ATI (ATI) 8-K 22 May 20 2019 FY Other Events Financial data

Cover

Cover	May 22, 2020
Cover [Abstract]
Document Type	8-K
Document Period End Date	May 22, 2020
Entity Registrant Name	Allegheny Technologies Incorporated
Entity Incorporation, State or Country Code	DE
Entity File Number	1-12001
Entity Tax Identification Number	25-1792394
Entity Address, Address Line One	1000 Six PPG Place,
Entity Address, City or Town	Pittsburgh,
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	15222-5479
City Area Code	412
Local Phone Number	394-2800
Written Communications	false
Soliciting Material	false
Pre-commencement Tender Offer	false
Pre-commencement Issuer Tender Offer	false
Title of 12(b) Security	Common Stock, par value $0.10 per share
Trading Symbol	ATI
Security Exchange Name	NYSE
Entity Emerging Growth Company	false
Entity Central Index Key	0001018963
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Sales	$ 1,018.6	$ 1,018.7	$ 1,080.4	$ 1,004.8	$ 1,037.9	$ 1,020.2	$ 1,009.5	$ 979	$ 4,122.5	$ 4,046.6	$ 3,525.1
Costs and expenses:
Cost of sales									3,484.7	3,416.3	3,028.1
Gross profit	169.3	159.7	177.7	131.1	147.6	160.4	173.7	148.6	637.8	630.3	497
Selling and administrative expenses									267.2	268.2	248
Impairment of goodwill									0	0	114.4
Restructuring charges									4.5	0	0
Operating income									366.1	362.1	134.6
Nonoperating retirement benefit expense									(73.6)	(33.9)	(54.3)
Interest expense, net									(99)	(101)	(133.8)
Debt extinguishment charge	(21.6)								(21.6)	0	(37)
Other income, net									69.7	20.5	4
Income (loss) before income taxes									241.6	247.7	(86.5)
Income tax provision (benefit)									(28.5)	11	(6.8)
Net income (loss)	60	115.3	78.5	16.3	45	55.6	75.6	60.5	270.1	236.7	(79.7)
Less: Net income attributable to noncontrolling interests									12.5	14.3	12.2
Net income (loss) attributable to ATI	$ 56.5	$ 111	$ 75.1	$ 15	$ 41.1	$ 50.5	$ 72.8	$ 58	$ 257.6	$ 222.4	$ (91.9)
Basic net income (loss) per common share
Continuing operations attributable to ATI per common share (in dollars per share)									$ 2.05	$ 1.78	$ (0.83)
Basic net income (loss) attributable to ATI per common share (in dollars per share)	$ 0.45	$ 0.88	$ 0.60	$ 0.12	$ 0.33	$ 0.40	$ 0.58	$ 0.46	2.05	1.78	(0.83)
Diluted net income (loss) per common share
Continuing operations attributable to ATI per common share (in dollars per share)									1.85	1.61	(0.83)
Diluted net income (loss) attributable to ATI per common share (in dollars per share)	$ 0.41	$ 0.78	$ 0.54	$ 0.12	$ 0.30	$ 0.37	$ 0.52	$ 0.42	$ 1.85	$ 1.61	$ (0.83)

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 270.1	$ 236.7	$ (79.7)
Currency translation adjustment
Unrealized net change arising during the period	(4)	(26.6)	39.1
Derivatives
Net derivatives gain (loss) on hedge transactions	9.7	(6.4)	14.3
Reclassification to net income (loss) of net realized loss gain	(4.1)	(11.7)	(7.2)
Income taxes on derivative transactions	(4.7)	0	0
Total	10.3	(18.1)	7.1
Postretirement benefit plans- Actuarial loss
Amortization of net actuarial loss	87.2	76.5	71.6
Net loss arising during the period	(180.5)	(141.4)	(42.7)
Postretirement benefit plans- Prior Service Cost
Amortization to net income (loss) of net prior service cost (credits)	(2.6)	(2.6)	(1.6)
Income taxes on postretirement benefit plans	(20.4)	0	0
Total	(75.5)	(67.5)	27.3
Other comprehensive income (loss), net of tax	(69.2)	(112.2)	73.5
Comprehensive income (loss)	200.9	124.5	(6.2)
Less: Comprehensive income attributable to noncontrolling interests	11.2	8.1	19.8
Comprehensive income (loss) attributable to ATI	$ 189.7	$ 116.4	$ (26)

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Assets
Cash and cash equivalents	$ 490.8	$ 382
Accounts receivable, net	554.1	527.8
Short-term contract assets	38.5	51.2
Inventories, net	1,155.3	1,211.1
Prepaid expenses and other current assets	64.3	74.6
Total Current Assets	2,303	2,246.7
Property, plant and equipment, net	2,450.1	2,475
Goodwill	525.8	534.7
Other assets	355.7	245.4
Total Assets	5,634.6	5,501.8
Liabilities and Stockholders’ Equity
Accounts payable	521.2	498.8
Short-term contract liabilities	78.7	71.4
Short-term debt and current portion of long-term debt	11.5	6.6
Other current liabilities	237.8	260.1
Total Current Liabilities	849.2	836.9
Long-term debt	1,387.4	1,535.5
Accrued postretirement benefits	312.5	318.4
Pension liabilities	731.5	730
Other long-term liabilities	160.8	89.4
Total Liabilities	3,441.4	3,510.2
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- 126,695,171 shares at December 31, 2019 and 2018; outstanding-126,085,348 shares at December 31, 2019 and 125,684,396 shares at December 31, 2018	12.7	12.7
Additional paid-in capital	1,618	1,615.4
Retained earnings	1,679.3	1,422
Treasury stock: 609,823 shares at December 31, 2019 and 1,010,775 shares at December 31, 2018	(18.2)	(30.6)
Accumulated other comprehensive loss, net of tax	(1,201.7)	(1,133.8)
Total ATI Stockholders’ Equity	2,090.1	1,885.7
Noncontrolling interests
Noncontrolling Interests	103.1	105.9
Total Stockholders’ Equity	2,193.2	1,991.6
Total Liabilities and Stockholders’ Equity	$ 5,634.6	$ 5,501.8

Consolidated Balance Sheets (PA

Consolidated Balance Sheets (PARENTHETICAL) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
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	126,695,171	126,695,171
Common stock, oustanding	126,085,348	125,684,396
Treasury Stock	609,823	1,010,775

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Activities:
Net income (loss)	$ 270.1	$ 236.7	$ (79.7)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	151.1	156.4	160.8
Deferred taxes	(40.9)	2.1	(1.4)
Gain on joint venture deconsolidation	0	(15.9)	0
Impairment of goodwill	0	0	114.4
Debt extinguishment charge	21.6	0	37
Gain from disposal of property, plant and equipment, net	(90.6)	(1.2)	(0.5)
Net loss from sales of businesses	1.8	0	0
Non-cash joint venture impairment charge	11.4	0	0
Change in operating assets and liabilities:
Retirement benefits	(103.3)	(32.6)	(110.3)
Accounts receivable	(52.1)	16	(93.2)
Inventories	25.4	(108.5)	(139.2)
Accounts payable	30.1	153.7	125.8
Accrued income taxes	4.9	1.4	(1.9)
Accrued liabilities and other	0.6	(15.3)	10.6
Cash provided by operating activities	230.1	392.8	22.4
Investing Activities:
Purchases of property, plant and equipment	(168.2)	(139.2)	(122.7)
Proceeds from disposal of property, plant and equipment	92	2.8	2.7
Purchases of businesses	0	(10)	0
Proceeds from sale of business, net of transaction costs	158.1	0	0
Other	(0.2)	1.3	0.4
Cash flows provided by (used in) investing activities	81.7	(145.1)	(119.6)
Financing Activities:
Borrowings on long-term debt	350	7.1	8.5
Payments on long-term debt and finance leases	(507.6)	(6.4)	(353)
Net borrowings (payments) under credit facilities	4.9	(5.9)	1.6
Debt issuance costs	(5.5)	0	(0.8)
Debt extinguishment charge	(20.9)	0	(35.8)
Issuance of common stock	0	0	397.8
Dividends paid to noncontrolling interests	(14)	(10)	(8)
Sale to noncontrolling interest	0	14.4	3.7
Shares repurchased for income tax withholding on share-based compensation	(9.9)	(6.5)	(4.8)
Cash (used in) provided by financing activities	(203)	(7.3)	9.2
Increase (decrease) in cash and cash equivalents	108.8	240.4	(88)
Cash and cash equivalents at beginning of year	382	141.6	229.6
Cash and cash equivalents at end of year	$ 490.8	$ 382	$ 141.6

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, 2016	$ 1,444.8	$ 11	$ 1,188.8	$ 1,277.1	$ (28)	$ (1,093.7)	$ 89.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(79.7)			(91.9)			12.2
Other comprehensive income (loss)	73.5					65.9	7.6
Issuance of common stock	397.8	1.7	396.1
Dividends paid to noncontrolling interest	(8)						(8)
Sales of subsidiary shares to noncontrolling interest	3.7						3.7
Employee Stock Plans	12.4		11.4	(0.9)	1.9
Ending balance at Dec. 31, 2017	1,844.5	12.7	1,596.3	1,184.3	(26.1)	(1,027.8)	105.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	236.7			222.4			14.3
Other comprehensive income (loss)	(112.2)					(106)	(6.2)
Cumulative effect of adoption of new accounting standard	15.5			15.5
Dividends paid to noncontrolling interest	(10)						(10)
Sales of subsidiary shares to noncontrolling interest	2.7						2.7
Employee Stock Plans	14.4		19.1	(0.2)	(4.5)
Ending balance at Dec. 31, 2018	1,991.6	12.7	1,615.4	1,422	(30.6)	(1,133.8)	105.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	270.1			257.6			12.5
Other comprehensive income (loss)	(69.2)					(67.9)	(1.3)
Dividends paid to noncontrolling interest	(14)						(14)
Employee Stock Plans	14.7		2.6	(0.3)	12.4
Ending balance at Dec. 31, 2019	$ 2,193.2	$ 12.7	$ 1,618	$ 1,679.3	$ (18.2)	$ (1,201.7)	$ 103.1

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Principles of Consolidation The consolidated financial statements include the accounts of Allegheny Technologies Incorporated 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. 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 statement of financial position is the capital investment and any undistributed profit or loss, and is classified in Other (noncurrent) assets. 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, “Allegheny Technologies,” “ATI” and the “Company” refer to Allegheny Technologies Incorporated 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. Certain prior year amounts have been reclassified in order to conform with the 2019 presentation. 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 the ATI’s products are customers in the aerospace & defense, energy, automotive, construction and mining, food equipment and appliances, and medical markets. At December 31, 2019, ATI has approximately 8,100 full-time employees, of which approximately 17% are located outside the United States. Approximately 40% 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 is currently involved in negotiation on its next significant CBA with approximately 1,500 full-time employees that expire on February 29, 2020 involving USW-represented employees located primarily within Advanced Alloys & Solutions segment operations. 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 $4.6 million and $6.0 million at December 31, 2019 and 2018 , respectively. Trade credit is extended based upon evaluations of each customer’s ability to perform its obligations, which are updated periodically. Accounts receivable reserves are determined based upon an aging of accounts and a review for collectability of specific accounts. 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 (last-in, first-out (LIFO), first-in, first-out (FIFO), and average cost methods) or market. Costs include direct material, direct labor and applicable manufacturing and engineering overhead, and other direct costs. Most of the Company’s inventory is valued utilizing the LIFO costing methodology. Inventory of the Company’s non-U.S. operations is valued using average cost or FIFO methods. The Company evaluates product lines on a quarterly basis to identify inventory carrying values that exceed estimated net realizable value. In applying the lower of cost or market principle, market means current replacement cost, subject to a ceiling (market value shall not exceed net realizable value) and a floor (market shall not be less than net realizable value reduced by an allowance for a normal profit margin). The calculation of a resulting reserve, if any, is recognized as an expense in the period that the need for the reserve is identified. However, in cases where inventory at FIFO cost is lower than the LIFO carrying value, a write-down of the inventory to market may be required, subject to the ceiling and floor. 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 orders 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. Property, plant and equipment associated with the Hot-Rolling and Processing Facility (HRPF) in the Advanced Alloys & Solutions segment is being depreciated utilizing the units of production method of depreciation, which the Company believes provides a better matching of costs and revenues. 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. 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 On January 1, 2019 the Company adopted Accounting Standards Codification Topic 842 (ASC 842), Leases. This new guidance requires a lessee to recognize assets and liabilities on the balance sheet for all leases, with the result being the recognition of a right of use (ROU) asset and a lease liability. 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 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. The criteria used for a lease to be classified as a finance lease is generally consistent with the criteria under the previous lease accounting guidance, ASC 840, for capital leases. 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 income. Finance leases have front-loaded expense recognition which is reported as amortization expense and interest expense on the consolidated statement of income. ROU assets for operating leases are classified in other long-term assets, and ROU assets for finance leases are classified in property, plant and equipment on the consolidated balance sheet. For operating leases, short-term lease liabilities are classified in other current liabilities, and long-term lease liabilities are classified in other long-term liabilities on the consolidated balance sheet. For finance leases, short-term lease liabilities are classified in short-term debt, and long-term lease liabilities are classified in long-term debt on the consolidated balance sheet. On the cash flow statement, payments for operating leases are classified as operating activities. Payments for finance leases are classified as a financing activity, with the exception of the interest component of the payment which is classified as an operating activity. 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 standards 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 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 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 do not take into account the effects of inflation, and anticipated expenditures 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), 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. This approach is consistent with our revenue recognition approach in prior years. Certain customer agreements involving production of parts and components in the High Performance Materials and Components segment 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 Our 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 $17.8 million in 2019 , $22.7 million in 2018 , and $13.3 million in 2017 . Customer funded research and development costs were $2.4 million in 2019 , $2.2 million in 2018 , and $1.4 million in 2017 . 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 estimate 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. 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 January 2019, the Company adopted changes issued by the Financial Accounting Standards Board (FASB) related to leases. See Note 11 for further explanation related to this adoption, including all newly expanded disclosure requirements. Pending Accounting Pronouncements In August 2018, the FASB issued new disclosure guidance on fair value measurement. This new guidance modifies the disclosure requirements on fair value measurements, including removal and modifications of various current disclosures as well as some additional disclosure requirements for Level 3 fair value measurements. Some of these disclosure changes must be applied prospectively while others retrospectively depending on requirement. This guidance is required to be adopted by the Company beginning in fiscal year 2020, with early adoption permitted. The Company did not early adopt this guidance. The adoption of these changes is not expected to have an impact on the Company’s consolidated financial statements other than disclosures. In June 2016, the FASB added a new impairment model (known as the current expected credit loss (CECL) model) that is based on expected losses rather than incurred losses. Under the new guidance, an entity recognizes as an allowance its estimate of expected credit losses. The CECL model applies to trade receivables, other receivables, contract assets and most debt instruments. The CECL model does not have a minimum threshold for recognition of impairment losses, and entities will need to measure expected credit losses on assets that have a low risk of loss. This guidance was adopted by the Company in fiscal year 2020 without significant impact to the consolidated financial statements. In December 2019, the FASB issued new guidance to simplify the accounting for income taxes. The areas for simplification in the guidance involve the removal of certain exceptions to the general principals in the current guidance, including intraperiod allocation and the calculation of income taxes in an interim period when a year to date loss exceeds the anticipated loss for the year. The new guidance also simplifies the accounting for income taxes in the area of franchise taxes. This new guidance is effective for the Company in fiscal year 2021, with early adoption permitted. This guidance was early adopted by the Company in fiscal year 2020 without significant impact to the consolidated financial statements.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	12 Months Ended
	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	Revenue from Contracts with Customers Adoption Method and Impact On January 1, 2018, the Company adopted ASC 606, Revenue from Contracts with Customers. The Company applied ASC 606 to all contracts not completed at January 1, 2018 and adopted the accounting standard using the modified retrospective method, with the cumulative effect of initially applying ASC 606 recognized at the beginning of the 2018 fiscal year. Comparative information has not been adjusted and continues to be reported under the previous accounting guidance. The Company recognized a $15.5 million increase to retained earnings at the beginning of the 2018 fiscal year for the cumulative effect of adoption of this standard, representing the favorable impact to prior results had the over-time revenue recognition requirements under ASC 606 been applied to several customer agreements. In addition, as a result of this over-time recognition of these customer agreements, fiscal year 2018 sales on the consolidated statement of operations were lower by $4.3 million and cost of sales were lower by $5.4 million as compared to what those amounts would have been under the previous revenue recognition guidance. On the consolidated balance sheet, inventories, net, were $5.4 million higher at December 31, 2018 as compared to what this amount would have been under the previous guidance. Also, $45.3 million of contract assets were recognized on the consolidated balance sheet at December 31, 2018 ( $45.2 million in short-term contract assets and $0.1 million in other long-term assets) related to this over-time revenue recognition. There was no impact to cash flow from operating activities on the consolidated statement of cash flows as a result of this accounting standard adoption. 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, 2019 , 2018 and 2017 were as follows: (in millions) 2019 2018 2017 HPMC AA&S Total HPMC AA&S Total HPMC AA&S Total Diversified Global Markets: Aerospace & Defense $ 1,624.1 $ 506.3 $ 2,130.4 $ 1,562.9 $ 402.6 $ 1,965.5 $ 1,377.0 $ 341.1 $ 1,718.1 Energy* 153.6 643.3 796.9 133.9 646.8 780.7 119.7 490.7 610.4 Automotive 10.5 286.1 296.6 9.5 313.9 323.4 8.8 264.9 273.7 Food Equipment & Appliances 0.3 205.5 205.8 0.4 244.5 244.9 0.4 225.6 226.0 Construction/Mining 42.5 152.5 195.0 72.7 153.3 226.0 51.2 141.7 192.9 Medical 85.4 87.0 172.4 106.0 77.1 183.1 81.1 101.9 183.0 Electronics/Computers/Communications 0.5 162.7 163.2 1.5 155.4 156.9 1.0 150.6 151.6 Other 61.6 100.6 162.2 76.2 89.9 166.1 65.6 103.8 169.4 Total $ 1,978.5 $ 2,144.0 $ 4,122.5 $ 1,963.1 $ 2,083.5 $ 4,046.6 $ 1,704.8 $ 1,820.3 $ 3,525.1 *Includes the oil & gas, hydrocarbon and chemical processing, and electrical energy markets. (in millions) 2019 2018 2017 HPMC AA&S Total HPMC AA&S Total HPMC AA&S Total Primary Geographical Market: United States $ 1,042.6 $ 1,412.0 $ 2,454.6 $ 983.6 $ 1,364.5 $ 2,348.1 $ 874.3 $ 1,196.3 $ 2,070.6 China 93.9 261.7 355.6 71.2 248.8 320.0 44.3 221.3 265.6 Germany 147.2 72.1 219.3 159.0 88.2 247.2 131.9 85.2 217.1 United Kingdom 156.7 17.1 173.8 225.6 16.5 242.1 200.8 30.8 231.6 France 132.7 22.8 155.5 146.3 37.3 183.6 143.3 22.3 165.6 Japan 95.0 52.7 147.7 128.1 86.8 214.9 88.5 43.2 131.7 Rest of World 310.4 305.6 616.0 249.3 241.4 490.7 221.7 221.2 442.9 Total $ 1,978.5 $ 2,144.0 $ 4,122.5 $ 1,963.1 $ 2,083.5 $ 4,046.6 $ 1,704.8 $ 1,820.3 $ 3,525.1 Comparative information of the Company’s major high-value and standard products based on their percentages of sales is included in the following table. Hot-Rolling and Processing Facility conversion service sales in the AA&S segment are excluded from this presentation. 2019 2018 2017 HPMC AA&S Total HPMC AA&S Total HPMC AA&S Total Diversified Products: High-Value Products Nickel-based alloys and specialty alloys 38 % 27 % 32 % 37 % 24 % 30 % 37 % 20 % 28 % Precision forgings, castings and components 36 % — % 18 % 40 % — % 20 % 38 % — % 19 % Titanium and titanium-based alloys 26 % 11 % 18 % 23 % 10 % 17 % 25 % 10 % 17 % Precision rolled strip products — % 23 % 12 % — % 23 % 12 % — % 24 % 12 % Zirconium and related alloys — % 11 % 6 % — % 11 % 5 % — % 12 % 6 % Total High-Value Products 100 % 72 % 86 % 100 % 68 % 84 % 100 % 66 % 82 % Standard Products Standard stainless products — % 28 % 14 % — % 32 % 16 % — % 34 % 18 % Total 100 % 100 % 100 % 100 % 100 % 100 % 100 % 100 % 100 % The Company maintains a backlog of confirmed orders totaling $2.3 billion , $2.2 billion and $2.1 billion at December 31, 2019 , 2018 and 2017 , respectively. Due to the structure of the Company’s LTAs, 81% of this backlog at December 31, 2019 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, 2019 and 2018 , accounts receivable with customers were $558.7 million and $533.8 million , respectively. The following represents the rollforward of accounts receivable - reserve for doubtful accounts for the fiscal years ended December 31, 2019 , 2018 and 2017 : (in millions) Accounts Receivable - Reserve for Doubtful Accounts Balance as of December 31, 2016 $ 7.3 Expense to increase the reserve 0.1 Write-off of uncollectible accounts (1.5 ) Balance as of December 31, 2017 5.9 Expense to increase the reserve 1.9 Write-off of uncollectible accounts (1.8 ) Balance as of December 31, 2018 6.0 Expense to increase the reserve 0.2 Write-off of uncollectible accounts (1.6 ) Balance as of December 31, 2019 $ 4.6 Contract balances The following represents the rollforward of contract assets and liabilities for the fiscal years ended December 31, 2019 and 2018 : (in millions) Contract Assets Short-term 2019 2018 Balance as of beginning of fiscal year $ 51.2 $ 36.5 Recognized in current year 74.5 92.9 Reclassified to accounts receivable (79.9 ) (95.8 ) Impairment — — Reclassification to/from long-term — 16.8 Divestiture (7.3 ) — Other — 0.8 Balance as of period end $ 38.5 $ 51.2 Long-term 2019 2018 Balance as of beginning of fiscal year $ 0.1 $ 16.9 Recognized in current year — — Reclassified to accounts receivable — — Impairment — — Reclassification to/from short-term — (16.8 ) Balance as of period end $ 0.1 $ 0.1 (in millions) Contract Liabilities Short-term 2019 2018 Balance as of beginning of fiscal year $ 71.4 $ 69.7 Recognized in current year 126.1 76.7 Amounts in beginning balance reclassified to revenue (49.2 ) (49.6 ) Current year amounts reclassified to revenue (76.0 ) (42.7 ) Other 1.9 2.7 Reclassification to/from long-term 4.5 14.6 Balance as of period end $ 78.7 $ 71.4 Long-term 2019 2018 Balance as of beginning of fiscal year $ 7.3 $ 22.2 Recognized in current year 24.2 0.7 Amounts in beginning balance reclassified to revenue (1.1 ) (1.0 ) Current year amounts reclassified to revenue — — Other — — Reclassification to/from short-term (4.5 ) (14.6 ) Balance as of period end $ 25.9 $ 7.3 Contract costs for obtaining and fulfilling a contract were $6.5 million and $5.2 million as of December 31, 2019 and 2018 , respectively, which are reported in other long-term assets on the consolidated balance sheet. Amortization expense for the fiscal years ended December 31, 2019 and 2018 of these contract costs was $1.4 million and $1.2 million

Inventories

Inventories	12 Months Ended
	Dec. 31, 2019
Inventory Disclosure [Abstract]
Inventories	Inventories Inventories at December 31, 2019 and 2018 were as follows (in millions): 2019 2018 Raw materials and supplies $ 164.9 $ 191.5 Work-in-process 899.6 914.1 Finished goods 161.3 191.1 Total inventories at current cost 1,225.8 1,296.7 Adjustment from current cost to LIFO cost basis 33.6 2.9 Inventory valuation reserves (104.1 ) (88.5 ) Total inventories, net $ 1,155.3 $ 1,211.1 Inventories determined on the LIFO method were $776.1 million at December 31, 2019 , and $794.3 million at December 31, 2018 . The remainder of the inventory was determined using the FIFO and average cost methods, and these inventory values do not differ materially from current cost. Due to deflationary impacts primarily related to raw materials, the carrying value of the Company’s inventory as valued on LIFO exceeds current replacement cost, and based on a lower of cost or market value analysis, the Company maintains net realizable value (NRV) inventory valuation reserves to adjust carrying value of LIFO inventory to current replacement cost. These NRV reserves were $33.6 million and $8.0 million at December 31, 2019 and 2018 , respectively. In applying the lower of cost or market principle, market means current replacement cost, subject to a ceiling (market value shall not exceed net realizable value) and a floor (market shall not exceed net realizable value reduced by an allowance for a normal profit margin). Impacts to cost of sales for changes in the LIFO costing methodology and associated NRV inventory reserves were as follows (in millions): Fiscal year ended December 31, 2019 2018 2017 LIFO benefit (charge) $ 25.5 $ (28.6 ) $ (54.2 ) NRV benefit (charge) (25.6 ) 27.9 54.0 Net cost of sales impact $ (0.1 ) $ (0.7 ) $ (0.2 ) During 2019 and 2017, inventory usage resulted in liquidations of LIFO inventory quantities, increasing cost of sales by $1.8 million and $4.6 million , respectively. During 2018, inventory usage resulted in liquidations of LIFO inventory quantities, decreasing cost of sales by $0.8 million . These inventories were carried at differing costs prevailing in prior years as compared with the cost of current manufacturing cost and purchases. The results for fiscal year 2017 included $17.7 million in inventory valuation charges related to the market-based valuation of titanium products. ATI’s overall LIFO inventory valuation reserves also increased above replacement cost by $5.2 million at December 31, 2019 compared to December 31, 2018 due to the second quarter 2019 sale of the industrial forgings business, which used the LIFO costing methodology and maintained a LIFO valuation below current replacement cost.

