on expected credit losses. Amounts are written-off against the reserve in the period it is determined that the receivable is uncollectible.
Inventories	Inventories Inventories are stated at the lower of cost (first-in, first-out (FIFO) and average cost methods) or net realizable value. Costs include direct material, direct labor and applicable manufacturing and engineering overhead, and other direct costs. The term net realizable value is defined as estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. The Company evaluates product lines on a quarterly basis to identify inventory carrying values that exceed estimated net realizable value. The calculation of a resulting reserve, if any, is recognized as an expense in the period that the need for the reserve is identified. It is the Company’s general policy to write-down to scrap value any inventory that is identified as slow-
Long-Lived Assets	Long-Lived Assets Property, plant and equipment are recorded at cost, including capitalized interest, and include long-lived assets acquired under finance leases. Depreciation is primarily recorded using the straight-line method. Prior to December 2020, property, plant and equipment associated with the Hot-Rolling and Processing Facility (HRPF) in the AA&S segment was being depreciated utilizing the units of production method of depreciation, which the Company believed provided a better matching of costs and revenues. However, based on changed business conditions resulting from the decision to exit production of standard stainless sheet products and the recognition of an impairment charge on the property, plant and equipment associated with the HRPF in December 2020 (see Note 19 for further discussion), depreciation of the remaining carrying value of the HRPF began using the straight-line method in December 2020. The Company periodically reviews estimates of useful life and production capacity assigned to new and in service assets. Significant enhancements, including major maintenance activities that extend the lives of property and equipment, are capitalized. Costs related to repairs and maintenance are charged to expense in the period incurred. The cost and related accumulated depreciation of property and equipment retired or disposed of are removed from the accounts and any related gains or losses are included in income. The Company monitors the recoverability of the carrying value of its long-lived assets. An impairment charge is recognized when an indicator of impairment occurs and the expected net undiscounted future cash flows from an asset’s use (including any proceeds from disposition) are less than the asset’s carrying value and the asset’s carrying value exceeds its fair value. If an impairment loss is recognized, the adjusted carrying value of the long-lived asset is its new cost basis and this new cost basis is depreciated over the remaining useful life of the asset. Assets to be disposed of by sale are stated at the lower of their fair values or carrying amounts and depreciation is no longer recognized.
Leases	Leases The Company classifies leases as either operating or financing, and records a right-of-use (ROU) asset and a lease liability on the consolidated balance sheets as further discussed below. The lease liability is equal to the present value of the minimum lease payments for the term of the lease, including any optional renewal periods determined to be reasonably certain to be exercised, using the discount rate determined at lease commencement. This discount rate is the rate implicit in the lease, if known; otherwise, the incremental borrowing rate (IBR) for the expected lease term is used. The Company’s IBRs approximate the rate the Company would have to pay to borrow on a collateralized basis over a similar term at lease inception. The ROU asset is equal to the initial measurement of the lease liability plus any lease payments made to the lessor at or before the commencement date and any unamortized initial direct costs incurred by the lessee, less any unamortized lease incentives received. The Company has elected to not separate lease components from non-lease components for all asset classes, and has made an accounting policy election to apply the short-term exception, which does not require the capitalization of leases with terms of 12 months or less. The Company has lease contracts for real property and machinery and equipment, primarily for mobile, office and information technology equipment. At inception of a contract, the Company determines whether the contract is or contains a lease. If the Company has a right to obtain substantially all of the economic benefits from the use of the identified asset and the right to direct the use of the asset, then the contract contains a lease. Several of the Company’s real property lease contracts include options to extend the lease term, and the Company reassesses the likelihood of renewal on at least an annual basis. In addition, several real property leases include variable lease payments, for items such as common area maintenance and utilities, which are expensed as incurred as variable lease expense. There are two types of leases: operating leases and finance leases. Lease classification is determined at lease commencement. A finance lease exists when specific criteria are met that indicate that all the risk and rewards related to the leased assets are transferred to the lessee. All other leases not meeting the finance lease criteria are classified as operating leases. Operating lease expense is recognized on a straight-line basis on the consolidated statement of operations. Finance leases have front-loaded expense recognition which is reported as amortization expense and interest expense on the consolidated statement of operations. ROU assets for operating leases are classified in other long-term assets property, plant and equipment other current liabilities other long-term liabilities short-term debt long-term debt
Goodwill	Goodwill Goodwill is reviewed annually for impairment, or more frequently if impairment indicators arise. The review for goodwill impairment requires a comparison of the fair value of each reporting unit that has goodwill associated with its operations with its carrying amount, including goodwill. If this comparison reflects impairment, then the loss would be measured as the excess of the carrying value over the calculated fair value. Generally accepted accounting principles provide the option to qualitatively assess goodwill for impairment before completing a quantitative assessment. Under the qualitative approach, if, after assessing the totality of events or circumstances, including both macroeconomic, industry and market factors, and entity-specific factors, the Company determines it is likely (more likely than not) that the fair value of a reporting unit is greater than its carrying amount, then the quantitative impairment analysis is not required. The quantitative assessment may be performed each year for a reporting unit at the Company’s option without first performing a qualitative assessment. The Company’s quantitative assessment of goodwill for possible impairment includes estimating the fair market value of a reporting unit which has goodwill associated with its operations using discounted cash flow and multiples of cash earnings valuation techniques, plus valuation comparisons to recent public sale transactions of similar businesses, if any. These impairment assessments and valuation methods require the Company to make estimates and assumptions regarding revenue growth, changes in working capital and capital expenditures, selling prices and profitability that drive cash flows, and the weighted average cost of capital. Many of these assumptions are determined by reference to market participants identified by the Company. Although management believes that the estimates and assumptions used were reasonable, actual results could differ from those estimates and assumptions. Other events and changes in circumstances may also require goodwill to be tested for impairment between annual measurement dates. While a decline in stock price and market capitalization is not specifically cited as a goodwill impairment indicator, a company’s stock price and market capitalization should be considered in determining whether it is more likely than not that the fair value of a reporting unit is less that its carrying value. Additionally, a significant decline in a company’s stock price may suggest that an adverse change in the business climate may have caused the fair value of one or more reporting units to fall below carrying value. A sustained decline in market capitalization below book value may be determined to require an interim goodwill impairment review.
Environmental	Environmental Costs that mitigate or prevent future environmental contamination or extend the life, increase the capacity or improve the safety or efficiency of property utilized in current operations are capitalized. Other costs that relate to current operations or an existing condition caused by past operations are expensed. Environmental liabilities are recorded when the Company’s liability is probable and the costs are reasonably estimable, but generally not later than the completion of the feasibility study or the Company’s recommendation of a remedy or commitment to an appropriate plan of action. The accruals are reviewed periodically and, as investigations and remediations proceed, adjustments of the accruals are made to reflect new information as appropriate. Accruals for losses from environmental remediation obligations are not discounted to their present value. The accruals are not reduced by possible recoveries from insurance carriers or other third parties, but do reflect allocations among potentially responsible parties (PRPs) at Federal Superfund sites or similar state-managed sites after an assessment is made of the likelihood that such parties will fulfill their obligations at such sites and after appropriate cost-sharing or other agreements are entered. The measurement of environmental liabilities by the Company is based on currently available facts, present laws and regulations, and current technology. Such estimates take into consideration the Company’s prior experience in site investigation and remediation, the data concerning cleanup costs available from other companies and regulatory authorities, and the professional judgment of the Company’s environmental experts in consultation with outside environmental specialists, when necessary.
Foreign Currency Translation	Foreign Currency Translation Assets and liabilities of international operations are translated into U.S. dollars using year-end exchange rates, while revenues and expenses are translated at average exchange rates during the period. The resulting net translation adjustments are recorded as a component of accumulated other comprehensive income (loss) in stockholders’ equity.
Sales Recognition	Sales Recognition The following is the Company’s accounting policy as it relates to Accounting Standards Codification Topic 606 (ASC 606), Contracts with Revenue from Customers. This guidance provides a five-step analysis of transactions to determine when and how revenue is recognized, and requires an entity to recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The following is the Company’s accounting policy as it relates to the five-step analysis for revenue recognition: 1. Identify the contract : The Company has determined that the contract with the customer is established when the customer purchase order is accepted or acknowledged. Long-term agreements (LTAs), which typically extend multiple years, are used by the Company and certain of its customers for its specialty materials, in the form of mill products, powders, parts and components, to reduce their supply uncertainty. While these LTAs generally define commercial terms including pricing, termination clauses and other contractual requirements, they do not represent the contract with the customer. 2. Identify the performance obligation in the contract : When the Company accepts or acknowledges the customer purchase order, the type of good or service is defined on a line by line basis. Individual performance obligations are established by virtue of the individual line items identified on the sales order acknowledgment at the time of issuance. Generally, the Company’s revenue relates to the sale of goods and contains a single performance obligation for each distinct good. Conversion services that transform customer-owned inventory to a different dimension, product form, and/or changed mechanical properties are classified as “goods”. 3. Determine the transaction price : Pricing is also defined on a sales order acknowledgment on a line item basis and includes an estimate of variable consideration when required by the terms of the individual customer contract. Variable consideration is when the selling price of the good is not known or is subject to adjustment under certain conditions. Types of variable consideration may include volume discounts, customer rebates and surcharges. ATI also provides assurances that goods or services will meet the product specifications contained within the acknowledged customer contract. As such, returns and refunds reserves are estimated based upon past product line history or, at certain locations, on a claim by claim basis. 4. Allocate the transaction price to the performance obligation : Since a customer contract generally contains only one performance obligation, this step of the analysis is generally not applicable to the Company. 5. Recognize revenue when or as the performance obligation is satisfied : Performance obligations generally occur at a point in time and are satisfied when control passes to the customer. For most transactions, control passes at the time of shipment in accordance with agreed upon delivery terms. On occasion, shipping and handling charges occur after the customer obtains control of the good. When this occurs, the shipping and handling services are considered activities to fulfill the promise to transfer the good. Certain customer agreements involving production of parts and components require revenue to be recognized over time due to there being no alternative use for the product without significant economic loss and an enforceable right to payment including a normal profit margin from the customer in the event of contract termination. The Company uses an input method for determining the amount of revenue, and associated standard cost, to recognize over-time revenue, cost and gross margin for these customer agreements. The input methods used for these agreements include costs incurred and labor hours expended, both of which give an accurate representation of the progress made toward complete satisfaction of that particular performance obligation. Contract assets are recognized when ATI’s conditional right to consideration for goods or services have transferred to the customer. A conditional right indicates that additional performance obligations associated with the contract are yet to be satisfied. Contract assets are assessed separately for impairment purposes. If ATI’s right to consideration from the customer is unconditional, this asset is accounted for as a receivable and presented separately from other contract assets. A right is unconditional if nothing other than the passage of time is required before payment of that consideration is due. Performance obligations that are recognized as revenue at a point-in-time and are billed to the customer are recognized as accounts receivable. Payment terms vary from customer to customer depending upon credit worthiness, prior payment history and other credit considerations. Contract costs are the incremental costs of obtaining and fulfilling a contract (i.e., costs that would not have been incurred if the contract had not been obtained) to provide goods and services to customers. Contract costs for ATI largely consist of design and development costs for molds, dies and other tools that ATI will own and that will be used in producing the products under the supply arrangement. Contract costs are classified as non-current assets and amortized to expense on a systematic and rational basis over a period consistent with the transfer to the customer of the goods or services to which the asset relates. Contract liabilities are recognized when ATI has received consideration from a customer to transfer goods or services at a future point in time when the Company performs under the contract. Elements of variable consideration discussed above may be recorded as contract liabilities. In addition, progress billings and advance payments from customers for costs incurred to date are also reported as contract liabilities.
Research and Development	Research and Development Research, development and technical service activities are closely interrelated and are directed toward development of new products, improvement of existing products, cost reduction, process improvement and control, quality assurance and control, development of new manufacturing methods, and improvement of existing manufacturing methods. Research and development costs are expensed as incurred. Company funded research and development costs were $16.3 million in 2022, $16.5 million in 2021, and $14.1 million in 2020. Customer funded research and development costs were $1.4 million in 2022, $3.5 million in 2021, and $0.7 million in 2020.
Government Assistance	Government Assistance The Company enters into agreements with U.S. federal agencies, U.S. state and local governments, and foreign governments that provide financial assistance and incentives supporting both new capital projects to expand and enhance manufacturing capabilities and also to sustain and maintain existing operations. Depending on the nature of the government program, the financial impacts may be recorded as a reduction to cost of sales through direct offset of labor and overhead costs or lower depreciation expense, or as a reduction of selling, general and administrative expenses for property tax abatement or other similar categories. Benefits from government assistance are recognized as the activities are incurred, subject to ongoing assessments of meeting other relevant terms such as employment or expenditure levels. In November 2021, ATI entered into an agreement with the U.S. Department of Transportation under the Aviation Manufacturing Jobs Protection (AMJP) program for a grant of up to $22.2 million. The receipt of the award was primarily conditioned upon the Company committing to not furlough or lay off a defined group of employees in High Performance Materials & Components (HPMC) segment operations during the six-month period of performance between November 2021 and May 2022. The AMJP grant benefit was recognized over the six-month performance period as a reduction to cost of sales in proportion to the compensation expense that the award was intended to defray, with $16.6 million recognized in 2022 operating results. Cash receipts from the AMJP program were $11.0 million in 2022, and this program is now completed. ATI is a party to various U.S. states’ economic development incentive programs that provide economic benefits in the forms of property tax relief or cash payments to offset capital expenditures. These programs generally include requirements for levels of capital spending and/or employment to qualify for the government assistance. For the year ended December 31, 2022, these state-level programs reduced selling, general and administrative expenses by $1.6 million and cash receipts were $2.8 million. Receivables for ongoing programs are $3.7 million as of December 31, 2022.
Stock-based Compensation	Stock-based Compensation The Company accounts for stock-based compensation transactions, such as nonvested restricted stock or stock units and performance equity awards, using fair value. Compensation expense for an award is estimated at the date of grant and is recognized over the requisite service period. Compensation expense is adjusted for equity awards that do not vest because service or performance conditions are not satisfied. However, compensation expense already recognized on plans which vest based solely on the attainment of market conditions, such as total shareholder return measures, is not adjusted based on the award attainment status at the end of the measurement period. Compensation expense is adjusted for estimated forfeitures over the award measurement period.
Income Taxes	Income Taxes The provision for, or benefit from, income taxes includes deferred taxes resulting from temporary differences in income for financial and tax purposes using the liability method. Such temporary differences result primarily from differences in the carrying value of assets and liabilities. Future realization of deferred income tax assets requires sufficient taxable income within the carryback and/or carryforward period available under tax law. The Company evaluates on a quarterly basis whether, based on all available evidence, it is probable that the deferred income tax assets are realizable. Valuation allowances are established when it is estimated that it is more likely than not that the tax benefit of the deferred tax asset will not be realized. The evaluation includes the consideration of all available evidence, both positive and negative, regarding the estimated future reversals of existing taxable temporary differences, estimated future taxable income exclusive of reversing temporary differences and carryforwards, historical taxable income in prior carryback periods if carryback is permitted, and potential tax planning strategies which may be employed to prevent an operating loss or tax credit carryforward from expiring unused. The verifiable evidence such as future reversals of existing temporary differences and the ability to carryback are considered before the subjective sources such as estimated future taxable income exclusive of temporary differences and tax planning strategies. It is the Company’s policy to classify interest and penalties recognized on underpayment of income taxes as income tax expense. It is also the Company’s policy to recognize deferred tax amounts stranded in accumulated other comprehensive
Net Income Per Common Share	Net Income Per Common Share Basic and diluted net income per share are calculated by dividing the net income available to common stockholders by the weighted average number of common shares outstanding during the year. Diluted amounts assume the issuance of common stock for all potentially dilutive share equivalents outstanding. The calculations of all diluted income/loss per share figures for a period exclude the potentially dilutive effect of dilutive share equivalents if there is a net loss since the inclusion in the calculation of additional shares in the net loss per share would result in a lower per share loss and therefore be anti-dilutive.
New Accounting Pronouncements Adopted and Pending Accounting Pronouncements	New Accounting Pronouncements Adopted In November 2021, the Financial Accounting Standards Board (FASB) issued new accounting guidance related to disclosures about certain types of government assistance. This new guidance requires business entities that account for transactions with a government by analogizing to a grant or contribution accounting model to make certain annual disclosures. It requires disclosure of the nature and significant terms and considerations of the transactions, the accounting policies used and the effects of those transactions on an entity’s financial statements. This new guidance is effective for the Company in fiscal year 2022, with early adoption permitted. The Company adopted this new accounting guidance effective January 1, 2022. The adoption of these changes did not have an impact on the Company’s consolidated financial statements other than the annual disclosure requirements included in the accounting policies discussion above. In August 2020, the FASB issued new accounting guidance related to accounting for convertible instruments. Under this new guidance, embedded conversion features are no longer separated from the host contract for convertible instruments with conversion features that are not required to be accounted for as derivatives, or that do not result in substantial premiums accounted for as paid-in capital. As such, a convertible debt instrument will be accounted for as a single liability measured at its amortized cost, as long as no other features require bifurcation and recognition as derivatives. By removing those separation models, the reported interest rate of convertible debt instruments typically will be closer to the coupon interest rate. The new guidance also addresses how convertible instruments are accounted for in the diluted earnings per share calculation, requiring the if-converted method, and requires enhanced disclosures about the terms of convertible instruments and contracts in an entity’s own equity. This new guidance was effective for the Company in fiscal year 2022, with early adoption permitted. The Company early adopted this new accounting guidance related to accounting for convertible instruments effective January 1, 2021 using the modified transition approach with the cumulative effect recognized as an adjustment to the opening balance of retained earnings. This new guidance was applicable to the Company’s 3.5% Convertible Senior Notes due 2025 (the 2025 Convertible Notes) that were issued in June 2020, for which the embedded conversion option was required to be separately accounted for as a component of stockholders’ equity. Upon adoption on January 1, 2021, long-term debt increased by $45.4 million and stockholders’ equity decreased by the same amount, representing the net impact of two adjustments: (1) the $49.8 million value of the embedded conversion, which is net of allocated offering costs, previously classified in additional paid-in capital in stockholders’ equity, and (2) a $4.4 million increase to retained earnings for the cumulative effect of adoption primarily related to the non-cash interest expense recorded in fiscal year 2020 for the amortization of the portion of the 2025 Convertible Notes allocated to stockholders’ equity. Prospectively, the reported interest expense for the 2025 Convertible Notes no longer included the non-cash interest expense of the equity component as required under prior accounting standards and is closer to the 3.5% cash coupon rate. There was no impact to the Company’s earnings per share calculation as it previously applied the if-converted method to the 2025 Convertible Notes given ATI’s flexibility to settle conversions of the 2025 Convertible Notes in cash, shares of ATI’s common stock or a combination thereof, at ATI’s election. Pending Accounting Pronouncements In September 2022, the FASB issued new accounting guidance related to disclosures about supplier finance programs. Supplier finance programs allow a buyer to offer its suppliers the option for access to payment in advance of an invoice due date, which is paid by a third-party finance provider or intermediary on the basis of invoices that the buyer has confirmed as valid. This new guidance requires a buyer in a supplier finance program to disclose sufficient information about the program to allow a user of financial statements to understand the program’s nature, activity during the period, changes from period to period, and potential magnitude, using both qualitative and quantitative information about its supplier finance programs. This new
Asset Retirement Obligations	Asset Retirement Obligations The Company maintains reserves where a legal obligation exists to perform an asset retirement activity and the fair value of the liability can be reasonably estimated. These asset retirement obligations (AROs) include liabilities where the timing and (or) method of settlement may be conditional on a future event, that may or may not be within the control of the entity. At December 31, 2022, the Company had recognized AROs of $17.8 million related to landfill closures, decommissioning costs, facility leases and conditional AROs associated with manufacturing activities using what may be characterized as potentially hazardous materials. Estimates of AROs are evaluated annually in the fourth quarter, or more frequently if material new information becomes known. Accounting for asset retirement obligations requires significant estimation and in certain cases, the Company has determined that an ARO exists, but the amount of the obligation is not reasonably estimable. The Company may determine that additional AROs are required to be recognized as new information becomes available.
Derivative Financial Instruments and Hedging	Derivative Financial Instruments and Hedging As part of its risk management strategy, the Company, from time-to-time, utilizes derivative financial instruments to manage its exposure to changes in raw material prices, energy costs, foreign currencies, and interest rates. In accordance with applicable accounting standards, the Company accounts for most of these contracts as hedges. The Company sometimes uses futures and swap contracts to manage exposure to changes in prices for forecasted purchases of raw materials, such as nickel, and natural gas. Under these contracts, which are generally accounted for as cash flow hedges, the price of the item being hedged is fixed at the time that the contract is entered into and the Company is obligated to make or receive a payment equal to the net change between this fixed price and the market price at the date the contract matures. The majority of ATI’s products are sold utilizing raw material surcharges and index mechanisms. However, as of December 31, 2022, the Company had entered into financial hedging arrangements primarily at the request of its customers, related to firm orders, for an aggregate notional amount of approximately 6 million pounds of nickel with hedge dates through 2024. The aggregate notional amount hedged is approximately 8% of a single year’s estimated nickel raw material purchase requirements. These derivative instruments are used to hedge the variability of a selling price that is based on the London Metals Exchange (LME) index for nickel, as well as to hedge the variability of the purchase cost of nickel based on this LME index. Any gain or loss associated with these hedging arrangements is included in sales or cost of sales, depending on whether the underlying risk being hedged was the variable selling price or the variable raw material cost, respectively. At December 31, 2022, the outstanding financial derivatives used to hedge the Company’s exposure to energy cost volatility included natural gas cost hedges. At December 31, 2022, the company hedged approximately 70% of the Company’s annual forecasted domestic requirements for natural gas for 2023 and approximately 25% for 2024. While the majority of the Company’s direct export sales are transacted in U.S. dollars, foreign currency exchange contracts are used, from time-to-time, to limit transactional exposure to changes in currency exchange rates for those transactions denominated in a non-U.S. currency. The Company sometimes purchases foreign currency forward contracts that permit it to sell specified amounts of foreign currencies expected to be received from its export sales for pre-established U.S. dollar amounts at specified dates. The forward contracts are denominated in the same foreign currencies in which export sales are denominated. These contracts are designated as hedges of the variability in cash flows of a portion of the forecasted future export sales transactions which otherwise would expose the Company to foreign currency risk, primarily euros. In addition, the Company may also hedge forecasted capital expenditures and designate cash balances held in foreign currencies as hedges of forecasted foreign currency transactions. At December 31, 2022, the Company had no significant outstanding foreign currency forward contracts. The Company may enter into derivative interest rate contracts to maintain a reasonable balance between fixed- and floating-rate debt. The Company has a $50 million floating-for-fixed interest rate swap that matures in June 2024 which converts half of the ABL Term Loan to a 4.21% fixed rate. The Company designated the interest rate swap as a cash flow hedge of the Company’s exposure to the variability of the payment of interest on a portion of its ABL Term Loan borrowings. The ineffective portion at hedge inception, determined from the fair value of the swap immediately prior to amendment in July 2019, was amortized to interest expense over the initial ABL Term Loan swap maturity date of January 12, 2021. There are no credit risk-related contingent features in the Company’s derivative contracts, and the contracts contained no provisions under which the Company has posted, or would be required to post, collateral. The counterparties to the Company’s derivative contracts were substantial and creditworthy commercial banks that are recognized market makers. The Company controls its credit exposure by diversifying across multiple counterparties and by monitoring credit ratings and credit default swap spreads of its counterparties. The Company also enters into master netting agreements with counterparties when possible.
Pension Plans and Other Postretirement Benefits	The Company has defined contribution retirement plans or defined benefit pension plans covering substantially all employees. Company contributions to defined contribution retirement plans are generally based on a percentage of eligible pay or based on hours worked. Benefits under the defined benefit pension plans are generally based on years of service and/or final average pay. The Company also sponsors several postretirement plans covering certain collectively-bargained salaried and hourly employees. The plans provide health care and life insurance benefits for eligible retirees. In most retiree health care plans, Company contributions towards premiums are capped based on the cost as of a certain date, thereby creating a defined contribution.