Property Plant And Equipment

Property Plant And Equipment	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Property Plant and Equipment	Property, Plant and Equipment Property, plant and equipment at December 31, 2019 and 2018 was as follows: (In millions) 2019 2018 Land $ 34.6 $ 31.5 Buildings 832.7 851.7 Equipment and leasehold improvements 3,671.3 3,622.7 4,538.6 4,505.9 Accumulated depreciation and amortization (2,088.5 ) (2,030.9 ) Total property, plant and equipment, net $ 2,450.1 $ 2,475.0 Construction in progress at December 31, 2019 and 2018 was $177.3 million and $83.7 million , respectively. Depreciation and amortization for the years ended December 31, 2019 , 2018 and 2017 was as follows: (In millions) 2019 2018 2017 Depreciation of property, plant and equipment $ 127.1 $ 131.9 $ 135.2 Software and other amortization 24.0 24.5 25.6 Total depreciation and amortization $ 151.1 $ 156.4 $ 160.8

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets At December 31, 2019 , the Company had $525.8 million of goodwill on its consolidated balance sheet, all of which relates to the HPMC segment. Goodwill decreased $8.9 million in 2019 due to the allocation of $10.4 million to the sale of two non-core forging facilities (see Note 6), partially offset by a $1.5 million increase from the impact of foreign currency translation on goodwill denominated in functional currencies other than the U.S. dollar. On July 12, 2018, the Company acquired the assets of Addaero for $10.0 million of cash consideration. Addaero is a metal alloy-based additive manufacturer for the aerospace & defense industries, located in New Britain, CT. This business is reported as part of the HPMC segment from the date of the acquisition. The purchase price allocation included a $2.0 million technology intangible asset and goodwill of $6.0 million , which is deductible for tax purposes. The final allocation of the purchase price was completed in the third quarter of 2018. The Company performs its annual goodwill impairment evaluations in the fourth quarter of each year. For the Company’s annual goodwill impairment evaluation performed in the fourth quarter of 2019 , quantitative goodwill assessments were performed for the two HPMC reporting units with goodwill. Both of these reporting units had fair values that were significantly in excess of carrying value, and as a result, no impairments were determined to exist from the annual goodwill impairment evaluation for the year ended December 31, 2019 . 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. During the third quarter of 2017, the Company performed an interim goodwill impairment analysis on ATI Cast Products, a titanium investment casting business, due to impairment indicators including lower actual results versus projections. This reporting unit had a fair value that exceeded carrying value by 12% according to the 2016 annual goodwill impairment evaluation. For the 2017 interim impairment analysis, fair value was determined by using a quantitative assessment using a discounted cash flow technique, which represents Level 3 unobservable information in the fair value hierarchy. As a result of the 2017 interim goodwill impairment evaluation, the Company determined that the fair value of the Cast Products business was significantly below the carrying value, including goodwill. This was primarily due to lower projected revenues, profitability and cash flows associated with revised expectations for the rate of operational improvement and profitability of this business based on current customer agreements. Consequently, during the third quarter of 2017, the Company recorded a $114.4 million pre-tax impairment charge to write-off all of the goodwill associated with ATI Cast Products, 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 2017 HPMC business segment results. Accumulated goodwill impairment losses as of December 31, 2019, 2018 and 2017 were $241.0 million . Other intangible assets, which are included in Other assets on the accompanying consolidated balance sheets as of December 31, 2019 and 2018 were as follows: December 31, 2019 December 31, 2018 (in millions) Gross carrying amount Accumulated amortization Gross carrying amount Accumulated amortization Technology $ 76.8 $ (29.7 ) $ 93.4 $ (31.9 ) Customer relationships 27.0 (9.3 ) 35.7 (10.6 ) Trademarks 52.4 (20.9 ) 64.6 (21.5 ) Total amortizable intangible assets $ 156.2 $ (59.9 ) $ 193.7 $ (64.0 ) During 2019, total amortizable intangible assets net, decreased $23.8 million due to the sale of the Company’s Cast Products business. This decrease consists of the sale of $33.2 million gross intangible assets, net of $12.7 million accumulated amortization, associated with the divested business and the impairment of $4.3 million gross intangible assets, net of $1.0 million accumulated amortization, pertaining to the retained Salem, OR operations. See Note 6 for further information. Amortization expense related to intangible assets was approximately $9.5 million for the year ended December 31, 2019 and approximately $10 million for the years ended December 31, 2018 and 2017 . For each of the years ending December 31, 2020 through 2024, annual amortization expense is expected to be approximately $8 million

Divestitures - (Notes)

Divestitures - (Notes)	12 Months Ended
	Dec. 31, 2019
Discontinued Operations and Disposal Groups [Abstract]
Divestitures	Divestitures On June 3, 2019, the Company completed the sale of two non-core forging facilities for $37 million . Located in Portland, IN and Lebanon, KY, these operations primarily use traditional forging methods to produce carbon steel forged products for use in the oil & gas, transportation and construction & mining industries. The Company received cash proceeds, net of transaction costs and net working capital adjustments, of $33.0 million on the sale of this business during the fiscal year ended December 31, 2019, which is reported as an investing activity on the consolidated statement of cash flows. With $10.4 million of goodwill allocated to these operations from ATI’s Forged Products reporting unit, the Company recognized an $8.1 million pre-tax loss in 2019, which is recorded in other income, net, on the consolidated statement of income and is excluded from HPMC segment results. This business is reported as part of the HPMC segment through the date of sale. Sales from these two forging facilities in 2018 were $86 million in the aggregate. On July 22, 2019, the Company completed the sale of its Cast Products business, which produces titanium investment castings that are primarily used by aerospace & defense OEMs in the production of commercial jet airframes and engines. As part of the $127 million transaction, ATI retained a small post-casting machining facility in Salem, OR and continues to provide these services to the buyer and others. The Company received cash proceeds, net of transaction costs and net working capital adjustments, of $125.1 million on the sale of this business in 2019, which is reported as an investing activity on the consolidated statement of cash flows. The Company recognized a $6.2 million gain in 2019, which included a $10.2 million impairment charge on the carrying value of long-lived assets of the retained Salem operation ( $4.5 million for property, plant and equipment, $1.4 million for operating lease right of use assets, $1.0 million for finance lease right of use assets, and $3.3 million of finite-lived intangible assets). This long-lived asset impairment charge was based on an analysis of the estimated fair values, including asset appraisals using market approaches, which represent Level 3 unobservable information in the fair value hierarchy. This gain on the sale of the Cast Products business is recorded in other income, net, on the consolidated statement of income and is excluded from HPMC segment results. This business is reported as part of the HPMC segment through the date of sale. Cast Products’ sales were $105 million

Joint Ventures

Joint Ventures	12 Months Ended
	Dec. 31, 2019
Equity Method Investments and Joint Ventures [Abstract]
Joint Ventures	Joint Ventures 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. 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 $14.5 million at December 31, 2019 . Majority-Owned Joint Ventures STAL: The Company has a 60% interest in the Chinese joint venture known as Shanghai STAL Precision Stainless Steel Company Limited (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 stainless products mainly for the electronics, communication equipment, computers and automotive markets located in Asia. Cash and cash equivalents held by STAL as of December 31, 2019 were $22.9 million . Next Gen Alloys LLC: During 2017, the Company formed Next Gen Alloys LLC, a joint venture with GE Aviation for the development of a new meltless titanium alloy powder manufacturing technology. ATI owns a 51% interest in this joint venture. The titanium alloy powders are being developed for use in additive manufacturing applications, including 3D printing. Next Gen Alloys LLC funds its development activities through the sale of shares to the two joint venture partners, and in 2018 the Company received $2.7 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, 2019 were $9.9 million . Equity Method Joint Ventures A&T Stainless: On March 1, 2018, the Company announced the formation of the Allegheny & Tsingshan Stainless (A&T Stainless) 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 a 50% joint venture interest in A&T Stainless for $17.5 million , of which $12.0 million was received in 2018 and reported as a financing activity on the consolidated statements of cash flows. The A&T Stainless operations include the Company’s previously-idled direct roll and pickle facility in Midland, PA. ATI provides hot-rolling conversion services to A&T Stainless using the AA&S segment’s Hot-Rolling and Processing Facility. As a result of this sale of a 50% noncontrolling interest and the subsequent deconsolidation of the A&T Stainless entity, the Company recognized a $15.9 million gain during the first quarter of 2018 under deconsolidation and derecognition accounting guidance covering the loss of control of a subsidiary determined to be a business. The gain, including ATI’s retained 50% share, was based on the fair value of the joint venture, as determined by the cash purchase price for the noncontrolling interest, and is reported in other income, net on the consolidated statement of operations, and is excluded from AA&S segment results. Following this deconsolidation, 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 imports 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 a new request on behalf of A&T Stainless for exclusion from the Section 232 tariffs in October 2019, and A&T Stainless continues to be subject to the 25% tariff levied on its imports of semi-finished stainless slab products from Indonesia pending the outcome of this new request. Results of A&T Stainless have been and will continue to be negatively impacted by these tariffs on imported stainless slab products. As the tariff exclusion denial represents a potential impairment indicator, A&T Stainless evaluated its long-lived assets for impairment. The joint venture partners have continued to evaluate longer-term solutions to return this strategic initiative to profitability, and determined during the fourth quarter of 2019 that idling this facility is probable if a near-term tariff exclusion is not received. In addition, based on the current financial forecast, the undiscounted cash flows of the joint venture indicate that the carrying value of the long-lived assets is not recoverable. As a result, A&T Stainless recorded a $14.2 million non-cash impairment charge during December 2019 on its long-lived assets. ATI recognized a $7.1 million equity loss for its 50% share of this $14.2 million impairment. In addition, as of December 31, 2019 and 2018, ATI had net receivables for working capital advances and administrative services from A&T Stainless of $36.8 million and $10.5 million , respectively. For the 2019 net receivables, $8.3 million was reported in prepaid expenses and other current assets and $28.5 million in other long-term assets on the consolidated balance sheet, while all $10.5 million for 2018 was reported in prepaid expenses and other current assets. These balances were also evaluated for collectability, and a $4.3 million reserve was recorded in December 2019 based on ATI’s share of the estimated fair value of the joint venture’s net assets. The total $11.4 million joint venture impairment charge for the long-lived asset impairment and receivables reserve is reported within other income, net on the consolidated statement of operations in December 2019 and is excluded from AA&S segment results. ATI’s share of the A&T Stainless results were losses of $19.3 million and $3.9 million for the fiscal years ended December 31, 2019 and 2018, respectively. For 2019, ATI’s share of A&T Stainless results includes the $7.1 million loss related to the long-lived asset impairment charge for the joint venture’s Midland, PA operations, which is excluded from segment results. AA&S segment results in 2019 and 2018 include equity method recognition of A&T Stainless operating losses of $12.2 million and $3.9 million , respectively. Sales to A&T Stainless, which are included in ATI’s consolidated statement of operations for the 2019 and 2018 fiscal years, were $14.6 million and $4.1 million , respectively. At December 31, 2019 and 2018, accounts receivable from A&T Stainless were $0.1 million and $0.6 million , respectively. 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 $1.5 million in 2019 , $2.9 million in 2018 , and $0.6 million in 2017 , which is included in AA&S segment’s operating results, and within other income, net in fiscal year ended December 31, 2019 and 2018 on the consolidated statement of operations. This equity income is classified in cost of sales for the fiscal year ended December 31, 2017 on the consolidated statements of operations. Sales to Uniti, which are included in ATI’s consolidated statements of operations, were $31.3 million in 2019 , $49.4 million in 2018 , and $38.6 million in 2017 . Accounts receivable from Uniti were $0.2 million and $1.8 million at December 31, 2019 and 2018

Asset Retirement Obligations

Asset Retirement Obligations	12 Months Ended
	Dec. 31, 2019
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, 2019 , the Company had recognized AROs of $23.7 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, 2019 and 2018 were as follows: (In millions) 2019 2018 Balance at beginning of year $ 23.1 $ 23.5 Accretion expense 0.9 0.8 Payments (0.3 ) (1.2 ) Balance at end of year $ 23.7 $ 23.1

Supplemental Financial Statemen

Supplemental Financial Statement Information	12 Months Ended
	Dec. 31, 2019
Additional Financial Information Disclosure [Abstract]
Supplemental Financial Statement Information	Supplemental Financial Statement Information Cash and cash equivalents at December 31, 2019 and 2018 were as follows: (In millions) 2019 2018 Cash $ 190.8 $ 264.4 Other short-term investments 300.0 117.6 Total cash and cash equivalents $ 490.8 $ 382.0 Other current liabilities included salaries, wages and other payroll-related liabilities of $94.5 million and $95.8 million , and accrued interest of $25.0 million and $36.6 million at December 31, 2019 and 2018 , respectively. Other income (expense) for the years ended December 31, 2019 , 2018 , and 2017 was as follows: (in millions) 2019 2018 2017 Rent, royalty income and other income $ 2.9 $ 3.1 $ 3.5 Gains from disposal of property, plant and equipment, net 90.7 1.3 0.5 Equity loss on joint ventures (See Note 7) (10.7 ) (1.0 ) — Loss on sales of businesses, net (See Note 6) (1.9 ) — — Gain on joint venture deconsolidation (See Note 7) — 15.9 — Joint venture impairment charge (See Note 7) (11.4 ) — — Other 0.1 1.2 — Total other income, net $ 69.7 $ 20.5 $ 4.0 Gains from disposal of property, plant and equipment, net for the year ended December 31, 2019 includes a $91.7 million gain on the sale of certain oil and gas rights in Eddy County, NM. This cash gain is reported as an investing activity on the consolidated statement of cash flows for the year ended December 31, 2019, and is 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 2019.

Debt

Debt	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Debt	Debt Debt at December 31, 2019 and 2018 was as follows: (In millions) 2019 2018 Allegheny Technologies $500 million 5.875% Senior Notes due 2023 (a) $ 500.0 $ 500.0 Allegheny Technologies $500 million 5.95% Senior Notes due 2021 — 500.0 Allegheny Technologies $350 million 5.875% Senior Notes due 2027 350.0 — Allegheny Technologies $287.5 million 4.75% Convertible Senior Notes due 2022 287.5 287.5 Allegheny Ludlum 6.95% Debentures due 2025 150.0 150.0 Term Loan due 2024 100.0 100.0 U.S. revolving credit facility — — Foreign credit agreements 4.9 — Finance leases and other 18.8 15.0 Debt issuance costs (12.3 ) (10.4 ) Total short-term and long-term debt 1,398.9 1,542.1 Short-term debt and current portion of long-term debt 11.5 6.6 Total long-term debt $ 1,387.4 $ 1,535.5 (a) Bearing interest at 7.875% effective February 15, 2016. In December 2019, the Company redeemed all $500 million aggregate principal amount outstanding of the 5.95% Senior Notes due 2021 (2021 Notes), which had a January 15, 2021 maturity date, resulting in a $21.6 million pre-tax debt extinguishment charge, which included a $20.9 million cash make-whole payment related to the early extinguishment of the Notes as required by the applicable indenture, and a $0.7 million charge for deferred debt issue costs. In December 2017, the Company redeemed all $350 million aggregate principal amount outstanding of the 9.375% Senior Notes due 2019, resulting in a $37.0 million pre-tax debt extinguishment charge, which included a $35.8 million cash make- whole payment related to the early extinguishment of the Notes as required by the applicable indenture, and a $1.2 million charge for deferred debt issue costs. Interest expense was $104.9 million in 2019 , $102.1 million in 2018 , and $134.9 million in 2017 . Interest expense was reduced by $4.7 million , $4.1 million , and $2.6 million , in 2019 , 2018 , and 2017 , respectively, from interest capitalization on capital projects. Interest and commitment fees paid were $105.7 million in 2019 , $102.6 million in 2018 , and $133.8 million in 2017 . Net interest expense includes interest income of $5.9 million in 2019 , $1.1 million in 2018 , and $1.1 million in 2017 . Scheduled principal payments during the next five years are $11.5 million in 2020, $4.8 million in 2021, $291.5 million in 2022, $502.7 million in 2023, and $100.7 million in 2024. See Note 11, Leases, for the portion of these payments that are related to finance leases. 2027 Notes On November 22, 2019, ATI issued $350 million aggregate principal amount of 5.875% Senior Note due 2027 (2027 Notes). Interest on the 2027 Notes is payable semi-annually in arrears at a rate of 5.875% per year and will mature on December 1, 2027. Net proceeds of $344.5 million from this issuance, as well as cash on hand, were used to retire the 2021 Notes as discussed above. Underwriting fees and other third-party expenses for the issuance of the 2027 notes were $5.5 million , and are being amortized to interest expense over the 8-year term of the 2027 Notes. The 2027 Notes are unsecured and unsubordinated obligations of the Company and equally ranked with all of its existing and future senior unsecured debt. The 2027 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 2027 Notes, as a whole or in part, at any time or from time to time, on at least 30 days, but not more than 60 days, prior notice to the holders of the Notes at redemption prices specified in the 2027 Notes. The 2027 Notes are subject to repurchase upon the occurrence of a change in control repurchase event (as defined in the 2027 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 2027 Notes repurchased. 2023 Notes The 5.875% stated interest rate payable on the Company’s Senior Notes due 2023 (2023 Notes) is subject to adjustment in the event of changes in the credit ratings on the 2023 Notes by either Moody’s or Standard & Poor’s (S&P). Each notch of credit rating downgrade from the credit ratings in effect when the 2023 Notes were issued in July 2013 increases 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 has been at the maximum 7.875% since February 2016. Any further credit rating downgrades have no effect on the interest rate of the 2023 Notes, and increases in the Company’s credit ratings from these ratings agencies would reduce interest expense incrementally on the 2023 Notes to the original 5.875% interest rate in a similar manner. Credit Agreements On September 30, 2019, 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 domestic operations. This amendment and restatement extends the ABL facility through September 30, 2024 and includes an increase of $100 million in the revolving credit facility to $500 million , a letter of credit sub-facility of up to $200 million , and a $100 million term loan (Term Loan). Additionally, the amendment and restatement gives the Company the ability, through June 30, 2020 and as long as no default or event of default has occurred and is continuing, to borrow an additional term loan of up to $100 million in total, using one or two draws (the Delayed-Draw Term Loan). The Company also has the right to request an increase of up to $200 million in the maximum amount available under the revolving credit facility for the duration of the ABL. The Term Loan has an amended interest rate of 2.0% plus a LIBOR spread and can be prepaid in increments of $25 million if certain minimum liquidity conditions are satisfied. In July 2019, the Company amended its $50 million floating-for-fixed interest rate swap which converts half of the Term Loan to a fixed rate (now 4.21% following the September 30, 2019 ABL amendment and restatement) with a June 2024 maturity. As amended and restated, 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 LIBOR-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) 12.5% of the then applicable maximum borrowing amount under the revolving credit portion of the ABL and any outstanding Term Loan balance, or (ii) $62.5 million . The Company was in compliance with the fixed charge coverage ratio covenant at December 31, 2019. Additionally, the Company must demonstrate minimum liquidity, as calculated in accordance with the terms of the ABL facility, during the 90 day period immediately preceding the stated maturity date of each of the 4.75% Convertible Notes due 2022 and 5.875% Notes due 2023. Costs associated with entering into the 2019 ABL amendment were $2.2 million , and are being amortized to interest expense over the extended term of the facility ending September 2024, along with $2.1 million of unamortized deferred costs previously recorded for the ABL. There were no revolving credit borrowings under the ABL during 2019, however $35.3 million of available capacity was utilized to support the issuance of letters of credit at December 31, 2019. Average borrowings under the ABL for the fiscal year ended December 31, 2018 were $43 million , bearing an average annual interest rate of 3.7% . Convertible Notes In 2016, the Company issued and sold $287.5 million aggregate principal amount of 4.75% Convertible Senior Notes due 2022 (2022 Convertible Notes). Interest on the 2022 Convertible Notes is payable in cash semi-annually in arrears on each January 1 and July 1, commencing January 1, 2017. The Company does not have the right to redeem the 2022 Convertible Notes prior to their stated maturity date. Holders of the 2022 Convertible Notes have the option to convert their notes into shares of the Company’s common stock, at any time prior to the close of business on the business day immediately preceding the stated maturity date (July 1, 2022). The initial conversion rate for the 2022 Convertible Notes is 69.2042 shares of ATI common stock per $1,000 (in whole dollars) principal amount of Notes ( 19.9 million shares), equivalent to conversion price of $14.45 per share, subject to adjustment in certain events. Other than receiving cash in lieu of fractional shares, holders do not have the option to receive cash instead of shares of common stock upon conversion. Accrued and unpaid interest that exists upon conversion of a note will be deemed paid by the delivery of shares of ATI common stock and no cash payment or additional shares will be given to the holders. If the Company undergoes a fundamental change as defined in the agreement, holders of the 2022 Convertible Notes may require the Company to repurchase the notes in whole or in part for cash at a price equal to 100% of the principal amount of the notes to be purchased plus any accrued and unpaid interest to, but excluding, the repurchase date. Foreign and Other Credit Facilities STAL, the Company’s Chinese joint venture company in which ATI has a 60% interest, has a separate $20 million revolving credit facility. Borrowings under the STAL revolving credit facility are in U.S. dollars based on U.S. interbank offered rates. The credit facility is supported solely by STAL’s financial capability without any guarantees from the joint venture partners. The credit facility requires STAL to maintain a minimum level of shareholders’ equity, and certain financial ratios. 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, 2019 , the Company had not guaranteed any third-party indebtedness.

Leases (Notes)

Leases (Notes)	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Leases	Leases Adoption Method and Impact On January 1, 2019 the Company adopted ASC 842, Leases. The Company applied ASC 842 to all leases in effect at January 1, 2019 and adopted the accounting standard using the alternative transition method, which does not require the restatement of prior years. Comparative information has not been adjusted and continues to be reported under the previous accounting guidance. The Company has elected the package of practical expedients, which allows entities to not reassess (1) whether contracts are or contain leases, (2) lease classification and (3) initial direct costs. The Company has also elected the practical expedient to not separate lease components from non-lease components for all asset classes, and did not elect the hindsight practical expedient to determine the lease term. The Company 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. On January 1, 2019, the Company recognized $51.7 million of ROU assets and $55.6 million of lease liabilities ( $12.5 million short-term and $43.1 million long-term) on the consolidated balance sheet for operating leases, with the difference due to deferred rent balances as of December 31, 2018 that reduced the ROU asset balance on January 1, 2019. The adoption did not have a material impact on the Company’s results of operations or cash flows, and had no impact to the net deferred tax position on the consolidated balance sheet due to the Company’s income tax valuation allowances for federal and state purposes (see Note 17). The Company has entered into finance lease contracts with lenders for progress payments on machinery and equipment that is being constructed at the request and specification of the Company. As of December 31, 2019 , the lenders had made $5.3 million of progress payments on behalf of the Company, and $8.2 million of progress payments are scheduled to be paid. Upon payment of the final progress payments by the lenders, finance leases will commence, and $13.5 million , discounted using the applicable discount rates at lease inceptions, of ROU assets and lease liabilities will be recognized by the Company. The following represents the components of lease cost and other information for both operating and financing leases for the fiscal year ending December 31, 2019 : ($ in millions) Fiscal year ended December 31, 2019 Lease Cost Finance Lease Cost: Amortization of right of use asset $ 1.7 Interest on lease liabilities 0.5 Operating lease cost 20.5 Short-term lease cost 3.1 Variable lease cost 0.8 Sublease income — Total lease cost $ 26.6 Other information Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from finance leases $ 0.5 Operating cash flows from operating leases $ 20.8 Financing cash flows from finance leases $ 2.4 Right of use assets obtained in exchange for new finance lease liabilities $ 14.1 Right of use assets obtained in exchange for new operating lease liabilities (a) $ 35.9 Weighted average remaining lease term - finance leases 4 years Weighted average remaining lease term - operating leases 6 years Weighted average discount rate - finance leases 5.3 % Weighted average discount rate - operating leases 7.0 % (a) Several of the Company’s real property lease contracts include options to extend the lease term. During the fourth quarter of 2019, the Company reassessed the likelihood of renewal and has included $10.2 million for the renewal options for several of these operating leases in the ROU asset and lease liability because the likelihood of renewal was determined to be reasonably certain. Rental expense under operating leases was $24.4 million in 2018 and $21.1 million in 2017 . 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, 2019 (in millions): December 31, 2019 2020 $ 20.0 2021 18.2 2022 15.3 2023 11.7 2024 8.0 2025 and thereafter 24.6 Total undiscounted lease payments $ 97.8 Present value adjustment (20.1 ) Operating lease liabilities $ 77.7 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, 2019 (in millions): December 31, 2019 2020 $ 4.5 2021 4.2 2022 3.9 2023 2.7 2024 0.7 2025 and thereafter — Total undiscounted lease payments $ 16.0 Present value adjustment (1.5 ) Finance lease liabilities $ 14.5
Leases	Leases Adoption Method and Impact On January 1, 2019 the Company adopted ASC 842, Leases. The Company applied ASC 842 to all leases in effect at January 1, 2019 and adopted the accounting standard using the alternative transition method, which does not require the restatement of prior years. Comparative information has not been adjusted and continues to be reported under the previous accounting guidance. The Company has elected the package of practical expedients, which allows entities to not reassess (1) whether contracts are or contain leases, (2) lease classification and (3) initial direct costs. The Company has also elected the practical expedient to not separate lease components from non-lease components for all asset classes, and did not elect the hindsight practical expedient to determine the lease term. The Company 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. On January 1, 2019, the Company recognized $51.7 million of ROU assets and $55.6 million of lease liabilities ( $12.5 million short-term and $43.1 million long-term) on the consolidated balance sheet for operating leases, with the difference due to deferred rent balances as of December 31, 2018 that reduced the ROU asset balance on January 1, 2019. The adoption did not have a material impact on the Company’s results of operations or cash flows, and had no impact to the net deferred tax position on the consolidated balance sheet due to the Company’s income tax valuation allowances for federal and state purposes (see Note 17). The Company has entered into finance lease contracts with lenders for progress payments on machinery and equipment that is being constructed at the request and specification of the Company. As of December 31, 2019 , the lenders had made $5.3 million of progress payments on behalf of the Company, and $8.2 million of progress payments are scheduled to be paid. Upon payment of the final progress payments by the lenders, finance leases will commence, and $13.5 million , discounted using the applicable discount rates at lease inceptions, of ROU assets and lease liabilities will be recognized by the Company. The following represents the components of lease cost and other information for both operating and financing leases for the fiscal year ending December 31, 2019 : ($ in millions) Fiscal year ended December 31, 2019 Lease Cost Finance Lease Cost: Amortization of right of use asset $ 1.7 Interest on lease liabilities 0.5 Operating lease cost 20.5 Short-term lease cost 3.1 Variable lease cost 0.8 Sublease income — Total lease cost $ 26.6 Other information Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from finance leases $ 0.5 Operating cash flows from operating leases $ 20.8 Financing cash flows from finance leases $ 2.4 Right of use assets obtained in exchange for new finance lease liabilities $ 14.1 Right of use assets obtained in exchange for new operating lease liabilities (a) $ 35.9 Weighted average remaining lease term - finance leases 4 years Weighted average remaining lease term - operating leases 6 years Weighted average discount rate - finance leases 5.3 % Weighted average discount rate - operating leases 7.0 % (a) Several of the Company’s real property lease contracts include options to extend the lease term. During the fourth quarter of 2019, the Company reassessed the likelihood of renewal and has included $10.2 million for the renewal options for several of these operating leases in the ROU asset and lease liability because the likelihood of renewal was determined to be reasonably certain. Rental expense under operating leases was $24.4 million in 2018 and $21.1 million in 2017 . 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, 2019 (in millions): December 31, 2019 2020 $ 20.0 2021 18.2 2022 15.3 2023 11.7 2024 8.0 2025 and thereafter 24.6 Total undiscounted lease payments $ 97.8 Present value adjustment (20.1 ) Operating lease liabilities $ 77.7 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, 2019 (in millions): December 31, 2019 2020 $ 4.5 2021 4.2 2022 3.9 2023 2.7 2024 0.7 2025 and thereafter — Total undiscounted lease payments $ 16.0 Present value adjustment (1.5 ) Finance lease liabilities $ 14.5

Derivative Financial Instrument

Derivative Financial Instruments and Hedging	12 Months Ended
	Dec. 31, 2019
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, 2019 , 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 7 million pounds of nickel with hedge dates through 2023 . The aggregate notional amount hedged is approximately 7% of a single year’s estimated nickel raw material purchase requirements. At December 31, 2019 , the outstanding financial derivatives used to hedge the Company’s exposure to energy cost volatility included natural gas cost hedges. At December 31, 2019 , the company hedged approximately 70% of the Company’s annual forecasted domestic requirements for natural gas for 2020 and approximately 50% for 2021. 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, 2019 , the Company held euro forward purchase contracts for forecasted capital expenditures designated as cash flow hedges with a notional value of approximately 2 million euro with maturity dates through May 2020. In 2015, the Company entered into 244.7 million euro notional value of foreign currency forward contracts designated as fair value hedges maturity dates through 2017. The Company recorded $2.7 million of charges during the fiscal year ended December 31, 2017 in costs of sales on the consolidated statement of operations for maturities and mark-to-market changes on these fair value hedges. There were no outstanding fair value hedges as of December 31, 2019, 2018 and 2017. The Company may enter into derivative interest rate contracts to maintain a reasonable balance between fixed- and floating-rate debt. In July 2019, the Company amended its $50 million floating-for-fixed interest rate swap which converts half of the Term Loan to a fixed rate (now 4.21% following the September 30, 2019 ABL amendment), with a June 2024 maturity. 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 Term Loan borrowings. The ineffectiveness at hedge inception, determined from the fair value of the swap immediately prior to amendment, will be amortized to interest expense over the initial 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 counterpart 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: Natural gas contracts Prepaid expenses and other current assets $ — $ 0.8 Nickel and other raw material contracts Prepaid expenses and other current assets 4.4 1.2 Natural gas contracts Other assets — 0.2 Nickel and other raw material contracts Other assets 1.2 0.8 Total derivatives designated as hedging instruments 5.6 3.0 Derivatives not designated as hedging instruments: Foreign exchange contracts Prepaid expenses and other current assets — 0.4 Total derivatives not designated as hedging instruments: — 0.4 Total asset derivatives $ 5.6 $ 3.4 Liability derivatives Balance sheet location Derivatives designated as hedging instruments: Interest rate swap Other current liabilities $ 0.3 $ 0.2 Foreign exchange contracts Other current liabilities — 0.6 Natural gas contracts Other current liabilities 2.5 0.1 Nickel and other raw material contracts Other current liabilities 2.5 6.8 Interest rate swap Other long-term liabilities 1.2 0.3 Natural gas contracts Other long-term liabilities 1.0 0.3 Nickel and other raw material contracts Other long-term liabilities — 2.1 Total derivatives designated as hedging instruments 7.5 10.4 Total liability derivatives $ 7.5 $ 10.4 Assuming market prices remain constant with those at December 31, 2019 , a pre-tax loss of $0.9 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. 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. The 2019 income tax provision includes $6.0 million of tax expense for the recognition of a stranded deferred tax balance arising from deferred tax valuation allowances that was associated with a cash flow hedge portfolio that fully settled in the fourth quarter of 2019 (see Notes 15 and 17 for further explanation on tax impacts within accumulated other comprehensive income (loss)). This tax impact is also excluded from the table below. Activity with regard to derivatives designated as cash flow hedges for the years ended December 31, 2019 and 2018 were as follows (in millions): Derivatives in Cash Flow Hedging Relationships Amount of Gain (Loss) Recognized in OCI on Derivatives Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (a) 2019 2018 2019 2018 Nickel and other raw material contracts $ 11.3 $ (6.4 ) $ 3.9 $ 7.7 Natural gas contracts (4.0 ) 1.5 (0.9 ) 0.4 Foreign exchange contracts 1.0 0.5 0.5 1.0 Interest rate swap (0.9 ) (0.5 ) (0.4 ) (0.2 ) Total $ 7.4 $ (4.9 ) $ 3.1 $ 8.9 (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 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 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. Changes in the fair value of foreign exchange contract derivatives not designated as hedging instruments are recorded in cost of sales and are reported as changes within accrued liabilities and other on the consolidated statements of cash flows. The Company has no outstanding foreign currency forward contracts not designated as hedges as of December 31, 2019 . (In millions) Amount of Gain (Loss) Recognized in Income on Derivatives Derivatives Not Designated as Hedging Instruments 2019 2018 Foreign exchange contracts $ 0.1 $ 0.3

Fair Value Of Financial Instrum

Fair Value Of Financial Instruments	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Of Financial Instruments	Fair Value of Financial Instruments The estimated fair value of financial instruments at December 31, 2019 was as follows: Fair Value Measurements at Reporting Date Using (In millions) Total Carrying Amount Total Estimated Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Observable Inputs (Level 2) Cash and cash equivalents $ 490.8 $ 490.8 $ 490.8 $ — Derivative financial instruments: Assets 5.6 5.6 — 5.6 Liabilities 7.5 7.5 — 7.5 Debt (a) 1,411.2 1,676.5 1,552.8 123.7 The estimated fair value of financial instruments at December 31, 2018 was as follows: Fair Value Measurements at Reporting Date Using (In millions) Total Carrying Amount Total Estimated Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Observable Inputs (Level 2) Cash and cash equivalents $ 382.0 $ 382.0 $ 382.0 $ — Derivative financial instruments: Assets 3.4 3.4 — 3.4 Liabilities 10.4 10.4 — 10.4 Debt (a) 1,552.5 1,739.4 1,624.4 115.0 (a) The total carrying amount for debt excludes debt issuance costs related to the recognized debt liability which is presented in the consolidated balance sheet 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. No transfers between levels were reported in 2019 or 2018 . 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 2021 Notes (prior to redemption in December 2019), the 2022 Convertible Notes, the 2023 Notes, the Allegheny Ludlum 6.95% Debentures due 2025 and the 2027 Notes (subsequent to issuance in November 2019) 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, 2019
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 actions over the last few years as part of its retirement benefit liability management 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 approximately 1,300 participants, or less than 10% 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 now 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. Costs for defined contribution retirement plans were $44.8 million in 2019 , $39.9 million in 2018 , and $35.5 million in 2017 . Company contributions to these defined contribution plans are funded with cash. Other postretirement benefit costs for a defined contribution plan were $1.0 million , $1.0 million , and $1.7 million for the fiscal years ended December 31, 2019, 2018 and 2017, respectively. 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) 2019 2018 2017 2019 2018 2017 Service cost—benefits earned during the year $ 12.7 $ 16.4 $ 14.1 $ 1.9 $ 2.5 $ 2.4 Interest cost on benefits earned in prior years 105.5 104.8 116.7 14.8 12.7 14.6 Expected return on plan assets (131.3 ) (157.9 ) (146.9 ) — — — Amortization of prior service cost (credit) 0.3 0.3 1.3 (2.9 ) (2.9 ) (2.9 ) Amortization of net actuarial loss 73.7 65.9 62.6 13.5 10.6 9.0 Curtailment loss — 0.4 — — — — Total retirement benefit expense $ 60.9 $ 29.9 $ 47.8 $ 27.3 $ 22.9 $ 23.1 On June 1, 2018, a new CBA was ratified by USW-represented employees of the Company’s Specialty Alloys & Components (SAC) operations in Millersburg, OR. The new SAC CBA resulted in changes to retirement benefit programs, including a freeze to new entrants to the U.S. defined benefit pension plan and to postretirement health care benefits, and a hard freeze for most current pension plan participants covered by the SAC CBA, effective July 31, 2018. New hires covered by the CBA, and pension plan participants who are subject to the hard freeze, will receive Company contributions to a defined contribution retirement plan. The CBA also included pension benefit increases for all current pension plan participants affecting both prior and future service. The Company recognized a $0.4 million pension curtailment charge in the second quarter 2018 for the prior service cost of these pension benefit increases in connection with employees being hard frozen in the pension plan. 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 2019 2018 2017 2019 2018 2017 Discount rate 4.40 % 3.85 % 4.45 % 4.35 % 3.80 % 4.35 % Rate of increase in future compensation levels 0.50 - 1.00% 0.50 - 1.00% 0.50 - 1.00% — — — Weighted average expected long-term rate of return on assets 7.52 % 7.75 % 7.75 % 4.0 % 4.0 % 4.0 % 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 2019 2018 2019 2018 Discount rate 3.40 % 4.40 % 3.25 % 4.35 % Rate of increase in future compensation levels 0.50 - 1.00% 0.50 - 1.00% — — A reconciliation of the funded status for the Company’s defined benefit pension and other postretirement benefit plans at December 31, 2019 and 2018 was as follows: Pension Benefits Other Postretirement Benefits (In millions) 2019 2018 2019 2018 Change in benefit obligations: Benefit obligation at beginning of year $ 2,497.7 $ 2,829.8 $ 359.1 $ 349.9 Service cost 12.7 16.4 1.9 2.5 Interest cost 105.5 104.8 14.8 12.7 Benefits paid (274.6 ) (294.5 ) (37.7 ) (36.5 ) Subsidy paid — — — — Effect of currency rates 2.8 (4.5 ) — — Net actuarial (gains) losses – discount rate change 266.0 (150.4 ) 30.5 (17.8 ) – other 14.3 (5.7 ) (18.1 ) 48.3 Plan curtailments — 0.4 — — Plan amendments 9.5 1.4 (5.2 ) — Benefit obligation at end of year $ 2,633.9 $ 2,497.7 $ 345.3 $ 359.1 Pension plan amendments in 2019 pertain to an updated actuarial equivalence evaluation for alternate forms of benefit payments for certain covered groups. Other postretirement benefit plan amendments in 2019 are the result of converting certain covered groups to prospectively receive post-age 65 subsidies on a third-party retiree medical plan exchange, rather than continuing to receive Company-provided health plan benefits. Pension plan curtailments and amendments in 2018 are the result of changes to retirement benefit programs in the SAC CBA as discussed above. Actuarial effects of changes in discount rates are separately identified in the preceding table. During 2018, an actuarial loss was recognized on the Company’s other postretirement benefit obligations due to an updated study on attrition rates of participants in certain retiree medical plans. Pension Benefits Other Postretirement Benefits (In millions) 2019 2018 2019 2018 Change in plan assets: Fair value of plan assets at beginning of year $ 1,772.2 $ 2,129.6 $ 0.1 $ 0.6 Actual returns on plan assets and plan expenses 248.2 (107.2 ) — (0.5 ) Employer contributions 153.4 49.3 — — Effect of currency rates 2.9 (5.0 ) — — Benefits paid (274.6 ) (294.5 ) — — Fair value of plan assets at end of year $ 1,902.1 $ 1,772.2 $ 0.1 $ 0.1 Pension benefit payments in 2019 include $96 million for the annuity buyout of smaller pension balances in a U.S. defined benefit pension plan involving approximately 1,800 , or 10% of participants. Pension benefit payments in 2018 include $97 million for the annuity buyout of smaller pension balances in a U.S. defined benefit pension plan involving approximately 3,700 , or 17% of participants. These actions were also 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 2019 2018 2019 2018 Noncurrent assets $ 4.8 $ 9.2 $ — $ — Current liabilities (5.1 ) (4.7 ) (32.7 ) (40.6 ) Noncurrent liabilities (731.5 ) (730.0 ) (312.5 ) (318.4 ) Total amount recognized $ (731.8 ) $ (725.5 ) $ (345.2 ) $ (359.0 ) Changes to accumulated other comprehensive loss related to pension and other postretirement benefit plans in 2019 and 2018 were as follows: Pension Benefits Other Postretirement Benefits (In millions) 2019 2018 2019 2018 Beginning of year accumulated other comprehensive loss $ (1,470.3 ) $ (1,426.1 ) $ (107.0 ) $ (83.7 ) Amortization of net actuarial loss 73.7 65.9 13.5 10.6 Amortization of prior service cost (credit) 0.3 0.3 (2.9 ) (2.9 ) Remeasurements (173.4 ) (110.4 ) (7.1 ) (31.0 ) End of year accumulated other comprehensive loss $ (1,569.7 ) $ (1,470.3 ) $ (103.5 ) $ (107.0 ) Net change in accumulated other comprehensive loss $ (99.4 ) $ (44.2 ) $ 3.5 $ (23.3 ) Amounts included in accumulated other comprehensive loss at December 31, 2019 and 2018 were as follows: Pension Benefits Other Postretirement Benefits (In millions) 2019 2018 2019 2018 Prior service (cost) credit $ (11.2 ) $ (2.1 ) $ 11.0 $ 8.8 Net actuarial loss (1,558.5 ) (1,468.2 ) (114.5 ) (115.8 ) Accumulated other comprehensive loss (1,569.7 ) (1,470.3 ) (103.5 ) (107.0 ) Deferred tax effect 555.7 536.2 34.4 35.3 Accumulated other comprehensive loss, net of tax $ (1,014.0 ) $ (934.1 ) $ (69.1 ) $ (71.7 ) 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 2020 for defined benefit plans is estimated to be approximately $60 million , comprised of $40 million for pension expense and $20 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 18 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 2020 are: (In millions) Pension Benefits Other Postretirement Benefits Total Amortization of prior service cost (credit) $ 0.6 $ (3.8 ) $ (3.2 ) Amortization of net actuarial loss 74.5 10.8 85.3 Amortization of accumulated other comprehensive loss $ 75.1 $ 7.0 $ 82.1 The accumulated benefit obligation for all defined benefit pension plans was $2,621.1 million and $2,482.5 million at December 31, 2019 and 2018 , respectively. Additional information for pension plans with accumulated benefit obligations and projected benefit obligations in excess of plan assets: Pension Benefits (In millions) 2019 2018 Projected benefit obligation $ 2,538.9 $ 2,420.8 Accumulated benefit obligation $ 2,526.1 $ 2,405.6 Fair value of plan assets $ 1,802.4 $ 1,686.1 Cash contributions to ATI’s U.S. qualified defined benefit pension plans were $145 million in 2019, $40 million in 2018 and $135 million in 2017. 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. Based upon current regulations and actuarial studies, the Company expects to make approximately $130 million in cash contributions to its U.S. qualified defined benefit pension plans in 2020. In addition, for 2020, the Company expects approximately $9 million of payments for U.S. nonqualified pension benefits and for contributions to its U.K. defined benefit pension plan. The following table summarizes expected benefit payments from the Company’s various pension and other postretirement defined benefit plans through 2029, 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 and the U.K. defined benefit plan are made from pension plan assets. (In millions) Pension Benefits Other Postretirement Benefits Medicare Part D Subsidy 2020 $ 174.7 $ 32.8 $ 0.3 2021 172.0 34.1 0.3 2022 170.3 31.6 0.2 2023 168.3 29.4 0.2 2024 166.0 27.4 0.2 2025- 2029 786.5 110.1 0.7 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 6.0% in 2020 and is assumed to gradually decrease to 4.5% in the year 2038 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, 2019 were as follows: (In millions) Quoted Prices in Active Markets for Identical Assets Significant Observable Inputs Significant Unobservable Inputs Asset category Total NAV (Level 1) (Level 2) (Level 3) Equity securities: U.S. equities 443.6 254.7 188.9 — — International equities 326.1 299.6 26.5 — — Debt securities and cash: Fixed income and cash equivalents 650.7 419.9 58.7 172.1 — Floating rate 51.0 51.0 — — — Private equity 129.0 129.0 — — — Hedge funds 263.9 263.9 — — — Real estate and other 37.8 37.8 — — — Total assets $ 1,902.1 $ 1,455.9 $ 274.1 $ 172.1 $ — The fair values of the Company’s pension plan assets at December 31, 2018 were as follows: (In millions) Quoted Prices in Active Markets for Identical Assets Significant Observable Inputs Significant Unobservable Inputs Asset category Total NAV (Level 1) (Level 2) (Level 3) Equity securities: U.S. equities 362.9 219.9 143.0 — — International equities 377.4 335.7 41.7 — — Debt securities and cash: Fixed income and cash equivalents 493.7 116.9 6.3 370.5 — Floating rate 90.1 68.9 21.2 — — Private equity 137.1 137.1 — — — Hedge funds 258.3 258.3 — — — Real estate and other 52.7 52.7 — — — Total assets $ 1,772.2 $ 1,189.5 $ 212.2 $ 370.5 $ — 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, or are publicly traded securities and are classified as Level 1. 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. Hedge fund investments are made as a limited partner in hedge 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. Real estate investments are made as a limited partner in a portfolio of properties 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 2020 , the weighted average expected long-term rate of return on defined benefit pension assets is 7.16% . 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 15.1% for 2019 , (4.8)% for 2018 , 16.9% for 2017 , 5.3% for 2016 , and (1.2)% for 2015 . The plan assets for the ATI Pension Plan, the Company’s primary U.S. qualified defined benefit pension plan, represent over 90% of total pension plan assets at December 31, 2019 . 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 2020 , by major investment category, are: Asset category Target asset allocation range U.S. equity 18% - 40% Global equity 10% - 30% Debt securities and cash 15% - 40% Private equity 0% - 15% Hedge funds 10% - 20% Real estate and other 0% - 10% As of December 31, 2019 , the Company’s pension plans had outstanding commitments to invest up to $46 million in global debt securities, $91 million in private equity investments and $51 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. The Company’s participation in multiemployer plans for the years ended December 31, 2019 , 2018 and 2017 is reported in the following table. The Company’s contributions to the Steelworkers Western Independent Shops Pension Plan exceed 5% of this plan’s total contributions for the plan year ended September 30, 2018, which is the most recent information available from the Plan Administrator. Pension Protection Act Zone Status (1) FIP / RP Status Pending / Implemented (2) in millions Expiration Dates of Collective Bargaining Agreements EIN / Pension Plan Number Company Contributions Surcharge Imposed (3) Pension Fund 2019 2018 2019 2018 2017 Steelworkers Western Independent Shops Pension Plan 90-0169564 / 001 Green Green N/A $ 0.9 $ 0.8 $ 0.6 No 2/29/2020 Boilermakers-Blacksmiths National Pension Trust 48-6168020 / 001 Red Yellow Yes 2.5 2.5 2.2 No 9/30/2026 IAM National Pension Fund 51-6031295 / 002 Red Green Yes 2.2 2.1 1.7 Yes Various between 2021-2022 (4) Total contributions $ 5.6 $ 5.4 $ 4.5 (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 “red” zone had been determined to be in “critical status”, based on criteria established by the Internal Revenue Code (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. A 5% contribution surcharge has been imposed as of June 1, 2019 for the rest of 2019, increasing to a 10% surcharge rate beginning January 1, 2020 in addition to the contribution rate specified in the applicable collective bargaining agreements. The contribution surcharge 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 notification 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. (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” zone, is pending or has been implemented as of the end of the plan year that ended in 2019 . (3) The “Surcharge Imposed” column indicates whether ATI’s contribution rate for 2019 included an amount in addition to the contribution rate specified in the applicable collective bargaining agreement, as imposed by a plan in “critical 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 14, 2021 and July 14, 2022.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2019
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, 2019 , 2018 and 2017 were as follows (in millions): Post- retirement benefit plans Currency translation adjustment Derivatives Deferred Tax Asset Valuation Allowance Total Attributable to ATI: Balance, December 31, 2016 $ (965.5 ) $ (85.0 ) $ 2.4 $ (45.6 ) $ (1,093.7 ) OCI before reclassifications (32.5 ) 31.5 11.1 — 10.1 Amounts reclassified from AOCI (a) 43.5 (b) — (c) (4.5 ) (d) 16.8 55.8 Net current-period OCI 11.0 31.5 6.6 16.8 65.9 Balance, December 31, 2017 (954.5 ) (53.5 ) 9.0 (28.8 ) (1,027.8 ) OCI before reclassifications (107.2 ) (20.4 ) (4.9 ) — (132.5 ) Amounts reclassified from AOCI (a) 55.9 (b) — (c) (8.9 ) (d) (20.5 ) 26.5 Net current-period OCI (51.3 ) (20.4 ) (13.8 ) (20.5 ) (106.0 ) Balance, December 31, 2018 (1,005.8 ) (73.9 ) (4.8 ) (49.3 ) (1,133.8 ) OCI before reclassifications (141.6 ) (2.7 ) 7.4 — (136.9 ) Amounts reclassified from AOCI (a) 64.3 (b) — (c) (3.1 ) (d) 7.8 69.0 Net current-period OCI (77.3 ) (2.7 ) 4.3 7.8 (67.9 ) Balance, December 31, 2019 $ (1,083.1 ) $ (76.6 ) $ (0.5 ) $ (41.5 ) $ (1,201.7 ) Attributable to noncontrolling interests: Balance, December 31, 2016 $ — $ 9.7 $ — $ — $ 9.7 OCI before reclassifications — 7.6 — — 7.6 Amounts reclassified from AOCI — (b) — — — — Net current-period OCI — 7.6 — — 7.6 Balance, December 31, 2017 — 17.3 — — 17.3 OCI before reclassifications — (6.2 ) — — (6.2 ) Amounts reclassified from AOCI — (b) — — — — Net current-period OCI — (6.2 ) — — (6.2 ) Balance, December 31, 2018 — 11.1 — — 11.1 OCI before reclassifications — (1.3 ) — — (1.3 ) Amounts reclassified from AOCI — (b) — — — — Net current-period OCI — (1.3 ) — — (1.3 ) Balance, December 31, 2019 $ — $ 9.8 $ — $ — $ 9.8 (a) Amounts were included in net periodic benefit cost for pension and other postretirement benefit plans (see Note 14). (b) No amounts were reclassified to earnings. (c) For 2018, following the Company’s January 1, 2018 adoption of changes issued by the FASB related to accounting guidance for derivatives, amounts related to derivatives are included in cost of goods sold or interest expense in the period or periods the hedged item affects earnings (see Note 12). For 2017, amounts related to the effective portion of the derivatives were included in cost of goods sold in the period or periods the hedged item affects earnings, and amounts related to the ineffective portion of the derivatives were presented in selling and administrative expenses on the consolidated statements of operations (see Note 12). (d) Represents the net change in deferred tax asset valuation allowances on changes in AOCI balances between the balance sheet dates. The 2019 income tax provision includes $6.0 million of tax expense for the recognition of a stranded deferred tax balance arising from deferred tax valuation allowances that was associated with a cash flow hedge portfolio that fully settled in the fourth quarter of 2019. 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, 2019 , 2018 and 2017 were as follows: Amount reclassified from AOCI (c) Fiscal year ended Details about AOCI Components (In millions) December 31, 2019 December 31, 2018 December 31, 2017 Affected line item in the consolidated statement of operations Postretirement benefit plans Prior service credit $ 2.6 (a) $ 2.6 (a) $ 1.6 (a) Actuarial losses (87.2 ) (a) (76.5 ) (a) (71.6 ) (a) (84.6 ) (c) (73.9 ) (c) (70.0 ) (c) Total before tax (20.3 ) (18.0 ) (26.5 ) Tax benefit (d) $ (64.3 ) $ (55.9 ) $ (43.5 ) Net of tax Derivatives Nickel and other raw material contracts $ 5.1 (b) $ 10.2 (b) $ (3.4 ) (b) Natural gas contracts (1.2 ) (b) 0.5 (b) (5.3 ) (b) Foreign exchange contracts 0.7 (b) 1.3 (b) 15.9 (b) Interest rate swap (0.5 ) (b) (0.3 ) (b) — (b) 4.1 (c) 11.7 (c) 7.2 (c) Total before tax 1.0 2.8 2.7 Tax provision (d) $ 3.1 $ 8.9 $ 4.5 Net of tax (a) Amounts are included in nonoperating retirement benefit expense (see Note 14). (b) For 2018, following the Company’s January 1, 2018 adoption of changes issued by the FASB related to accounting guidance for derivatives, amounts related to derivatives, with the exception of the interest rate swap are included in 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 Term Loan is recognized in earnings (see Note 12). For 2017, amounts related to the effective portion of the derivatives were included in cost of goods sold in the period or periods the hedged item affects earnings, and amounts related to the ineffective portion of the derivatives were presented in selling and administrative expenses on the consolidated statements of operations (see Note 12). (c) 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. (d) 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, 2019
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, 2019 , there were no shares of preferred stock issued. Common Stock On November 7, 2017, the Company issued 17 million shares of common stock at $24.00 per share before expenses in an underwritten registered public offering. This equity offering resulted in proceeds, net of transaction costs, of $397.8 million . In December 2017, the Company used the proceeds from the equity offering to redeem all of the Senior Notes due 2019 (see Note 10). 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 $150 million and 30% of the maximum revolving credit availability, 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 $150 million and 30% of the maximum revolving credit advance amount but more than the greater of $75 million and 15% of the maximum revolving credit advance amount, 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 15% of the maximum revolving credit availability, 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 During 2015, the Company adopted the Allegheny Technologies Incorporated 2015 Incentive Plan (the “2015 Incentive Plan”). In May 2017, the Company adopted the Allegheny Technologies Incorporated 2017 Incentive Plan (the “2017 Incentive Plan”). Upon adoption of the 2017 Incentive Plan, all new awards are being made under the 2017 Incentive Plan. Shares previously remaining available for grant under the 2015 Incentive Plan, or which become available for award due to the forfeiture or cancellation of prior awards under the 2015 Incentive Plan, are available for award under the 2017 Incentive Plan. Outstanding grants previously made under the 2015 Incentive Plan remain in effect in accordance with their terms and the terms of their respective Plan. 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, 2019 , 4.1 million shares of common stock were available for future awards under the 2017 Incentive Plan. The general terms of each arrangement granted under the 2015 Incentive Plan or the 2017 Incentive Plan, and predecessor plans, the method of estimating fair value for each arrangement, and award activity is reported below. Beginning in 2016, the Company implemented a new share-based incentive compensation program, the Long-Term Incentive Plan (LTIP). The LTIP consists of both Restricted Share Units (RSU) and Performance Share Units (PSU). For years prior to 2016, the Company’s two principal share-based incentive compensation programs were the Performance/Restricted Stock Program (PRSP) of nonvested stock awards and the Long-Term Performance Plan (LTPP). The LTPP was adopted in 2014 and included performance shares under the Total Shareholder Return (TSR) portion and nonvested stock awards under the Long-Term Shareholder Value (LTSV) portion. Nonvested stock awards/units: Restricted Share Units: Beginning in 2016, annual awards of RSUs were granted to employees, with service conditions. 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. 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. In 2017, 2018 and 2019, 320,808 , 253,393 and 345,400 RSUs, respectively, were awarded to employees under the LTIP. In February 2019, one-third of the 2016, 2017 and 2018 RSU awards vested, comprising 175,287 , 102,188 and 83,312 shares, respectively. In February 2018, one-third of the 2016 and 2017 RSU awards vested, comprising 178,335 and 102,279 shares, respectively. In February 2017, one-third of the 2016 RSU award vested, comprising 190,421 shares. Nonvested stock awards: Prior to 2016, awards of nonvested stock were granted to employees under the PRSP, with either performance and/or service conditions. Awards of nonvested stock are also granted to non-employee directors, with service conditions. For nonvested stock awards, dividend equivalents, whether in stock or cash form, accumulate but are not paid until the underlying award vests. LTSV awards vest at the end of a three-year measurement period subject to the achievement, in whole or in part, of specified operational goals. At December 31, 2017, 60% of the operational goals for the 2015 LTSV were attained and 73,734 shares vested and 49,148 shares were forfeited. As of December 31, 2017, there were no remaining LTSV awards outstanding. The fair value of nonvested stock awards is measured based on the stock price at the grant date, adjusted for non-participating dividends, as applicable, based on the current dividend rate. For nonvested stock awards to employees in 2012, 2013, 2014 and 2015 under the Company’s PRSP, one-half of the nonvested stock (“performance shares”) vested only on the attainment of an income target, measured cumulatively over a three-year period. The remaining nonvested stock awarded to most employees under the 2015 PRSP vests over a service period of three years ; for certain senior executives this service period is five years for the 2015 award. The remaining PRSP nonvested stock awarded to employees under the 2012, 2013 and 2014 vest over a service period of five years , with accelerated vesting to three years if the performance shares’ vesting criterion was attained. Expense for each of these awards was recognized based on estimates of attaining the performance criterion, including estimated forfeitures. The three-year cumulative income statement metrics in 2012, 2013, 2014 and 2015 PRSP awards were not met, and performance share forfeitures were 171,083 , 244,899 , 214,571 and 196,196 shares, respectively. The remaining service portion of the 2014 PRSP, comprising 207,751 shares, vested in February 2019. The remaining service portion of the 2013 PRSP, comprising 233,896 shares, vested in February 2018. The remaining service portion of the 2012 PRSP, comprising of 166,929 shares, vested in February 2017. The remaining service portion of the 2015 PRSP for all employees except certain senior executives, comprising of 126,585 shares, vested at December 31, 2017. Vesting of the remaining service portion of the 2015 PRSP awards for certain senior executives continues over the five-year service period through February 2020. Compensation expense related to all nonvested stock awards and units was $9.8 million in 2019 , $9.7 million in 2018 , and $9.8 million in 2017 . Approximately $5.9 million of unrecognized fair value compensation expense relating to nonvested stock awards and restricted stock units is expected to be recognized through 2022, including $4.6 million expected to be recognized in 2020, based on estimated service period forfeitures. Activity under the Company’s nonvested stock awards and restricted share units for the years ended December 31, 2019 , 2018 , and 2017 was as follows: (Shares in thousands, $ in millions) 2019 2018 2017 Number of shares/units Weighted Average Grant Date Fair Value Number of shares/units Weighted Average Grant Date Fair Value Number of shares Weighted Average Grant Date Fair Value Nonvested, beginning of year 1,055 $ 28.3 1,320 $ 32.5 1,852 $ 51.5 Granted 396 10.8 290 7.8 378 7.1 Vested (681 ) (14.5 ) (540 ) (11.7 ) (591 ) (16.9 ) Forfeited (14 ) (0.4 ) (15 ) (0.3 ) (319 ) (9.2 ) Nonvested, end of year 756 $ 24.2 1,055 $ 28.3 1,320 $ 32.5 Performance awards: Performance Share Units: In 2016, the Company established the PSU award. PSU award opportunities are determined at a target number of shares, and the number of shares awarded is based on attainment of two ATI financial performance metrics. The metrics for awards through 2018 measured (1) net income attributable to ATI and (2) return on invested capital, over a three-year performance period. The metrics for the 2019 award measured (1) net income attributable to ATI and (2) return on capital employed, over a three-year performance period. For certain senior executives, the number of PSUs to be awarded based on the performance criteria is modified up or down by up to 20% based on the Company’s relative total shareholder return over the performance measurement period (“TSR Modifier”), but not above the maximum number of PSUs to be vested. The TSR Modifier is measured as 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 is measured based on the stock price at the grant date, including the effect of the TSR Modifier. The fair value of the TSR Modifier is estimated 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. In 2017, 2018 and 2019, the Company awarded 589,980 , 456,318 and 479,364 share units, respectively, at the target level with a weighted average grant date fair value of $12.4 million , $12.9 million and $14.7 million respectively. The 2017 PSU performance, and share units, each have a threshold attainment of 25% and a maximum attainment of 150% of the target financial performance metrics and target share units, measured over the applicable three-year performance period. The 2018 and 2019 PSU performance, and share units, each have 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. At December 31, 2019, a maximum of 1.8 million shares have been reserved for issuance for the PSU awards. At December 31, 2019, the 2017 PSU awards vested above target and at + 20% for the TSR Modifier, resulting in the issuance of 669,898 shares. At December 31, 2018, the 2016 PSU awards vested with financial performance attainment between threshold and target and at + 20% for the TSR Modifier, resulting in the issuance of 329,897 shares. Aggregate compensation expense recognized over the three year performance periods for the 2018 and 2019 PSU awards could range from zero to $51 million , including estimated forfeitures, based on the actual financial performance attained. Compensation expense for the PSUs during the performance period is recognized based on estimates of attaining the performance criteria, including estimated forfeitures, which is evaluated on a quarterly basis. The Company recognized $3.8 million , $11.4 million and $14.6 million of compensation expense in 2017, 2018 and 2019, respectively, for the PSU awards. As of December 31, 2019, ATI estimates achieving financial performance attainment for the 2018 and 2019 PSU awards slightly above target levels. Based on these estimates, there is $12.9 million of cumulative unrecognized compensation expense remaining for the PSU awards, including estimated forfeitures, which is expected to be recognized over the remaining performance periods through fiscal year 2021. This includes $7.7 million expected to be recognized in 2020. Forfeited share units in 2017, 2018 and 2019 were 67,521 , 21,848 and 48,598 , respectively, with a weighted average grant date fair value of $1.0 million , $0.5 million and $1.1 million , respectively. Total Shareholder Return: Award opportunities under the TSR portion of the formerly-used LTPP incentive compensation program were determined at a target number of shares, and performance equity awards paid out based on the measured return of the Company’s stock price and dividend performance at the end of three-year periods as compared to the stock price and dividend performance of a group of industry peers. The actual number of shares awarded at the end of the performance measurement period may range from a minimum of zero to a maximum of two times target. Fair values for these performance awards were estimated using Monte Carlo simulations of stock price correlation, projected dividend yields and other variables over three-year time horizons matching the total shareholder return performance measurement periods. Compensation expense was $3.6 million in 2017