Derivative Instruments and Hedg

Derivative Instruments and Hedging Activities (Policies)	12 Months Ended
	Dec. 31, 2022
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments and Hedging	Derivative Financial Instruments and Hedging As part of its risk management strategy, the Company, from time-to-time, utilizes derivative financial instruments to manage its exposure to changes in raw material prices, energy costs, foreign currencies, and interest rates. In accordance with applicable accounting standards, the Company accounts for most of these contracts as hedges. The Company sometimes uses futures and swap contracts to manage exposure to changes in prices for forecasted purchases of raw materials, such as nickel, and natural gas. Under these contracts, which are generally accounted for as cash flow hedges, the price of the item being hedged is fixed at the time that the contract is entered into and the Company is obligated to make or receive a payment equal to the net change between this fixed price and the market price at the date the contract matures. The majority of ATI’s products are sold utilizing raw material surcharges and index mechanisms. However, as of December 31, 2022, the Company had entered into financial hedging arrangements primarily at the request of its customers, related to firm orders, for an aggregate notional amount of approximately 6 million pounds of nickel with hedge dates through 2024. The aggregate notional amount hedged is approximately 8% of a single year’s estimated nickel raw material purchase requirements. These derivative instruments are used to hedge the variability of a selling price that is based on the London Metals Exchange (LME) index for nickel, as well as to hedge the variability of the purchase cost of nickel based on this LME index. Any gain or loss associated with these hedging arrangements is included in sales or cost of sales, depending on whether the underlying risk being hedged was the variable selling price or the variable raw material cost, respectively. At December 31, 2022, the outstanding financial derivatives used to hedge the Company’s exposure to energy cost volatility included natural gas cost hedges. At December 31, 2022, the company hedged approximately 70% of the Company’s annual forecasted domestic requirements for natural gas for 2023 and approximately 25% for 2024. While the majority of the Company’s direct export sales are transacted in U.S. dollars, foreign currency exchange contracts are used, from time-to-time, to limit transactional exposure to changes in currency exchange rates for those transactions denominated in a non-U.S. currency. The Company sometimes purchases foreign currency forward contracts that permit it to sell specified amounts of foreign currencies expected to be received from its export sales for pre-established U.S. dollar amounts at specified dates. The forward contracts are denominated in the same foreign currencies in which export sales are denominated. These contracts are designated as hedges of the variability in cash flows of a portion of the forecasted future export sales transactions which otherwise would expose the Company to foreign currency risk, primarily euros. In addition, the Company may also hedge forecasted capital expenditures and designate cash balances held in foreign currencies as hedges of forecasted foreign currency transactions. At December 31, 2022, the Company had no significant outstanding foreign currency forward contracts. The Company may enter into derivative interest rate contracts to maintain a reasonable balance between fixed- and floating-rate debt. The Company has a $50 million floating-for-fixed interest rate swap that matures in June 2024 which converts half of the ABL Term Loan to a 4.21% fixed rate. The Company designated the interest rate swap as a cash flow hedge of the Company’s exposure to the variability of the payment of interest on a portion of its ABL Term Loan borrowings. The ineffective portion at hedge inception, determined from the fair value of the swap immediately prior to amendment in July 2019, was amortized to interest expense over the initial ABL Term Loan swap maturity date of January 12, 2021. There are no credit risk-related contingent features in the Company’s derivative contracts, and the contracts contained no provisions under which the Company has posted, or would be required to post, collateral. The counterparties to the Company’s derivative contracts were substantial and creditworthy commercial banks that are recognized market makers. The Company controls its credit exposure by diversifying across multiple counterparties and by monitoring credit ratings and credit default swap spreads of its counterparties. The Company also enters into master netting agreements with counterparties when possible.

Commitment and Contingencies (P

Commitment and Contingencies (Policies)	12 Months Ended
	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Environmental	Environmental Costs that mitigate or prevent future environmental contamination or extend the life, increase the capacity or improve the safety or efficiency of property utilized in current operations are capitalized. Other costs that relate to current operations or an existing condition caused by past operations are expensed. Environmental liabilities are recorded when the Company’s liability is probable and the costs are reasonably estimable, but generally not later than the completion of the feasibility study or the Company’s recommendation of a remedy or commitment to an appropriate plan of action. The accruals are reviewed periodically and, as investigations and remediations proceed, adjustments of the accruals are made to reflect new information as appropriate. Accruals for losses from environmental remediation obligations are not discounted to their present value. The accruals are not reduced by possible recoveries from insurance carriers or other third parties, but do reflect allocations among potentially responsible parties (PRPs) at Federal Superfund sites or similar state-managed sites after an assessment is made of the likelihood that such parties will fulfill their obligations at such sites and after appropriate cost-sharing or other agreements are entered. The measurement of environmental liabilities by the Company is based on currently available facts, present laws and regulations, and current technology. Such estimates take into consideration the Company’s prior experience in site investigation and remediation, the data concerning cleanup costs available from other companies and regulatory authorities, and the professional judgment of the Company’s environmental experts in consultation with outside environmental specialists, when necessary.

Business Segments (Tables)

Business Segments (Tables)	12 Months Ended
	Dec. 31, 2022
Segment Reporting [Abstract]
Schedule of sales by segment	(In millions) 2022 2021 2020 Total sales: High Performance Materials & Components $ 1,815.7 $ 1,248.3 $ 1,235.4 Advanced Alloys & Solutions 2,433.7 1,762.4 1,947.5 Total sales 4,249.4 3,010.7 3,182.9 Intersegment sales: High Performance Materials & Components 174.5 93.2 70.8 Advanced Alloys & Solutions 238.9 117.7 130.0 Total intersegment sales 413.4 210.9 200.8 Sales to external customers: High Performance Materials & Components 1,641.2 1,155.1 1,164.6 Advanced Alloys & Solutions 2,194.8 1,644.7 1,817.5 Total sales to external customers $ 3,836.0 $ 2,799.8 $ 2,982.1
Schedule of operating profit (loss) by segment	(In millions) 2022 2021 2020 EBITDA: High Performance Materials & Components $ 296.0 $ 159.9 $ 129.6 Advanced Alloys & Solutions 327.8 191.7 115.0 Total segment EBITDA 623.8 351.6 244.6 Corporate expenses (62.4) (55.9) (40.9) Closed operations and other expenses (12.1) (4.8) (7.4) Depreciation & amortization (142.9) (143.9) (143.3) Interest expense, net (87.4) (96.9) (94.4) Restructuring and other credits (charges) (See Note 19) (23.7) 10.5 (1,132.1) Strike related costs — (63.2) — Retirement benefit settlement gain (See Note 14) — 64.9 — Impairment of goodwill (See Note 5) — — (287.0) Joint venture restructuring credit (charge) (See Note 7) 0.9 — (2.4) Debt extinguishment charge (See Note 10) — (65.5) (21.5) Gain (loss) on asset sales and sale of business, net (134.2) 13.8 2.5 Income (loss) before income taxes $ 162.0 $ 10.6 $ (1,481.9)
Schedule of other financial information by segment	Certain additional information regarding the Company’s business segments is presented below: (In millions) 2022 2021 2020 Depreciation and amortization: High Performance Materials & Components $ 68.3 $ 75.0 $ 78.1 Advanced Alloys & Solutions 67.4 64.5 62.1 Other 7.2 4.4 3.1 Total depreciation and amortization $ 142.9 $ 143.9 $ 143.3 Capital expenditures: High Performance Materials & Components $ 33.3 $ 40.2 $ 83.1 Advanced Alloys & Solutions 89.6 110.6 45.9 Corporate 8.0 1.8 7.5 Total capital expenditures $ 130.9 $ 152.6 $ 136.5 Identifiable assets: 2022 2021 2020 High Performance Materials & Components $ 1,749.3 $ 1,624.8 $ 1,594.6 Advanced Alloys & Solutions 1,981.1 1,914.0 1,664.0 Corporate: Deferred Taxes 4.7 6.3 5.1 Cash and cash equivalents and other 710.5 740.1 771.2 Total assets $ 4,445.6 $ 4,285.2 $ 4,034.9
Schedule of company assets by country	($ in millions) 2022 Percent 2021 Percent 2020 Percent Total assets: United States $ 3,942.7 89 % $ 3,587.0 84 % $ 3,356.8 83 % China 321.1 7 % 406.4 9 % 325.5 8 % United Kingdom 13.4 — % 153.9 4 % 122.4 3 % Other 168.4 4 % 137.9 3 % 230.2 6 % Total Assets $ 4,445.6 100 % $ 4,285.2 100 % $ 4,034.9 100 %

Restructuring and Related Activ

Restructuring and Related Activities (Tables)	12 Months Ended
	Dec. 31, 2022
Restructuring and Related Activities [Abstract]
Restructuring and Related Costs	Restructuring reserves for severance cost activity is as follows: Severance and Employee Benefit Costs December 31, 2022 December 31, 2021 December 31, 2020 Beginning of year balance $ 17.7 $ 43.4 $ 4.5 Additions/(Adjustments) (4.8) (12.0) 60.5 Payments (3.1) (13.7) (21.6) End of year balance $ 9.8 $ 17.7 $ 43.4

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2022
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Finite-Lived Intangible Assets	Other intangible assets, which are included in Other assets on the accompanying consolidated balance sheets as of December 31, 2022 and 2021 were as follows: December 31, 2022 December 31, 2021 (in millions) Gross Accumulated Gross Accumulated Technology $ 61.2 $ (35.4) $ 61.2 $ (32.3) Customer relationships 24.8 (11.6) 24.8 (10.6) Trademarks 48.8 (29.3) 48.8 (26.0) Total amortizable intangible assets $ 134.8 $ (76.3) $ 134.8 $ (68.9)

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	12 Months Ended
	Dec. 31, 2022
Revenue from Contract with Customer [Abstract]
Schedule of Disaggregation of Revenue	Comparative information of the Company’s overall revenues (in millions) by global and geographical markets for the fiscal years ended December 31, 2022, 2021 and 2020 is as follows: (in millions) 2022 2021 2020 HPMC AA&S Total HPMC AA&S Total HPMC AA&S Total Diversified Global Markets: Aerospace & Defense: Jet-Engines- Commercial $ 975.7 $ 87.8 $ 1,063.5 $ 480.9 $ 36.3 $ 517.2 $ 542.7 $ 58.2 $ 600.9 Airframes- Commercial 184.1 284.8 468.9 132.8 129.9 262.7 219.8 191.0 410.8 Defense 158.2 183.0 341.2 221.8 131.0 352.8 184.4 163.9 348.3 Total Aerospace & Defense $ 1,318.0 $ 555.6 $ 1,873.6 $ 835.5 $ 297.2 $ 1,132.7 $ 946.9 $ 413.1 $ 1,360.0 Energy: Oil & Gas 35.0 441.7 476.7 42.2 290.1 332.3 37.3 328.5 365.8 Specialty Energy 113.6 163.0 276.6 136.1 123.5 259.6 68.9 184.2 253.1 Total Energy 148.6 604.7 753.3 178.3 413.6 591.9 106.2 512.7 618.9 Automotive 11.2 290.9 302.1 8.7 296.4 305.1 5.5 257.7 263.2 Electronics 2.4 197.6 200.0 1.2 213.9 215.1 0.9 176.8 177.7 Construction/Mining 34.1 142.3 176.4 24.0 98.2 122.2 18.6 123.4 142.0 Medical 73.2 89.9 163.1 60.3 71.2 131.5 47.7 71.4 119.1 Food Equipment & Appliances 0.2 158.3 158.5 0.1 153.0 153.1 — 159.2 159.2 Other 53.5 155.5 209.0 47.0 101.2 148.2 38.8 103.2 142.0 Total $ 1,641.2 $ 2,194.8 $ 3,836.0 $ 1,155.1 $ 1,644.7 $ 2,799.8 $ 1,164.6 $ 1,817.5 $ 2,982.1 (in millions) 2022 2021 2020 HPMC AA&S Total HPMC AA&S Total HPMC AA&S Total Primary Geographical Market: United States $ 742.9 $ 1,475.7 $ 2,218.6 $ 571.3 $ 963.6 $ 1,534.9 $ 641.0 $ 1,168.1 $ 1,809.1 China 59.8 292.0 351.8 49.5 320.9 370.4 31.0 284.5 315.5 United Kingdom 165.7 52.0 217.7 136.7 17.2 153.9 101.9 24.6 126.5 Germany 148.4 52.5 200.9 74.1 47.2 121.3 76.6 48.8 125.4 France 125.7 31.5 157.2 48.7 9.8 58.5 66.5 18.4 84.9 Canada 46.2 41.2 87.4 36.3 39.6 75.9 28.3 40.6 68.9 Rest of World 352.5 249.9 602.4 238.5 246.4 484.9 219.3 232.5 451.8 Total $ 1,641.2 $ 2,194.8 $ 3,836.0 $ 1,155.1 $ 1,644.7 $ 2,799.8 $ 1,164.6 $ 1,817.5 $ 2,982.1 Comparative information of the Company’s major products based on their percentages of sales is included in the following table. The Company no longer reports standard stainless product sales as a separate product category. Prior period information includes these sales within the nickel-based alloys and specialty alloys category. HRPF conversion service sales in the AA&S segment are excluded from this presentation. 2022 2021 2020 HPMC AA&S Total HPMC AA&S Total HPMC AA&S Total Diversified Products: Nickel-based alloys and specialty alloys 49 % 54 % 52 % 43 % 44 % 43 % 38 % 49 % 45 % Precision forgings, castings and components 34 % — % 15 % 38 % — % 16 % 34 % — % 14 % Precision rolled strip — % 25 % 14 % — % 33 % 19 % — % 25 % 15 % Titanium and titanium-based alloys 17 % 7 % 11 % 19 % 6 % 12 % 28 % 11 % 17 % Zirconium and related alloys — % 14 % 8 % — % 17 % 10 % — % 15 % 9 % Total 100 % 100 % 100 % 100 % 100 % 100 % 100 % 100 % 100 %
Schedule of Accounts Receivable - Reserve for Doubtful Accounts	The following represents the rollforward of accounts receivable - reserve for doubtful accounts for the fiscal years ended December 31, 2022, 2021 and 2020: (in millions) Accounts Receivable - Reserve for Doubtful Accounts Balance as of December 31, 2019 4.6 Expense to increase the reserve 0.2 Write-off of uncollectible accounts (0.5) Balance as of December 31, 2020 4.3 Expense to increase the reserve 0.3 Write-off of uncollectible accounts (0.8) Balance as of December 31, 2021 3.8 Expense to increase the reserve 4.6 Write-off of uncollectible accounts (0.7) Balance as of December 31, 2022 $ 7.7
Schedule of Contract Assets and Liabilities	The following represents the rollforward of contract assets and liabilities for the fiscal years ended December 31, 2022, 2021 and 2020: (in millions) Contract Assets Short-term 2022 2021 2020 Balance as of beginning of fiscal year $ 53.9 $ 38.9 $ 38.5 Recognized in current year 105.0 93.8 84.2 Reclassified to accounts receivable (88.0) (76.2) (83.9) Reclassification to/from long-term and contract liability (6.8) (2.6) 0.1 Balance as of period end $ 64.1 $ 53.9 $ 38.9 Long-term (a) 2022 2021 2020 Balance as of beginning of fiscal year $ — $ — $ 0.1 Reclassification to/from short-term — — (0.1) Balance as of period end $ — $ — $ — (in millions) Contract Liabilities Short-term 2022 2021 2020 Balance as of beginning of fiscal year $ 116.2 $ 111.8 $ 78.7 Recognized in current year 183.1 161.5 170.3 Amounts in beginning balance reclassified to revenue (99.8) (85.1) (55.9) Current year amounts reclassified to revenue (72.3) (72.9) (90.1) Divestiture — (0.8) — Other 0.7 0.1 — Reclassification to/from long-term and contract asset 21.2 1.6 8.8 Balance as of period end $ 149.1 $ 116.2 $ 111.8 Long-term (a) 2022 2021 2020 Balance as of beginning of fiscal year $ 84.4 $ 32.0 $ 25.9 Recognized in current year 10.4 56.6 14.9 Reclassification to/from short-term (28.0) (4.2) (8.8) Balance as of period end $ 66.8 $ 84.4 $ 32.0 (a) Long-term contract assets are included in Other long-term assets and long-term contract liabilities are included in Other long-term liabilities on the consolidated balance sheets.

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Dec. 31, 2022
Inventory Disclosure [Abstract]
Schedule of Inventory	Inventories at December 31, 2022 and 2021 were as follows (in millions): 2022 2021 Raw materials and supplies $ 213.6 $ 160.3 Work-in-process 941.1 829.6 Finished goods 111.9 121.8 1,266.6 1,111.7 Inventory valuation reserves (70.9) (65.4) Total inventories, net $ 1,195.7 $ 1,046.3 Inventories are stated at the lower of cost (FIFO and average cost methods) or net realizable value.