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
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) 2019 2018 2017 U.S. $ 190.2 $ 190.8 $ (119.8 ) Non-U.S. 51.4 56.9 33.3 Income (loss) before income taxes $ 241.6 $ 247.7 $ (86.5 ) The income tax provision (benefit) was as follows: (In millions) 2019 2018 2017 Current: Federal $ 2.2 $ 1.0 $ (0.8 ) State 0.2 (0.8 ) (1.3 ) Foreign 8.1 10.1 6.2 Total 10.5 10.3 4.1 Deferred: Federal (4.6 ) 1.3 2.4 State (40.4 ) (0.5 ) (14.4 ) Foreign 6.0 (0.1 ) 1.1 Total (39.0 ) 0.7 (10.9 ) Income tax provision (benefit) $ (28.5 ) $ 11.0 $ (6.8 ) 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) 2019 2018 2017 Taxes computed at the federal rate $ 50.7 $ 52.0 $ (30.3 ) Goodwill impairment — — 36.6 State and local income taxes, net of federal tax benefit 0.3 (0.5 ) — Valuation allowance (90.1 ) (48.0 ) (14.5 ) Repatriation of foreign earnings (GILTI starting in 2018) 3.5 5.4 14.2 Restructuring 4.2 — — Impacts of U.S. Tax Act — 5.9 (4.1 ) Foreign earnings taxed at different rate 2.7 3.2 (3.5 ) Adjustment to prior years’ taxes — (5.8 ) (5.2 ) Withholding taxes 2.7 2.7 2.2 Preferential tax rate (4.1 ) (4.8 ) (3.7 ) Other 1.6 0.9 1.5 Income tax provision (benefit) $ (28.5 ) $ 11.0 $ (6.8 ) On December 22, 2017, the U.S. government enacted comprehensive tax legislation commonly referred to as the Tax Cuts and Jobs Act (the “Tax Act”). The Tax Act made broad and complex changes to the U.S. tax code. Changes impacting the Company’s tax provision for the past three years include the following: (1) Reducing the U.S. federal current and deferred rate to 21% ; The change in the U.S. federal corporate tax rate from 35% to 21% resulted in a $2.6 million benefit, which was recognized in 2017, as it related to the remeasurement of indefinite lived deferred tax liabilities. In addition, the reconciliation of income taxes utilized a 35% U.S. federal tax rate for 2017 compared to 2019 and 2018 which utilized a 21% federal tax rate. (2) Repeal of the alternative minimum tax, which resulted in a $1.5 million decrease in the deferred tax asset valuation allowance that was recognized in 2017. This tax benefit, along with the benefit related to the remeasurement of indefinite lived deferred tax assets is combined for a total benefit of $4.1 million and presented within the 2017 income tax reconciliation as Impact from U.S. tax reform in the above table. (3) Requiring companies to pay a one-time transition tax on certain unrepatriated earnings of foreign subsidiaries, with $5.9 million included in the 2018 tax provision. This is also reported as Impact from U.S. tax reform for 2018. (4) Requiring a current year inclusion in U.S. federal taxable income of certain earnings of controlled foreign corporations, commonly referred to as Global Intangible Low-Taxed Income (GILTI), for which the Company is currently utilizing pre-January 1, 2018 net operating losses (NOLs) to offset the 2019 income inclusion of $16.8 million ( $3.5 million net tax effect) and utilized pre-January 1, 2018 losses in 2018 to offset the $25.7 million ( $5.4 million net tax effect) inclusion. The Company has elected to recognize GILTI liabilities as an element of income tax expense in the period incurred. (5) Creating a new limitation on deductible interest expense, for which the Company has estimated the federal limitation to be $24 million in 2019, creating an indefinite lived deferred tax asset for which a valuation allowance was not established. This limitation is affected by the interpretation of the meaning of depreciation in the proposed regulations, which could change as additional guidance and/or final regulations are issued. The Company continues to analyze additional planning around the overall calculation and continues to wait for final regulations. In 2018, the Company was granted a preferential tax rate related to the STAL joint venture operations in China for tax years 2018 through 2020. The preferential tax rate is 15% , compared to the statutory rate of 25% . The Company has benefited from past preferential tax rate grants by the Chinese government, and the previous 15% three-year preferential tax rate expired on December 31, 2017. In 2019, the Company restructured certain foreign legal entities, including the elimination of entities that were no longer cost-effective following changes of the Tax Act, which resulted in $4.2 million of tax expense related to previously-recognized net operating loss carryforwards. 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 estimate future taxable income exclusive of temporary differences and tax planning strategies. In situations where a three-year cumulative loss position exists, accounting standards limit the ability to consider projections of future results as positive evidence to assess the realizability of deferred tax assets. 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. Beginning in 2015, the Company’s results reflected a three year cumulative loss from U.S. operations, and valuation allowances were established on its’ federal and state deferred tax assets. In 2017, the Company’s results reflected a partial release of the valuation allowance related to the federal and state deferred tax assets, along with the one-time transition tax inclusion in 2017. In 2018 based upon updated guidance, approximately $28.2 million of available tax credits were used instead of the NOL to offset the transition tax inclusion. This overall change in presentation was reflected within the 2018 effective tax rate. In 2018, the Company reported income before tax of $247.7 million , of which $190.8 million was attributable to the U.S. The overall income, along with the GILTI inclusion for the year, resulted in the Company utilizing NOL deferred tax assets in 2018, which resulted in a U.S. valuation allowance release of $46.3 million for 2018. At December 31, 2018, the Company continued to maintain a valuation allowance on the net deferred tax assets for U.S. federal and state income tax purposes, with the exception of the indefinite lived deferred tax liability related to goodwill and the withholding tax liability associated with its permanent reinvestment assertion, as well as valuation allowances for certain foreign operations. At December 31, 2019, the Company’s U.S. results have switched from a three-year cumulative loss position to a three-year cumulative income position, allowing the Company to utilize forecasts of future profits as a source of income when evaluating the overall need for a valuation allowance. The Company determined that valuation allowances on net deferred tax asset balances for federal and certain state jurisdictions are no longer required. Certain individual tax attributes still require a valuation allowance based on expected utilization. The change in the overall valuation allowance for 2019 includes amounts utilized during the year as part of the reported effective tax rate, as well as a $45.1 million reduction at December 31, 2019 based on a change in judgment on the realizability of deferred tax assets. The Company also established valuation allowances on deferred tax amounts recorded in accumulated other comprehensive loss in 2017, 2018 and 2019 of $28.8 million , $49.3 million and $41.5 million , respectively, which are not reflected in the preceding table reconciling amounts recognized in the income tax provision (benefit) recorded on the statement of operations (see Note 15). Due to the change in judgment on the realizability of deferred tax assets at December 31, 2019, no changes to the beginning of year balances for U.S deferred tax valuation allowances were recognized in accumulated other comprehensive loss in 2019. The 2019 income tax provision includes $6.0 million of tax expense for the recognition of a stranded deferred tax balance in accumulated other comprehensive loss arising from deferred tax valuation allowances that was associated with a cash flow hedge portfolio that fully settled in the fourth quarter of 2019. See Notes 12 and 15 for additional information on cash flow hedge activity. 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, 2019 and 2018 were as follows: (In millions) 2019 2018 Deferred income tax assets Pensions $ 155.5 $ 159.4 Postretirement benefits other than pensions 83.8 87.3 Net operating loss tax carryovers 264.4 307.5 Tax credits 42.6 49.7 Other items 86.1 69.7 Gross deferred income tax assets 632.4 673.6 Valuation allowance for deferred tax assets (94.5 ) (194.8 ) Total deferred income tax assets 537.9 478.8 Deferred income tax liabilities Bases of property, plant and equipment 364.2 371.5 Inventory valuation 65.5 67.1 Bases of amortizable intangible assets 23.7 29.9 Other items 27.0 14.5 Total deferred tax liabilities 480.4 483.0 Net deferred tax asset (liability) $ 57.5 $ (4.2 ) 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 $766 20 years $— $766 U.S. Foreign Tax Credit $30 10 years $7 $23 U.S. Research and Development Credit $2 20 years $— $2 State NOL $136 Various $30 $106 State Credits $11 Various $3 $8 U.K. NOL $23 Indefinite $— $— Poland Economic Zone Credit $2 7 years $— $2 Income taxes paid and amounts received as refunds were as follows: (In millions) 2019 2018 2017 Income taxes paid $ 15.1 $ 9.7 $ 10.4 Income tax refunds received (9.2 ) (1.6 ) (7.1 ) Income taxes paid, net $ 5.9 $ 8.1 $ 3.3 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 $3.5 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, 2019 , 2018 and 2017 were as follows: (In millions) 2019 2018 2017 Balance at beginning of year $ 14.7 $ 14.7 $ 22.7 Increases in prior period tax positions — — — Decreases in prior period tax positions — (0.1 ) (0.7 ) Increases in current period tax positions 0.9 0.7 0.7 Expiration of the statute of limitations (1.2 ) (0.6 ) (0.4 ) Settlements — — (7.6 ) Balance at end of year $ 14.4 $ 14.7 $ 14.7 For years ended December 31, 2019, 2018 and 2017, the liability includes $11.5 million , $12.1 million and $11.7 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 $3 million . At this time, the Company believes that it is reasonably possible that approximately $2 million of the estimated unrecognized tax benefits as of December 31, 2019 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, 2019, 2018 and 2017 were not significant. At both December 31, 2019 and 2018, the accrued liabilities for interest and penalties related to unrecognized tax benefits were $2.7 million . 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 2018 States: Pennsylvania 2016 Foreign: China 2016 Poland 2013 United Kingdom 2017

Business Segments

Business Segments	12 Months Ended
	Dec. 31, 2019
Segment Reporting [Abstract]
Business Segments	Business Segments The Company operates in two business segments: High Performance Materials & Components (HPMC) and Advanced Alloys & Solutions (AA&S). Business segment references within Notes 1 and 7 reflect these two business segments. Over 80% of 2019 HPMC business segment sales are to the aerospace & defense markets, and over half of HPMC’s total sales are products for commercial jet engines. Other major HPMC end markets include medical and energy. HPMC produces a wide range of high performance materials, and components, and advanced metallic powder alloys made from titanium and titanium-based alloys, nickel-based alloys and superalloys, 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 serves a diverse group of end markets, with sales to the energy market and aerospace & defense markets collectively representing over 50% of 2019 sales. Other important end markets for AA&S include automotive, food processing equipment and appliances, consumer electronics, and construction & mining. AA&S produces nickel-based alloys, specialty alloys, and titanium and titanium-based alloys, and stainless steel products in a variety of forms including plate, sheet, and strip products. This segment includes STAL, in which the Company has a 60% ownership interest, and ATI’s 50% interests in the A&T Stainless and Uniti joint ventures, which are accounted for under the equity method. See Note 7 for further information on the Company’s joint ventures. The measure of segment operating profit excludes all effects of LIFO inventory accounting and any related changes in net realizable value inventory reserves which offset the Company’s aggregate net debit LIFO valuation balance, income taxes, corporate expenses, net interest expense, closed operations and other expenses, charges for goodwill impairment, restructuring and asset impairment charges, debt extinguishment charges and non-operating gains or losses. Management believes segment operating profit, 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) 2019 2018 2017 Total sales: High Performance Materials & Components $ 2,054.2 $ 2,039.2 $ 1,751.1 Advanced Alloys & Solutions 2,392.2 2,302.4 2,006.9 Total sales 4,446.4 4,341.6 3,758.0 Intersegment sales: High Performance Materials & Components 75.7 76.1 46.3 Advanced Alloys & Solutions 248.2 218.9 186.6 Total intersegment sales 323.9 295.0 232.9 Sales to external customers: High Performance Materials & Components 1,978.5 1,963.1 1,704.8 Advanced Alloys & Solutions 2,144.0 2,083.5 1,820.3 Total sales to external customers $ 4,122.5 $ 4,046.6 $ 3,525.1 Total international sales were $1,667.9 million in 2019 , $1,698.4 million in 2018 , and $1,454.5 million in 2017 . Of these amounts, sales by operations in the United States to customers in other countries were $1,262.6 million in 2019 , $1,303.8 million in 2018 , and $1,078.6 million in 2017 . (In millions) 2019 2018 2017 Operating profit: High Performance Materials & Components $ 271.6 $ 269.7 $ 191.4 Advanced Alloys & Solutions 109.1 143.5 92.0 Total operating profit 380.7 413.2 283.4 LIFO and net realizable value reserves (See Note 3) (0.1 ) (0.7 ) (0.2 ) Corporate expenses (66.8 ) (58.1 ) (50.5 ) Closed operations and other expenses (25.5 ) (21.6 ) (34.0 ) Restructuring and other charges (4.5 ) — — Impairment of goodwill (See Note 5) — — (114.4 ) Debt extinguishment charge (See Note 10) (21.6 ) — (37.0 ) Gain on joint venture deconsolidation (See Note 7) — 15.9 — Joint venture impairment charge (See Note 7) (11.4 ) — — Gain on asset sales, net 89.8 — — Interest expense, net (99.0 ) (101.0 ) (133.8 ) Income (loss) before income taxes $ 241.6 $ 247.7 $ (86.5 ) 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 our European Treasury Center operation. Restructuring and other charges for 2019 are comprised of severance obligations for the reduction of approximately 70 positions in order to streamline ATI’s salaried workforce primarily to improve the cost competitiveness of the U.S.-based Flat Rolled Products business. The entire $4.5 million will be paid in 2020 upon completion of these reductions. The $89.8 million net gain on asset sales for 2019 consists of a $91.7 million gain on the sale of certain oil and gas rights in Eddy County, NM (see Note 9) and a $6.2 million gain on the sale of the Company’s Cast Products business, partially offset by an $8.1 million loss on the sale of two non-core forging facilities, located in Portland, IN and Lebanon, KY. See Note 6 for further explanation regarding the sale of business transactions. Certain additional information regarding the Company’s business segments is presented below: (In millions) 2019 2018 2017 Depreciation and amortization: High Performance Materials & Components $ 84.7 $ 90.6 $ 91.5 Advanced Alloys & Solutions 63.5 62.9 63.4 Corporate 2.9 2.9 5.9 Total depreciation and amortization $ 151.1 $ 156.4 $ 160.8 Capital expenditures: High Performance Materials & Components $ 119.9 $ 71.7 $ 52.7 Advanced Alloys & Solutions 47.4 64.5 69.1 Corporate 0.9 3.0 0.9 Total capital expenditures $ 168.2 $ 139.2 $ 122.7 Identifiable assets: 2019 2018 2017 High Performance Materials & Components $ 2,324.6 $ 2,400.7 $ 2,329.9 Advanced Alloys & Solutions 2,621.1 2,590.4 2,550.8 Discontinued Operations — — 0.2 Corporate: Deferred Taxes 64.5 8.7 7.6 Cash and cash equivalents and other 624.4 502.0 296.9 Total assets $ 5,634.6 $ 5,501.8 $ 5,185.4 ($ in millions) 2019 Percent of total 2018 Percent of total 2017 Percent of total Total assets: United States $ 4,956.4 88 % $ 4,859.1 88 % $ 4,547.7 88 % China 288.1 5 % 287.3 5 % 276.0 5 % United Kingdom 141.3 3 % 136.7 3 % 122.7 2 % Other 248.8 4 % 218.7 4 % 239.0 5 % Total Assets $ 5,634.6 100 % $ 5,501.8 100 % $ 5,185.4 100 %

Per Share Information

Per Share Information	12 Months Ended
	Dec. 31, 2019
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, 2019 2018 2017 Numerator: Numerator for basic net income (loss) per common share - Net income (loss) attributable to ATI $ 257.6 $ 222.4 $ (91.9 ) Effect of dilutive securities: 4.75% Convertible Senior Notes due 2022 12.8 12.9 — Numerator for diluted net income (loss) per common share - Net income (loss) attributable to ATI after assumed conversions $ 270.4 $ 235.3 $ (91.9 ) Denominator: Denominator for basic net income (loss) per common share—weighted average shares 125.8 125.2 110.1 Effect of dilutive securities: Share-based compensation 0.8 0.8 — 4.75% Convertible Senior Notes due 2022 19.9 19.9 — Denominator for diluted net income (loss) per common share—adjusted weighted average shares and assumed conversions 146.5 145.9 110.1 Basic net income (loss) attributable to ATI per common share $ 2.05 $ 1.78 $ (0.83 ) Diluted net income (loss) attributable to ATI per common share $ 1.85 $ 1.61 $ (0.83 ) Common stock that would be issuable upon the assumed conversion of the 2022 Convertible Notes 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 would have been anti-dilutive. There were no anti-dilutive shares for 2019 and 2018 . There were 20.8 million anti-dilutive shares for 2017

Financial Information for Subsi

Financial Information for Subsidiary and Guarantor Parent	12 Months Ended
	Dec. 31, 2019
Financial Information for Subsidiary and Guarantor Parent [Abstract]
Financial Information for Subsidiary and Guarantor Parent	Financial Information for Subsidiary and Guarantor Parent The payment obligations under the $150.0 million 6.95% Debentures due 2025 issued by Allegheny Ludlum, LLC (formerly known as Allegheny Ludlum Corporation) (the “Subsidiary”) are fully and unconditionally guaranteed by ATI (the “Guarantor Parent”). In accordance with positions established by the U.S. Securities and Exchange Commission, the following financial information sets forth separately financial information with respect to the Subsidiary, the Non-guarantor Subsidiaries and the Guarantor Parent. The principal elimination entries eliminate investments in subsidiaries and certain intercompany balances and transactions. ATI is the plan sponsor for the U.S. qualified defined benefit pension plans, which cover certain current and former employees of the Subsidiary and the Non-guarantor Subsidiaries. As a result, the balance sheets presented for the Subsidiary and the Non-guarantor Subsidiaries do not include any U.S. qualified defined benefit pension assets or liabilities, or the related deferred taxes. These assets, liabilities and related deferred taxes and pension income or expense are recognized by the Guarantor Parent. Management and royalty fees charged to the Subsidiary and to the Non-guarantor Subsidiaries by the Guarantor Parent have been excluded solely for purposes of this presentation. The effects of income tax valuation allowances on U.S. Federal and State deferred tax assets are excluded from the Subsidiary’s financial results, and are reported by the Guarantor Parent or the Non-guarantor Subsidiaries, as applicable. Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Balance Sheets December 31, 2019 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Assets: Cash and cash equivalents $ 0.3 $ 4.2 $ 486.3 $ — $ 490.8 Accounts receivable, net — 123.7 430.4 — 554.1 Intercompany notes receivable — — 4,402.8 (4,402.8 ) — Short-term contract assets — — 38.5 — 38.5 Inventories, net — 213.0 942.3 — 1,155.3 Prepaid expenses and other current assets 5.6 18.5 40.2 — 64.3 Total current assets 5.9 359.4 6,340.5 (4,402.8 ) 2,303.0 Property, plant and equipment, net 6.5 1,539.3 904.3 — 2,450.1 Goodwill — — 525.8 — 525.8 Intercompany notes receivable — — 200.0 (200.0 ) — Investments in subsidiaries 6,434.3 37.7 — (6,472.0 ) — Other assets 98.3 83.1 174.3 — 355.7 Total assets $ 6,545.0 $ 2,019.5 $ 8,144.9 $ (11,074.8 ) $ 5,634.6 Liabilities and stockholders’ equity: Accounts payable $ 4.6 $ 184.0 $ 332.6 $ — $ 521.2 Intercompany notes payable 2,457.1 1,945.7 — (4,402.8 ) — Short-term contract liabilities — 26.4 52.3 — 78.7 Short-term debt and current portion of long-term debt 1.4 0.2 9.9 — 11.5 Other current liabilities 51.5 68.1 118.2 — 237.8 Total current liabilities 2,514.6 2,224.4 513.0 (4,402.8 ) 849.2 Long-term debt 1,130.1 150.4 106.9 — 1,387.4 Intercompany notes payable — 200.0 — (200.0 ) — Accrued postretirement benefits — 261.2 51.3 — 312.5 Pension liabilities 678.8 3.8 48.9 — 731.5 Other long-term liabilities 28.3 44.1 88.4 — 160.8 Total liabilities 4,351.8 2,883.9 808.5 (4,602.8 ) 3,441.4 Total stockholders’ equity (deficit) 2,193.2 (864.4 ) 7,336.4 (6,472.0 ) 2,193.2 Total liabilities and stockholders’ equity $ 6,545.0 $ 2,019.5 $ 8,144.9 $ (11,074.8 ) $ 5,634.6 Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Operations For the year ended December 31, 2019 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Sales $ — $ 1,429.0 $ 2,693.5 $ — $ 4,122.5 Cost of sales 13.5 1,302.8 2,168.4 — 3,484.7 Gross profit (loss) (13.5 ) 126.2 525.1 — 637.8 Selling and administrative expenses 116.5 33.2 117.5 — 267.2 Restructuring charges 4.5 — — — 4.5 Operating income (loss) (134.5 ) 93.0 407.6 — 366.1 Nonoperating retirement benefit expense (47.5 ) (24.7 ) (1.4 ) — (73.6 ) Interest income (expense), net (148.2 ) (131.6 ) 180.8 — (99.0 ) Debt extinguishment charge (21.6 ) — — — (21.6 ) Other income (expense) including equity in income of unconsolidated subsidiaries 593.4 (22.0 ) 90.2 (591.9 ) 69.7 Income (loss) before income taxes 241.6 (85.3 ) 677.2 (591.9 ) 241.6 Income tax provision (benefit) (28.5 ) (18.3 ) 115.6 (97.3 ) (28.5 ) Net income (loss) 270.1 (67.0 ) 561.6 (494.6 ) 270.1 Less: Net income attributable to noncontrolling interest — — 12.5 — 12.5 Net income (loss) attributable to ATI $ 270.1 $ (67.0 ) $ 549.1 $ (494.6 ) $ 257.6 Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Comprehensive Income (Loss) For the year ended December 31, 2019 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Net income (loss) $ 270.1 $ (67.0 ) $ 561.6 $ (494.6 ) $ 270.1 Other comprehensive income (loss) Currency translation adjustment arising during the period (4.0 ) — (4.0 ) 4.0 (4.0 ) Net derivative gain on hedge transactions 10.3 — — — 10.3 Pension and postretirement benefits (75.5 ) 3.8 (15.2 ) 11.4 (75.5 ) Other comprehensive income (loss), net of tax (69.2 ) 3.8 (19.2 ) 15.4 (69.2 ) Comprehensive income (loss) 200.9 (63.2 ) 542.4 (479.2 ) 200.9 Less: Comprehensive income attributable to noncontrolling interest — — 11.2 — 11.2 Comprehensive income (loss) attributable to ATI $ 200.9 $ (63.2 ) $ 531.2 $ (479.2 ) $ 189.7 Condensed Statements of Cash Flows For the year ended December 31, 2019 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Cash flows provided by (used in) operating activities $ 16.1 $ (109.1 ) $ 344.1 $ (21.0 ) $ 230.1 Investing Activities: Purchases of property, plant and equipment (0.7 ) (33.4 ) (134.1 ) — (168.2 ) Net receipts (payments) on intercompany activity — — (308.0 ) 308.0 — Proceeds from disposals of property, plant and equipment — 0.1 91.9 — 92.0 Proceeds from sales of businesses, net of transaction costs — — 158.1 — 158.1 Other (0.2 ) — — — (0.2 ) Cash flows provided by (used in) investing activities (0.9 ) (33.3 ) (192.1 ) 308.0 81.7 Financing Activities: Borrowings on long-term debt 350.0 — — — 350.0 Payments on long-term debt and finance leases (500.7 ) (0.2 ) (6.7 ) — (507.6 ) Net borrowings under credit facilities — — 4.9 — 4.9 Debt issuance costs (5.5 ) — — — (5.5 ) Debt extinguishment charge (20.9 ) — — — (20.9 ) Net receipts (payments) on intercompany activity 172.0 136.0 — (308.0 ) — Dividends paid to stockholders — — (21.0 ) 21.0 — Dividends paid to noncontrolling interests — — (14.0 ) — (14.0 ) Shares repurchased for income tax withholding on share-based compensation and other (9.9 ) — — — (9.9 ) Cash flows provided by (used in) financing activities (15.0 ) 135.8 (36.8 ) (287.0 ) (203.0 ) Increase (decrease) in cash and cash equivalents $ 0.2 $ (6.6 ) $ 115.2 $ — $ 108.8 Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Balance Sheets December 31, 2018 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Assets: Cash and cash equivalents $ 0.1 $ 10.8 $ 371.1 $ — $ 382.0 Accounts receivable, net — 126.3 401.5 — 527.8 Intercompany notes receivable — — 3,968.8 (3,968.8 ) — Short-term contract assets — — 51.2 — 51.2 Inventories, net — 216.1 995.0 — 1,211.1 Prepaid expenses and other current assets 12.9 29.3 32.4 — 74.6 Total current assets 13.0 382.5 5,820.0 (3,968.8 ) 2,246.7 Property, plant and equipment, net 1.7 1,548.4 924.9 — 2,475.0 Goodwill — — 534.7 — 534.7 Intercompany notes receivable — — 200.0 (200.0 ) — Investments in subsidiaries 6,096.4 37.7 — (6,134.1 ) — Other assets 35.6 30.7 179.1 — 245.4 Total assets $ 6,146.7 $ 1,999.3 $ 7,658.7 $ (10,302.9 ) $ 5,501.8 Liabilities and stockholders’ equity: Accounts payable $ 3.3 $ 177.5 $ 318.0 $ — $ 498.8 Intercompany notes payable 2,102.8 1,866.0 — (3,968.8 ) — Short-term contract liabilities — 33.0 38.4 — 71.4 Short-term debt and current portion of long-term debt 0.2 0.7 5.7 — 6.6 Other current liabilities 59.1 71.7 129.3 — 260.1 Total current liabilities 2,165.4 2,148.9 491.4 (3,968.8 ) 836.9 Long-term debt 1,278.8 151.8 104.9 — 1,535.5 Intercompany notes payable — 200.0 — (200.0 ) — Accrued postretirement benefits — 259.2 59.2 — 318.4 Pension liabilities 681.6 4.0 44.4 — 730.0 Other long-term liabilities 29.3 17.6 42.5 — 89.4 Total liabilities 4,155.1 2,781.5 742.4 (4,168.8 ) 3,510.2 Total stockholders’ equity (deficit) 1,991.6 (782.2 ) 6,916.3 (6,134.1 ) 1,991.6 Total liabilities and stockholders’ equity $ 6,146.7 $ 1,999.3 $ 7,658.7 $ (10,302.9 ) $ 5,501.8 Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Operations For the year ended December 31, 2018 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Sales $ — $ 1,410.3 $ 2,636.3 $ — $ 4,046.6 Cost of sales 16.6 1,302.4 2,097.3 — 3,416.3 Gross profit (loss) (16.6 ) 107.9 539.0 — 630.3 Selling and administrative expenses 101.7 34.2 132.3 — 268.2 Operating income (loss) (118.3 ) 73.7 406.7 — 362.1 Nonoperating retirement benefit expense (12.7 ) (19.5 ) (1.7 ) — (33.9 ) Interest income (expense), net (138.8 ) (114.6 ) 152.4 — (101.0 ) Other income (expense) including equity in income of unconsolidated subsidiaries 517.5 16.8 0.8 (514.6 ) 20.5 Income (loss) before income taxes 247.7 (43.6 ) 558.2 (514.6 ) 247.7 Income tax provision (benefit) 11.0 (8.7 ) 83.9 (75.2 ) 11.0 Net income (loss) 236.7 (34.9 ) 474.3 (439.4 ) 236.7 Less: Net income attributable to noncontrolling interest — — 14.3 — 14.3 Net income (loss) attributable to ATI $ 236.7 $ (34.9 ) $ 460.0 $ (439.4 ) $ 222.4 Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Comprehensive Income (Loss) For the year ended December 31, 2018 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Net income (loss) $ 236.7 $ (34.9 ) $ 474.3 $ (439.4 ) $ 236.7 Other comprehensive income (loss) Currency translation adjustment arising during the period (26.6 ) — (26.6 ) 26.6 (26.6 ) Net derivative loss on hedge transactions (18.1 ) — — — (18.1 ) Pension and postretirement benefits (67.5 ) (19.1 ) 0.7 18.4 (67.5 ) Other comprehensive income (loss), net of tax (112.2 ) (19.1 ) (25.9 ) 45.0 (112.2 ) Comprehensive income (loss) 124.5 (54.0 ) 448.4 (394.4 ) 124.5 Less: Comprehensive income attributable to noncontrolling interest — — 8.1 — 8.1 Comprehensive income (loss) attributable to ATI $ 124.5 $ (54.0 ) $ 440.3 $ (394.4 ) $ 116.4 Condensed Statements of Cash Flows For the year ended December 31, 2018 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Cash flows provided by (used in) operating activities $ (107.0 ) $ (223.9 ) $ 738.7 $ (15.0 ) $ 392.8 Investing Activities: Purchases of property, plant and equipment (2.1 ) (26.2 ) (110.9 ) — (139.2 ) Net receipts (payments) on intercompany activity — — (346.5 ) 346.5 — Proceeds from disposal of property, plant and equipment — 2.6 0.2 — 2.8 Purchases of businesses — — (10.0 ) — (10.0 ) Other 1.3 — — — 1.3 Cash flows provided by (used in) investing activities (0.8 ) (23.6 ) (467.2 ) 346.5 (145.1 ) Financing Activities: Borrowings on long-term debt — — 7.1 — 7.1 Payments on long-term debt and finance leases (0.2 ) (0.9 ) (5.3 ) — (6.4 ) Net payments under credit facilities — — (5.9 ) — (5.9 ) Net receipts (payments) on intercompany activity 112.5 234.0 — (346.5 ) — Dividends paid to stockholders — — (15.0 ) 15.0 — Dividends paid to noncontrolling interests — — (10.0 ) — (10.0 ) Sale of noncontrolling interests — 11.7 2.7 — 14.4 Shares repurchased for income tax withholding on share-based compensation and other (6.5 ) — — — (6.5 ) Cash flows provided by (used in) financing activities 105.8 244.8 (26.4 ) (331.5 ) (7.3 ) Increase (decrease) in cash and cash equivalents $ (2.0 ) $ (2.7 ) $ 245.1 $ — $ 240.4 Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Operations For the year ended December 31, 2017 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Sales $ — $ 1,178.9 $ 2,346.2 $ — $ 3,525.1 Cost of sales 14.6 1,085.5 1,928.0 — 3,028.1 Gross profit (loss) (14.6 ) 93.4 418.2 — 497.0 Selling and administrative expenses 86.6 36.9 124.5 — 248.0 Impairment of goodwill — — 114.4 — 114.4 Operating income (loss) (101.2 ) 56.5 179.3 — 134.6 Nonoperating retirement benefit expense (32.2 ) (18.7 ) (3.4 ) — (54.3 ) Interest income (expense), net (155.8 ) (90.0 ) 112.0 — (133.8 ) Debt extinguishment charge (37.0 ) — — — (37.0 ) Other income (expense) including equity in income of unconsolidated subsidiaries 239.7 1.6 2.4 (239.7 ) 4.0 Income (loss) before income taxes (86.5 ) (50.6 ) 290.3 (239.7 ) (86.5 ) Income tax provision (benefit) (6.8 ) (16.6 ) 131.4 (114.8 ) (6.8 ) Net income (loss) (79.7 ) (34.0 ) 158.9 (124.9 ) (79.7 ) Less: Net income attributable to noncontrolling interest — — 12.2 — 12.2 Net income (loss) attributable to ATI $ (79.7 ) $ (34.0 ) $ 146.7 $ (124.9 ) $ (91.9 ) Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Comprehensive Income (Loss) For the year ended December 31, 2017 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Net income (loss) $ (79.7 ) $ (34.0 ) $ 158.9 $ (124.9 ) $ (79.7 ) Other comprehensive income (loss) Currency translation adjustment arising during the period 39.1 — 39.1 (39.1 ) 39.1 Net derivative gain on hedge transactions 7.1 — — — 7.1 Pension and postretirement benefits 27.3 (5.8 ) (10.7 ) 16.5 27.3 Other comprehensive income (loss), net of tax 73.5 (5.8 ) 28.4 (22.6 ) 73.5 Comprehensive income (loss) (6.2 ) (39.8 ) 187.3 (147.5 ) (6.2 ) Less: Comprehensive income attributable to noncontrolling interest — — 19.8 — 19.8 Comprehensive income (loss) attributable to ATI $ (6.2 ) $ (39.8 ) $ 167.5 $ (147.5 ) $ (26.0 ) Condensed Statements of Cash Flows For the year ended December 31, 2017 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Cash flows provided by (used in) operating activities $ (78.8 ) $ (101.5 ) $ 214.7 $ (12.0 ) $ 22.4 Investing Activities: Purchases of property, plant and equipment (0.9 ) (38.5 ) (83.3 ) — (122.7 ) Net receipts (payments) on intercompany activity — — (223.9 ) 223.9 — Proceeds from disposal of property, plant and equipment — 0.1 2.6 — 2.7 Other — — 0.4 — 0.4 Cash flows provided by (used in) investing activities (0.9 ) (38.4 ) (304.2 ) 223.9 (119.6 ) Financing Activities: Borrowings on long-term debt — — 8.5 — 8.5 Payments on long-terms debt and finance leases (350.4 ) (0.3 ) (2.3 ) — (353.0 ) Net borrowings under credit facilities — — 1.6 — 1.6 Debt issuance costs — — (0.8 ) — (0.8 ) Debt extinguishment charge (35.8 ) — — — (35.8 ) Net receipts (payments) on intercompany activity 72.7 151.2 — (223.9 ) — Issuance of common stock 397.8 — — — 397.8 Dividends paid to stockholders — — (12.0 ) 12.0 — Dividends paid to noncontrolling interests — — (8.0 ) — (8.0 ) Sale to noncontrolling interest — — 3.7 — 3.7 Shares repurchased for income tax withholding on share-based compensation (4.8 ) — — — (4.8 ) Cash flows provided by (used in) financing activities 79.5 150.9 (9.3 ) (211.9 ) 9.2 Increase (decrease) in cash and cash equivalents $ (0.2 ) $ 11.0 $ (98.8 ) $ — $ (88.0 )