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
Schedule of property plant and equipment, net	Property, plant and equipment at December 31, 2022 and 2021 was as follows: (In millions) 2022 2021 Land $ 31.5 $ 34.4 Buildings 601.6 575.5 Equipment and leasehold improvements 2,895.5 2,870.2 3,528.6 3,480.1 Accumulated depreciation and amortization (1,979.5) (1,951.6) Total property, plant and equipment, net $ 1,549.1 $ 1,528.5
Schedule depreciation and amortization	Depreciation and amortization for the years ended December 31, 2022, 2021 and 2020 was as follows: (In millions) 2022 2021 2020 Depreciation of property, plant and equipment $ 115.4 $ 117.4 $ 119.5 Software and other amortization 27.5 26.5 23.8 Total depreciation and amortization $ 142.9 $ 143.9 $ 143.3

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2022
Asset Retirement Obligation Disclosure [Abstract]
Schedule of changes in asset retirement obligations	Changes in asset retirement obligations for the years ended December 31, 2022 and 2021 were as follows: (In millions) 2022 2021 Balance at beginning of year $ 19.0 $ 24.0 Accretion expense 0.8 0.8 Payments (2.0) (5.6) Divestiture — (0.2) Balance at end of year $ 17.8 $ 19.0

Supplemental Financial Statem_2

Supplemental Financial Statement Information (Tables)	12 Months Ended
	Dec. 31, 2022
Additional Financial Information Disclosure [Abstract]
Schedule of cash and cash equivalents	Cash and cash equivalents at December 31, 2022 and 2021 were as follows: (In millions) 2022 2021 Cash $ 164.9 $ 222.8 Other short-term investments 419.1 464.9 Total cash and cash equivalents $ 584.0 $ 687.7
Schedule of other non-operating income (expense)	Other income (expense) for the years ended December 31, 2022, 2021, and 2020 was as follows: (in millions) 2022 2021 2020 Rent, royalty income and other income $ 2.3 $ 1.1 $ 0.9 Gains from disposal of property, plant and equipment, net 0.2 2.9 2.9 Net equity income (loss) on joint ventures (See Note 7) 12.6 0.1 (7.0) Gain on sales of businesses, net (See Note 6) — 13.8 — Joint venture restructuring credit (charge) (See Note 7) 0.9 — (2.4) Adjustment to indemnification for conditional ARO costs — — 4.3 Litigation settlement (See Note 21) (28.5) — — Other — 0.3 0.1 Total other income (expense), net $ (12.5) $ 18.2 $ (1.2)

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2022
Debt Disclosure [Abstract]
Schedule of debt	Debt at December 31, 2022 and 2021 was as follows: (In millions) 2022 2021 ATI Inc. 5.875% Senior Notes due 2027 350.0 350.0 ATI Inc. 5.125% Senior Notes due 2031 350.0 350.0 ATI Inc. 4.875% Notes due 2029 325.0 325.0 ATI Inc. 3.5% Convertible Senior Notes due 2025 291.4 291.4 ATI Inc. 4.75% Convertible Senior Notes due 2022 — 84.2 Allegheny Ludlum 6.95% Debentures due 2025 (a) 150.0 150.0 ABL Term Loan 200.0 200.0 U.S. revolving credit facility — — Foreign credit agreements 19.4 27.4 Finance leases and other 79.4 85.7 Debt issuance costs (17.2) (20.8) Total short-term and long-term debt 1,748.0 1,842.9 Short-term debt and current portion of long-term debt 41.7 131.3 Total long-term debt $ 1,706.3 $ 1,711.6 (a) The payment obligations of these debentures issued by Allegheny Ludlum, LLC are fully and unconditionally guaranteed by ATI.
Interest Income and Interest Expense Disclosure	Interest expense on the 2025 Convertible Notes was as follows: Fiscal year ended December 31, (in millions) 2022 2021 2020 Contractual coupon rate $ 10.2 $ 10.2 $ 5.3 Amortization of debt issuance costs 1.8 1.7 0.7 Total interest expense $ 12.0 $ 11.9 $ 6.0 Fiscal year ended December 31, (in millions) 2022 2021 2020 Contractual coupon rate $ 2.0 $ 4.0 $ 8.6 Amortization of debt issuance costs 0.3 0.5 1.0 Total interest expense $ 2.3 $ 4.5 $ 9.6

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2022
Leases [Abstract]
Schedule of Lease Cost Components	The following represents the components of lease cost and other information for both operating and financing leases for the years ending December 31, 2022, 2021 and 2020: ($ in millions) Year ended December 31, 2022 December 31, 2021 December 31, 2020 Lease Cost Finance Lease Cost: Amortization of right of use asset $ 8.9 $ 7.1 $ 3.5 Interest on lease liabilities 4.1 3.1 1.0 Operating lease cost 16.4 22.7 20.8 Short-term lease cost 2.9 1.6 1.9 Variable lease cost 1.0 0.9 0.9 Sublease income — (0.3) (0.1) Total lease cost $ 33.3 $ 35.1 $ 28.0 Other information Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from finance leases $ 4.1 $ 3.0 $ 1.0 Operating cash flows from operating leases $ 17.4 $ 20.0 $ 21.7 Financing cash flows from finance leases $ 20.9 $ 14.3 $ 6.2 Right of use assets obtained in exchange for new finance lease liabilities $ 15.3 $ 58.9 $ 42.3 Right of use assets obtained in exchange for new operating lease liabilities $ 18.0 $ 4.8 $ 12.4 Weighted average remaining lease term - finance leases 4 years 5 years 4 years Weighted average remaining lease term - operating leases 6 years 5 years 6 years Weighted average discount rate - finance leases 5.6 % 5.2 % 6.2 % Weighted average discount rate - operating leases 6.8 % 6.5 % 6.9 %
Schedule of Operating Lease Liability Maturities	The following table reconciles future minimum undiscounted rental commitments for operating leases to the operating lease liabilities recorded on the consolidated balance sheet as of December 31, 2022 (in millions): December 31, 2022 2023 $ 15.5 2024 12.7 2025 10.3 2026 8.0 2027 6.6 2028 and thereafter 16.5 Total undiscounted lease payments $ 69.6 Present value adjustment (14.4) Operating lease liabilities $ 55.2
Schedule of Finance Lease Liability Maturities	The following table reconciles future minimum undiscounted rental commitments for finance leases to the finance lease liabilities recorded on the consolidated balance sheet as of December 31, 2022 (in millions): December 31, 2022 2023 $ 26.2 2024 22.4 2025 17.9 2026 11.0 2027 7.8 2028 and thereafter 3.0 Total undiscounted lease payments $ 88.3 Present value adjustment (9.5) Finance lease liabilities $ 78.8

Derivative Financial Instrume_2

Derivative Financial Instruments and Hedging (Tables)	12 Months Ended
	Dec. 31, 2022
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of derivative instruments	The fair values of the Company’s derivative financial instruments are presented below, representing the gross amounts recognized which are not offset by counterparty or by type of item hedged. All fair values for these derivatives were measured using Level 2 information as defined by the accounting standard hierarchy, which includes quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and inputs derived principally from or corroborated by observable market data. (In millions) December 31, December 31, Asset derivatives Balance sheet location Derivatives designated as hedging instruments: Interest rate swap Prepaid expenses and other current assets $ 1.4 $ — Natural gas contracts Prepaid expenses and other current assets 2.4 2.0 Nickel and other raw material contracts Prepaid expenses and other current assets 12.5 5.0 Interest rate swap Other assets 0.5 — Natural gas contracts Other assets 0.7 0.5 Nickel and other raw material contracts Other assets 0.5 0.1 Total derivatives designated as hedging instruments 18.0 7.6 Total asset derivatives $ 18.0 $ 7.6 Liability derivatives Balance sheet location Derivatives designated as hedging instruments: Interest rate swap Other current liabilities $ — $ 0.9 Natural gas contracts Other current liabilities 2.0 0.7 Nickel and other raw material contracts Other current liabilities 2.1 0.2 Interest rate swap Other long-term liabilities — 0.7 Natural gas contracts Other long-term liabilities 0.5 0.2 Total derivatives designated as hedging instruments 4.6 2.7 Total liability derivatives $ 4.6 $ 2.7
Schedule of derivative instruments gain (loss)	Activity with regard to derivatives designated as cash flow hedges for the years ended December 31, 2022 and 2021 were as follows (in millions): Derivatives in Cash Flow Hedging Relationships Amount of Gain (Loss) Amount of Gain (Loss) 2022 2021 2022 2021 Nickel and other raw material contracts $ 27.1 $ 6.2 $ 20.5 $ 5.4 Natural gas contracts 10.9 5.2 11.5 4.0 Foreign exchange contracts 0.7 0.2 0.7 0.1 Interest rate swap 2.3 0.1 (0.1) (0.8) Total $ 41.0 $ 11.7 $ 32.6 $ 8.7 (a) The gains (losses) reclassified from accumulated OCI into income related to the derivatives, with the exception of the interest rate swap, are presented in sales and cost of sales in the same period or periods in which the hedged item affects earnings. The gains (losses) reclassified from accumulated OCI into income on the interest rate swap are presented in interest expense in the same period as the interest expense on the ABL Term Loan is recognized in earnings.

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Schedule of financial instrument fair value	The estimated fair value of financial instruments at December 31, 2022 was as follows: Fair Value Measurements at Reporting Date Using (In millions) Total Total Quoted Prices in Significant Cash and cash equivalents $ 584.0 $ 584.0 $ 584.0 $ — Derivative financial instruments: Assets 18.0 18.0 — 18.0 Liabilities 4.6 4.6 — 4.6 Debt (a) 1,765.2 1,964.5 1,665.7 298.8 The estimated fair value of financial instruments at December 31, 2021 was as follows: Fair Value Measurements at Reporting Date Using (In millions) Total Total Quoted Prices in Significant Cash and cash equivalents $ 687.7 $ 687.7 $ 687.7 $ — Derivative financial instruments: Assets 7.6 7.6 — 7.6 Liabilities 2.7 2.7 — 2.7 Debt (a) 1,863.7 2,003.2 1,690.1 313.1

Retirement Benefits (Tables)

Retirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2022
Retirement Benefits [Abstract]
Schedule of defined benefit plans	The components of pension and other postretirement benefit expense for the Company’s defined benefit plans included the following: Pension Benefits Other Postretirement Benefits (In millions) 2022 2021 2020 2022 2021 2020 Service cost—benefits earned during the year $ 11.9 $ 15.1 $ 12.7 $ 1.1 $ 1.5 $ 2.3 Interest cost on benefits earned in prior years 69.7 68.4 86.3 7.7 8.0 10.7 Expected return on plan assets (128.2) (136.4) (134.5) — — — Amortization of prior service cost (credit) 0.4 0.6 0.7 (0.9) (2.4) (3.8) Amortization of net actuarial loss 63.5 75.6 74.5 13.2 13.9 10.8 Settlement loss (gain) 29.5 — — — (64.9) — Curtailment gain — — — — — (0.2) Termination benefits — — 10.9 — — 6.7 Total retirement benefit expense (income) $ 46.8 $ 23.3 $ 50.6 $ 21.1 $ (43.9) $ 26.5
Schedule of assumptions used	Actuarial assumptions used to develop the components of defined benefit pension expense and other postretirement benefit expense were as follows: Pension Benefits Other Postretirement Benefits 2022 2021 2020 2022 2021 2020 Discount rate 2.95 % 2.60 % 3.40 % 2.80 % 2.45 % 3.25 % Rate of increase in future compensation levels 2.00% - 3.00% 1.00 % 1.00 % — — — Weighted average expected long-term rate of return on assets 6.43 % 6.71 % 7.16 % — % — % — %
Schedule of assumptions used for year end valuation	Actuarial assumptions used for the valuation of defined benefit pension and other postretirement benefit obligations at the end of the respective periods were as follows: Pension Benefits Other Postretirement Benefits 2022 2021 2022 2021 Discount rate 5.55 % 2.95 % 5.45 % 2.80 % Rate of increase in future compensation levels 3.00 % 2.00% - 3.00% — —
Schedule of changes in projected benefit obligations	A reconciliation of the funded status for the Company’s defined benefit pension and other postretirement benefit plans at December 31, 2022 and 2021 was as follows: Pension Benefits Other Postretirement Benefits (In millions) 2022 2021 2022 2021 Change in benefit obligations: Benefit obligation at beginning of year $ 2,517.0 $ 2,720.1 $ 287.3 $ 357.6 Service cost 11.9 15.1 1.1 1.5 Interest cost 69.7 68.4 7.7 8.0 Benefits paid (155.6) (235.0) (29.7) (28.9) Subsidy received — — 0.3 0.4 Divestiture (75.8) — — — Effect of currency rates (3.2) (1.3) — — Net actuarial (gains) losses – discount rate change (556.8) (104.0) (48.2) (9.0) – other 11.1 53.7 (5.8) 0.7 Settlement gain — — — (43.0) Benefit obligation at end of year $ 1,818.3 $ 2,517.0 $ 212.7 $ 287.3
Schedule of changes in fair value of plan assets	Pension Benefits Other Postretirement Benefits (In millions) 2022 2021 2022 2021 Change in plan assets: Fair value of plan assets at beginning of year $ 2,120.9 $ 2,046.4 $ — $ — Actual returns on plan assets and plan expenses (317.0) 233.8 — — Employer contributions 57.4 77.3 — — Divestiture (101.8) — — — Effect of currency rates (4.4) (1.6) — — Benefits paid (155.6) (235.0) — — Fair value of plan assets at end of year $ 1,599.5 $ 2,120.9 $ — $ —
Schedule of amounts recognized in balance sheet	Assets (liabilities) recognized in the consolidated balance sheets: Pension Benefits Other Postretirement Benefits 2022 2021 2022 2021 Noncurrent assets $ 12.5 $ 25.0 $ — $ — Current liabilities (5.7) (5.7) (27.8) (29.2) Noncurrent liabilities (225.6) (415.4) (184.9) (258.1) Total amount recognized $ (218.8) $ (396.1) $ (212.7) $ (287.3)
Schedule of amounts recognized in other comprehensive income	Changes to accumulated other comprehensive loss related to pension and other postretirement benefit plans in 2022 and 2021 were as follows: Pension Benefits Other Postretirement Benefits (In millions) 2022 2021 2022 2021 Beginning of year accumulated other comprehensive loss $ (1,376.5) $ (1,600.3) $ (121.2) $ (119.1) Amortization of net actuarial loss 63.5 75.6 13.2 13.9 Amortization of prior service cost (credit) 0.4 0.6 (0.9) (2.4) Settlement loss (gain) 29.5 — — (21.9) Remeasurements 101.9 147.6 53.1 8.3 End of year accumulated other comprehensive loss $ (1,181.2) $ (1,376.5) $ (55.8) $ (121.2) Net change in accumulated other comprehensive loss $ 195.3 $ 223.8 $ 65.4 $ (2.1)
Schedule of net periodic benefit cost not yet recognized	Amounts included in accumulated other comprehensive loss at December 31, 2022 and 2021 were as follows: Pension Benefits Other Postretirement Benefits (In millions) 2022 2021 2022 2021 Prior service (cost) credit $ (8.8) $ (9.9) $ 2.5 $ 3.4 Net actuarial loss (1,172.4) (1,366.6) (58.3) (124.6) Accumulated other comprehensive loss (1,181.2) (1,376.5) (55.8) (121.2) Deferred tax effect 473.1 507.6 27.8 42.4 Accumulated other comprehensive loss, net of tax $ (708.1) $ (868.9) $ (28.0) $ (78.8)
Schedule of amounts in accumulated other comprehensive income to be recognized	Amounts in accumulated other comprehensive loss that are expected to be recognized as components of net periodic benefit cost in 2023 are: (In millions) Pension Other Total Amortization of prior service cost (credit) $ 0.4 $ (0.9) $ (0.5) Amortization of net actuarial loss 57.7 6.0 63.7 Amortization of accumulated other comprehensive loss $ 58.1 $ 5.1 $ 63.2
Schedule of accumulated benefit obligations in excess of fair value of plan assets	Additional information for pension plans with accumulated benefit obligations and projected benefit obligations in excess of plan assets: Pension Benefits (In millions) 2022 2021 Projected benefit obligation $ 1,727.3 $ 2,417.0 Accumulated benefit obligation $ 1,716.8 $ 2,398.0 Fair value of plan assets $ 1,496.0 $ 1,995.9
Schedule of expected benefit payments	The following table summarizes expected benefit payments from the Company’s various pension and other postretirement defined benefit plans through 2032, and also includes estimated Medicare Part D subsidies projected to be received during this period based on currently available information. Pension benefit payments for the U.S. qualified defined benefit pension plans are made from pension plan assets. (In millions) Pension Other Medicare Part 2023 $ 157.5 $ 27.8 $ — 2024 155.0 26.0 — 2025 152.3 24.0 — 2026 149.6 22.1 — 2027 146.8 20.4 — 2028-2032 684.0 77.5 —
Schedule of allocation of plan assets	The fair values of the Company’s pension plan assets are determined using net asset value (NAV) as a practical expedient, or by information categorized in the fair value hierarchy level based on the inputs used to determine fair value, as further discussed in Note 13. The fair values at December 31, 2022 were as follows: (In millions) Quoted Prices in Significant Significant Asset category Total NAV (Level 1) (Level 2) (Level 3) Equity securities: U.S. equities $ 363.1 $ 202.6 $ 160.5 $ — $ — International equities 299.7 284.8 14.9 — — Fixed income and cash equivalents 455.4 330.8 13.8 110.8 — Private equity 224.3 224.3 — — — Alternative investments- hedge funds, real estate and other 257.0 257.0 — — — Total assets $ 1,599.5 $ 1,299.5 $ 189.2 $ 110.8 $ — The fair values of the Company’s pension plan assets at December 31, 2021 were as follows: (In millions) Quoted Prices in Significant Significant Asset category Total NAV (Level 1) (Level 2) (Level 3) Equity securities: U.S. equities $ 509.8 $ 281.4 $ 228.4 $ — $ — International equities 408.8 396.6 12.2 — — Fixed income and cash equivalents 707.7 482.3 24.5 200.9 — Private equity 176.7 176.7 — — — Alternative investments- hedge funds, real estate and other 317.9 317.9 — — — Total assets $ 2,120.9 $ 1,654.9 $ 265.1 $ 200.9 $ —
Schedule of target asset allocations for pension plans	The target asset allocations for ATI Pension Plan for 2023, by major investment category, are: Asset category Target asset allocation range Equities 30% - 70% Fixed income and cash equivalents 15% - 40% Private equity 0% - 30% Alternative investments- hedge funds, real estate and other 10% - 30%
Schedule of multiemployer plans	The Company’s participation in multiemployer plans for the years ended December 31, 2022, 2021 and 2020 is reported in the following table. Pension FIP / RP Status in millions Expiration Dates EIN / Pension Company Contributions Surcharge Pension Fund 2022 2021 2022 2021 2020 Steelworkers Western Independent Shops Pension Plan 90-0169564 Green Green N/A $ 0.1 $ 0.1 $ 0.7 No 2/28/2025 Boilermakers-Blacksmiths National Pension Trust 48-6168020 Green Yellow Yes 2.3 2.0 2.1 No 9/30/2026 IAM National Pension Fund 51-6031295 Red Red Yes 1.9 1.9 2.0 Yes Various between 2023-2028 (4) Total contributions $ 4.3 $ 4.0 $ 4.8 (1) The most recent Pension Protection Act Zone Status is based on information provided to ATI and other participating employers by each plan, as certified by the plan’s actuary. A plan in the “deep red” zone had been determined to be in “critical and declining status”, based on criteria established by the Internal Revenue Code (Code), and is in critical status (as defined by the “red” zone) and is projected to become insolvent (run out of money to pay benefits) within 15 years (or within 20 years if a special rule applies). A plan in the “red” zone had been determined to be in “critical status”, based on criteria established by the Code, and is generally less than 65% funded. A plan in the “yellow” zone has been determined to be in “endangered status”, based on criteria established under the Code, and is generally less than 80% funded. A plan in the “green” zone has been determined to be neither in “critical status” nor in “endangered status”, and is generally at least 80% funded. Additionally, a plan may voluntarily place itself into a rehabilitation plan. In April 2019, the Company received notification from the IAM National Pension Fund (IAM Fund) that its’ actuary certified the IAM Fund as “endangered status” for the plan year beginning January 1, 2019, and that the IAM Fund was voluntarily placing itself in “red” zone status and implementing a rehabilitation plan. In April 2020, 2021 and 2022, the Company received notification from the IAM Fund that it was certified by its actuary as being in “red” zone status for the plan years beginning January 1, 2020 and 2021. A contribution surcharge was imposed as of June 1, 2019 in addition to the contribution rate specified in the applicable collective bargaining agreements. The contribution surcharge remains in effect, and ends when an employer begins contributing under a collective bargaining agreement that includes terms consistent with the rehabilitation plan. In April 2019, the Company received notifications from the Boilermakers-Blacksmiths National Pension Trust (Blacksmiths Trust) that it was certified by its actuary as being in “red” zone status for the plan year beginning January 1, 2019. A rehabilitation plan has been adopted for the Blacksmiths Trust, and the Company and the Blacksmiths union agreed to adopt the rehabilitation plan in 2019 prior to a contribution surcharge being imposed. In April 2020 and 2021, the funding status improved for the Blacksmiths Trust as it was certified by its actuary as being in the “yellow” zone for the plan years beginning January 1, 2020 and 2021. In April 2022, the funding status further improved to being in the "green" zone for the plan year beginning January 1, 2022. (2) The “FIP / RP Status Pending / Implemented” column indicates whether a Funding Improvement Plan, as required under the Code by plans in the “yellow” zone, or a Rehabilitation Plan, as required under the Code to be adopted by plans in the “red” or “deep red” zones, is pending or has been implemented as of the end of the plan year that ended in 2022. (3) The “Surcharge Imposed” column indicates whether ATI’s contribution rate for 2022 included an amount in addition to the contribution rate specified in the applicable collective bargaining agreement, as imposed by a plan in “critical status” or “critical and declining status”, in accordance with the requirements of the Code. (4) The Company is party to five separate bargaining agreements that require contributions to this plan. Expiration dates of these collective bargaining agreements range between November 13, 2023 and July 14, 2028.

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2022
Equity [Abstract]
Schedule of accumulated other comprehensive income (loss)	The changes in AOCI by component, net of tax, for the fiscal years ended December 31, 2022, 2021 and 2020 were as follows (in millions): Post- Currency Derivatives Deferred Tax Asset Valuation Allowance Total Balance, December 31, 2019 $ (1,083.1) $ (76.6) $ (0.5) $ (41.5) $ (1,201.7) OCI before reclassifications (99.3) 21.1 (2.0) — (80.2) Amounts reclassified from AOCI (a) 62.5 (b) — (d) 4.6 (e) (8.8) 58.3 Net current-period OCI (36.8) 21.1 2.6 (8.8) (21.9) Balance, December 31, 2020 (1,119.9) (55.5) 2.1 (50.3) (1,223.6) OCI before reclassifications 118.3 (9.4) 11.7 — 120.6 Amounts reclassified from AOCI (a) 53.9 (b) — (d) (8.7) (e) 66.1 111.3 Net current-period OCI 172.2 (9.4) 3.0 66.1 231.9 Balance, December 31, 2021 (947.7) (64.9) 5.1 15.8 (991.7) OCI before reclassifications 117.9 (25.2) 41.0 — 133.7 Amounts reclassified from AOCI (a) 93.7 (c) 20.0 (d) (32.6) (e) 51.7 132.8 Net current-period OCI 211.6 (5.2) 8.4 51.7 266.5 Balance, December 31, 2022 $ (736.1) $ (70.1) 13.5 $ 67.5 $ (725.2) Attributable to noncontrolling interests: Balance, December 31, 2019 $ — $ 9.8 $ — $ — $ 9.8 OCI before reclassifications — 11.4 — — 11.4 Amounts reclassified from AOCI — (b) — — — — Net current-period OCI — 11.4 — — 11.4 Balance, December 31, 2020 — 21.2 — — 21.2 OCI before reclassifications — 4.8 — — 4.8 Amounts reclassified from AOCI — (b) — — — — Net current-period OCI — 4.8 — — 4.8 Balance, December 31, 2021 — 26.0 — — 26.0 OCI before reclassifications — (18.3) — — (18.3) Amounts reclassified from AOCI — (b) — — — — Net current-period OCI — (18.3) — — (18.3) Balance, December 31, 2022 $ — $ 7.7 $ — $ — $ 7.7 (a) Amounts were included in net periodic benefit cost for pension and other postretirement benefit plans (see Note 14) and/or loss on asset sales and sales of businesses, net, as part of the loss on sale of the Sheffield, UK operations (see Note 6). (b) No amounts were reclassified to earnings. (c) Amounts were included in loss on asset sales and sales of businesses, net, as part of the loss on sale of the Sheffield, UK operations (see Note 6). (d) Amounts related to derivatives are included in sales, cost of goods sold or interest expense in the period or periods the hedged item affects earnings (see Note 12).
Reclassification out of accumulated other comprehensive income	Reclassifications out of AOCI for the fiscal years ended December 31, 2022, 2021 and 2020 were as follows: Amount reclassified from AOCI (d) Fiscal year ended Details about AOCI Components (In millions) December 31, 2022 December 31, 2021 December 31, 2020 Affected line item in the Postretirement benefit plans Prior service credit $ 0.5 (a) $ 1.8 (a) $ 3.1 (a) Actuarial losses (76.7) (a) (89.5) (a) (85.3) (a) Settlement gain (loss) (29.5) (b) 21.9 (a) — (105.7) (d) (65.8) (d) (82.2) (d) Total before tax (12.0) (11.9) (19.7) Tax benefit (e) $ (93.7) $ (53.9) $ (62.5) Net of tax Currency translation adjustment (20.0) (b,d) — (d) — (d) Derivatives Nickel and other raw material contracts $ 26.9 (c) $ 7.1 (c) $ (0.8) (c) Natural gas contracts 15.1 (c) 5.3 (c) (3.7) (c) Foreign exchange contracts 0.9 (c) 0.1 (c) (0.1) (c) Interest rate swap (0.1) (c) (1.1) (c) (1.4) (c) 42.8 (d) 11.4 (d) (6.0) (d) Total before tax 10.2 2.7 (1.4) Tax provision (benefit) (e) $ 32.6 $ 8.7 $ (4.6) Net of tax (a) Amounts are included in nonoperating retirement benefit expense (see Note 14). (b) Amounts in 2022 were included in loss on asset sales and sales of businesses, net, as part of the loss on sale of the Sheffield, UK operations (see Note 6). (c) Amounts related to derivatives, with the exception of the interest rate swap, are included in sales or cost of goods sold in the period or periods the hedged item affects earnings. Amounts related to the interest rate swap are included in interest expense in the same period as the interest expense on the ABL Term Loan is recognized in earnings (see Note 12). (d) For pretax items, positive amounts are income and negative amounts are expense in terms of the impact to net income. Tax effects are presented in conformity with ATI’s presentation in the consolidated statements of operations. (e) These amounts exclude the impact of any deferred tax asset valuation allowances, when applicable, including recognition of stranded balances (see Note 17 for further explanation).

Stockholders' Equity Stockholde

Stockholders' Equity Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2022
Equity [Abstract]
Nonvested stock rollforward	Activity under the Company’s RSU awards for the years ended December 31, 2022, 2021, and 2020 was as follows: (Shares in thousands, $ in millions) 2022 2021 2020 Number of Weighted Number of Weighted Number of Weighted Nonvested, beginning of year 1,409 $ 25.6 929 $ 17.9 756 $ 19.6 Granted 831 14.8 1,033 17.5 647 10.1 Vested (634) (12.3) (505) (8.9) (450) (11.2) Forfeited (127) (2.1) (48) (0.9) (24) (0.6) Nonvested, end of year 1,479 $ 26.0 1,409 $ 25.6 929 $ 17.9
Disclosure of Fair Value of PSU Awards	The fair value of each PSU award, the target share units awarded and projected future compensation expense to be recognized for these awards, including actual and estimated forfeitures at December 31, 2022 was as follows: (Shares in thousands, $ in millions) PSU Award Performance Period Award Fair Value December 31, 2022 Unrecognized Compensation Expense Compensation Expense Expected to be Recognized in the next 12 months Target Share Units 2020-2022 $ 13.5 $ — $ — 674 2021-2023 $ 9.3 3.1 3.1 459 2022-2024 $ 11.0 8.9 3.9 494 2022-2025 BPA $ 18.5 12.1 3.3 811 Total $ 24.1 $ 10.3

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Schedule of income before income tax	Income (loss) before income taxes for the Company’s U.S. and non-U.S. operations was as follows: (In millions) 2022 2021 2020 U.S. $ 230.6 $ (42.1) $ (1,505.4) Non-U.S. (68.6) 52.7 23.5 Income (loss) before income taxes $ 162.0 $ 10.6 $ (1,481.9)
Schedule income tax provision (benefit)	The income tax provision (benefit) was as follows: (In millions) 2022 2021 2020 Current: Federal $ 5.0 $ 0.7 $ 0.6 State 3.7 (0.3) (1.1) Foreign 10.0 9.4 6.7 Total 18.7 9.8 6.2 Deferred: Federal (3.3) 18.6 26.6 State 0.2 (0.9) 47.1 Foreign (0.1) (0.7) (2.2) Total (3.2) 17.0 71.5 Income tax provision $ 15.5 $ 26.8 $ 77.7
Schedule of effective income tax rate reconciliation	The following is a reconciliation of income taxes computed at the statutory U.S. Federal income tax rate to the actual effective income tax provision (benefit): (In millions) 2022 2021 2020 Taxes computed at the federal rate $ 34.0 $ 2.2 $ (311.2) Goodwill — 2.6 50.4 State and local income taxes, net of federal tax benefit 2.9 0.4 (0.2) Valuation allowance (50.0) 17.6 335.5 Repatriation of foreign earnings (GILTI ) — 2.0 0.2 Divestiture 29.1 — — Recognition of stranded deferred tax balance — 3.9 — Foreign earnings taxed at different rate 3.2 3.0 1.7 Withholding taxes 2.6 3.4 2.1 Preferential tax rate (4.9) (6.2) (4.6) Other (1.4) (2.1) 3.8 Income tax provision $ 15.5 $ 26.8 $ 77.7
Schedule of deferred tax assets and liabilities	Deferred income taxes result from temporary differences in the recognition of income and expense for financial and income tax reporting purposes, and differences between the fair value of assets acquired in business combinations accounted for as purchases for financial reporting purposes and their corresponding tax bases. Deferred income taxes represent future tax benefits or costs to be recognized when those temporary differences reverse. The categories of assets and liabilities that have resulted in differences in the timing of the recognition of income and expense at December 31, 2022 and 2021 were as follows: (In millions) 2022 2021 Deferred income tax assets Net operating loss tax carryovers $ 184.1 $ 298.7 Pensions 51.7 94.3 Postretirement benefits other than pensions 51.5 69.8 Tax credits 42.0 40.2 Other items 95.6 103.9 Gross deferred income tax assets 424.9 606.9 Valuation allowance for deferred tax assets (266.9) (431.0) Total deferred income tax assets 158.0 175.9 Deferred income tax liabilities Bases of property, plant and equipment 122.2 114.0 Inventory valuation 17.1 32.5 Bases of amortizable intangible assets 9.0 18.0 Other items 23.0 24.7 Total deferred tax liabilities 171.3 189.2 Net deferred tax liability $ (13.3) $ (13.3)
Schedule of NOL's and tax credits	The following summarizes the carryforward periods for the tax attributes related to NOLs and credits by jurisdiction. ($ in millions, U.S. and U.K. NOL amounts are pre-tax and all other items are after-tax) Jurisdiction Attribute Amount Expiration Period Amount expiring within 5 years Amount expiring in 5-20 years U.S. NOL $439 20 years $— $439 U.S. NOL $129 Indefinite $— $— U.S. Foreign Tax Credit $22 10 years $22 $— U.S. Research and Development Credit $7 20 years $— $7 State NOL $85 Various $16 $69 State NOL $1 Indefinite $— $— State Credits $10 Various $4 $6 U.K. NOL $3 Indefinite $— $— Poland Economic Zone Credit $5 7 years $5 $—
Schedule of income taxes paid	Income taxes paid and amounts received as refunds were as follows: (In millions) 2022 2021 2020 Income taxes paid $ 18.9 $ 14.2 $ 7.8 Income tax refunds received (0.4) (0.6) (2.5) Income taxes paid, net $ 18.5 $ 13.6 $ 5.3
Schedule of changes in unrecognized income tax benefits	The changes in the liability for unrecognized income tax benefits for the years ended December 31, 2022, 2021 and 2020 were as follows: (In millions) 2022 2021 2020 Balance at beginning of year $ 14.2 $ 15.2 $ 14.4 Decreases in prior period tax positions (3.3) — — Increases in current period tax positions — 0.3 2.7 Expiration of the statute of limitations (1.8) (1.3) (1.9) Balance at end of year $ 9.1 $ 14.2 $ 15.2
Summary of income tax examinations	A summary of tax years that remain subject to examination, by major tax jurisdiction, is as follows: Jurisdiction Earliest Year Open to U.S. Federal 2020 States: Pennsylvania 2019 Foreign: China 2019 Poland 2016 United Kingdom 2020

Per Share Information (Tables)

Per Share Information (Tables)	12 Months Ended
	Dec. 31, 2022
Earnings Per Share [Abstract]
Schedule earnings per share	The following table sets forth the computation of basic and diluted net income (loss) per common share: (In millions, except per share amounts) For the Years Ended December 31, 2022 2021 2020 Numerator: Numerator for basic net income (loss) per common share - Net income (loss) attributable to ATI $ 130.9 $ (38.2) $ (1,572.6) Effect of dilutive securities: 4.75% Convertible Senior Notes due 2022 2.2 — — 3.5% Convertible Senior Notes due 2025 11.3 — — Numerator for diluted net income (loss) per common share - Net income (loss) attributable to ATI after assumed conversions $ 144.4 $ (38.2) $ (1,572.6) Denominator: Denominator for basic net income (loss) per common share—weighted average shares 127.5 127.1 126.5 Effect of dilutive securities: Share-based compensation 2.1 — — 4.75% Convertible Senior Notes due 2022 2.8 — — 3.5% Convertible Senior Notes due 2025 18.8 — — Denominator for diluted net income (loss) per common share—adjusted weighted average shares and assumed conversions 151.2 127.1 126.5 Basic net income (loss) attributable to ATI per common share $ 1.03 $ (0.30) $ (12.43) Diluted net income (loss) attributable to ATI per common share $ 0.96 $ (0.30) $ (12.43)

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Principles of Consolidation (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Uniti [Member]
Noncontrolling Interest [Line Items]
Equity method investment ownership percentage	50%
Related party accounts receivable	$ 4.5	$ 6.1
Allegheny & Tsingshan Stainless
Noncontrolling Interest [Line Items]
Equity method investment ownership percentage	50%
Shanghai STAL Precision Stainless Steel Co Ltd [Member] | Allegheny Technologies Inc
Noncontrolling Interest [Line Items]
Joint venture ownership percentage	60%

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Risks and Uncertainties and Use of Estimates (Details)	12 Months Ended
	Dec. 31, 2022 employee
Accounting Policies [Abstract]
Number of employees	6,700
Percent of employees located outside of the U.S.	15%
Percent of employees covered by collective bargaining agreements	35%
Entity Number Of Employees Covered By USW Collective Bargaining Agreements Expiring February 28 2021	1,100

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Accounts Receivable (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Allowances for Doubtful Accounts	$ 7.7	$ 3.8	$ 4.3	$ 4.6

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Leases (Details)	Dec. 31, 2022
Accounting Policies [Abstract]
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Other assets
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Property, plant and equipment, net
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other current liabilities
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other long-term liabilities
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Short-term debt and current portion of long-term debt
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Long-term debt

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Government Receivable (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Nov. 30, 2021
Aviation Manufacturing Jobs Protection
Accounting Policies [Abstract]
Grants receivable		$ 22.2
Government Assistance [Line Items]
Grants receivable		$ 22.2
Government assistance, transaction duration	6 months
Reduction of expenses from grant benefits	$ 16.6
Cash receipts from government assistance	11
US States' Economic Development Incentive Program
Accounting Policies [Abstract]
Grants receivable	3.7
Government Assistance [Line Items]
Grants receivable	3.7
Reduction of expenses from grant benefits	1.6
Cash receipts from government assistance	$ 2.8

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Research and Development (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Accounting Policies [Abstract]
Research and Development Expense	$ 16.3	$ 16.5	$ 14.1
Customer funded research and development costs	$ 1.4	$ 3.5	$ 0.7

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - New and Pending Accounting Pronouncements (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Jan. 01, 2021	Dec. 31, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity, including portion attributable to noncontrolling interest	$ 1,157.2	$ 832.7		$ 641.4	$ 2,193.2
Additional Paid-In Capital
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity, including portion attributable to noncontrolling interest	1,668.1	1,596.7		1,625.5	1,618
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity, including portion attributable to noncontrolling interest	$ 176.9	$ 72.7		$ 106.5	$ 1,679.3
Accounting Standards Update 2020-06 | Additional Paid-In Capital
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity, including portion attributable to noncontrolling interest			$ (49.8)
Accounting Standards Update 2020-06 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity, including portion attributable to noncontrolling interest			4.4
ATI Convertible Senior Notes, 3.5%, Due 2025 [Member] | Convertible Debt [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.50%	3.50%
ATI Inc., Convertible Senior Notes, 3.5%, Due 2025 | Convertible Debt [Member] | Accounting Standards Update 2020-06
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity, including portion attributable to noncontrolling interest			$ (45.4)

Business Segments - Narrative (

Business Segments - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($) position
Segment Reporting Information [Line Items]
Gain (loss) on asset sales and sale of business, net	$ (134.2)	$ 13.8	$ 2.5
Restructuring and Related Cost, Expected Number of Positions Eliminated | position			1,400
Restructuring and other credits (charges)	(23.7)	10.5	$ (1,132.1)
Income (loss) from equity method investments	12.6	0.1	(7)
Total international sales	1,617.4	1,264.9	1,173
Sales by U.S. operations to foreign countries	1,217.9	846.3	812.3
Inventory valuation reserves	70.9	65.4
Closed operations and other expenses	(12.1)	(4.8)	(7.4)
Net gain (loss) on sale of businesses	(134.2)	0	0
Income From Government Assistance, CARES Act	34
Sheffield, UK Operations
Segment Reporting Information [Line Items]
Net gain (loss) on sale of businesses	(141)
Pico Rivera, CA Operations
Segment Reporting Information [Line Items]
Gain (Loss) on disposition of other assets	6.8
High Performance Materials & Components
Segment Reporting Information [Line Items]
Employee Retention Credits, Aviation Manufacturing Jobs Protection Program	27
Advanced Alloys & Solutions [Member]
Segment Reporting Information [Line Items]
Employee retention credits	$ 7
Allegheny & Tsingshan Stainless
Segment Reporting Information [Line Items]
Equity method investment ownership percentage	50%
Revenue from related parties	$ 0	0	18.4
Income (loss) from equity method investments	9.1	(0.9)	(10.6)
Allegheny & Tsingshan Stainless | Advanced Alloys & Solutions [Member]
Segment Reporting Information [Line Items]
Income (loss) from equity method investments	$ 8.2	(0.9)	(8.2)
Uniti [Member]
Segment Reporting Information [Line Items]
Equity method investment ownership percentage	50%
Revenue from related parties	$ 45	45.8	36.7
Uniti [Member] | Advanced Alloys & Solutions [Member]
Segment Reporting Information [Line Items]
Income (loss) from equity method investments	$ 4.4	$ 1	$ 1.2
Aerospace & Defense Market Concentration Risk [Member] | Revenue Benchmark [Member] | High Performance Materials & Components
Segment Reporting Information [Line Items]
Percentage of sales	80%
Energy and Aerospace & Defense Market Concentration [Member] | Revenue Benchmark [Member] | Advanced Alloys & Solutions [Member]
Segment Reporting Information [Line Items]
Percentage of sales	50%
Commercial Jet Engines Concentration | Revenue Benchmark [Member] | High Performance Materials & Components
Segment Reporting Information [Line Items]
Percentage of sales	60%
Allegheny Technologies Inc | STAL Precision Stainless Steel Company Limited [Member]
Segment Reporting Information [Line Items]
Joint venture ownership percentage	60%

Business Segments (Details)

Business Segments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Sales	$ 3,836	$ 2,799.8	$ 2,982.1
Operating Segments
Segment Reporting Information [Line Items]
Sales	4,249.4	3,010.7	3,182.9
Operating Segments | Intersegment Sales [Member]
Segment Reporting Information [Line Items]
Sales	413.4	210.9	200.8
Operating Segments | External Sales [Member]
Segment Reporting Information [Line Items]
Sales	3,836	2,799.8	2,982.1
Operating Segments | High Performance Materials & Components
Segment Reporting Information [Line Items]
Sales	1,815.7	1,248.3	1,235.4
Operating Segments | High Performance Materials & Components | Intersegment Sales [Member]
Segment Reporting Information [Line Items]
Sales	174.5	93.2	70.8
Operating Segments | High Performance Materials & Components | External Sales [Member]
Segment Reporting Information [Line Items]
Sales	1,641.2	1,155.1	1,164.6
Operating Segments | Advanced Alloys & Solutions [Member]
Segment Reporting Information [Line Items]
Sales	2,433.7	1,762.4	1,947.5
Operating Segments | Advanced Alloys & Solutions [Member] | Intersegment Sales [Member]
Segment Reporting Information [Line Items]
Sales	238.9	117.7	130
Operating Segments | Advanced Alloys & Solutions [Member] | External Sales [Member]
Segment Reporting Information [Line Items]
Sales	$ 2,194.8	$ 1,644.7	$ 1,817.5

Business Segments (Details8)

Business Segments (Details8) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Inventory valuation reserves		$ 70,900,000	$ 65,400,000
Segment EBITDA		623,800,000	351,600,000	$ 244,600,000
Corporate expenses		(62,400,000)	(55,900,000)	(40,900,000)
Closed operations and other expenses		(12,100,000)	(4,800,000)	(7,400,000)
Depreciation and amortization		(142,900,000)	(143,900,000)	(143,300,000)
Interest expense, net		(87,400,000)	(96,900,000)	(94,400,000)
Restructuring and other credits (charges)		(23,700,000)	10,500,000	(1,132,100,000)
Strike related costs		$ 0	(63,200,000)	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Settlement Gain (Loss), Statement Of Income Or Comprehensive Income, Extensible Enumeration, Not Disclosed Flag		Retirement benefit settlement gain (See Note 14)
Settlement gain		$ 0	64,900,000	0
Impairment of goodwill		0	0	(287,000,000)
Joint venture restructuring credit (charge)		900,000	0	(2,400,000)
Debt extinguishment charge		0	(65,500,000)	(21,500,000)
Gain (loss) on asset sales and sale of business, net		(134,200,000)	13,800,000	2,500,000
Income (loss) before income taxes		162,000,000	10,600,000	(1,481,900,000)
High Performance Materials & Components
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Strike related costs			3,500,000
Impairment of goodwill	$ 0	0	0
Various AA&S Segment Operations
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Strike related costs			59,700,000
Operating Segments
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Depreciation and amortization		(142,900,000)	(143,900,000)	(143,300,000)
Operating Segments | High Performance Materials & Components
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Segment EBITDA		296,000,000	159,900,000	129,600,000
Depreciation and amortization		(68,300,000)	(75,000,000)	(78,100,000)
Operating Segments | Advanced Alloys & Solutions [Member]
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Segment EBITDA		327,800,000	191,700,000	115,000,000
Depreciation and amortization		$ (67,400,000)	$ (64,500,000)	$ (62,100,000)