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
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, 2019 were approximately $116.5 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, 2019 , the Company’s reserves for environmental remediation obligations totaled approximately $18 million , of which $7 million was included in other current liabilities. The reserve includes estimated probable future costs of $3 million for federal Superfund and comparable state-managed sites; $13 million for formerly owned or operated sites for which the Company has remediation or indemnification obligations; $1 million for owned or controlled sites at which Company operations have been discontinued; and $1 million for sites utilized by the Company in its ongoing operations. The Company continues to evaluate whether it may be able to recover a portion of future costs for environmental liabilities from third parties and to pursue such recoveries where appropriate. 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 $16 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 of 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, patent infringement, commercial, government contracting, construction, employment, employee and retiree benefits, taxes, environmental, health and safety, occupational disease, 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 consolidated 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.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	Selected Quarterly Financial Data (Unaudited) Quarter Ended (In millions, except per share amounts) March 31 June 30 September 30 December 31 2019 - Sales $ 1,004.8 $ 1,080.4 $ 1,018.7 $ 1,018.6 Gross Profit 131.1 177.7 159.7 169.3 Net income 16.3 78.5 115.3 60.0 Net income attributable to ATI 15.0 75.1 111.0 56.5 Basic income attributable to ATI per common share $ 0.12 $ 0.60 $ 0.88 $ 0.45 Diluted income attributable to ATI per common share $ 0.12 $ 0.54 $ 0.78 $ 0.41 Average shares outstanding 125.8 126.1 126.1 126.1 2018 - Sales $ 979.0 $ 1,009.5 $ 1,020.2 $ 1,037.9 Gross Profit 148.6 173.7 160.4 147.6 Net income 60.5 75.6 55.6 45.0 Net income attributable to ATI 58.0 72.8 50.5 41.1 Basic income attributable to ATI per common share $ 0.46 $ 0.58 $ 0.40 $ 0.33 Diluted income attributable to ATI per common share $ 0.42 $ 0.52 $ 0.37 $ 0.30 Average shares outstanding 125.7 125.7 125.7 125.7 Quarterly earnings per share amounts above may not add to year-to-date amounts due to rounding as well as the impact of dilutive securities for each individual quarterly period versus the year-to-date period. Second quarter 2019 results include a $29.3 million pre-tax ( $27.3 million , net of tax) gain on the sale of oil and gas rights in New Mexico. See Note 9 for further explanation. Second quarter 2019 results also include a $7.7 million pre-tax ( $7.2 million , net of tax) loss on the sale of two non-core forging facilities. See Note 6 for further explanation. Third quarter 2019 results include a $62.4 million pre-tax ( $60.5 million , net of tax) gain on an additional sale of oil and gas rights in New Mexico. See Note 9 for further explanation. Third quarter 2019 results also include a $6.2 million pre-tax ( $6.0 million , net of tax) net gain on the sale of the Cast Products business. See Note 6 for further explanation. Fourth quarter 2019 results include the following: • $4.5 million pre-tax ( $4.3 million , net of tax) restructuring charge to streamline ATI’s salaried workforce primarily to improve the cost competitiveness of the U.S.-based Flat Rolled Products business. See Note 18 for further explanation. • $21.6 million pre-tax ( $20.5 million , net of tax) debt extinguishment charge for the full redemption of the 2021 Notes. See Note 10 for further explanation. • $11.4 million pre-tax ( $10.8 million , net of tax) joint venture impairment charge related to the A&T Stainless joint venture. See Note 7 for further explanation. • $41.9 million net discrete tax benefit primarily related to the reversal of a significant portion of the Company's deferred tax valuation allowances. See Note 17 for further explanation. First quarter 2018 results include a $15.9 million pre-tax ( $14.7 million , net of tax) gain on deconsolidation of A&T Stainless following the sale of a 50% noncontrolling interest and subsequent derecognition. See Note 7 for further explanation.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies - Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include the accounts of Allegheny Technologies Incorporated 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. 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 statement of financial position is the capital investment and any undistributed profit or loss, and is classified in Other (noncurrent) assets. 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, “Allegheny Technologies,” “ATI” and the “Company” refer to Allegheny Technologies Incorporated and its subsidiaries.
Use of Estimates	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. Certain prior year amounts have been reclassified in order to conform with the 2019 presentation.
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 the 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 $4.6 million and $6.0 million at December 31, 2019 and 2018 , respectively. Trade credit is extended based upon evaluations of each customer’s ability to perform its obligations, which are updated periodically. Accounts receivable reserves are determined based upon an aging of accounts and a review for collectability of specific accounts. 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 (last-in, first-out (LIFO), first-in, first-out (FIFO), and average cost methods) or market. Costs include direct material, direct labor and applicable manufacturing and engineering overhead, and other direct costs. Most of the Company’s inventory is valued utilizing the LIFO costing methodology. Inventory of the Company’s non-U.S. operations is valued using average cost or FIFO methods. The Company evaluates product lines on a quarterly basis to identify inventory carrying values that exceed estimated net realizable value. In applying the lower of cost or market principle, market means current replacement cost, subject to a ceiling (market value shall not exceed net realizable value) and a floor (market shall not be less than net realizable value reduced by an allowance for a normal profit margin). The calculation of a resulting reserve, if any, is recognized as an expense in the period that the need for the reserve is identified. However, in cases where inventory at FIFO cost is lower than the LIFO carrying value, a write-down of the inventory to market may be required, subject to the ceiling and floor. 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 orders 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	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. Property, plant and equipment associated with the Hot-Rolling and Processing Facility (HRPF) in the Advanced Alloys & Solutions segment is being depreciated utilizing the units of production method of depreciation, which the Company believes provides a better matching of costs and revenues. 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. 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 On January 1, 2019 the Company adopted Accounting Standards Codification Topic 842 (ASC 842), Leases. This new guidance requires a lessee to recognize assets and liabilities on the balance sheet for all leases, with the result being the recognition of a right of use (ROU) asset and a lease liability. 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 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.
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 standards 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 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 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 do not take into account the effects of inflation, and anticipated expenditures 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), 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. This approach is consistent with our revenue recognition approach in prior years. Certain customer agreements involving production of parts and components in the High Performance Materials and Components segment 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 Our 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 $17.8 million in 2019 , $22.7 million in 2018 , and $13.3 million in 2017 . Customer funded research and development costs were $2.4 million in 2019 , $2.2 million in 2018 , and $1.4 million in 2017 .
Stock-based Compensation	Stock-based Compensation
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 estimate 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.
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	New Accounting Pronouncements Adopted In January 2019, the Company adopted changes issued by the Financial Accounting Standards Board (FASB) related to leases. See Note 11 for further explanation related to this adoption, including all newly expanded disclosure requirements.
New Accounting Pronouncements Not yet Adopted	Pending Accounting Pronouncements In August 2018, the FASB issued new disclosure guidance on fair value measurement. This new guidance modifies the disclosure requirements on fair value measurements, including removal and modifications of various current disclosures as well as some additional disclosure requirements for Level 3 fair value measurements. Some of these disclosure changes must be applied prospectively while others retrospectively depending on requirement. This guidance is required to be adopted by the Company beginning in fiscal year 2020, with early adoption permitted. The Company did not early adopt this guidance. The adoption of these changes is not expected to have an impact on the Company’s consolidated financial statements other than disclosures. In June 2016, the FASB added a new impairment model (known as the current expected credit loss (CECL) model) that is based on expected losses rather than incurred losses. Under the new guidance, an entity recognizes as an allowance its estimate of expected credit losses. The CECL model applies to trade receivables, other receivables, contract assets and most debt instruments. The CECL model does not have a minimum threshold for recognition of impairment losses, and entities will need to measure expected credit losses on assets that have a low risk of loss. This guidance was adopted by the Company in fiscal year 2020 without significant impact to the consolidated financial statements. In December 2019, the FASB issued new guidance to simplify the accounting for income taxes. The areas for simplification in the guidance involve the removal of certain exceptions to the general principals in the current guidance, including intraperiod allocation and the calculation of income taxes in an interim period when a year to date loss exceeds the anticipated loss for the year. The new guidance also simplifies the accounting for income taxes in the area of franchise taxes. This new guidance is effective for the Company in fiscal year 2021, with early adoption permitted. This guidance was early adopted by the Company in fiscal year 2020 without significant impact to the consolidated financial statements.
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, 2019 , the Company had recognized AROs of $23.7 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	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. The Company did not use net investment hedges for the periods presented. 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, 2019 , 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 7 million pounds of nickel with hedge dates through 2023 . The aggregate notional amount hedged is approximately 7% of a single year’s estimated nickel raw material purchase requirements. At December 31, 2019 , the outstanding financial derivatives used to hedge the Company’s exposure to energy cost volatility included natural gas cost hedges. At December 31, 2019 , the company hedged approximately 70% of the Company’s annual forecasted domestic requirements for natural gas for 2020 and approximately 50% for 2021. 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, 2019 , the Company held euro forward purchase contracts for forecasted capital expenditures designated as cash flow hedges with a notional value of approximately 2 million euro with maturity dates through May 2020. In 2015, the Company entered into 244.7 million euro notional value of foreign currency forward contracts designated as fair value hedges maturity dates through 2017. The Company recorded $2.7 million of charges during the fiscal year ended December 31, 2017 in costs of sales on the consolidated statement of operations for maturities and mark-to-market changes on these fair value hedges. There were no outstanding fair value hedges as of December 31, 2019, 2018 and 2017. The Company may enter into derivative interest rate contracts to maintain a reasonable balance between fixed- and floating-rate debt. In July 2019, the Company amended its $50 million floating-for-fixed interest rate swap which converts half of the Term Loan to a fixed rate (now 4.21% following the September 30, 2019 ABL amendment), with a June 2024 maturity. 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 Term Loan borrowings. The ineffectiveness at hedge inception, determined from the fair value of the swap immediately prior to amendment, will be amortized to interest expense over the initial 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.

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	12 Months Ended
	Dec. 31, 2019
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, 2019 , 2018 and 2017 were as follows: (in millions) 2019 2018 2017 HPMC AA&S Total HPMC AA&S Total HPMC AA&S Total Diversified Global Markets: Aerospace & Defense $ 1,624.1 $ 506.3 $ 2,130.4 $ 1,562.9 $ 402.6 $ 1,965.5 $ 1,377.0 $ 341.1 $ 1,718.1 Energy* 153.6 643.3 796.9 133.9 646.8 780.7 119.7 490.7 610.4 Automotive 10.5 286.1 296.6 9.5 313.9 323.4 8.8 264.9 273.7 Food Equipment & Appliances 0.3 205.5 205.8 0.4 244.5 244.9 0.4 225.6 226.0 Construction/Mining 42.5 152.5 195.0 72.7 153.3 226.0 51.2 141.7 192.9 Medical 85.4 87.0 172.4 106.0 77.1 183.1 81.1 101.9 183.0 Electronics/Computers/Communications 0.5 162.7 163.2 1.5 155.4 156.9 1.0 150.6 151.6 Other 61.6 100.6 162.2 76.2 89.9 166.1 65.6 103.8 169.4 Total $ 1,978.5 $ 2,144.0 $ 4,122.5 $ 1,963.1 $ 2,083.5 $ 4,046.6 $ 1,704.8 $ 1,820.3 $ 3,525.1 *Includes the oil & gas, hydrocarbon and chemical processing, and electrical energy markets. (in millions) 2019 2018 2017 HPMC AA&S Total HPMC AA&S Total HPMC AA&S Total Primary Geographical Market: United States $ 1,042.6 $ 1,412.0 $ 2,454.6 $ 983.6 $ 1,364.5 $ 2,348.1 $ 874.3 $ 1,196.3 $ 2,070.6 China 93.9 261.7 355.6 71.2 248.8 320.0 44.3 221.3 265.6 Germany 147.2 72.1 219.3 159.0 88.2 247.2 131.9 85.2 217.1 United Kingdom 156.7 17.1 173.8 225.6 16.5 242.1 200.8 30.8 231.6 France 132.7 22.8 155.5 146.3 37.3 183.6 143.3 22.3 165.6 Japan 95.0 52.7 147.7 128.1 86.8 214.9 88.5 43.2 131.7 Rest of World 310.4 305.6 616.0 249.3 241.4 490.7 221.7 221.2 442.9 Total $ 1,978.5 $ 2,144.0 $ 4,122.5 $ 1,963.1 $ 2,083.5 $ 4,046.6 $ 1,704.8 $ 1,820.3 $ 3,525.1 Comparative information of the Company’s major high-value and standard products based on their percentages of sales is included in the following table. Hot-Rolling and Processing Facility conversion service sales in the AA&S segment are excluded from this presentation. 2019 2018 2017 HPMC AA&S Total HPMC AA&S Total HPMC AA&S Total Diversified Products: High-Value Products Nickel-based alloys and specialty alloys 38 % 27 % 32 % 37 % 24 % 30 % 37 % 20 % 28 % Precision forgings, castings and components 36 % — % 18 % 40 % — % 20 % 38 % — % 19 % Titanium and titanium-based alloys 26 % 11 % 18 % 23 % 10 % 17 % 25 % 10 % 17 % Precision rolled strip products — % 23 % 12 % — % 23 % 12 % — % 24 % 12 % Zirconium and related alloys — % 11 % 6 % — % 11 % 5 % — % 12 % 6 % Total High-Value Products 100 % 72 % 86 % 100 % 68 % 84 % 100 % 66 % 82 % Standard Products Standard stainless products — % 28 % 14 % — % 32 % 16 % — % 34 % 18 % 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, 2019 , 2018 and 2017 : (in millions) Accounts Receivable - Reserve for Doubtful Accounts Balance as of December 31, 2016 $ 7.3 Expense to increase the reserve 0.1 Write-off of uncollectible accounts (1.5 ) Balance as of December 31, 2017 5.9 Expense to increase the reserve 1.9 Write-off of uncollectible accounts (1.8 ) Balance as of December 31, 2018 6.0 Expense to increase the reserve 0.2 Write-off of uncollectible accounts (1.6 ) Balance as of December 31, 2019 $ 4.6
Schedule of Contract Assets and Liabilities	The following represents the rollforward of contract assets and liabilities for the fiscal years ended December 31, 2019 and 2018 : (in millions) Contract Assets Short-term 2019 2018 Balance as of beginning of fiscal year $ 51.2 $ 36.5 Recognized in current year 74.5 92.9 Reclassified to accounts receivable (79.9 ) (95.8 ) Impairment — — Reclassification to/from long-term — 16.8 Divestiture (7.3 ) — Other — 0.8 Balance as of period end $ 38.5 $ 51.2 Long-term 2019 2018 Balance as of beginning of fiscal year $ 0.1 $ 16.9 Recognized in current year — — Reclassified to accounts receivable — — Impairment — — Reclassification to/from short-term — (16.8 ) Balance as of period end $ 0.1 $ 0.1 (in millions) Contract Liabilities Short-term 2019 2018 Balance as of beginning of fiscal year $ 71.4 $ 69.7 Recognized in current year 126.1 76.7 Amounts in beginning balance reclassified to revenue (49.2 ) (49.6 ) Current year amounts reclassified to revenue (76.0 ) (42.7 ) Other 1.9 2.7 Reclassification to/from long-term 4.5 14.6 Balance as of period end $ 78.7 $ 71.4 Long-term 2019 2018 Balance as of beginning of fiscal year $ 7.3 $ 22.2 Recognized in current year 24.2 0.7 Amounts in beginning balance reclassified to revenue (1.1 ) (1.0 ) Current year amounts reclassified to revenue — — Other — — Reclassification to/from short-term (4.5 ) (14.6 ) Balance as of period end $ 25.9 $ 7.3

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Dec. 31, 2019
Inventory Disclosure [Abstract]
Schedule of Inventory	Inventories at December 31, 2019 and 2018 were as follows (in millions): 2019 2018 Raw materials and supplies $ 164.9 $ 191.5 Work-in-process 899.6 914.1 Finished goods 161.3 191.1 Total inventories at current cost 1,225.8 1,296.7 Adjustment from current cost to LIFO cost basis 33.6 2.9 Inventory valuation reserves (104.1 ) (88.5 ) Total inventories, net $ 1,155.3 $ 1,211.1
Schedule of Inventory Valuation Impact on Income	Fiscal year ended December 31, 2019 2018 2017 LIFO benefit (charge) $ 25.5 $ (28.6 ) $ (54.2 ) NRV benefit (charge) (25.6 ) 27.9 54.0 Net cost of sales impact $ (0.1 ) $ (0.7 ) $ (0.2 )

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Schedule of property plant and equipment, net	Property, plant and equipment at December 31, 2019 and 2018 was as follows: (In millions) 2019 2018 Land $ 34.6 $ 31.5 Buildings 832.7 851.7 Equipment and leasehold improvements 3,671.3 3,622.7 4,538.6 4,505.9 Accumulated depreciation and amortization (2,088.5 ) (2,030.9 ) Total property, plant and equipment, net $ 2,450.1 $ 2,475.0
Schedule depreciation and amortization	Depreciation and amortization for the years ended December 31, 2019 , 2018 and 2017 was as follows: (In millions) 2019 2018 2017 Depreciation of property, plant and equipment $ 127.1 $ 131.9 $ 135.2 Software and other amortization 24.0 24.5 25.6 Total depreciation and amortization $ 151.1 $ 156.4 $ 160.8

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2019
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, 2019 and 2018 were as follows: December 31, 2019 December 31, 2018 (in millions) Gross carrying amount Accumulated amortization Gross carrying amount Accumulated amortization Technology $ 76.8 $ (29.7 ) $ 93.4 $ (31.9 ) Customer relationships 27.0 (9.3 ) 35.7 (10.6 ) Trademarks 52.4 (20.9 ) 64.6 (21.5 ) Total amortizable intangible assets $ 156.2 $ (59.9 ) $ 193.7 $ (64.0 )

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2019
Asset Retirement Obligation Disclosure [Abstract]
Schedule of changes in asset retirement obligations	Changes in asset retirement obligations for the years ended December 31, 2019 and 2018 were as follows: (In millions) 2019 2018 Balance at beginning of year $ 23.1 $ 23.5 Accretion expense 0.9 0.8 Payments (0.3 ) (1.2 ) Balance at end of year $ 23.7 $ 23.1

Supplemental Financial Statem_2

Supplemental Financial Statement Information (Tables)	12 Months Ended
	Dec. 31, 2019
Additional Financial Information Disclosure [Abstract]
Schedule of cash and cash equivalents	Cash and cash equivalents at December 31, 2019 and 2018 were as follows: (In millions) 2019 2018 Cash $ 190.8 $ 264.4 Other short-term investments 300.0 117.6 Total cash and cash equivalents $ 490.8 $ 382.0
Schedule of other non-operating income (expense)	Other income (expense) for the years ended December 31, 2019 , 2018 , and 2017 was as follows: (in millions) 2019 2018 2017 Rent, royalty income and other income $ 2.9 $ 3.1 $ 3.5 Gains from disposal of property, plant and equipment, net 90.7 1.3 0.5 Equity loss on joint ventures (See Note 7) (10.7 ) (1.0 ) — Loss on sales of businesses, net (See Note 6) (1.9 ) — — Gain on joint venture deconsolidation (See Note 7) — 15.9 — Joint venture impairment charge (See Note 7) (11.4 ) — — Other 0.1 1.2 — Total other income, net $ 69.7 $ 20.5 $ 4.0

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Schedule of debt	Debt at December 31, 2019 and 2018 was as follows: (In millions) 2019 2018 Allegheny Technologies $500 million 5.875% Senior Notes due 2023 (a) $ 500.0 $ 500.0 Allegheny Technologies $500 million 5.95% Senior Notes due 2021 — 500.0 Allegheny Technologies $350 million 5.875% Senior Notes due 2027 350.0 — Allegheny Technologies $287.5 million 4.75% Convertible Senior Notes due 2022 287.5 287.5 Allegheny Ludlum 6.95% Debentures due 2025 150.0 150.0 Term Loan due 2024 100.0 100.0 U.S. revolving credit facility — — Foreign credit agreements 4.9 — Finance leases and other 18.8 15.0 Debt issuance costs (12.3 ) (10.4 ) Total short-term and long-term debt 1,398.9 1,542.1 Short-term debt and current portion of long-term debt 11.5 6.6 Total long-term debt $ 1,387.4 $ 1,535.5 (a) Bearing interest at 7.875% effective February 15, 2016.

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2019
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 fiscal year ending December 31, 2019 : ($ in millions) Fiscal year ended December 31, 2019 Lease Cost Finance Lease Cost: Amortization of right of use asset $ 1.7 Interest on lease liabilities 0.5 Operating lease cost 20.5 Short-term lease cost 3.1 Variable lease cost 0.8 Sublease income — Total lease cost $ 26.6 Other information Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from finance leases $ 0.5 Operating cash flows from operating leases $ 20.8 Financing cash flows from finance leases $ 2.4 Right of use assets obtained in exchange for new finance lease liabilities $ 14.1 Right of use assets obtained in exchange for new operating lease liabilities (a) $ 35.9 Weighted average remaining lease term - finance leases 4 years Weighted average remaining lease term - operating leases 6 years Weighted average discount rate - finance leases 5.3 % Weighted average discount rate - operating leases 7.0 % (a) Several of the Company’s real property lease contracts include options to extend the lease term. During the fourth quarter of 2019, the Company reassessed the likelihood of renewal and has included $10.2 million for the renewal options for several of these operating leases in the ROU asset and lease liability because the likelihood of renewal was determined to be reasonably certain.
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, 2019 (in millions): December 31, 2019 2020 $ 20.0 2021 18.2 2022 15.3 2023 11.7 2024 8.0 2025 and thereafter 24.6 Total undiscounted lease payments $ 97.8 Present value adjustment (20.1 ) Operating lease liabilities $ 77.7
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, 2019 (in millions): December 31, 2019 2020 $ 4.5 2021 4.2 2022 3.9 2023 2.7 2024 0.7 2025 and thereafter — Total undiscounted lease payments $ 16.0 Present value adjustment (1.5 ) Finance lease liabilities $ 14.5

Derivative Financial Instrume_2

Derivative Financial Instruments and Hedging (Tables)	12 Months Ended
	Dec. 31, 2019
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 counterpart 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: Natural gas contracts Prepaid expenses and other current assets $ — $ 0.8 Nickel and other raw material contracts Prepaid expenses and other current assets 4.4 1.2 Natural gas contracts Other assets — 0.2 Nickel and other raw material contracts Other assets 1.2 0.8 Total derivatives designated as hedging instruments 5.6 3.0 Derivatives not designated as hedging instruments: Foreign exchange contracts Prepaid expenses and other current assets — 0.4 Total derivatives not designated as hedging instruments: — 0.4 Total asset derivatives $ 5.6 $ 3.4 Liability derivatives Balance sheet location Derivatives designated as hedging instruments: Interest rate swap Other current liabilities $ 0.3 $ 0.2 Foreign exchange contracts Other current liabilities — 0.6 Natural gas contracts Other current liabilities 2.5 0.1 Nickel and other raw material contracts Other current liabilities 2.5 6.8 Interest rate swap Other long-term liabilities 1.2 0.3 Natural gas contracts Other long-term liabilities 1.0 0.3 Nickel and other raw material contracts Other long-term liabilities — 2.1 Total derivatives designated as hedging instruments 7.5 10.4 Total liability derivatives $ 7.5 $ 10.4
Schedule of derivative instruments gain (loss)	Activity with regard to derivatives designated as cash flow hedges for the years ended December 31, 2019 and 2018 were as follows (in millions): Derivatives in Cash Flow Hedging Relationships Amount of Gain (Loss) Recognized in OCI on Derivatives Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (a) 2019 2018 2019 2018 Nickel and other raw material contracts $ 11.3 $ (6.4 ) $ 3.9 $ 7.7 Natural gas contracts (4.0 ) 1.5 (0.9 ) 0.4 Foreign exchange contracts 1.0 0.5 0.5 1.0 Interest rate swap (0.9 ) (0.5 ) (0.4 ) (0.2 ) Total $ 7.4 $ (4.9 ) $ 3.1 $ 8.9 (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 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 Term Loan is recognized in earnings.
Schedule of derivatives not designated as hedging instruments, gain (loss)	(In millions) Amount of Gain (Loss) Recognized in Income on Derivatives Derivatives Not Designated as Hedging Instruments 2019 2018 Foreign exchange contracts $ 0.1 $ 0.3

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Schedule of financial instrument fair value	The estimated fair value of financial instruments at December 31, 2019 was as follows: Fair Value Measurements at Reporting Date Using (In millions) Total Carrying Amount Total Estimated Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Observable Inputs (Level 2) Cash and cash equivalents $ 490.8 $ 490.8 $ 490.8 $ — Derivative financial instruments: Assets 5.6 5.6 — 5.6 Liabilities 7.5 7.5 — 7.5 Debt (a) 1,411.2 1,676.5 1,552.8 123.7 The estimated fair value of financial instruments at December 31, 2018 was as follows: Fair Value Measurements at Reporting Date Using (In millions) Total Carrying Amount Total Estimated Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Observable Inputs (Level 2) Cash and cash equivalents $ 382.0 $ 382.0 $ 382.0 $ — Derivative financial instruments: Assets 3.4 3.4 — 3.4 Liabilities 10.4 10.4 — 10.4 Debt (a) 1,552.5 1,739.4 1,624.4 115.0

Retirement Benefits (Tables)

Retirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2019
Defined Benefit Plan [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) 2019 2018 2017 2019 2018 2017 Service cost—benefits earned during the year $ 12.7 $ 16.4 $ 14.1 $ 1.9 $ 2.5 $ 2.4 Interest cost on benefits earned in prior years 105.5 104.8 116.7 14.8 12.7 14.6 Expected return on plan assets (131.3 ) (157.9 ) (146.9 ) — — — Amortization of prior service cost (credit) 0.3 0.3 1.3 (2.9 ) (2.9 ) (2.9 ) Amortization of net actuarial loss 73.7 65.9 62.6 13.5 10.6 9.0 Curtailment loss — 0.4 — — — — Total retirement benefit expense $ 60.9 $ 29.9 $ 47.8 $ 27.3 $ 22.9 $ 23.1
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 2019 2018 2017 2019 2018 2017 Discount rate 4.40 % 3.85 % 4.45 % 4.35 % 3.80 % 4.35 % Rate of increase in future compensation levels 0.50 - 1.00% 0.50 - 1.00% 0.50 - 1.00% — — — Weighted average expected long-term rate of return on assets 7.52 % 7.75 % 7.75 % 4.0 % 4.0 % 4.0 %
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 2019 2018 2019 2018 Discount rate 3.40 % 4.40 % 3.25 % 4.35 % Rate of increase in future compensation levels 0.50 - 1.00% 0.50 - 1.00% — —
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, 2019 and 2018 was as follows: Pension Benefits Other Postretirement Benefits (In millions) 2019 2018 2019 2018 Change in benefit obligations: Benefit obligation at beginning of year $ 2,497.7 $ 2,829.8 $ 359.1 $ 349.9 Service cost 12.7 16.4 1.9 2.5 Interest cost 105.5 104.8 14.8 12.7 Benefits paid (274.6 ) (294.5 ) (37.7 ) (36.5 ) Subsidy paid — — — — Effect of currency rates 2.8 (4.5 ) — — Net actuarial (gains) losses – discount rate change 266.0 (150.4 ) 30.5 (17.8 ) – other 14.3 (5.7 ) (18.1 ) 48.3 Plan curtailments — 0.4 — — Plan amendments 9.5 1.4 (5.2 ) — Benefit obligation at end of year $ 2,633.9 $ 2,497.7 $ 345.3 $ 359.1
Schedule of changes in fair value of plan assets	Pension Benefits Other Postretirement Benefits (In millions) 2019 2018 2019 2018 Change in plan assets: Fair value of plan assets at beginning of year $ 1,772.2 $ 2,129.6 $ 0.1 $ 0.6 Actual returns on plan assets and plan expenses 248.2 (107.2 ) — (0.5 ) Employer contributions 153.4 49.3 — — Effect of currency rates 2.9 (5.0 ) — — Benefits paid (274.6 ) (294.5 ) — — Fair value of plan assets at end of year $ 1,902.1 $ 1,772.2 $ 0.1 $ 0.1
Schedule of amounts recognized in balance sheet	Assets (liabilities) recognized in the consolidated balance sheets: Pension Benefits Other Postretirement Benefits 2019 2018 2019 2018 Noncurrent assets $ 4.8 $ 9.2 $ — $ — Current liabilities (5.1 ) (4.7 ) (32.7 ) (40.6 ) Noncurrent liabilities (731.5 ) (730.0 ) (312.5 ) (318.4 ) Total amount recognized $ (731.8 ) $ (725.5 ) $ (345.2 ) $ (359.0 )
Schedule of amounts recognized in other comprehensive income	Changes to accumulated other comprehensive loss related to pension and other postretirement benefit plans in 2019 and 2018 were as follows: Pension Benefits Other Postretirement Benefits (In millions) 2019 2018 2019 2018 Beginning of year accumulated other comprehensive loss $ (1,470.3 ) $ (1,426.1 ) $ (107.0 ) $ (83.7 ) Amortization of net actuarial loss 73.7 65.9 13.5 10.6 Amortization of prior service cost (credit) 0.3 0.3 (2.9 ) (2.9 ) Remeasurements (173.4 ) (110.4 ) (7.1 ) (31.0 ) End of year accumulated other comprehensive loss $ (1,569.7 ) $ (1,470.3 ) $ (103.5 ) $ (107.0 ) Net change in accumulated other comprehensive loss $ (99.4 ) $ (44.2 ) $ 3.5 $ (23.3 )
Schedule of net periodic benefit cost not yet recognized	Amounts included in accumulated other comprehensive loss at December 31, 2019 and 2018 were as follows: Pension Benefits Other Postretirement Benefits (In millions) 2019 2018 2019 2018 Prior service (cost) credit $ (11.2 ) $ (2.1 ) $ 11.0 $ 8.8 Net actuarial loss (1,558.5 ) (1,468.2 ) (114.5 ) (115.8 ) Accumulated other comprehensive loss (1,569.7 ) (1,470.3 ) (103.5 ) (107.0 ) Deferred tax effect 555.7 536.2 34.4 35.3 Accumulated other comprehensive loss, net of tax $ (1,014.0 ) $ (934.1 ) $ (69.1 ) $ (71.7 )
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 2020 are: (In millions) Pension Benefits Other Postretirement Benefits Total Amortization of prior service cost (credit) $ 0.6 $ (3.8 ) $ (3.2 ) Amortization of net actuarial loss 74.5 10.8 85.3 Amortization of accumulated other comprehensive loss $ 75.1 $ 7.0 $ 82.1
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) 2019 2018 Projected benefit obligation $ 2,538.9 $ 2,420.8 Accumulated benefit obligation $ 2,526.1 $ 2,405.6 Fair value of plan assets $ 1,802.4 $ 1,686.1
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 2029, 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 and the U.K. defined benefit plan are made from pension plan assets. (In millions) Pension Benefits Other Postretirement Benefits Medicare Part D Subsidy 2020 $ 174.7 $ 32.8 $ 0.3 2021 172.0 34.1 0.3 2022 170.3 31.6 0.2 2023 168.3 29.4 0.2 2024 166.0 27.4 0.2 2025- 2029 786.5 110.1 0.7
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, 2019 were as follows: (In millions) Quoted Prices in Active Markets for Identical Assets Significant Observable Inputs Significant Unobservable Inputs Asset category Total NAV (Level 1) (Level 2) (Level 3) Equity securities: U.S. equities 443.6 254.7 188.9 — — International equities 326.1 299.6 26.5 — — Debt securities and cash: Fixed income and cash equivalents 650.7 419.9 58.7 172.1 — Floating rate 51.0 51.0 — — — Private equity 129.0 129.0 — — — Hedge funds 263.9 263.9 — — — Real estate and other 37.8 37.8 — — — Total assets $ 1,902.1 $ 1,455.9 $ 274.1 $ 172.1 $ — The fair values of the Company’s pension plan assets at December 31, 2018 were as follows: (In millions) Quoted Prices in Active Markets for Identical Assets Significant Observable Inputs Significant Unobservable Inputs Asset category Total NAV (Level 1) (Level 2) (Level 3) Equity securities: U.S. equities 362.9 219.9 143.0 — — International equities 377.4 335.7 41.7 — — Debt securities and cash: Fixed income and cash equivalents 493.7 116.9 6.3 370.5 — Floating rate 90.1 68.9 21.2 — — Private equity 137.1 137.1 — — — Hedge funds 258.3 258.3 — — — Real estate and other 52.7 52.7 — — — Total assets $ 1,772.2 $ 1,189.5 $ 212.2 $ 370.5 $ —
Schedule of target asset allocations for pension plans	The target asset allocations for ATI Pension Plan for 2020 , by major investment category, are: Asset category Target asset allocation range U.S. equity 18% - 40% Global equity 10% - 30% Debt securities and cash 15% - 40% Private equity 0% - 15% Hedge funds 10% - 20% Real estate and other 0% - 10%
Schedule of multiemployer plans	The Company’s participation in multiemployer plans for the years ended December 31, 2019 , 2018 and 2017 is reported in the following table. The Company’s contributions to the Steelworkers Western Independent Shops Pension Plan exceed 5% of this plan’s total contributions for the plan year ended September 30, 2018, which is the most recent information available from the Plan Administrator. Pension Protection Act Zone Status (1) FIP / RP Status Pending / Implemented (2) in millions Expiration Dates of Collective Bargaining Agreements EIN / Pension Plan Number Company Contributions Surcharge Imposed (3) Pension Fund 2019 2018 2019 2018 2017 Steelworkers Western Independent Shops Pension Plan 90-0169564 / 001 Green Green N/A $ 0.9 $ 0.8 $ 0.6 No 2/29/2020 Boilermakers-Blacksmiths National Pension Trust 48-6168020 / 001 Red Yellow Yes 2.5 2.5 2.2 No 9/30/2026 IAM National Pension Fund 51-6031295 / 002 Red Green Yes 2.2 2.1 1.7 Yes Various between 2021-2022 (4) Total contributions $ 5.6 $ 5.4 $ 4.5 (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 “red” zone had been determined to be in “critical status”, based on criteria established by the Internal Revenue Code (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. A 5% contribution surcharge has been imposed as of June 1, 2019 for the rest of 2019, increasing to a 10% surcharge rate beginning January 1, 2020 in addition to the contribution rate specified in the applicable collective bargaining agreements. The contribution surcharge 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 notification 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. (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” zone, is pending or has been implemented as of the end of the plan year that ended in 2019 . (3) The “Surcharge Imposed” column indicates whether ATI’s contribution rate for 2019 included an amount in addition to the contribution rate specified in the applicable collective bargaining agreement, as imposed by a plan in “critical 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 14, 2021 and July 14, 2022.

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2019
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, 2019 , 2018 and 2017 were as follows (in millions): Post- retirement benefit plans Currency translation adjustment Derivatives Deferred Tax Asset Valuation Allowance Total Attributable to ATI: Balance, December 31, 2016 $ (965.5 ) $ (85.0 ) $ 2.4 $ (45.6 ) $ (1,093.7 ) OCI before reclassifications (32.5 ) 31.5 11.1 — 10.1 Amounts reclassified from AOCI (a) 43.5 (b) — (c) (4.5 ) (d) 16.8 55.8 Net current-period OCI 11.0 31.5 6.6 16.8 65.9 Balance, December 31, 2017 (954.5 ) (53.5 ) 9.0 (28.8 ) (1,027.8 ) OCI before reclassifications (107.2 ) (20.4 ) (4.9 ) — (132.5 ) Amounts reclassified from AOCI (a) 55.9 (b) — (c) (8.9 ) (d) (20.5 ) 26.5 Net current-period OCI (51.3 ) (20.4 ) (13.8 ) (20.5 ) (106.0 ) Balance, December 31, 2018 (1,005.8 ) (73.9 ) (4.8 ) (49.3 ) (1,133.8 ) OCI before reclassifications (141.6 ) (2.7 ) 7.4 — (136.9 ) Amounts reclassified from AOCI (a) 64.3 (b) — (c) (3.1 ) (d) 7.8 69.0 Net current-period OCI (77.3 ) (2.7 ) 4.3 7.8 (67.9 ) Balance, December 31, 2019 $ (1,083.1 ) $ (76.6 ) $ (0.5 ) $ (41.5 ) $ (1,201.7 ) Attributable to noncontrolling interests: Balance, December 31, 2016 $ — $ 9.7 $ — $ — $ 9.7 OCI before reclassifications — 7.6 — — 7.6 Amounts reclassified from AOCI — (b) — — — — Net current-period OCI — 7.6 — — 7.6 Balance, December 31, 2017 — 17.3 — — 17.3 OCI before reclassifications — (6.2 ) — — (6.2 ) Amounts reclassified from AOCI — (b) — — — — Net current-period OCI — (6.2 ) — — (6.2 ) Balance, December 31, 2018 — 11.1 — — 11.1 OCI before reclassifications — (1.3 ) — — (1.3 ) Amounts reclassified from AOCI — (b) — — — — Net current-period OCI — (1.3 ) — — (1.3 ) Balance, December 31, 2019 $ — $ 9.8 $ — $ — $ 9.8 (a) Amounts were included in net periodic benefit cost for pension and other postretirement benefit plans (see Note 14). (b) No amounts were reclassified to earnings. (c) For 2018, following the Company’s January 1, 2018 adoption of changes issued by the FASB related to accounting guidance for derivatives, amounts related to derivatives are included in cost of goods sold or interest expense in the period or periods the hedged item affects earnings (see Note 12). For 2017, amounts related to the effective portion of the derivatives were included in cost of goods sold in the period or periods the hedged item affects earnings, and amounts related to the ineffective portion of the derivatives were presented in selling and administrative expenses on the consolidated statements of operations (see Note 12). (d) Represents the net change in deferred tax asset valuation allowances on changes in AOCI balances between the balance sheet dates. The 2019 income tax provision includes $6.0 million of tax expense for the recognition of a stranded deferred tax balance arising from deferred tax valuation allowances that was associated with a cash flow hedge portfolio that fully settled in the fourth quarter of 2019.
Reclassification out of accumulated other comprehensive income	Reclassifications out of AOCI for the fiscal years ended December 31, 2019 , 2018 and 2017 were as follows: Amount reclassified from AOCI (c) Fiscal year ended Details about AOCI Components (In millions) December 31, 2019 December 31, 2018 December 31, 2017 Affected line item in the consolidated statement of operations Postretirement benefit plans Prior service credit $ 2.6 (a) $ 2.6 (a) $ 1.6 (a) Actuarial losses (87.2 ) (a) (76.5 ) (a) (71.6 ) (a) (84.6 ) (c) (73.9 ) (c) (70.0 ) (c) Total before tax (20.3 ) (18.0 ) (26.5 ) Tax benefit (d) $ (64.3 ) $ (55.9 ) $ (43.5 ) Net of tax Derivatives Nickel and other raw material contracts $ 5.1 (b) $ 10.2 (b) $ (3.4 ) (b) Natural gas contracts (1.2 ) (b) 0.5 (b) (5.3 ) (b) Foreign exchange contracts 0.7 (b) 1.3 (b) 15.9 (b) Interest rate swap (0.5 ) (b) (0.3 ) (b) — (b) 4.1 (c) 11.7 (c) 7.2 (c) Total before tax 1.0 2.8 2.7 Tax provision (d) $ 3.1 $ 8.9 $ 4.5 Net of tax (a) Amounts are included in nonoperating retirement benefit expense (see Note 14). (b) For 2018, following the Company’s January 1, 2018 adoption of changes issued by the FASB related to accounting guidance for derivatives, amounts related to derivatives, with the exception of the interest rate swap are included in 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 Term Loan is recognized in earnings (see Note 12). For 2017, amounts related to the effective portion of the derivatives were included in cost of goods sold in the period or periods the hedged item affects earnings, and amounts related to the ineffective portion of the derivatives were presented in selling and administrative expenses on the consolidated statements of operations (see Note 12). (c) 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. (d) 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, 2019
Equity [Abstract]
Nonvested stock rollforward	Activity under the Company’s nonvested stock awards and restricted share units for the years ended December 31, 2019 , 2018 , and 2017 was as follows: (Shares in thousands, $ in millions) 2019 2018 2017 Number of shares/units Weighted Average Grant Date Fair Value Number of shares/units Weighted Average Grant Date Fair Value Number of shares Weighted Average Grant Date Fair Value Nonvested, beginning of year 1,055 $ 28.3 1,320 $ 32.5 1,852 $ 51.5 Granted 396 10.8 290 7.8 378 7.1 Vested (681 ) (14.5 ) (540 ) (11.7 ) (591 ) (16.9 ) Forfeited (14 ) (0.4 ) (15 ) (0.3 ) (319 ) (9.2 ) Nonvested, end of year 756 $ 24.2 1,055 $ 28.3 1,320 $ 32.5

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
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) 2019 2018 2017 U.S. $ 190.2 $ 190.8 $ (119.8 ) Non-U.S. 51.4 56.9 33.3 Income (loss) before income taxes $ 241.6 $ 247.7 $ (86.5 )
Schedule income tax provision (benefit)	The income tax provision (benefit) was as follows: (In millions) 2019 2018 2017 Current: Federal $ 2.2 $ 1.0 $ (0.8 ) State 0.2 (0.8 ) (1.3 ) Foreign 8.1 10.1 6.2 Total 10.5 10.3 4.1 Deferred: Federal (4.6 ) 1.3 2.4 State (40.4 ) (0.5 ) (14.4 ) Foreign 6.0 (0.1 ) 1.1 Total (39.0 ) 0.7 (10.9 ) Income tax provision (benefit) $ (28.5 ) $ 11.0 $ (6.8 )
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) 2019 2018 2017 Taxes computed at the federal rate $ 50.7 $ 52.0 $ (30.3 ) Goodwill impairment — — 36.6 State and local income taxes, net of federal tax benefit 0.3 (0.5 ) — Valuation allowance (90.1 ) (48.0 ) (14.5 ) Repatriation of foreign earnings (GILTI starting in 2018) 3.5 5.4 14.2 Restructuring 4.2 — — Impacts of U.S. Tax Act — 5.9 (4.1 ) Foreign earnings taxed at different rate 2.7 3.2 (3.5 ) Adjustment to prior years’ taxes — (5.8 ) (5.2 ) Withholding taxes 2.7 2.7 2.2 Preferential tax rate (4.1 ) (4.8 ) (3.7 ) Other 1.6 0.9 1.5 Income tax provision (benefit) $ (28.5 ) $ 11.0 $ (6.8 )
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, 2019 and 2018 were as follows: (In millions) 2019 2018 Deferred income tax assets Pensions $ 155.5 $ 159.4 Postretirement benefits other than pensions 83.8 87.3 Net operating loss tax carryovers 264.4 307.5 Tax credits 42.6 49.7 Other items 86.1 69.7 Gross deferred income tax assets 632.4 673.6 Valuation allowance for deferred tax assets (94.5 ) (194.8 ) Total deferred income tax assets 537.9 478.8 Deferred income tax liabilities Bases of property, plant and equipment 364.2 371.5 Inventory valuation 65.5 67.1 Bases of amortizable intangible assets 23.7 29.9 Other items 27.0 14.5 Total deferred tax liabilities 480.4 483.0 Net deferred tax asset (liability) $ 57.5 $ (4.2 )
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 $766 20 years $— $766 U.S. Foreign Tax Credit $30 10 years $7 $23 U.S. Research and Development Credit $2 20 years $— $2 State NOL $136 Various $30 $106 State Credits $11 Various $3 $8 U.K. NOL $23 Indefinite $— $— Poland Economic Zone Credit $2 7 years $— $2
Schedule of income taxes paid	Income taxes paid and amounts received as refunds were as follows: (In millions) 2019 2018 2017 Income taxes paid $ 15.1 $ 9.7 $ 10.4 Income tax refunds received (9.2 ) (1.6 ) (7.1 ) Income taxes paid, net $ 5.9 $ 8.1 $ 3.3
Schedule of changes in unrecognized income tax benefits	The changes in the liability for unrecognized income tax benefits for the years ended December 31, 2019 , 2018 and 2017 were as follows: (In millions) 2019 2018 2017 Balance at beginning of year $ 14.7 $ 14.7 $ 22.7 Increases in prior period tax positions — — — Decreases in prior period tax positions — (0.1 ) (0.7 ) Increases in current period tax positions 0.9 0.7 0.7 Expiration of the statute of limitations (1.2 ) (0.6 ) (0.4 ) Settlements — — (7.6 ) Balance at end of year $ 14.4 $ 14.7 $ 14.7
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 2018 States: Pennsylvania 2016 Foreign: China 2016 Poland 2013 United Kingdom 2017

Business Segments (Tables)

Business Segments (Tables)	12 Months Ended
	Dec. 31, 2019
Segment Reporting [Abstract]
Schedule of sales by segment	(In millions) 2019 2018 2017 Total sales: High Performance Materials & Components $ 2,054.2 $ 2,039.2 $ 1,751.1 Advanced Alloys & Solutions 2,392.2 2,302.4 2,006.9 Total sales 4,446.4 4,341.6 3,758.0 Intersegment sales: High Performance Materials & Components 75.7 76.1 46.3 Advanced Alloys & Solutions 248.2 218.9 186.6 Total intersegment sales 323.9 295.0 232.9 Sales to external customers: High Performance Materials & Components 1,978.5 1,963.1 1,704.8 Advanced Alloys & Solutions 2,144.0 2,083.5 1,820.3 Total sales to external customers $ 4,122.5 $ 4,046.6 $ 3,525.1
Schedule of operating profit (loss) by segment	(In millions) 2019 2018 2017 Operating profit: High Performance Materials & Components $ 271.6 $ 269.7 $ 191.4 Advanced Alloys & Solutions 109.1 143.5 92.0 Total operating profit 380.7 413.2 283.4 LIFO and net realizable value reserves (See Note 3) (0.1 ) (0.7 ) (0.2 ) Corporate expenses (66.8 ) (58.1 ) (50.5 ) Closed operations and other expenses (25.5 ) (21.6 ) (34.0 ) Restructuring and other charges (4.5 ) — — Impairment of goodwill (See Note 5) — — (114.4 ) Debt extinguishment charge (See Note 10) (21.6 ) — (37.0 ) Gain on joint venture deconsolidation (See Note 7) — 15.9 — Joint venture impairment charge (See Note 7) (11.4 ) — — Gain on asset sales, net 89.8 — — Interest expense, net (99.0 ) (101.0 ) (133.8 ) Income (loss) before income taxes $ 241.6 $ 247.7 $ (86.5 )
Schedule of other financial information by segment	Certain additional information regarding the Company’s business segments is presented below: (In millions) 2019 2018 2017 Depreciation and amortization: High Performance Materials & Components $ 84.7 $ 90.6 $ 91.5 Advanced Alloys & Solutions 63.5 62.9 63.4 Corporate 2.9 2.9 5.9 Total depreciation and amortization $ 151.1 $ 156.4 $ 160.8 Capital expenditures: High Performance Materials & Components $ 119.9 $ 71.7 $ 52.7 Advanced Alloys & Solutions 47.4 64.5 69.1 Corporate 0.9 3.0 0.9 Total capital expenditures $ 168.2 $ 139.2 $ 122.7 Identifiable assets: 2019 2018 2017 High Performance Materials & Components $ 2,324.6 $ 2,400.7 $ 2,329.9 Advanced Alloys & Solutions 2,621.1 2,590.4 2,550.8 Discontinued Operations — — 0.2 Corporate: Deferred Taxes 64.5 8.7 7.6 Cash and cash equivalents and other 624.4 502.0 296.9 Total assets $ 5,634.6 $ 5,501.8 $ 5,185.4
Schedule of company assets by country	($ in millions) 2019 Percent of total 2018 Percent of total 2017 Percent of total Total assets: United States $ 4,956.4 88 % $ 4,859.1 88 % $ 4,547.7 88 % China 288.1 5 % 287.3 5 % 276.0 5 % United Kingdom 141.3 3 % 136.7 3 % 122.7 2 % Other 248.8 4 % 218.7 4 % 239.0 5 % Total Assets $ 5,634.6 100 % $ 5,501.8 100 % $ 5,185.4 100 %

Per Share Information (Tables)

Per Share Information (Tables)	12 Months Ended
	Dec. 31, 2019
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, 2019 2018 2017 Numerator: Numerator for basic net income (loss) per common share - Net income (loss) attributable to ATI $ 257.6 $ 222.4 $ (91.9 ) Effect of dilutive securities: 4.75% Convertible Senior Notes due 2022 12.8 12.9 — Numerator for diluted net income (loss) per common share - Net income (loss) attributable to ATI after assumed conversions $ 270.4 $ 235.3 $ (91.9 ) Denominator: Denominator for basic net income (loss) per common share—weighted average shares 125.8 125.2 110.1 Effect of dilutive securities: Share-based compensation 0.8 0.8 — 4.75% Convertible Senior Notes due 2022 19.9 19.9 — Denominator for diluted net income (loss) per common share—adjusted weighted average shares and assumed conversions 146.5 145.9 110.1 Basic net income (loss) attributable to ATI per common share $ 2.05 $ 1.78 $ (0.83 ) Diluted net income (loss) attributable to ATI per common share $ 1.85 $ 1.61 $ (0.83 )