Business Segments (Details2)

Business Segments (Details2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Other Significant Reconciling Item [Line Items]
Depreciation and amortization	$ 142.9	$ 143.9	$ 143.3
Capital expenditures	130.9	152.6	136.5
Operating Segments
Segment Reporting Other Significant Reconciling Item [Line Items]
Depreciation and amortization	142.9	143.9	143.3
Capital expenditures	130.9	152.6	136.5
Operating Segments | High Performance Materials & Components
Segment Reporting Other Significant Reconciling Item [Line Items]
Depreciation and amortization	68.3	75	78.1
Capital expenditures	33.3	40.2	83.1
Operating Segments | Corporate [Member]
Segment Reporting Other Significant Reconciling Item [Line Items]
Depreciation and amortization	7.2	4.4	3.1
Capital expenditures	8	1.8	7.5
Operating Segments | Advanced Alloys & Solutions [Member]
Segment Reporting Other Significant Reconciling Item [Line Items]
Depreciation and amortization	67.4	64.5	62.1
Capital expenditures	$ 89.6	$ 110.6	$ 45.9

Business Segments (Details3)

Business Segments (Details3) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Asset Reconciling Item [Line Items]
Assets	$ 4,445.6	$ 4,285.2	$ 4,034.9
Deferred taxes	158	175.9
Cash and cash equivalents	584	687.7
Corporate, Non-Segment [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Deferred taxes	4.7	6.3	5.1
Cash and cash equivalents	710.5	740.1	771.2
High Performance Materials & Components
Segment Reporting Asset Reconciling Item [Line Items]
Assets	1,749.3	1,624.8	1,594.6
Advanced Alloys & Solutions [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	$ 1,981.1	$ 1,914	$ 1,664

Business Segments (Details4)

Business Segments (Details4) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Long-Lived Assets [Line Items]
Sales	$ 3,836	$ 2,799.8	$ 2,982.1
Assets	$ 4,445.6	$ 4,285.2	$ 4,034.9
Percent of total	100%	100%	100%
United States
Long-Lived Assets [Line Items]
Sales	$ 2,218.6	$ 1,534.9	$ 1,809.1
Assets	$ 3,942.7	$ 3,587	$ 3,356.8
Percent of total	89%	84%	83%
China
Long-Lived Assets [Line Items]
Sales	$ 351.8	$ 370.4	$ 315.5
Assets	$ 321.1	$ 406.4	$ 325.5
Percent of total	7%	9%	8%
UNITED KINGDOM
Long-Lived Assets [Line Items]
Sales	$ 217.7	$ 153.9	$ 126.5
Assets	$ 13.4	$ 153.9	$ 122.4
Percent of total	0%	4%	3%
Germany
Long-Lived Assets [Line Items]
Sales	$ 200.9	$ 121.3	$ 125.4
Other [Member]
Long-Lived Assets [Line Items]
Assets	$ 168.4	$ 137.9	$ 230.2
Percent of total	4%	3%	6%

Restructuring Costs (Details)

Restructuring Costs (Details) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) employee	Dec. 31, 2021 USD ($) employee	Dec. 31, 2020 USD ($) position
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (credits)	$ 23.7	$ (10.5)	$ 1,132.1
Non-cash restructuring charges	0	0	1,041.5
Restructuring charges (credits)	(4.8)	(11.3)	1,107.5
Severance costs			$ 60.5
Restructuring and Related Cost, Expected Number of Positions Eliminated | position			1,400
Inventory write-down		0.8	$ 7.2
Termination benefits			17.4
Restructuring Reserve [Roll Forward]
Other nonoperating income (expense), litigation reserve	$ (28.5)	0	0
Brackenridge PA Operations
Restructuring Cost and Reserve [Line Items]
Asset impairment charges			1,032.6
Fair value			$ 354
Brackenridge PA Operations | Weighted average cost of capital | Fair Value, Inputs, Level 3 [Member]
Restructuring Cost and Reserve [Line Items]
Long-Lived Asset, Measurement Input			0.093
Brackenridge PA Operations | Long-term growth rate | Fair Value, Inputs, Level 3 [Member]
Restructuring Cost and Reserve [Line Items]
Long-Lived Asset, Measurement Input			0.02
Various AA&S Segment Operations
Restructuring Cost and Reserve [Line Items]
Asset impairment charges			$ 8.9
Facility Idling
Restructuring Cost and Reserve [Line Items]
Restructuring charges (credits)			5.5
Restructuring Reserve [Roll Forward]
Restructuring Charges		$ 0.7
Employee Severance
Restructuring Cost and Reserve [Line Items]
Reduction in severance related reserves, workforce | employee	110	350
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Beginning Balance	$ 17.7	$ 43.4	4.5
Restructuring Charges	(4.8)	(12)	60.5
Payments for Restructuring	(3.1)	(13.7)	(21.6)
Restructuring Reserve, Ending Balance	9.8	17.7	$ 43.4
Other Current Liabilities [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Beginning Balance	11.4
Restructuring Reserve, Ending Balance	5.4	11.4
Other Noncurrent Liabilities [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Beginning Balance	6.3
Restructuring Reserve, Ending Balance	$ 4.4	$ 6.3

Goodwill and Other Intangible_3

Goodwill and Other Intangible Assets - Goodwill (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Aug. 13, 2021 USD ($)	Mar. 31, 2020 USD ($)
Goodwill [Line Items]
Goodwill		$ 227,200,000	$ 227,900,000
Impairment of goodwill		0	0	$ (287,000,000)
Accumulated goodwill impairment	$ 528,000,000	$ 528,000,000	528,000,000	$ 528,000,000
Flowform Products
Goodwill [Line Items]
Goodwill					$ 12,200,000
Weighted average cost of capital | Fair Value, Inputs, Level 3 [Member]
Goodwill [Line Items]
Goodwill, fair value measurement input		0.117
Long-term growth rate | Fair Value, Inputs, Level 3 [Member] | Minimum
Goodwill [Line Items]
Goodwill, fair value measurement input		0.03
Long-term growth rate | Fair Value, Inputs, Level 3 [Member] | Maximum
Goodwill [Line Items]
Goodwill, fair value measurement input		0.035
High Performance Materials & Components
Goodwill [Line Items]
Goodwill		$ 227,200,000
Impairment of goodwill	$ 0	0	$ 0
Goodwill, Foreign Currency Translation Gain (Loss)		700,000
Forged Products
Goodwill [Line Items]
Goodwill		$ 161,200,000				$ 460,400,000
Percentage of fair value in excess of carrying value		50%
Specialty Materials [Member]
Goodwill [Line Items]
Goodwill		$ 66,000,000

Goodwill and Other Intangible_4

Goodwill and Other Intangible Assets - Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets	$ 8	$ 8	$ 8
Gross carrying amount	134.8	134.8
Accumulated amortization	76.3	68.9
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2023	7
2024	7
2025	7
2026	7
2027	7
Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	61.2	61.2
Accumulated amortization	35.4	32.3
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	24.8	24.8
Accumulated amortization	11.6	10.6
Trademarks [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	48.8	48.8
Accumulated amortization	$ 29.3	$ 26

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Narrative (Details)	12 Months Ended
	Dec. 31, 2022 USD ($) segment	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Revenue from Contract with Customer [Abstract]
Inventories, net	$ 1,195,700,000	$ 1,046,300,000
Sales	3,836,000,000	2,799,800,000	$ 2,982,100,000
Cost of sales	3,121,800,000	2,466,600,000	2,689,300,000
Short-term contract assets	64,100,000	53,900,000	38,900,000	$ 38,500,000
Long-term contract assets	0	0	0	100,000
Other long-term liabilities	207,700,000	211,000,000
Short-term contract liabilities	149,100,000	116,200,000	111,800,000	78,700,000
Long-term contract liabilities	$ 66,800,000	84,400,000	32,000,000	$ 25,900,000
Number of business segments | segment	2
Revenue, Performance Obligation [Abstract]
Confirmed order backlog	$ 2,900,000,000	2,100,000,000	1,400,000,000
Confirmed orders with current performance obligations	0.80
Accounts receivable with customers	586,900,000	473,800,000
Contract costs for obtaining and fulfilling contracts	7,300,000	5,200,000
Amortization of contract costs	$ 1,000,000	$ 1,000,000	$ 1,400,000

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue	$ 3,836	$ 2,799.8	$ 2,982.1
Percent of total revenue	100%	100%	100%
Nickel-based alloys and specialty alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	52%	43%	45%
Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of total revenue	15%	16%	14%
Titanium and Titanium-based Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of total revenue	11%	12%	17%
Zirconium and related alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	8%	10%	9%
Precision rolled strip
Disaggregation of Revenue [Line Items]
Percent of total revenue	14%	19%	15%
United States
Disaggregation of Revenue [Line Items]
Revenue	$ 2,218.6	$ 1,534.9	$ 1,809.1
China
Disaggregation of Revenue [Line Items]
Revenue	351.8	370.4	315.5
Germany
Disaggregation of Revenue [Line Items]
Revenue	200.9	121.3	125.4
UNITED KINGDOM
Disaggregation of Revenue [Line Items]
Revenue	217.7	153.9	126.5
Rest of World
Disaggregation of Revenue [Line Items]
Revenue	602.4	484.9	451.8
France
Disaggregation of Revenue [Line Items]
Revenue	157.2	58.5	84.9
CANADA
Disaggregation of Revenue [Line Items]
Revenue	87.4	75.9	68.9
Total Aerospace & Defense
Disaggregation of Revenue [Line Items]
Revenue	1,873.6	1,132.7	1,360
Total Energy
Disaggregation of Revenue [Line Items]
Revenue	753.3	591.9	618.9
Automotive
Disaggregation of Revenue [Line Items]
Revenue	302.1	305.1	263.2
Food Equipment & Appliances
Disaggregation of Revenue [Line Items]
Revenue	158.5	153.1	159.2
Construction/Mining
Disaggregation of Revenue [Line Items]
Revenue	176.4	122.2	142
Medical Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	163.1	131.5	119.1
Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	200	215.1	177.7
Other
Disaggregation of Revenue [Line Items]
Revenue	209	148.2	142
Jet Engines- Commercial
Disaggregation of Revenue [Line Items]
Revenue	1,063.5	517.2	600.9
Airframes- Commercial
Disaggregation of Revenue [Line Items]
Revenue	468.9	262.7	410.8
Defense
Disaggregation of Revenue [Line Items]
Revenue	341.2	352.8	348.3
Oil & Gas
Disaggregation of Revenue [Line Items]
Revenue	476.7	332.3	365.8
Specialty Energy
Disaggregation of Revenue [Line Items]
Revenue	276.6	259.6	253.1
Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	4,249.4	3,010.7	3,182.9
Operating Segments | High Performance Materials & Components
Disaggregation of Revenue [Line Items]
Revenue	$ 1,815.7	$ 1,248.3	$ 1,235.4
Percent of total revenue	100%	100%	100%
Operating Segments | High Performance Materials & Components | Nickel-based alloys and specialty alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	49%	43%	38%
Operating Segments | High Performance Materials & Components | Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of total revenue	34%	38%	34%
Operating Segments | High Performance Materials & Components | Titanium and Titanium-based Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of total revenue	17%	19%	28%
Operating Segments | High Performance Materials & Components | Zirconium and related alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	0%	0%	0%
Operating Segments | High Performance Materials & Components | Precision rolled strip
Disaggregation of Revenue [Line Items]
Percent of total revenue	0%	0%	0%
Operating Segments | High Performance Materials & Components | United States
Disaggregation of Revenue [Line Items]
Revenue	$ 742.9	$ 571.3	$ 641
Operating Segments | High Performance Materials & Components | China
Disaggregation of Revenue [Line Items]
Revenue	59.8	49.5	31
Operating Segments | High Performance Materials & Components | Germany
Disaggregation of Revenue [Line Items]
Revenue	148.4	74.1	76.6
Operating Segments | High Performance Materials & Components | UNITED KINGDOM
Disaggregation of Revenue [Line Items]
Revenue	165.7	136.7	101.9
Operating Segments | High Performance Materials & Components | Rest of World
Disaggregation of Revenue [Line Items]
Revenue	352.5	238.5	219.3
Operating Segments | High Performance Materials & Components | France
Disaggregation of Revenue [Line Items]
Revenue	125.7	48.7	66.5
Operating Segments | High Performance Materials & Components | CANADA
Disaggregation of Revenue [Line Items]
Revenue	46.2	36.3	28.3
Operating Segments | High Performance Materials & Components | Total Aerospace & Defense
Disaggregation of Revenue [Line Items]
Revenue	1,318	835.5	946.9
Operating Segments | High Performance Materials & Components | Total Energy
Disaggregation of Revenue [Line Items]
Revenue	148.6	178.3	106.2
Operating Segments | High Performance Materials & Components | Automotive
Disaggregation of Revenue [Line Items]
Revenue	11.2	8.7	5.5
Operating Segments | High Performance Materials & Components | Food Equipment & Appliances
Disaggregation of Revenue [Line Items]
Revenue	0.2	0.1	0
Operating Segments | High Performance Materials & Components | Construction/Mining
Disaggregation of Revenue [Line Items]
Revenue	34.1	24	18.6
Operating Segments | High Performance Materials & Components | Medical Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	73.2	60.3	47.7
Operating Segments | High Performance Materials & Components | Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	2.4	1.2	0.9
Operating Segments | High Performance Materials & Components | Other
Disaggregation of Revenue [Line Items]
Revenue	53.5	47	38.8
Operating Segments | High Performance Materials & Components | Jet Engines- Commercial
Disaggregation of Revenue [Line Items]
Revenue	975.7	480.9	542.7
Operating Segments | High Performance Materials & Components | Airframes- Commercial
Disaggregation of Revenue [Line Items]
Revenue	184.1	132.8	219.8
Operating Segments | High Performance Materials & Components | Defense
Disaggregation of Revenue [Line Items]
Revenue	158.2	221.8	184.4
Operating Segments | High Performance Materials & Components | Oil & Gas
Disaggregation of Revenue [Line Items]
Revenue	35	42.2	37.3
Operating Segments | High Performance Materials & Components | Specialty Energy
Disaggregation of Revenue [Line Items]
Revenue	113.6	136.1	68.9
Operating Segments | Advanced Alloys & Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ 2,433.7	$ 1,762.4	$ 1,947.5
Percent of total revenue	100%	100%	100%
Operating Segments | Advanced Alloys & Solutions [Member] | Nickel-based alloys and specialty alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	54%	44%	49%
Operating Segments | Advanced Alloys & Solutions [Member] | Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of total revenue	0%	0%	0%
Operating Segments | Advanced Alloys & Solutions [Member] | Titanium and Titanium-based Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of total revenue	7%	6%	11%
Operating Segments | Advanced Alloys & Solutions [Member] | Zirconium and related alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	14%	17%	15%
Operating Segments | Advanced Alloys & Solutions [Member] | Precision rolled strip
Disaggregation of Revenue [Line Items]
Percent of total revenue	25%	33%	25%
Operating Segments | Advanced Alloys & Solutions [Member] | United States
Disaggregation of Revenue [Line Items]
Revenue	$ 1,475.7	$ 963.6	$ 1,168.1
Operating Segments | Advanced Alloys & Solutions [Member] | China
Disaggregation of Revenue [Line Items]
Revenue	292	320.9	284.5
Operating Segments | Advanced Alloys & Solutions [Member] | Germany
Disaggregation of Revenue [Line Items]
Revenue	52.5	47.2	48.8
Operating Segments | Advanced Alloys & Solutions [Member] | UNITED KINGDOM
Disaggregation of Revenue [Line Items]
Revenue	52	17.2	24.6
Operating Segments | Advanced Alloys & Solutions [Member] | Rest of World
Disaggregation of Revenue [Line Items]
Revenue	249.9	246.4	232.5
Operating Segments | Advanced Alloys & Solutions [Member] | France
Disaggregation of Revenue [Line Items]
Revenue	31.5	9.8	18.4
Operating Segments | Advanced Alloys & Solutions [Member] | CANADA
Disaggregation of Revenue [Line Items]
Revenue	41.2	39.6	40.6
Operating Segments | Advanced Alloys & Solutions [Member] | Total Aerospace & Defense
Disaggregation of Revenue [Line Items]
Revenue	555.6	297.2	413.1
Operating Segments | Advanced Alloys & Solutions [Member] | Total Energy
Disaggregation of Revenue [Line Items]
Revenue	604.7	413.6	512.7
Operating Segments | Advanced Alloys & Solutions [Member] | Automotive
Disaggregation of Revenue [Line Items]
Revenue	290.9	296.4	257.7
Operating Segments | Advanced Alloys & Solutions [Member] | Food Equipment & Appliances
Disaggregation of Revenue [Line Items]
Revenue	158.3	153	159.2
Operating Segments | Advanced Alloys & Solutions [Member] | Construction/Mining
Disaggregation of Revenue [Line Items]
Revenue	142.3	98.2	123.4
Operating Segments | Advanced Alloys & Solutions [Member] | Medical Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	89.9	71.2	71.4
Operating Segments | Advanced Alloys & Solutions [Member] | Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	197.6	213.9	176.8
Operating Segments | Advanced Alloys & Solutions [Member] | Other
Disaggregation of Revenue [Line Items]
Revenue	155.5	101.2	103.2
Operating Segments | Advanced Alloys & Solutions [Member] | Jet Engines- Commercial
Disaggregation of Revenue [Line Items]
Revenue	87.8	36.3	58.2
Operating Segments | Advanced Alloys & Solutions [Member] | Airframes- Commercial
Disaggregation of Revenue [Line Items]
Revenue	284.8	129.9	191
Operating Segments | Advanced Alloys & Solutions [Member] | Defense
Disaggregation of Revenue [Line Items]
Revenue	183	131	163.9
Operating Segments | Advanced Alloys & Solutions [Member] | Oil & Gas
Disaggregation of Revenue [Line Items]
Revenue	441.7	290.1	328.5
Operating Segments | Advanced Alloys & Solutions [Member] | Specialty Energy
Disaggregation of Revenue [Line Items]
Revenue	163	123.5	184.2
External Customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	3,836	2,799.8	2,982.1
External Customers | Operating Segments | High Performance Materials & Components
Disaggregation of Revenue [Line Items]
Revenue	1,641.2	1,155.1	1,164.6
External Customers | Operating Segments | Advanced Alloys & Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ 2,194.8	$ 1,644.7	$ 1,817.5

Revenue from Contracts with C_5

Revenue from Contracts with Customers - Accounts Receivable Reserve for Doubtful Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	$ 3.8	$ 4.3	$ 4.6
Expense to increase the reserve	4.6	0.3	0.2
Write-off of uncollectible accounts	(0.7)	(0.8)	(0.5)
Ending Balance	$ 7.7	$ 3.8	$ 4.3

Revenue from Contracts with C_6

Revenue from Contracts with Customers - Contract Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Contract Assets, Current [Roll Forward]
Balance as of beginning of fiscal year	$ 53.9	$ 38.9	$ 38.5
Recognized in current year	105	93.8	84.2
Reclassified to accounts receivable	(88)	(76.2)	(83.9)
Reclassification to/from long-term and contract liability	(6.8)	(2.6)	0.1
Balance as of period end	64.1	53.9	38.9
Contract Assets, Noncurrent [Roll Forward]
Balance as of beginning of fiscal year	0	0	0.1
Reclassification to/from short-term	0	0	(0.1)
Balance as of period end	0	0	0
Contract Liabilities, Current [Roll Forward]
Balance as of beginning of fiscal year	116.2	111.8	78.7
Recognized in current year	183.1	161.5	170.3
Amounts in beginning balance reclassified to revenue	(99.8)	(85.1)	(55.9)
Current year amounts reclassified to revenue	(72.3)	(72.9)	(90.1)
Divestiture	0	(0.8)	0
Other	0.7	0.1	0
Reclassification to/from long-term and contract asset	21.2	1.6	8.8
Balance as of period end	149.1	116.2	111.8
Contract Liabilities, Noncurrent [Roll Forward]
Balance as of beginning of fiscal year	84.4	32	25.9
Recognized in current year	10.4	56.6	14.9
Reclassification to/from short-term	(28)	(4.2)	(8.8)
Balance as of period end	$ 66.8	$ 84.4	$ 32

Inventories Schedule of Invento

Inventories Schedule of Inventory (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Inventory, Gross [Abstract]
Raw materials and supplies	$ 213.6	$ 160.3
Work-in-process	941.1	829.6
Finished goods	111.9	121.8
Total inventories at current cost	1,266.6	1,111.7
Inventory valuation reserves	(70.9)	(65.4)
Total inventories, net	$ 1,195.7	$ 1,046.3

Property, Plant and Equipment_2

Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Property Plant And Equipment Details [Abstract]
Land	$ 31.5	$ 34.4
Buildings	601.6	575.5
Equipment and leasehold improvements	2,895.5	2,870.2
Property plant and equipment, gross	3,528.6	3,480.1
Accumulated depreciation and amortization	(1,979.5)	(1,951.6)
Property, plant and equipment, net	1,549.1	1,528.5
Construction in progress	262.1	215.3
Depreciation, Depletion and Amortization [Abstract]
Software and other amortization	8	8	$ 8
Total depreciation and amortization	142.9	143.9	143.3
Capital Expenditures Incurred but Not yet Paid	38.3
Operating Segments
Depreciation, Depletion and Amortization [Abstract]
Depreciation of property, plant and equipment	115.4	117.4	119.5
Software and other amortization	27.5	26.5	23.8
Total depreciation and amortization	$ 142.9	$ 143.9	$ 143.3

Divestitures - Narrative (Detai

Divestitures - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Aug. 13, 2021
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Goodwill	$ 227.2	$ 227.9
Gain (loss) on disposal	(134.2)	0	$ 0
Proceeds from sale of businesses, net of transaction costs	0.3	53.1	0
Flowform Products
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received				$ 55
Proceeds from sale of businesses, net of transaction costs		53.1
Goodwill				$ 12.2
Gain (loss) on disposal		13.8
Prior year revenue from facilities sold			$ 26
Sheffield, UK Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on disposal	(141)
Prior year revenue from facilities sold		36
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal, Defined Benefit Pension Plan	(55.6)
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal, Net Pension Asset	(26.1)
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal, AOCI Pension	(29.5)
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal, Cumulative Translation Adjustment	(20)
Disposal Group, Including Discontinued Operation, Operating Income (Loss)		$ (9)
Sheffield, UK Operations | Total Energy | Revenue Benchmark | Product Concentration Risk
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage of sales		80%
Pico Rivera, CA Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on disposition of other assets	6.8
Proceeds from Sale of Other Assets	$ 6.2

Joint Ventures (Details)

Joint Ventures (Details) - USD ($) $ in Millions	3 Months Ended	10 Months Ended	12 Months Ended			58 Months Ended
	Dec. 31, 2022	Dec. 31, 2018	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2022
Schedule of Equity Method Investments [Line Items]
Cash and cash equivalents	$ 584		$ 584	$ 687.7		$ 584
Income (loss) from equity method investments			12.6	0.1	$ (7)
Undistributed earnings of investees accounted for under equity method	7.8		7.8			7.8
Sale to noncontrolling interests			6.4	0	0
Sales of subsidiary shares to noncontrolling interest			0.9
Noncontrolling Interests
Schedule of Equity Method Investments [Line Items]
Sales of subsidiary shares to noncontrolling interest			0.9
Shanghai STAL Precision Stainless Steel Co Ltd [Member]
Schedule of Equity Method Investments [Line Items]
Cash and cash equivalents	53.5		53.5			53.5
Next Gen Alloys LLC [Member]
Schedule of Equity Method Investments [Line Items]
Cash and cash equivalents	$ 1.2		$ 1.2			$ 1.2
Allegheny & Tsingshan Stainless
Schedule of Equity Method Investments [Line Items]
Equity method investment ownership percentage	50%		50%			50%
Income (loss) from equity method investments			$ 9.1	(0.9)	(10.6)
Revenue from related parties			0	0	18.4
Business Exit Costs			$ (1.8)		4.8
Uniti [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment ownership percentage	50%		50%			50%
Revenue from related parties			$ 45	45.8	36.7
Related party accounts receivable	$ 4.5		4.5	6.1		$ 4.5
Advanced Alloys & Solutions [Member] | Allegheny & Tsingshan Stainless
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments			8.2	(0.9)	(8.2)
Due from affiliates	3.2		3.2	2.9		3.2
Advanced Alloys & Solutions [Member] | Uniti [Member]
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments			4.4	1	$ 1.2
Prepaid expenses and other current assets [Member] | Advanced Alloys & Solutions [Member] | Allegheny & Tsingshan Stainless
Schedule of Equity Method Investments [Line Items]
Due from affiliates	0.4		0.4	0.7		0.4
Other Noncurrent Assets [Member] | Advanced Alloys & Solutions [Member] | Allegheny & Tsingshan Stainless
Schedule of Equity Method Investments [Line Items]
Due from affiliates	$ 2.8		$ 2.8	$ 2.2		$ 2.8
Allegheny Technologies Inc | Shanghai STAL Precision Stainless Steel Co Ltd [Member]
Schedule of Equity Method Investments [Line Items]
Joint venture ownership percentage	60%		60%			60%
Allegheny Technologies Inc | Next Gen Alloys LLC [Member]
Schedule of Equity Method Investments [Line Items]
Joint venture ownership percentage	51%		51%			51%
Allegheny Technologies Inc | China Baowu Steel Group Corporation Limited [Member] | Shanghai STAL Precision Stainless Steel Co Ltd [Member]
Schedule of Equity Method Investments [Line Items]
Joint venture ownership percentage by unaffiliated entity	40%		40%			40%
VSMPO | VSMPO | Uniti [Member]
Schedule of Equity Method Investments [Line Items]
Joint venture ownership percentage by unaffiliated entity	50%		50%			50%
Tsingshan Group | Allegheny & Tsingshan Stainless
Schedule of Equity Method Investments [Line Items]
Equity method investment ownership percentage	50%		50%			50%
Sale to noncontrolling interests	$ 5.5	$ 12				$ 17.5
Allegheny & Tsingshan Stainless
Schedule of Equity Method Investments [Line Items]
Income from Tariff Refunds			$ 19.7
Allegheny & Tsingshan Stainless | Import Duties
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments			$ 9.9

Asset Retirement Obligations (D

Asset Retirement Obligations (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Loss Contingencies [Line Items]
Asset retirement obligation	$ 17.8	$ 19	$ 24

Asset Retirement Obligations -

Asset Retirement Obligations - Change in Asset Retirement Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Asset Retirement Obligation Disclosure [Abstract]
Balance at beginning of year	$ 19	$ 24
Accretion expense	0.8	0.8
Payments	(2)	(5.6)
Divestiture	0	(0.2)
Balance at end of year	$ 17.8	$ 19

Supplemental Financial Statem_3

Supplemental Financial Statement Information - Cash and Cash Equivalents (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Cash and Cash Equivalents [Abstract]
Cash	$ 164.9	$ 222.8
Other short-term investments	419.1	464.9
Total cash and cash equivalents	$ 584	$ 687.7

Supplemental Financial Statem_4

Supplemental Financial Statement Information - Accrued Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Additional Financial Information Disclosure [Abstract]
Accrued salaries, wages and payroll liabilities	$ 100.8	$ 92.7
Accrued interest	$ 11.8	$ 15.2

Supplemental Financial Statem_5

Supplemental Financial Statement Information - Other Non-operating Income (Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Rent, royalty income and other income	$ 2.3	$ 1.1	$ 0.9
Gains from disposal of property, plant and equipment, net	0.2	2.9	2.9
Income (loss) from equity method investments	12.6	0.1	(7)
Net loss (gain) on sale of business	141	(13.8)	0
Joint venture restructuring credit (charge)	0.9	0	(2.4)
Other nonoperating income (expense), litigation reserve	(28.5)	0	0
Other	0	0.3	0.1
Other income (loss), net	(12.5)	18.2	(1.2)
Gain (loss) on asset sales and sale of business, net	(134.2)	13.8	2.5
Buyer of Formerly-Owned Business
Disaggregation of Revenue [Line Items]
Revisions of estimates	$ 0	$ 0	$ 4.3

Debt - Schedule of Debt (Detail

Debt - Schedule of Debt (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Sep. 09, 2022	Sep. 08, 2022	Dec. 31, 2020	Jul. 02, 2020
Debt Instrument [Line Items]
Debt Issuance Costs, Net	$ 17,200,000	$ 20,800,000
Total short-term and long-term debt	1,748,000,000	1,842,900,000
Short-term debt and current portion of long-term debt	41,700,000	131,300,000
Total long-term debt	$ 1,706,300,000	$ 1,711,600,000
ATI $350 million 5.875% Senior Notes due 2027
Debt Instrument [Line Items]
Debt instrument issuer	ATI Inc.	ATI Inc.
Debt instrument interest rate stated percentage	5.875%	5.875%
Debt instrument carrying amount	$ 350,000,000	$ 350,000,000
Debt Instrument, Maturity Date	Dec. 01, 2027	Dec. 01, 2027
ATI $287.5 million Convertible Senior Notes, 4.75%, Due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument issuer		ATI Inc.
Debt instrument interest rate stated percentage		4.75%
Debt instrument carrying amount	$ 0	$ 84,200,000
Debt Instrument, Maturity Date		Jul. 01, 2022
Allegheny Ludlum 6.95% Debentures due 2025 [Member]
Debt Instrument [Line Items]
Debt instrument issuer	Allegheny Ludlum	Allegheny Ludlum
Debt instrument interest rate stated percentage	6.95%	6.95%
Debt instrument carrying amount	$ 150,000,000	$ 150,000,000
Debt Instrument, Maturity Date	Dec. 15, 2025	Dec. 15, 2025
ATI 2031Notes
Debt Instrument [Line Items]
Debt instrument issuer	ATI Inc.	ATI Inc.
Debt instrument interest rate stated percentage	5.125%	5.125%
Debt instrument carrying amount	$ 350,000,000	$ 350,000,000
Debt Instrument, Maturity Date	Oct. 01, 2031	Oct. 01, 2031
Debt instrument, term	10 years
ATI 2029 Notes
Debt Instrument [Line Items]
Debt instrument issuer	ATI Inc.	ATI Inc.
Debt instrument interest rate stated percentage	4.875%	4.875%
Debt instrument carrying amount	$ 325,000,000	$ 325,000,000
Debt Instrument, Maturity Date	Oct. 01, 2029	Oct. 01, 2029
Debt instrument, term	8 years
2027 Term Loan
Debt Instrument [Line Items]
Debt instrument issuer	ATI Inc.	ATI Inc.
Debt instrument interest rate stated percentage	4.21%
Debt instrument carrying amount	$ 200,000,000	$ 200,000,000
Debt Instrument, Maturity Date	Sep. 30, 2027	Sep. 30, 2027
Domestic Bank Group $600 million asset-based credit facility
Debt Instrument [Line Items]
Short-Term Debt	$ 0	$ 0
Finance leases and other [Member]
Debt Instrument [Line Items]
Debt instrument carrying amount	79,400,000	85,700,000
Foreign credit agreements [Member]
Debt Instrument [Line Items]
Debt instrument carrying amount	$ 19,400,000	$ 27,400,000
Convertible Debt [Member] | ATI $287.5 million Convertible Senior Notes, 4.75%, Due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage		4.75%
Debt Issuance Costs, Net		$ 300,000
Convertible Debt [Member] | ATI Convertible Senior Notes, 3.5%, Due 2025 [Member]
Debt Instrument [Line Items]
Debt instrument issuer	ATI Inc.	ATI Inc.
Debt instrument interest rate stated percentage	3.50%	3.50%
Debt instrument carrying amount	$ 291,400,000	$ 291,400,000
Debt Issuance Costs, Net	$ 4,800,000	$ 6,500,000
Equity component of convertible debt					$ (46,800,000)	$ (51,400,000)
Debt Instrument, Maturity Date	Jun. 15, 2025	Jun. 15, 2025
Revolving Credit Facility [Member] | Domestic Bank Group $600 million asset-based credit facility
Debt Instrument [Line Items]
Debt Issuance Costs, Net			$ 2,400,000	$ 1,700,000

Debt - Narrative (Details)

Debt - Narrative (Details) $ / shares in Units, shares in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) tradingDays $ / shares shares	Dec. 31, 2021 USD ($) $ / shares	Dec. 31, 2020 USD ($)	Sep. 09, 2027 USD ($)	Sep. 09, 2022 USD ($)	Sep. 08, 2022 USD ($)	Jan. 01, 2021 USD ($)	Jul. 02, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2013
Interest Costs Incurred [Abstract]
Interest expense	$ 92,100,000	$ 97,600,000	$ 96,100,000
Interest costs capitalized	5,100,000	4,300,000	7,700,000
Interest costs paid	92,800,000	97,500,000	95,400,000
Interest income	4,700,000	700,000	1,700,000
Long-term Debt, Fiscal Year Maturity [Abstract]
2023	41,700,000
2024	19,900,000
2025	457,800,000
2026	10,500,000
2027	557,400,000
Debt Instrument [Line Items]
Payments of debt issuance costs	0	9,500,000	9,100,000
Debt extinguishment charge	0	65,500,000	21,500,000
Payment for Debt Extinguishment or Debt Prepayment Cost	0	64,500,000	19,100,000
Debt Issuance Costs, Net	17,200,000	20,800,000
Purchase of convertible note capped call	0	0	(19,400,000)
Equity component of convertible note			49,800,000
Stockholders' equity, including portion attributable to noncontrolling interest	1,157,200,000	832,700,000	641,400,000						$ 2,193,200,000
Interest expense, net	87,400,000	96,900,000	94,400,000
Percentage of Forecast [Abstract]
Conversion of convertible notes	$ 82,500,000
Stock Issued During Period, Shares, Conversion of Convertible Securities | shares	5.7
Repayment of Long-term Debt, Long-term Lease Obligation, and Capital Security	$ 23,100,000	515,600,000	212,100,000
Pico Rivera, CA Operations
Percentage of Forecast [Abstract]
Proceeds from Sale of Other Assets	6,200,000
Fair Value Measurements at Reporting Date Using Total Estimated Fair Value
Debt Instrument [Line Items]
Debt	1,964,500,000	2,003,200,000
Fair Value Measurements at Reporting Date Using Quoted Prices in Active Markets for Identical Assets (Level 1)
Debt Instrument [Line Items]
Debt	1,665,700,000	1,690,100,000
Additional Paid-In Capital
Debt Instrument [Line Items]
Equity component of convertible note			49,800,000
Stockholders' equity, including portion attributable to noncontrolling interest	1,668,100,000	1,596,700,000	$ 1,625,500,000						$ 1,618,000,000
Percentage of Forecast [Abstract]
Conversion of convertible notes	45,400,000
Additional Paid-In Capital | Accounting Standards Update 2020-06
Debt Instrument [Line Items]
Stockholders' equity, including portion attributable to noncontrolling interest							$ (49,800,000)
ATI $500 million 5.875% Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage										5.875%
Increase in interest expense per downgrade notch, percent			0.25%
Maximum number of downgrade notches			4
Maximum increase in interest rate expense, percent			2%
Debt instrument carrying amount			$ 500,000,000
Write off of Deferred Debt Issuance Cost		$ 1,000,000
ATI $500 million 5.875% Senior Notes due 2023 [Member] | Maximum
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage			7.875%
ATI Convertible Senior Notes, 4.75%, Due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage		4.75%
Debt instrument carrying amount	$ 0	$ 84,200,000
ATI Convertible Senior Notes, 4.75%, Due 2022 [Member] | Convertible Debt [Member]
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage		4.75%
Convertible debt conversion rate in shares of stock		0.0692042
Conversion price of convertible notes | $ / shares		$ 14.45
Write off of Deferred Debt Issuance Cost			$ 2,400,000
Debt Instrument, Repurchased Face Amount			$ 203,200,000
Debt Issuance Costs, Net		$ 300,000
Debt Instrument, Interest Rate, Effective Percentage	5.40%	5.40%	5.40%
Interest Expense, Debt, Excluding Amortization	$ 2,000,000	$ 4,000,000	$ 8,600,000
Amortization of Debt Issuance Costs	300,000	500,000	1,000,000
Interest expense, net	$ 2,300,000	4,500,000	9,600,000
ATI Convertible Senior Notes, 4.75%, Due 2022 [Member] | Convertible Debt [Member] | Fair Value Measurements at Reporting Date Using Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measurements at Reporting Date Using Total Estimated Fair Value
Debt Instrument [Line Items]
Debt		$ 102,000,000
ATI $350 million 5.875% Senior Notes due 2027
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	5.875%	5.875%
Debt instrument carrying amount	$ 350,000,000	$ 350,000,000
ATI Convertible Senior Notes, 3.5%, Due 2025 [Member] | Convertible Debt [Member]
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	3.50%	3.50%
Debt instrument carrying amount	$ 291,400,000	$ 291,400,000
Convertible debt conversion rate in shares of stock	0.0645745
Number of equity instruments issuable	18,800,000
Conversion price of convertible notes | $ / shares	$ 15.49
Debt Instrument, Convertible, Redemption Price As A Percent Of Principal Amount	100%
Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger	130%
Debt Instrument, Convertible, Threshold Trading Days | tradingDays	20
Debt Instrument, Convertible, Threshold Consecutive Trading Days | tradingDays	30
Equity component of convertible debt			$ 46,800,000					$ 51,400,000
Debt Issuance Costs, Net	$ 4,800,000	$ 6,500,000
Debt Instrument, Interest Rate, Effective Percentage	4.20%	4.20%	8.40%
Debt Instrument, Convertible, Cap Price | $ / shares	$ 19.76
Interest Expense, Debt, Excluding Amortization	$ 10,200,000	$ 10,200,000	$ 5,300,000
Amortization of Debt Issuance Costs	1,800,000	1,700,000	700,000
Interest expense, net	12,000,000	11,900,000	6,000,000
ATI Convertible Senior Notes, 3.5%, Due 2025 [Member] | Convertible Debt [Member] | Fair Value Measurements at Reporting Date Using Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measurements at Reporting Date Using Total Estimated Fair Value
Debt Instrument [Line Items]
Debt	$ 590,000,000	379,000,000
ATI Convertible Senior Notes, 3.5%, Due 2025 [Member] | Convertible Debt [Member] | Additional Paid in Capital
Debt Instrument [Line Items]
Debt Issuance Costs, Net			$ 1,600,000
ATI 2029 and 2031 Notes
Debt Instrument [Line Items]
Debt instrument, redemption price, percentage	101%
Proceeds from Debt, Net of Issuance Costs		$ 665,700,000
ATI 2029 and 2031 Notes | Minimum
Debt Instrument [Line Items]
Debt instrument, notice period required for redemption	15 days
ATI 2029 and 2031 Notes | Maximum
Debt Instrument [Line Items]
Debt instrument, notice period required for redemption	60 days
ATI 2029 Notes
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	4.875%	4.875%
Payments of debt issuance costs		$ 4,700,000
Debt instrument carrying amount	$ 325,000,000	$ 325,000,000
Debt instrument, term	8 years
ATI 2031Notes
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	5.125%	5.125%
Payments of debt issuance costs		$ 4,700,000
Debt instrument carrying amount	$ 350,000,000	350,000,000
Debt instrument, term	10 years
ATI Inc., Convertible Senior Notes, 4.75%, Due 2022
Percentage of Forecast [Abstract]
Repayment of Long-term Debt, Long-term Lease Obligation, and Capital Security	$ 1,700,000
Domestic Bank Group $600 million asset-based credit facility
Debt Instrument [Line Items]
Line of credit facility amount outstanding	39,800,000
Average outstanding amount	0	0
Percentage of Forecast [Abstract]
Bridge Loan	60,000,000
Short-Term Debt	$ 0	0
2027 Term Loan
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	4.21%
Debt instrument carrying amount	$ 200,000,000	$ 200,000,000
Debt Instrument, Prepayment Increments, Minimum	$ 25,000,000
2027 Term Loan | Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Variable rate spread	2%
ATI Inc., Convertible Senior Notes, 3.5%, Due 2025 | Convertible Debt [Member] | Accounting Standards Update 2020-06
Debt Instrument [Line Items]
Stockholders' equity, including portion attributable to noncontrolling interest							$ (45,400,000)
Revolving Credit Facility [Member] | Domestic Bank Group $600 million asset-based credit facility
Debt Instrument [Line Items]
Line of credit maximum borrowing capacity	$ 600,000,000
Fixed charge coverage ratio	1
Remaining borrowing capacity, percent of minimum borrowing capacity	10%
Minimum remaining borrowing capacity	$ 60,000,000
Debt Issuance Costs, Net					$ 2,400,000	$ 1,700,000
Debt Covenant, Undrawn Availability Requirement, Amount	$ 120,000,000
Debt Covenant, Undrawn Availability Requirement, Percent Of Total Available Liquidity	20%
Percentage of Forecast [Abstract]
Line of Credit Facility, Increase (Decrease), Net	$ 100,000,000
Revolving Credit Facility [Member] | Domestic Bank Group $600 million asset-based credit facility | Minimum | Base Rate [Member]
Debt Instrument [Line Items]
Variable rate spread	0.25%
Revolving Credit Facility [Member] | Domestic Bank Group $600 million asset-based credit facility | Minimum | Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Variable rate spread	1.25%
Revolving Credit Facility [Member] | Domestic Bank Group $600 million asset-based credit facility | Maximum | Base Rate [Member]
Debt Instrument [Line Items]
Variable rate spread	0.75%
Revolving Credit Facility [Member] | Domestic Bank Group $600 million asset-based credit facility | Maximum | Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Variable rate spread	1.75%
Letter of Credit [Member] | Domestic Bank Group $600 million asset-based credit facility
Debt Instrument [Line Items]
Line of credit maximum borrowing capacity	$ 200,000,000
Foreign Line of Credit
Debt Instrument [Line Items]
Line of credit maximum borrowing capacity	60,000,000
Interest Rate Swap [Member] | 2027 Term Loan
Debt Instrument [Line Items]
Derivative notional amount	$ 50,000,000
Forecast | Revolving Credit Facility [Member] | Domestic Bank Group $600 million asset-based credit facility
Debt Instrument [Line Items]
Line of Credit Facility, Increase to Maximum Borrowing Capacity				$ 300,000,000

Leases - Narrative (Details)

Leases - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Jan. 01, 2023
Leases [Abstract]
Progress payments made on behalf of company, paid	$ 27.9
Progress payments made on behalf of company, scheduled to be paid			$ 13.7
Lessee, finance lease, lease not yet commenced, right-of-use asset to be recognized			41.6
Lessee, finance lease, lease not yet commenced, liability to be recognized			$ 41.6
Proceeds from sale of ongoing CIP projects converted to leases	$ 1.8	$ 16.2

Leases - Schedule of Lease Cost

Leases - Schedule of Lease Cost Components (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Finance Lease Cost:
Amortization of right of use asset	$ 8.9	$ 7.1	$ 3.5
Interest on lease liabilities	4.1	3.1	1
Operating lease cost	16.4	22.7	20.8
Short-term lease cost	2.9	1.6	1.9
Variable lease cost	1	0.9	0.9
Sublease income	0	(0.3)	(0.1)
Total lease cost	33.3	35.1	28
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from finance leases	4.1	3	1
Operating cash flows from operating leases	17.4	20	21.7
Financing cash flows from finance leases	20.9	14.3	6.2
Right of use assets obtained in exchange for new finance lease liabilities	15.3	58.9	42.3
Right of use assets obtained in exchange for new operating lease liabilities	$ 18	$ 4.8	$ 12.4
Weighted average remaining lease term - finance leases	4 years	5 years	4 years
Weighted average remaining lease term - operating leases	6 years	5 years	6 years
Weighted average discount rate - finance leases	5.60%	5.20%	6.20%
Weighted average discount rate - operating leases	6.80%	6.50%	6.90%

Leases - Schedule of Operating

Leases - Schedule of Operating Lease Liability Maturities (Details) $ in Millions	Dec. 31, 2022 USD ($)
Leases [Abstract]
2023	$ 15.5
2024	12.7
2025	10.3
2026	8
2027	6.6
2028 and thereafter	16.5
Total undiscounted lease payments	69.6
Present value adjustment	(14.4)
Operating lease liabilities	$ 55.2

Leases - Schedule of Finance Le

Leases - Schedule of Finance Lease Liability Maturities (Details) $ in Millions	Dec. 31, 2022 USD ($)
Leases [Abstract]
2023	$ 26.2
2024	22.4
2025	17.9
2026	11
2027	7.8
2028 and thereafter	3
Total undiscounted lease payments	88.3
Present value adjustment	(9.5)
Finance lease liabilities	$ 78.8
Finance Lease, Liability, Statement of Financial Position [Extensible Enumeration]	Liabilities

Derivative Financial Instrume_3

Derivative Financial Instruments and Hedging - Narrative (Details) - 12 months ended Dec. 31, 2022 € in Millions, lb in Millions, $ in Millions	USD ($) lb	EUR (€)	USD ($)
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Percentage of estimated annual nickel requirements	8%
Derivative [Line Items]
Pre-tax cash flow hedge gain (loss) to be reclassified within twelve months	$ 12.2
Nickel [Member]
Derivative [Line Items]
Derivative notional amount (in pounds of nickel) | lb	6
Cash Flow Hedging [Member] | Natural gas contracts [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Percentage Of Forecasted Natural Gas Usage Hedged for 2023	70%
Percentage of forecasted natural gas usage hedged for 2024	25%
Cash Flow Hedging [Member] | Foreign Exchange Forward [Member] | Designated as Hedging Instrument [Member] | Maturity Dates Through 2022
Derivative [Line Items]
Derivative notional amount | €		€ 0
2027 Term Loan
Derivative [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		4.21%	4.21%
2027 Term Loan | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative notional amount			$ 50

Derivative Financial Instrume_4

Derivative Financial Instruments and Hedging - Schedule of Derivative Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	$ 18	$ 7.6
Fair value of derivative liability	4.6	2.7
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	18	7.6
Fair value of derivative liability	4.6	2.7
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Prepaid expenses and other current assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	1.4	0
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	0.5	0
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liability	0	0.9
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liability	0	0.7
Nickel and other raw material contracts [Member] | Designated as Hedging Instrument [Member] | Prepaid expenses and other current assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	12.5	5
Nickel and other raw material contracts [Member] | Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	0.5	0.1
Nickel and other raw material contracts [Member] | Designated as Hedging Instrument [Member] | Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liability	2.1	0.2
Natural gas contracts [Member] | Designated as Hedging Instrument [Member] | Prepaid expenses and other current assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	2.4	2
Natural gas contracts [Member] | Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	0.7	0.5
Natural gas contracts [Member] | Designated as Hedging Instrument [Member] | Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liability	2	0.7
Natural gas contracts [Member] | Designated as Hedging Instrument [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liability	$ 0.5	$ 0.2

Derivative Financial Instrume_5

Derivative Financial Instruments and Hedging - Schedule of Derivative Instruments Gain (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Net derivatives gain (loss) on hedge transactions	$ 53.8	$ 15.5	$ (2.8)
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (a)	42.8	11.4	$ (6)
Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net derivatives gain (loss) on hedge transactions	41	11.7
Cost of Sales and Interest Expense [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (a)	32.6	8.7
Nickel and other raw material contracts [Member] | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net derivatives gain (loss) on hedge transactions	27.1	6.2
Nickel and other raw material contracts [Member] | Cost of Sales [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (a)	20.5	5.4
Natural gas contracts [Member] | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net derivatives gain (loss) on hedge transactions	10.9	5.2
Natural gas contracts [Member] | Cost of Sales [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (a)	11.5	4
Foreign Exchange Contract [Member] | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net derivatives gain (loss) on hedge transactions	0.7	0.2
Foreign Exchange Contract [Member] | Cost of Sales [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (a)	0.7	0.1
Interest Rate Swap [Member] | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net derivatives gain (loss) on hedge transactions	2.3	0.1
Interest Rate Swap [Member] | Interest Expense [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (a)	$ (0.1)	$ (0.8)

Fair Value of Financial Instr_3

Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Jul. 02, 2020
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Derivative Asset Statement Of Financial Position Extensible Enumeration Not Disclosed Flag	Assets
Derivative Liability Statement Of Financial Position Extensible Enumeration Not Disclosed Flag	Liabilities
ATI Convertible Senior Notes, 3.5%, Due 2025 [Member] | Convertible Debt [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Equity component of convertible debt			$ 46.8	$ 51.4
Fair Value Measurements at Reporting Date Using Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 584	$ 687.7
Derivative financial instruments: Assets	0	0
Derivative financial instruments: Liabilities	0	0
Debt	1,665.7	1,690.1
Fair Value Measurements at Reporting Date Using Significant Observable Inputs (Level 2)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Derivative financial instruments: Assets	18	7.6
Derivative financial instruments: Liabilities	4.6	2.7
Debt	298.8	313.1
Total Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	584	687.7
Derivative financial instruments: Assets	18	7.6
Derivative financial instruments: Liabilities	4.6	2.7
Debt	1,765.2	1,863.7
Fair Value Measurements at Reporting Date Using Total Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	584	687.7
Derivative financial instruments: Assets	18	7.6
Derivative financial instruments: Liabilities	4.6	2.7
Debt	1,964.5	2,003.2
Fair Value Measurements at Reporting Date Using Total Estimated Fair Value | Fair Value Measurements at Reporting Date Using Quoted Prices in Active Markets for Identical Assets (Level 1) | ATI Convertible Senior Notes, 3.5%, Due 2025 [Member] | Convertible Debt [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt	$ 590	$ 379

Fair Value Of Financial Instr_4

Fair Value Of Financial Instruments - Narrative (Details)	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2013
ATI Convertible Senior Notes, 4.75%, Due 2022 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument interest rate stated percentage		4.75%
ATI $500 million 5.875% Senior Notes due 2023 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument interest rate stated percentage			5.875%
Allegheny Ludlum 6.95% Debentures due 2025 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument interest rate stated percentage	6.95%	6.95%
Allegheny Ludlum 6.95% Debentures due 2025 [Member] | Fair Value Measurements at Reporting Date Using Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument interest rate stated percentage	6.95%
Convertible Debt [Member] | ATI Convertible Senior Notes, 4.75%, Due 2022 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument interest rate stated percentage		4.75%

Retirement Benefits - Narrative

Retirement Benefits - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022 USD ($) employee	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Projected Retirement Benefit Expense In Next 12 months		$ 74
Defined Contribution Plan, Cost		$ 31.1	$ 20.4	$ 29.9
Termination benefits				17.4
Multiemployer Plans, Withdrawal Obligation, Payment Period		15 years
Income tax provision		$ 15.5	26.8	77.7
Settlement loss (gain) included in net income (loss)		29.5	(21.9)	0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Post- retirement benefit plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Income tax provision		(12)	(11.9)	(19.7)
Settlement loss (gain) included in net income (loss)		29.5	(21.9)	0
Collective-Bargaining Arrangement, Other
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Income tax provision			15.5
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Curtailment loss (gain)		0	0	(0.2)
Employer contributions		0	0
Projected Retirement Benefit Expense In Next 12 months		16
Defined Contribution Plan, Cost		$ 1	$ 0	$ 0.7
Assumed increase in per capita cost of covered benefits in next 12 months		7.80%
Assumed ultimate health care cost trend rate		4%
Expected long-term rate of return on assets		0%	0%	0%
Fair value of plan assets		$ 0	$ 0	$ 0
Termination benefits		0	0	6.7
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement		0	43
Settlement loss (gain) included in net income (loss)		0	(21.9)
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Curtailment loss (gain)		0	0	$ 0
Employer contributions		57.4	77.3
Projected Retirement Benefit Expense In Next 12 months		58
Accumulated benefit obligation		$ 1,716.8	$ 2,398
Expected long-term rate of return on assets		6.43%	6.71%	7.16%
Actual return on plan assets		(14.50%)	12.40%	15.20%	15.10%	(4.80%)
Fair value of plan assets		$ 1,599.5	$ 2,120.9	$ 2,046.4
Defined Benefit Plan, Weighted Average Life Expectancy		17 years
Termination benefits		$ 0	0	10.9
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement		0	0
Settlement loss (gain) included in net income (loss)		29.5	0
Pension Benefits [Member] | Global debt securities and cash [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unfunded commitments		45
Pension Benefits [Member] | Private equity [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unfunded commitments		125
Fair value of plan assets		224.3	176.7
Pension Benefits [Member] | Real estate and other [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unfunded commitments		29
Pension Benefits [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0
Pension Benefits [Member] | Fair Value, Inputs, Level 3 [Member] | Private equity [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0
Pension Benefits [Member] | Forecast
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected long-term rate of return on assets	6.57%
Pension Benefits [Member] | MultiemployerPlan1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Multiemployer Plans, Withdrawal Obligation		27
Pension Benefits [Member] | Nonqualified plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated employer contributions in next 12 months		$ 6
Pension Benefits [Member] | United States
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, number of employees accruing benefit service | employee		900
Defined Benefit Plan, Percent Of Employees accruing benefit service		7%
Percent reduction in defined benefit plan participation		60%
Employer contributions		$ 50	67	$ 130
Expected future voluntary contributions to pension plan		50
Estimated employer contributions in next 12 months		$ 0
Percentage of total assets		95%
Small annuity buy out [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits paid			$ 70

Retirement Benefits (Details 1)

Retirement Benefits (Details 1) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Settlement loss (gain)	$ 0	$ (64.9)	$ 0
Termination benefits			17.4
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefits earned during the year	11.9	15.1	12.7
Interest cost on benefits earned in prior years	69.7	68.4	86.3
Expected return on plan assets	(128.2)	(136.4)	(134.5)
Amortization of prior service cost (credit)	0.4	0.6	0.7
Amortization of net actuarial loss	63.5	75.6	74.5
Settlement loss (gain)	29.5	0	0
Curtailment loss (gain)	0	0	0
Termination benefits	0	0	10.9
Total retirement benefit expense (income)	46.8	23.3	50.6
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefits earned during the year	1.1	1.5	2.3
Interest cost on benefits earned in prior years	7.7	8	10.7
Expected return on plan assets	0	0	0
Amortization of prior service cost (credit)	(0.9)	(2.4)	(3.8)
Amortization of net actuarial loss	13.2	13.9	10.8
Settlement loss (gain)	0	(64.9)	0
Curtailment loss (gain)	0	0	(0.2)
Termination benefits	0	0	6.7
Total retirement benefit expense (income)	$ 21.1	$ (43.9)	$ 26.5

Retirement Benefits (Details 2)

Retirement Benefits (Details 2)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.95%	2.60%	3.40%
Rate of increase in future compensation levels		1%	1%
Expected long-term rate of return on assets	6.43%	6.71%	7.16%
Pension Benefits [Member] | Minimum
Defined Benefit Plan Disclosure [Line Items]
Rate of increase in future compensation levels	2%
Pension Benefits [Member] | Maximum
Defined Benefit Plan Disclosure [Line Items]
Rate of increase in future compensation levels	3%
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.80%	2.45%	3.25%
Rate of increase in future compensation levels	0%	0%	0%
Expected long-term rate of return on assets	0%	0%	0%

Retirement Benefits (Details 3)

Retirement Benefits (Details 3)	Dec. 31, 2022	Dec. 31, 2021
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	5.55%	2.95%
Rate of increase in future compensation levels	3%
Pension Benefits [Member] | Minimum
Defined Benefit Plan Disclosure [Line Items]
Rate of increase in future compensation levels		2%
Pension Benefits [Member] | Maximum
Defined Benefit Plan Disclosure [Line Items]
Rate of increase in future compensation levels		3%
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	5.45%	2.80%
Rate of increase in future compensation levels	0%	0%

Retirement Benefits (Details 4)

Retirement Benefits (Details 4) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Termination benefits			$ 17.4
Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	$ 2,517	$ 2,720.1
Service cost	11.9	15.1	12.7
Interest cost	69.7	68.4	86.3
Benefits paid	(155.6)	(235)
Subsidy paid	0	0
Divestiture	(75.8)	0
Effect of currency rates	(3.2)	(1.3)
Net actuarial (gains) losses - discount rate change	(556.8)	(104)
Net actuarial (gains) losses - other	11.1	53.7
Settlement gain	0	0
Termination benefits	0	0	10.9
Benefit obligation at end of year	1,818.3	2,517	2,720.1
Other Postretirement Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	287.3	357.6
Service cost	1.1	1.5	2.3
Interest cost	7.7	8	10.7
Benefits paid	(29.7)	(28.9)
Subsidy paid	0.3	0.4
Divestiture	0	0
Effect of currency rates	0	0
Net actuarial (gains) losses - discount rate change	(48.2)	(9)
Net actuarial (gains) losses - other	(5.8)	0.7
Settlement gain	0	(43)
Termination benefits	0	0	6.7
Benefit obligation at end of year	$ 212.7	$ 287.3	$ 357.6

Retirement Benefits (Details 5)

Retirement Benefits (Details 5) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Pension Benefits [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	$ 2,120.9	$ 2,046.4
Actual returns on plan assets and plan expenses	(317)	233.8
Employer contributions	57.4	77.3
Divestiture	(101.8)	0
Effect of currency rates	(4.4)	(1.6)
Benefits paid	(155.6)	(235)
Fair value of plan assets at end of year	1,599.5	2,120.9
Other Postretirement Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	0	0
Actual returns on plan assets and plan expenses	0	0
Employer contributions	0	0
Divestiture	0	0
Effect of currency rates	0	0
Benefits paid	0	0
Fair value of plan assets at end of year	$ 0	$ 0

Retirement Benefits (Details 6)

Retirement Benefits (Details 6) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	$ 12.5	$ 25
Current liabilities	(5.7)	(5.7)
Noncurrent liabilities	(225.6)	(415.4)
Total amount recognized	(218.8)	(396.1)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	0	0
Current liabilities	(27.8)	(29.2)
Noncurrent liabilities	(184.9)	(258.1)
Total amount recognized	$ (212.7)	$ (287.3)

Retirement Benefits (Details 7)

Retirement Benefits (Details 7) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Amortization of net actuarial loss	$ 76.7	$ 89.5	$ 85.3
Amortization to net income (loss) of net prior service credits	(0.5)	(1.8)	(3.1)
Settlement loss (gain) included in net income (loss)	29.5	(21.9)	0
Net gain (loss) arising during the period	155	155.9	(128.4)
Pension Benefits [Member]
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Beginning of year accumulated other comprehensive loss	(1,376.5)	(1,600.3)
Amortization of net actuarial loss	63.5	75.6
Amortization to net income (loss) of net prior service credits	0.4	0.6
Settlement loss (gain) included in net income (loss)	29.5	0
Net gain (loss) arising during the period	101.9	147.6
End of year accumulated other comprehensive loss	(1,181.2)	(1,376.5)	(1,600.3)
Net change in accumulated other comprehensive loss	195.3	223.8
Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Beginning of year accumulated other comprehensive loss	(121.2)	(119.1)
Amortization of net actuarial loss	13.2	13.9
Amortization to net income (loss) of net prior service credits	(0.9)	(2.4)
Settlement loss (gain) included in net income (loss)	0	(21.9)
Net gain (loss) arising during the period	53.1	8.3
End of year accumulated other comprehensive loss	(55.8)	(121.2)	$ (119.1)
Net change in accumulated other comprehensive loss	$ 65.4	$ (2.1)

Retirement Benefits (Details 8)

Retirement Benefits (Details 8) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service (cost) credit	$ (8.8)	$ (9.9)
Net actuarial loss	(1,172.4)	(1,366.6)
Accumulated other comprehensive loss	(1,181.2)	(1,376.5)	$ (1,600.3)
Deferred tax effect	473.1	507.6
Accumulated other comprehensive loss, net of tax	(708.1)	(868.9)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Prior service (cost) credit	2.5	3.4
Net actuarial loss	(58.3)	(124.6)
Accumulated other comprehensive loss	(55.8)	(121.2)	$ (119.1)
Deferred tax effect	27.8	42.4
Accumulated other comprehensive loss, net of tax	$ (28)	$ (78.8)

Retirement Benefits (Details 9)

Retirement Benefits (Details 9) $ in Millions	Dec. 31, 2022 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service cost (credit)	$ (0.5)
Amortization of net actuarial loss	63.7
Amortization of accumulated other comprehensive loss	63.2
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service cost (credit)	0.4
Amortization of net actuarial loss	57.7
Amortization of accumulated other comprehensive loss	58.1
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service cost (credit)	(0.9)
Amortization of net actuarial loss	6
Amortization of accumulated other comprehensive loss	$ 5.1

Retirement Benefits (Details 10

Retirement Benefits (Details 10) - Pension Benefits [Member] - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 1,727.3	$ 2,417
Accumulated benefit obligation	1,716.8	2,398
Fair value of plan assets	$ 1,496	$ 1,995.9

Retirement Benefits (Details 14

Retirement Benefits (Details 14) $ in Millions	Dec. 31, 2022 USD ($)
Pension Benefits [Member]
Defined Benefit Plan Expected Future Benefit Payments [Abstract]
2023	$ 157.5
2024	155
2025	152.3
2026	149.6
2027	146.8
2028-2032	684
Other Postretirement Benefits
Defined Benefit Plan Expected Future Benefit Payments [Abstract]
2023	27.8
2024	26
2025	24
2026	22.1
2027	20.4
2028-2032	77.5
Medicare Part D Subsidy [Abstract]
2023	0
2024	0
2025	0
2026	0
2027	0
2028-2032	$ 0

Retirement Benefits (Details 11

Retirement Benefits (Details 11) - Pension Benefits [Member] - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 1,599.5	$ 2,120.9	$ 2,046.4
NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,299.5	1,654.9
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	189.2	265.1
Significant Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	110.8	200.9
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Equity Securities: Other U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	363.1	509.8
Equity Securities: Other U.S. equities [Member] | NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	202.6	281.4
Equity Securities: Other U.S. equities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	160.5	228.4
Equity Securities: Other U.S. equities [Member] | Significant Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Equity Securities: Other U.S. equities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Equity Securities: International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	299.7	408.8
Equity Securities: International equities [Member] | NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	284.8	396.6
Equity Securities: International equities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14.9	12.2
Equity Securities: International equities [Member] | Significant Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Equity Securities: International equities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fixed income and cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	455.4	707.7
Fixed income and cash equivalents [Member] | NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	330.8	482.3
Fixed income and cash equivalents [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13.8	24.5
Fixed income and cash equivalents [Member] | Significant Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	110.8	200.9
Fixed income and cash equivalents [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Private equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	224.3	176.7
Private equity [Member] | NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	224.3	176.7
Private equity [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Private equity [Member] | Significant Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Private equity [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	257	317.9
Alternative investments | NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	257	317.9
Alternative investments | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Alternative investments | Significant Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Alternative investments | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0

Retirement Benefits (Details 13

Retirement Benefits (Details 13) - Pension Benefits [Member]	12 Months Ended
	Dec. 31, 2022
Minimum | Equity Securities: Other U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	30
Minimum | Global debt securities and cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	15
Minimum | Private equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	0
Minimum | Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	10
Maximum | Equity Securities: Other U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	70
Maximum | Global debt securities and cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	40
Maximum | Private equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	30
Maximum | Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	30

Retirement Benefits (Details 17

Retirement Benefits (Details 17) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Multiemployer Plan Disclosure [Line Items]
Multiemployer Plans, Withdrawal Obligation, Payment Period	15 years
Pension Benefits [Member]
Multiemployer Plan Disclosure [Line Items]
Company Contributions	$ 4.3	$ 4	$ 4.8
Steelworkers Western Independent Shops Pension Plan [Member] | Pension Benefits [Member]
Multiemployer Plan Disclosure [Line Items]
Pension Protection Act Zone Status	Green	Green
Company Contributions	$ 0.1	$ 0.1	0.7
Surcharge Imposed	No
Boilermakers-Blacksmiths National Pension Trust [Member] | Pension Benefits [Member]
Multiemployer Plan Disclosure [Line Items]
Pension Protection Act Zone Status	Green	Yellow
Company Contributions	$ 2.3	$ 2	2.1
Surcharge Imposed	No
IAM National Pension Fund [Member] | Pension Benefits [Member]
Multiemployer Plan Disclosure [Line Items]
Pension Protection Act Zone Status	Red	Red
Company Contributions	$ 1.9	$ 1.9	$ 2
Surcharge Imposed	Yes

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ (991.7)	$ (1,223.6)	$ (1,201.7)
OCI before reclassifications	133.7	120.6	(80.2)
Amounts reclassified from AOCI	132.8	111.3	58.3
Net current-period OCI	266.5	231.9	(21.9)
Ending balance	(725.2)	(991.7)	(1,223.6)
Increase (Decrease) in Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance	26	21.2	9.8
OCI before reclassifications	(18.3)	4.8	11.4
Amounts reclassified from AOCI	0	0	0
Net current-period OCI	(18.3)	4.8	11.4
Ending balance	7.7	26	21.2
Tax expense for the recognition of a stranded deferred tax balance arising from deferred tax valuation allowances that was associated with certain postretirement medical benefits due to plan termination		6.4
Post- retirement benefit plans [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(947.7)	(1,119.9)	(1,083.1)
OCI before reclassifications	117.9	118.3	(99.3)
Amounts reclassified from AOCI	93.7	53.9	62.5
Net current-period OCI	211.6	172.2	(36.8)
Ending balance	(736.1)	(947.7)	(1,119.9)
Increase (Decrease) in Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance	0	0	0
OCI before reclassifications	0	0	0
Amounts reclassified from AOCI	0	0	0
Net current-period OCI	0	0	0
Ending balance	0	0	0
Currency translation adjustment [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(64.9)	(55.5)	(76.6)
OCI before reclassifications	(25.2)	(9.4)	21.1
Amounts reclassified from AOCI	20	0	0
Net current-period OCI	(5.2)	(9.4)	21.1
Ending balance	(70.1)	(64.9)	(55.5)
Increase (Decrease) in Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance	26	21.2	9.8
OCI before reclassifications	(18.3)	4.8	11.4
Amounts reclassified from AOCI	0	0	0
Net current-period OCI	(18.3)	4.8	11.4
Ending balance	7.7	26	21.2
Derivatives [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	5.1	2.1	(0.5)
OCI before reclassifications	41	11.7	(2)
Amounts reclassified from AOCI	(32.6)	(8.7)	4.6
Net current-period OCI	8.4	3	2.6
Ending balance	13.5	5.1	2.1
Increase (Decrease) in Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance	0	0	0
OCI before reclassifications	0	0	0
Amounts reclassified from AOCI	0	0	0
Net current-period OCI	0	0	0
Ending balance	0	0	0
Accumulated Deferred Tax Asset Valuation Allowance
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	15.8	(50.3)	(41.5)
OCI before reclassifications	0	0	0
Amounts reclassified from AOCI	51.7	66.1	(8.8)
Net current-period OCI	51.7	66.1	(8.8)
Ending balance	67.5	15.8	(50.3)
Increase (Decrease) in Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance	0	0	0
OCI before reclassifications	0	0	0
Amounts reclassified from AOCI	0	0	0
Net current-period OCI	0	0	0
Ending balance	$ 0	$ 0	$ 0

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income (Loss) (Details2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization to net income (loss) of net prior service credits	$ (0.5)	$ (1.8)	$ (3.1)
Amortization of net actuarial loss	76.7	89.5	85.3
Settlement gain (loss)	(29.5)	21.9	0
Cost of sales	(3,121.8)	(2,466.6)	(2,689.3)
Income (loss) before income taxes	162	10.6	(1,481.9)
Income tax provision	15.5	26.8	77.7
Reclassification adjustment included in net income (loss)	20	0	0
Revenue from Contract with Customer, Excluding Assessed Tax	(3,836)	(2,799.8)	(2,982.1)
Other Postretirement Benefits
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization to net income (loss) of net prior service credits	(0.9)	(2.4)
Amortization of net actuarial loss	13.2	13.9
Settlement gain (loss)	0	21.9
Reclassification out of Accumulated Other Comprehensive Income [Member] | Post- retirement benefit plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization to net income (loss) of net prior service credits	0.5	1.8	3.1
Amortization of net actuarial loss	(76.7)	(89.5)	(85.3)
Settlement gain (loss)	(29.5)	21.9	0
Income (loss) before income taxes	(105.7)	(65.8)	(82.2)
Income tax provision	(12)	(11.9)	(19.7)
Income (loss)	(93.7)	(53.9)	(62.5)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Currency translation adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification adjustment included in net income (loss)	(20)	0	0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income taxes	42.8	11.4	(6)
Income tax provision	10.2	2.7	(1.4)
Income (loss)	32.6	8.7	(4.6)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member] | Nickel and other raw material contracts [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of sales	26.9	7.1	(0.8)
Revenue from Contract with Customer, Excluding Assessed Tax	26.9	7.1	(0.8)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member] | Natural gas contracts [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of sales	15.1	5.3	(3.7)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member] | Foreign Exchange Contract [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of sales	0.9	0.1	(0.1)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member] | Interest Rate Swap [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	$ (0.1)	$ (1.1)	$ (1.4)

Stockholders' Equity (Details)

Stockholders' Equity (Details) $ / shares in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, issued		0	0
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares available for future awards		4,600,000
Restricted stock and RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (shares)		831,000	1,033,000	647,000
Share based compensation expense | $		$ 13,400,000	$ 14,300,000	$ 9,600,000
Unrecognized compensation expense | $		$ 8,200,000
Shares vested		634,000	505,000	450,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Nonvested beginning of the year (shares)	1,479,000	1,409,000	929,000	756,000
Granted (shares)		831,000	1,033,000	647,000
Vested (shares)		(634,000)	(505,000)	(450,000)
Forfeited (shares)		(127,000)	(48,000)	(24,000)
Nonvested end of the year (shares)		1,479,000	1,409,000	929,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Beginning balance (in dollars per share) | $ / shares	$ 26	$ 25.6	$ 17.9	$ 19.6
Granted (in dollars per share) | $ / shares		14.8	17.5	10.1
Vested (in dollars per share) | $ / shares		(12.3)	(8.9)	(11.2)
Forfeited (in dollars per share) | $ / shares		(2.1)	(0.9)	(0.6)
Ending balance (in dollars per share) | $ / shares		$ 26	$ 25.6	$ 17.9
Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense | $		$ 24,100,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Forfeited (shares)		(159,298)	(71,801)	(50,050)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Forfeited (in dollars per share) | $ / shares		$ (3.4)	$ (1.7)	$ (1.4)
TSR Modifier [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance measurement period			3 years
2018 PSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Adjustment percentage				(10.00%)
2018 PSU [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vested				301,170
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Vested (shares)				(301,170)
2019 PSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Adjustment percentage			(20.00%)
2019 PSU [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vested			103,621
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Vested (shares)			(103,621)
2019 and 2020 PSU | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance measurement period		3 years
PSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Adjustment percentage		20%
PSU [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense | $		$ 12,600,000	$ 6,800,000	$ (6,700,000)
Common stock shares available for future awards		5,200,000
2020 PSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Adjustment percentage		0%
2020 PSU [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vested		182,628
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Vested (shares)		(182,628)
Breakout Performance Award | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance measurement period			4 years
Minimum | 2019 and 2020 PSU | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Attainment level range (percent)		25%
Minimum | Breakout Performance Award | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance measurement period			4 years
Maximum | 2019 and 2020 PSU | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Attainment level range (percent)		200%
Maximum | Breakout Performance Award | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance measurement period			5 years
Forecast | Restricted stock and RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense | $	$ 6,300,000
Revolving Credit Facility [Member] | Domestic Bank Group $600 million asset-based credit facility
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Debt covenant, line of credit facility remaining borrowing capacity after dividends, upper threshold | $		$ 120,000,000
Debt covenant, line of credit facility remaining borrowing capacity after dividends as percent of maximum borrowing capacity, upper threshold		20%
Debt covenant, line of credit facility remaining borrowing capacity after dividends, lower threshold | $		$ 75,000,000
Debt covenant, line of credit facility remaining borrowing capacity after dividends as percent of maximum borrowing capacity, lower threshold		12.50%
Fixed charge coverage ratio		1

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Fair Value of PSU Awards (Details) - Performance Shares - USD ($) shares in Thousands, $ / shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 24.1
Unrecognized compensation expense to be recognized in the next 12 months	10.3
2020-2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)			$ 13.5
Unrecognized compensation expense	0
Unrecognized compensation expense to be recognized in the next 12 months	0
Granted (shares)			674
2021-2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)		$ 9.3
Unrecognized compensation expense	3.1
Unrecognized compensation expense to be recognized in the next 12 months	$ 3.1
Granted (shares)		459
2022-2024
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)	$ 11
Unrecognized compensation expense	$ 8.9
Unrecognized compensation expense to be recognized in the next 12 months	$ 3.9
Granted (shares)	494
2022-2025
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)	$ 18.5
Unrecognized compensation expense	$ 12.1
Unrecognized compensation expense to be recognized in the next 12 months	$ 3.3
Granted (shares)	811

Income Taxes Income by Region (

Income Taxes Income by Region (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
U.S.	$ 230.6	$ (42.1)	$ (1,505.4)
Non-U.S.	(68.6)	52.7	23.5
Income (loss) before income taxes	$ 162	$ 10.6	$ (1,481.9)

Schedule of Income Tax Provisio

Schedule of Income Tax Provision (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Components Of Income Tax Expense Benefit Continuing Operations Abstract
Current: Federal	$ 5	$ 0.7	$ 0.6
Current: State	3.7	(0.3)	(1.1)
Current: Foreign	10	9.4	6.7
Total Current	18.7	9.8	6.2
Deferred: Federal	(3.3)	18.6	26.6
Deferred: State	0.2	(0.9)	47.1
Deferred: Foreign	(0.1)	(0.7)	(2.2)
Total Deferred	(3.2)	17	71.5
Income tax provision	$ 15.5	$ 26.8	$ 77.7

Reconciliation of Federal Tax R

Reconciliation of Federal Tax Rate to Effective Tax Rate (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Taxes computed at the federal rate	$ 34	$ 2.2	$ (311.2)
Goodwill	0	2.6	50.4
State and local income taxes, net of federal tax benefit	2.9	0.4	(0.2)
Valuation allowance	(50)	17.6	335.5
Repatriation of foreign earnings (GILTI )	0	2	0.2
Divestiture	29.1	0	0
Recognition of stranded deferred tax balance	0	3.9	0
Foreign earnings taxed at different rate	3.2	3	1.7
Withholding taxes	2.6	3.4	2.1
Preferential tax rate	(4.9)	(6.2)	(4.6)
Other	(1.4)	(2.1)	3.8
Income tax provision	$ 15.5	$ 26.8	$ 77.7

Narrative (Details)

Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Aug. 13, 2021	Dec. 31, 2019
NOL and Tax Credit Carryforwards [Line Items]
Repatriation of foreign earnings (GILTI )	$ 0	$ 2	$ 0.2
Valuation allowance	(50)	17.6	335.5
Discrete tax effects related to valuation allowance		11.6
Additional valuation allowance required		5.2
Accumulated other comprehensive loss, net of tax	725.2	991.7	1,223.6		$ 1,201.7
Impairment of goodwill	0	0	287
Goodwill	0	2.6	50.4
Deferred taxes for foreign withholding taxes	5.3
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(132.8)	(111.3)	(58.3)
Goodwill	(227.2)	(227.9)
Income tax provision	15.5	26.8	77.7
Recognition of stranded deferred tax balance	0	3.9	0
Settlement gain (loss)	(29.5)	21.9	0
Tax expense for the recognition of a stranded deferred tax balance arising from deferred tax valuation allowances that was associated with certain postretirement medical benefits due to plan termination		6.4
Loss on asset sales and sales of businesses, net	134.2	0	0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	266.5	231.9	(21.9)
Collective-Bargaining Arrangement, Other
NOL and Tax Credit Carryforwards [Line Items]
Income tax provision		15.5
Flowform Products
NOL and Tax Credit Carryforwards [Line Items]
Goodwill				$ (12.2)
Loss on asset sales and sales of businesses, net		(13.8)
Sheffield, UK Operations
NOL and Tax Credit Carryforwards [Line Items]
Valuation allowance decrease due to change in judgment on the realizability of deferred tax assets	(13.6)
Loss on asset sales and sales of businesses, net	141
Accumulated Deferred Tax Asset Valuation Allowance
NOL and Tax Credit Carryforwards [Line Items]
Accumulated other comprehensive loss, net of tax	(67.5)	(15.8)	50.3		41.5
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(51.7)	(66.1)	8.8
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	51.7	66.1	(8.8)
Post- retirement benefit plans [Member]
NOL and Tax Credit Carryforwards [Line Items]
Accumulated other comprehensive loss, net of tax	736.1	947.7	1,119.9		$ 1,083.1
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(93.7)	(53.9)	(62.5)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	211.6	172.2	(36.8)
Post- retirement benefit plans [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
NOL and Tax Credit Carryforwards [Line Items]
Income tax provision	(12)	(11.9)	(19.7)
Settlement gain (loss)	(29.5)	$ 21.9	$ 0
State [Member]
NOL and Tax Credit Carryforwards [Line Items]
Valuation allowance decrease due to change in judgment on the realizability of deferred tax assets	$ (43.4)

Schedule of Deferred Tax Assets

Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Deferred income tax assets
Net operating loss tax carryovers	$ 184.1	$ 298.7
Pensions	51.7	94.3
Postretirement benefits other than pensions	51.5	69.8
Tax credits	42	40.2
Other items	95.6	103.9
Gross deferred income tax assets	424.9	606.9
Valuation allowance for deferred tax assets	(266.9)	(431)
Total deferred income tax assets	158	175.9
Deferred income tax liabilities
Bases of property, plant and equipment	122.2	114
Inventory valuation	17.1	32.5
Bases of amortizable intangible assets	9	18
Other items	23	24.7
Total deferred tax liabilities	171.3	189.2
Net deferred tax (liability)	$ (13.3)	$ (13.3)

Schedule of Income Taxes Paid a

Schedule of Income Taxes Paid and Refunded (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Taxes Paid, Net [Abstract]
Income Taxes Paid	$ 18.9	$ 14.2	$ 7.8
Income tax refunds received	(0.4)	(0.6)	(2.5)
Income Taxes Paid (Received), Net, Total	$ 18.5	$ 13.6	$ 5.3

Income Taxes NOL and Tax Credit

Income Taxes NOL and Tax Credit Carryforwards (Details) $ in Millions	Dec. 31, 2022 USD ($)
United States
NOL and Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	$ 439
State [Member]
NOL and Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	85
Tax credit carryforwards	10
UNITED KINGDOM
NOL and Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	3
Within 5 years [Member] | United States
NOL and Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	0
Within 5 years [Member] | State [Member]
NOL and Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	16
Tax credit carryforwards	4
Within 5 years [Member] | UNITED KINGDOM
NOL and Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	0
Indefinite Expiration Period, Within 5 Years | United States
NOL and Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	0
Indefinite Expiration Period, Within 5 Years | State [Member]
NOL and Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	0
Within 5-20 years [Member] | United States
NOL and Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	439
Within 5-20 years [Member] | State [Member]
NOL and Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	69
Tax credit carryforwards	6
Within 5-20 years [Member] | UNITED KINGDOM
NOL and Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	0
Indefinite Expiration Period | United States
NOL and Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	129
Indefinite Expiration Period | State [Member]
NOL and Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	1
Indefinite Expiration Period, 5-20 Years | United States
NOL and Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	0
Indefinite Expiration Period, 5-20 Years | State [Member]
NOL and Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	0
Foreign Tax Credits [Member] | United States
NOL and Tax Credit Carryforwards [Line Items]
Tax credit carryforwards	22
Foreign Tax Credits [Member] | Within 5 years [Member] | United States
NOL and Tax Credit Carryforwards [Line Items]
Tax credit carryforwards	22
Foreign Tax Credits [Member] | Within 5-20 years [Member] | United States
NOL and Tax Credit Carryforwards [Line Items]
Tax credit carryforwards	0
Research Tax Credit Carryforward [Member] | United States
NOL and Tax Credit Carryforwards [Line Items]
Tax credit carryforwards	7
Research Tax Credit Carryforward [Member] | Within 5 years [Member] | United States
NOL and Tax Credit Carryforwards [Line Items]
Tax credit carryforwards	0
Research Tax Credit Carryforward [Member] | Within 5-20 years [Member] | United States
NOL and Tax Credit Carryforwards [Line Items]
Tax credit carryforwards	7
Economic Zone Credit [Member] | Poland [Member]
NOL and Tax Credit Carryforwards [Line Items]
Tax credit carryforwards	5
Economic Zone Credit [Member] | Within 5 years [Member] | Poland [Member]
NOL and Tax Credit Carryforwards [Line Items]
Tax credit carryforwards	5
Economic Zone Credit [Member] | Within 5-20 years [Member] | Poland [Member]
NOL and Tax Credit Carryforwards [Line Items]
Tax credit carryforwards	$ 0

Schedule of Changes in Unrecogn

Schedule of Changes in Unrecognized Income Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Uncertainties [Abstract]
Unrecognized tax benefits classified within deferred taxes as a reduction of net operating loss carryforwards	$ 7.8	$ 12.3	$ 13
Reconciliation Of Unrecognized Tax Benefits Excluding Amounts Pertaining To Examined Tax Returns Roll Forward
Decreases in prior period tax positions	(3.3)	0	0
Increases in current period tax positions	0	0.3	2.7
Unrecognized tax benefits	9.1	14.2	15.2	$ 14.4
Expiration of the statute of limitations	(1.8)	(1.3)	(1.9)
Ending balance	9.1	14.2	$ 15.2
Income tax penalties and interest accrued	1.4	$ 1.9
Unrecognized tax benefits that would impact effective tax rate	1
Unrecognized tax benefits that will be recognized within 12 months of year end	$ 1.4

Per Share Information (Details)

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
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	25.6	22.8
Authorized amount				$ 150
Purchase of treasury stock	$ (139.9)	$ 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
Effect of dilutive securities: Convertible Senior Notes	2.8	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
Effect of dilutive securities: Convertible Senior Notes	18.8	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%

Commitments and Contingencies (

Commitments and Contingencies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Purchase obligation, property, plant, and equipment	$ 39.9
Accrual for Environmental Loss Contingencies [Abstract]
Accrual for environmental remediation obligations	13
Accrued environmental loss contingencies recorded in other current liabilities	5
Components of Environmental Loss Accrual [Abstract]
Federal Superfund and comparable state-managed sites	3
Formerly owned or operated sites	8
Owned or controlled sites at which Company operations have been or plan to be discontinued	2
Reasonably possible amount by which current matters may exceed reserves	15
Other nonoperating income (expense), litigation reserve	$ (28.5)	$ 0	$ 0
Environmental Loss Contingency, Statement Of Financial Position, Extensible Enumeration, Not Disclosed Flag	other
Environmental Loss Contingency, Current, Statement of Financial Position [Extensible Enumeration]	Other current liabilities

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Sales	$ 3,836	$ 2,799.8	$ 2,982.1
Gross profit	714.2	333.2	292.8
Net income (loss)	$ 146.5	$ (16.2)	$ (1,559.6)
Basic income (loss) attributable to ATI per common share (in dollars per share)	$ 1.03	$ (0.30)	$ (12.43)
Basic net 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)
Diluted net income (loss) attributable to ATI per common share (in dollars per share)	$ 0.96	$ (0.30)	$ (12.43)
Average shares outstanding (shares)	127.5	127.1	126.5

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Unaudited) - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Unusual Or Infrequent Item [Line Items]
Net gain (loss) on sale of businesses	$ (134.2)	$ 0	$ 0
Restructuring and other credits (charges)	(23.7)	10.5	(1,132.1)
Impairment of goodwill	0	0	(287)
Severance Costs			(60.5)
Termination benefits			(17.4)
Other Asset Impairment Charges	0	0	(1,041.5)
Other Postretirement Benefits
Unusual Or Infrequent Item [Line Items]
Termination benefits	$ 0	$ 0	$ (6.7)
Allegheny & Tsingshan Stainless
Unusual Or Infrequent Item [Line Items]
Equity method investment ownership percentage	50%
Tsingshan Group | Allegheny & Tsingshan Stainless
Unusual Or Infrequent Item [Line Items]
Equity method investment ownership percentage	50%