Financial Information for Sub_2

Financial Information for Subsidiary and Guarantor Parent (Tables)	12 Months Ended
	Dec. 31, 2019
Financial Information for Subsidiary and Guarantor Parent [Abstract]
Schedule of condensed consolidating balance sheets	Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Balance Sheets December 31, 2019 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Assets: Cash and cash equivalents $ 0.3 $ 4.2 $ 486.3 $ — $ 490.8 Accounts receivable, net — 123.7 430.4 — 554.1 Intercompany notes receivable — — 4,402.8 (4,402.8 ) — Short-term contract assets — — 38.5 — 38.5 Inventories, net — 213.0 942.3 — 1,155.3 Prepaid expenses and other current assets 5.6 18.5 40.2 — 64.3 Total current assets 5.9 359.4 6,340.5 (4,402.8 ) 2,303.0 Property, plant and equipment, net 6.5 1,539.3 904.3 — 2,450.1 Goodwill — — 525.8 — 525.8 Intercompany notes receivable — — 200.0 (200.0 ) — Investments in subsidiaries 6,434.3 37.7 — (6,472.0 ) — Other assets 98.3 83.1 174.3 — 355.7 Total assets $ 6,545.0 $ 2,019.5 $ 8,144.9 $ (11,074.8 ) $ 5,634.6 Liabilities and stockholders’ equity: Accounts payable $ 4.6 $ 184.0 $ 332.6 $ — $ 521.2 Intercompany notes payable 2,457.1 1,945.7 — (4,402.8 ) — Short-term contract liabilities — 26.4 52.3 — 78.7 Short-term debt and current portion of long-term debt 1.4 0.2 9.9 — 11.5 Other current liabilities 51.5 68.1 118.2 — 237.8 Total current liabilities 2,514.6 2,224.4 513.0 (4,402.8 ) 849.2 Long-term debt 1,130.1 150.4 106.9 — 1,387.4 Intercompany notes payable — 200.0 — (200.0 ) — Accrued postretirement benefits — 261.2 51.3 — 312.5 Pension liabilities 678.8 3.8 48.9 — 731.5 Other long-term liabilities 28.3 44.1 88.4 — 160.8 Total liabilities 4,351.8 2,883.9 808.5 (4,602.8 ) 3,441.4 Total stockholders’ equity (deficit) 2,193.2 (864.4 ) 7,336.4 (6,472.0 ) 2,193.2 Total liabilities and stockholders’ equity $ 6,545.0 $ 2,019.5 $ 8,144.9 $ (11,074.8 ) $ 5,634.6 Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Balance Sheets December 31, 2018 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Assets: Cash and cash equivalents $ 0.1 $ 10.8 $ 371.1 $ — $ 382.0 Accounts receivable, net — 126.3 401.5 — 527.8 Intercompany notes receivable — — 3,968.8 (3,968.8 ) — Short-term contract assets — — 51.2 — 51.2 Inventories, net — 216.1 995.0 — 1,211.1 Prepaid expenses and other current assets 12.9 29.3 32.4 — 74.6 Total current assets 13.0 382.5 5,820.0 (3,968.8 ) 2,246.7 Property, plant and equipment, net 1.7 1,548.4 924.9 — 2,475.0 Goodwill — — 534.7 — 534.7 Intercompany notes receivable — — 200.0 (200.0 ) — Investments in subsidiaries 6,096.4 37.7 — (6,134.1 ) — Other assets 35.6 30.7 179.1 — 245.4 Total assets $ 6,146.7 $ 1,999.3 $ 7,658.7 $ (10,302.9 ) $ 5,501.8 Liabilities and stockholders’ equity: Accounts payable $ 3.3 $ 177.5 $ 318.0 $ — $ 498.8 Intercompany notes payable 2,102.8 1,866.0 — (3,968.8 ) — Short-term contract liabilities — 33.0 38.4 — 71.4 Short-term debt and current portion of long-term debt 0.2 0.7 5.7 — 6.6 Other current liabilities 59.1 71.7 129.3 — 260.1 Total current liabilities 2,165.4 2,148.9 491.4 (3,968.8 ) 836.9 Long-term debt 1,278.8 151.8 104.9 — 1,535.5 Intercompany notes payable — 200.0 — (200.0 ) — Accrued postretirement benefits — 259.2 59.2 — 318.4 Pension liabilities 681.6 4.0 44.4 — 730.0 Other long-term liabilities 29.3 17.6 42.5 — 89.4 Total liabilities 4,155.1 2,781.5 742.4 (4,168.8 ) 3,510.2 Total stockholders’ equity (deficit) 1,991.6 (782.2 ) 6,916.3 (6,134.1 ) 1,991.6 Total liabilities and stockholders’ equity $ 6,146.7 $ 1,999.3 $ 7,658.7 $ (10,302.9 ) $ 5,501.8
Schedule of condensed consolidating statements of operations	Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Operations For the year ended December 31, 2018 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Sales $ — $ 1,410.3 $ 2,636.3 $ — $ 4,046.6 Cost of sales 16.6 1,302.4 2,097.3 — 3,416.3 Gross profit (loss) (16.6 ) 107.9 539.0 — 630.3 Selling and administrative expenses 101.7 34.2 132.3 — 268.2 Operating income (loss) (118.3 ) 73.7 406.7 — 362.1 Nonoperating retirement benefit expense (12.7 ) (19.5 ) (1.7 ) — (33.9 ) Interest income (expense), net (138.8 ) (114.6 ) 152.4 — (101.0 ) Other income (expense) including equity in income of unconsolidated subsidiaries 517.5 16.8 0.8 (514.6 ) 20.5 Income (loss) before income taxes 247.7 (43.6 ) 558.2 (514.6 ) 247.7 Income tax provision (benefit) 11.0 (8.7 ) 83.9 (75.2 ) 11.0 Net income (loss) 236.7 (34.9 ) 474.3 (439.4 ) 236.7 Less: Net income attributable to noncontrolling interest — — 14.3 — 14.3 Net income (loss) attributable to ATI $ 236.7 $ (34.9 ) $ 460.0 $ (439.4 ) $ 222.4 Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Operations For the year ended December 31, 2019 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Sales $ — $ 1,429.0 $ 2,693.5 $ — $ 4,122.5 Cost of sales 13.5 1,302.8 2,168.4 — 3,484.7 Gross profit (loss) (13.5 ) 126.2 525.1 — 637.8 Selling and administrative expenses 116.5 33.2 117.5 — 267.2 Restructuring charges 4.5 — — — 4.5 Operating income (loss) (134.5 ) 93.0 407.6 — 366.1 Nonoperating retirement benefit expense (47.5 ) (24.7 ) (1.4 ) — (73.6 ) Interest income (expense), net (148.2 ) (131.6 ) 180.8 — (99.0 ) Debt extinguishment charge (21.6 ) — — — (21.6 ) Other income (expense) including equity in income of unconsolidated subsidiaries 593.4 (22.0 ) 90.2 (591.9 ) 69.7 Income (loss) before income taxes 241.6 (85.3 ) 677.2 (591.9 ) 241.6 Income tax provision (benefit) (28.5 ) (18.3 ) 115.6 (97.3 ) (28.5 ) Net income (loss) 270.1 (67.0 ) 561.6 (494.6 ) 270.1 Less: Net income attributable to noncontrolling interest — — 12.5 — 12.5 Net income (loss) attributable to ATI $ 270.1 $ (67.0 ) $ 549.1 $ (494.6 ) $ 257.6 Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Operations For the year ended December 31, 2017 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Sales $ — $ 1,178.9 $ 2,346.2 $ — $ 3,525.1 Cost of sales 14.6 1,085.5 1,928.0 — 3,028.1 Gross profit (loss) (14.6 ) 93.4 418.2 — 497.0 Selling and administrative expenses 86.6 36.9 124.5 — 248.0 Impairment of goodwill — — 114.4 — 114.4 Operating income (loss) (101.2 ) 56.5 179.3 — 134.6 Nonoperating retirement benefit expense (32.2 ) (18.7 ) (3.4 ) — (54.3 ) Interest income (expense), net (155.8 ) (90.0 ) 112.0 — (133.8 ) Debt extinguishment charge (37.0 ) — — — (37.0 ) Other income (expense) including equity in income of unconsolidated subsidiaries 239.7 1.6 2.4 (239.7 ) 4.0 Income (loss) before income taxes (86.5 ) (50.6 ) 290.3 (239.7 ) (86.5 ) Income tax provision (benefit) (6.8 ) (16.6 ) 131.4 (114.8 ) (6.8 ) Net income (loss) (79.7 ) (34.0 ) 158.9 (124.9 ) (79.7 ) Less: Net income attributable to noncontrolling interest — — 12.2 — 12.2 Net income (loss) attributable to ATI $ (79.7 ) $ (34.0 ) $ 146.7 $ (124.9 ) $ (91.9 )
Schedule of condensed consolidating comprehensive income	Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Comprehensive Income (Loss) For the year ended December 31, 2017 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Net income (loss) $ (79.7 ) $ (34.0 ) $ 158.9 $ (124.9 ) $ (79.7 ) Other comprehensive income (loss) Currency translation adjustment arising during the period 39.1 — 39.1 (39.1 ) 39.1 Net derivative gain on hedge transactions 7.1 — — — 7.1 Pension and postretirement benefits 27.3 (5.8 ) (10.7 ) 16.5 27.3 Other comprehensive income (loss), net of tax 73.5 (5.8 ) 28.4 (22.6 ) 73.5 Comprehensive income (loss) (6.2 ) (39.8 ) 187.3 (147.5 ) (6.2 ) Less: Comprehensive income attributable to noncontrolling interest — — 19.8 — 19.8 Comprehensive income (loss) attributable to ATI $ (6.2 ) $ (39.8 ) $ 167.5 $ (147.5 ) $ (26.0 ) Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Comprehensive Income (Loss) For the year ended December 31, 2019 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Net income (loss) $ 270.1 $ (67.0 ) $ 561.6 $ (494.6 ) $ 270.1 Other comprehensive income (loss) Currency translation adjustment arising during the period (4.0 ) — (4.0 ) 4.0 (4.0 ) Net derivative gain on hedge transactions 10.3 — — — 10.3 Pension and postretirement benefits (75.5 ) 3.8 (15.2 ) 11.4 (75.5 ) Other comprehensive income (loss), net of tax (69.2 ) 3.8 (19.2 ) 15.4 (69.2 ) Comprehensive income (loss) 200.9 (63.2 ) 542.4 (479.2 ) 200.9 Less: Comprehensive income attributable to noncontrolling interest — — 11.2 — 11.2 Comprehensive income (loss) attributable to ATI $ 200.9 $ (63.2 ) $ 531.2 $ (479.2 ) $ 189.7 Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Comprehensive Income (Loss) For the year ended December 31, 2018 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Net income (loss) $ 236.7 $ (34.9 ) $ 474.3 $ (439.4 ) $ 236.7 Other comprehensive income (loss) Currency translation adjustment arising during the period (26.6 ) — (26.6 ) 26.6 (26.6 ) Net derivative loss on hedge transactions (18.1 ) — — — (18.1 ) Pension and postretirement benefits (67.5 ) (19.1 ) 0.7 18.4 (67.5 ) Other comprehensive income (loss), net of tax (112.2 ) (19.1 ) (25.9 ) 45.0 (112.2 ) Comprehensive income (loss) 124.5 (54.0 ) 448.4 (394.4 ) 124.5 Less: Comprehensive income attributable to noncontrolling interest — — 8.1 — 8.1 Comprehensive income (loss) attributable to ATI $ 124.5 $ (54.0 ) $ 440.3 $ (394.4 ) $ 116.4
Schedule of condensed consolidating statements of cash flow	Condensed Statements of Cash Flows For the year ended December 31, 2018 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Cash flows provided by (used in) operating activities $ (107.0 ) $ (223.9 ) $ 738.7 $ (15.0 ) $ 392.8 Investing Activities: Purchases of property, plant and equipment (2.1 ) (26.2 ) (110.9 ) — (139.2 ) Net receipts (payments) on intercompany activity — — (346.5 ) 346.5 — Proceeds from disposal of property, plant and equipment — 2.6 0.2 — 2.8 Purchases of businesses — — (10.0 ) — (10.0 ) Other 1.3 — — — 1.3 Cash flows provided by (used in) investing activities (0.8 ) (23.6 ) (467.2 ) 346.5 (145.1 ) Financing Activities: Borrowings on long-term debt — — 7.1 — 7.1 Payments on long-term debt and finance leases (0.2 ) (0.9 ) (5.3 ) — (6.4 ) Net payments under credit facilities — — (5.9 ) — (5.9 ) Net receipts (payments) on intercompany activity 112.5 234.0 — (346.5 ) — Dividends paid to stockholders — — (15.0 ) 15.0 — Dividends paid to noncontrolling interests — — (10.0 ) — (10.0 ) Sale of noncontrolling interests — 11.7 2.7 — 14.4 Shares repurchased for income tax withholding on share-based compensation and other (6.5 ) — — — (6.5 ) Cash flows provided by (used in) financing activities 105.8 244.8 (26.4 ) (331.5 ) (7.3 ) Increase (decrease) in cash and cash equivalents $ (2.0 ) $ (2.7 ) $ 245.1 $ — $ 240.4 Condensed Statements of Cash Flows For the year ended December 31, 2019 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Cash flows provided by (used in) operating activities $ 16.1 $ (109.1 ) $ 344.1 $ (21.0 ) $ 230.1 Investing Activities: Purchases of property, plant and equipment (0.7 ) (33.4 ) (134.1 ) — (168.2 ) Net receipts (payments) on intercompany activity — — (308.0 ) 308.0 — Proceeds from disposals of property, plant and equipment — 0.1 91.9 — 92.0 Proceeds from sales of businesses, net of transaction costs — — 158.1 — 158.1 Other (0.2 ) — — — (0.2 ) Cash flows provided by (used in) investing activities (0.9 ) (33.3 ) (192.1 ) 308.0 81.7 Financing Activities: Borrowings on long-term debt 350.0 — — — 350.0 Payments on long-term debt and finance leases (500.7 ) (0.2 ) (6.7 ) — (507.6 ) Net borrowings under credit facilities — — 4.9 — 4.9 Debt issuance costs (5.5 ) — — — (5.5 ) Debt extinguishment charge (20.9 ) — — — (20.9 ) Net receipts (payments) on intercompany activity 172.0 136.0 — (308.0 ) — Dividends paid to stockholders — — (21.0 ) 21.0 — Dividends paid to noncontrolling interests — — (14.0 ) — (14.0 ) Shares repurchased for income tax withholding on share-based compensation and other (9.9 ) — — — (9.9 ) Cash flows provided by (used in) financing activities (15.0 ) 135.8 (36.8 ) (287.0 ) (203.0 ) Increase (decrease) in cash and cash equivalents $ 0.2 $ (6.6 ) $ 115.2 $ — $ 108.8 Condensed Statements of Cash Flows For the year ended December 31, 2017 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Cash flows provided by (used in) operating activities $ (78.8 ) $ (101.5 ) $ 214.7 $ (12.0 ) $ 22.4 Investing Activities: Purchases of property, plant and equipment (0.9 ) (38.5 ) (83.3 ) — (122.7 ) Net receipts (payments) on intercompany activity — — (223.9 ) 223.9 — Proceeds from disposal of property, plant and equipment — 0.1 2.6 — 2.7 Other — — 0.4 — 0.4 Cash flows provided by (used in) investing activities (0.9 ) (38.4 ) (304.2 ) 223.9 (119.6 ) Financing Activities: Borrowings on long-term debt — — 8.5 — 8.5 Payments on long-terms debt and finance leases (350.4 ) (0.3 ) (2.3 ) — (353.0 ) Net borrowings under credit facilities — — 1.6 — 1.6 Debt issuance costs — — (0.8 ) — (0.8 ) Debt extinguishment charge (35.8 ) — — — (35.8 ) Net receipts (payments) on intercompany activity 72.7 151.2 — (223.9 ) — Issuance of common stock 397.8 — — — 397.8 Dividends paid to stockholders — — (12.0 ) 12.0 — Dividends paid to noncontrolling interests — — (8.0 ) — (8.0 ) Sale to noncontrolling interest — — 3.7 — 3.7 Shares repurchased for income tax withholding on share-based compensation (4.8 ) — — — (4.8 ) Cash flows provided by (used in) financing activities 79.5 150.9 (9.3 ) (211.9 ) 9.2 Increase (decrease) in cash and cash equivalents $ (0.2 ) $ 11.0 $ (98.8 ) $ — $ (88.0 )

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Schedule of quarterly financial information	Quarter Ended (In millions, except per share amounts) March 31 June 30 September 30 December 31 2019 - Sales $ 1,004.8 $ 1,080.4 $ 1,018.7 $ 1,018.6 Gross Profit 131.1 177.7 159.7 169.3 Net income 16.3 78.5 115.3 60.0 Net income attributable to ATI 15.0 75.1 111.0 56.5 Basic income attributable to ATI per common share $ 0.12 $ 0.60 $ 0.88 $ 0.45 Diluted income attributable to ATI per common share $ 0.12 $ 0.54 $ 0.78 $ 0.41 Average shares outstanding 125.8 126.1 126.1 126.1 2018 - Sales $ 979.0 $ 1,009.5 $ 1,020.2 $ 1,037.9 Gross Profit 148.6 173.7 160.4 147.6 Net income 60.5 75.6 55.6 45.0 Net income attributable to ATI 58.0 72.8 50.5 41.1 Basic income attributable to ATI per common share $ 0.46 $ 0.58 $ 0.40 $ 0.33 Diluted income attributable to ATI per common share $ 0.42 $ 0.52 $ 0.37 $ 0.30 Average shares outstanding 125.7 125.7 125.7 125.7

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Principles of Consolidation (Details) - Uniti [Member] - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Noncontrolling Interest [Line Items]
Equity method investment ownership percentage	50.00%
Related party accounts receivable	$ 0.2	$ 1.8

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Risks and Uncertainties and Use of Estimates (Details)	12 Months Ended
	Dec. 31, 2019employee
Segment Reporting Information [Line Items]
Number of employees	8,100
Percent of employees located outside of the U.S.	17.00%
Percent of employees covered by collective bargaining agreements	40.00%
Number of employees covered by USW collective bargaining agreement expiring February 29, 2020	1,500

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Accounts Receivable (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Allowances for Doubtful Accounts	$ 4.6	$ 6	$ 5.9	$ 7.3

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Research and Development (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Research and Development Expense	$ 17.8	$ 22.7	$ 13.3
Customer funded research and development costs	$ 2.4	$ 2.2	$ 1.4

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Recent Accounting Pronouncements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Income (Loss)	$ 366.1	$ 362.1	$ 134.6

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Narrative (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2019USD ($)segment	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Jan. 01, 2018USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Inventories, net	$ 1,155,300,000				$ 1,211,100,000				$ 1,155,300,000	$ 1,211,100,000
Adjustment from current cost to LIFO cost basis	(33,600,000)				(2,900,000)				(33,600,000)	(2,900,000)
Sales	1,018,600,000	$ 1,018,700,000	$ 1,080,400,000	$ 1,004,800,000	1,037,900,000	$ 1,020,200,000	$ 1,009,500,000	$ 979,000,000	4,122,500,000	4,046,600,000	$ 3,525,100,000
Cost of sales									3,484,700,000	3,416,300,000	3,028,100,000
Short-term contract assets	38,500,000				51,200,000				38,500,000	51,200,000		$ 36,500,000
Long-term contract assets	100,000				100,000				100,000	100,000		16,900,000
Other current liabilities	237,800,000				260,100,000				237,800,000	260,100,000
Other long-term liabilities	160,800,000				89,400,000				160,800,000	89,400,000
Short-term contract liabilities	78,700,000				71,400,000				78,700,000	71,400,000		69,700,000
Long-term contract liabilities	25,900,000				7,300,000				$ 25,900,000	7,300,000		22,200,000
Number of business segments | segment									2
Revenue, Performance Obligation [Abstract]
Confirmed order backlog	2,300,000,000				2,200,000,000				$ 2,300,000,000	2,200,000,000	$ 2,100,000,000
Confirmed orders with current performance obligations	0.81								0.81
Accounts receivable with customers	558,700,000				533,800,000				558,700,000	533,800,000
Contract costs for obtaining and fulfilling contracts	$ 6,500,000				5,200,000				6,500,000	5,200,000
Amortization of contract costs									$ 1,400,000	1,200,000
ASU 2014-09 | Revenue Recognized Over-time
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in retained earnings												$ 15,500,000
Contract assets					45,300,000					45,300,000
Inventories, net					5,400,000					5,400,000
Sales										(4,300,000)
Cost of sales										(5,400,000)
Short-term contract assets					45,200,000					45,200,000
Long-term contract assets					$ 100,000					$ 100,000

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 1,018.6	$ 1,018.7	$ 1,080.4	$ 1,004.8	$ 1,037.9	$ 1,020.2	$ 1,009.5	$ 979	$ 4,122.5	$ 4,046.6	$ 3,525.1
Percent of total revenue									100.00%	100.00%	100.00%
Total High-Value Products
Disaggregation of Revenue [Line Items]
Percent of total revenue									86.00%	84.00%	82.00%
Nickel-based alloys and specialty alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue									32.00%	30.00%	28.00%
Precision forgings, castings and components
Disaggregation of Revenue [Line Items]
Percent of total revenue									18.00%	20.00%	19.00%
Titanium and titanium-based alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue									18.00%	17.00%	17.00%
Precision rolled strip products
Disaggregation of Revenue [Line Items]
Percent of total revenue									12.00%	12.00%	12.00%
Zirconium and related alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue									6.00%	5.00%	6.00%
Standard stainless products
Disaggregation of Revenue [Line Items]
Percent of total revenue									14.00%	16.00%	18.00%
United States
Disaggregation of Revenue [Line Items]
Revenue									$ 2,454.6	$ 2,348.1	$ 2,070.6
China
Disaggregation of Revenue [Line Items]
Revenue									355.6	320	265.6
Germany
Disaggregation of Revenue [Line Items]
Revenue									219.3	247.2	217.1
United Kingdom
Disaggregation of Revenue [Line Items]
Revenue									173.8	242.1	231.6
France
Disaggregation of Revenue [Line Items]
Revenue									155.5	183.6	165.6
Japan
Disaggregation of Revenue [Line Items]
Revenue									147.7	214.9	131.7
Rest of World
Disaggregation of Revenue [Line Items]
Revenue									616	490.7	442.9
Aerospace & Defense
Disaggregation of Revenue [Line Items]
Revenue									2,130.4	1,965.5	1,718.1
Energy
Disaggregation of Revenue [Line Items]
Revenue									796.9	780.7	610.4
Automotive
Disaggregation of Revenue [Line Items]
Revenue									296.6	323.4	273.7
Food Equipment & Appliances
Disaggregation of Revenue [Line Items]
Revenue									205.8	244.9	226
Construction/Mining
Disaggregation of Revenue [Line Items]
Revenue									195	226	192.9
Medical
Disaggregation of Revenue [Line Items]
Revenue									172.4	183.1	183
Electronics/Computers/Communications
Disaggregation of Revenue [Line Items]
Revenue									163.2	156.9	151.6
Other
Disaggregation of Revenue [Line Items]
Revenue									162.2	166.1	169.4
Operating Segments
Disaggregation of Revenue [Line Items]
Revenue									4,446.4	4,341.6	3,758
Operating Segments | High Performance Materials & Components
Disaggregation of Revenue [Line Items]
Revenue									$ 2,054.2	$ 2,039.2	$ 1,751.1
Percent of total revenue									100.00%	100.00%	100.00%
Operating Segments | High Performance Materials & Components | Total High-Value Products
Disaggregation of Revenue [Line Items]
Percent of total revenue									100.00%	100.00%	100.00%
Operating Segments | High Performance Materials & Components | Nickel-based alloys and specialty alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue									38.00%	37.00%	37.00%
Operating Segments | High Performance Materials & Components | Precision forgings, castings and components
Disaggregation of Revenue [Line Items]
Percent of total revenue									36.00%	40.00%	38.00%
Operating Segments | High Performance Materials & Components | Titanium and titanium-based alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue									26.00%	23.00%	25.00%
Operating Segments | High Performance Materials & Components | Precision rolled strip products
Disaggregation of Revenue [Line Items]
Percent of total revenue									0.00%	0.00%	0.00%
Operating Segments | High Performance Materials & Components | Zirconium and related alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue									0.00%	0.00%	0.00%
Operating Segments | High Performance Materials & Components | Standard stainless products
Disaggregation of Revenue [Line Items]
Percent of total revenue									0.00%	0.00%	0.00%
Operating Segments | High Performance Materials & Components | United States
Disaggregation of Revenue [Line Items]
Revenue									$ 1,042.6	$ 983.6	$ 874.3
Operating Segments | High Performance Materials & Components | China
Disaggregation of Revenue [Line Items]
Revenue									93.9	71.2	44.3
Operating Segments | High Performance Materials & Components | Germany
Disaggregation of Revenue [Line Items]
Revenue									147.2	159	131.9
Operating Segments | High Performance Materials & Components | United Kingdom
Disaggregation of Revenue [Line Items]
Revenue									156.7	225.6	200.8
Operating Segments | High Performance Materials & Components | France
Disaggregation of Revenue [Line Items]
Revenue									132.7	146.3	143.3
Operating Segments | High Performance Materials & Components | Japan
Disaggregation of Revenue [Line Items]
Revenue									95	128.1	88.5
Operating Segments | High Performance Materials & Components | Rest of World
Disaggregation of Revenue [Line Items]
Revenue									310.4	249.3	221.7
Operating Segments | High Performance Materials & Components | Aerospace & Defense
Disaggregation of Revenue [Line Items]
Revenue									1,624.1	1,562.9	1,377
Operating Segments | High Performance Materials & Components | Energy
Disaggregation of Revenue [Line Items]
Revenue									153.6	133.9	119.7
Operating Segments | High Performance Materials & Components | Automotive
Disaggregation of Revenue [Line Items]
Revenue									10.5	9.5	8.8
Operating Segments | High Performance Materials & Components | Food Equipment & Appliances
Disaggregation of Revenue [Line Items]
Revenue									0.3	0.4	0.4
Operating Segments | High Performance Materials & Components | Construction/Mining
Disaggregation of Revenue [Line Items]
Revenue									42.5	72.7	51.2
Operating Segments | High Performance Materials & Components | Medical
Disaggregation of Revenue [Line Items]
Revenue									85.4	106	81.1
Operating Segments | High Performance Materials & Components | Electronics/Computers/Communications
Disaggregation of Revenue [Line Items]
Revenue									0.5	1.5	1
Operating Segments | High Performance Materials & Components | Other
Disaggregation of Revenue [Line Items]
Revenue									61.6	76.2	65.6
Operating Segments | Advanced Alloys & Solutions
Disaggregation of Revenue [Line Items]
Revenue									$ 2,392.2	$ 2,302.4	$ 2,006.9
Percent of total revenue									100.00%	100.00%	100.00%
Operating Segments | Advanced Alloys & Solutions | Total High-Value Products
Disaggregation of Revenue [Line Items]
Percent of total revenue									72.00%	68.00%	66.00%
Operating Segments | Advanced Alloys & Solutions | Nickel-based alloys and specialty alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue									27.00%	24.00%	20.00%
Operating Segments | Advanced Alloys & Solutions | Precision forgings, castings and components
Disaggregation of Revenue [Line Items]
Percent of total revenue									0.00%	0.00%	0.00%
Operating Segments | Advanced Alloys & Solutions | Titanium and titanium-based alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue									11.00%	10.00%	10.00%
Operating Segments | Advanced Alloys & Solutions | Precision rolled strip products
Disaggregation of Revenue [Line Items]
Percent of total revenue									23.00%	23.00%	24.00%
Operating Segments | Advanced Alloys & Solutions | Zirconium and related alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue									11.00%	11.00%	12.00%
Operating Segments | Advanced Alloys & Solutions | Standard stainless products
Disaggregation of Revenue [Line Items]
Percent of total revenue									28.00%	32.00%	34.00%
Operating Segments | Advanced Alloys & Solutions | United States
Disaggregation of Revenue [Line Items]
Revenue									$ 1,412	$ 1,364.5	$ 1,196.3
Operating Segments | Advanced Alloys & Solutions | China
Disaggregation of Revenue [Line Items]
Revenue									261.7	248.8	221.3
Operating Segments | Advanced Alloys & Solutions | Germany
Disaggregation of Revenue [Line Items]
Revenue									72.1	88.2	85.2
Operating Segments | Advanced Alloys & Solutions | United Kingdom
Disaggregation of Revenue [Line Items]
Revenue									17.1	16.5	30.8
Operating Segments | Advanced Alloys & Solutions | France
Disaggregation of Revenue [Line Items]
Revenue									22.8	37.3	22.3
Operating Segments | Advanced Alloys & Solutions | Japan
Disaggregation of Revenue [Line Items]
Revenue									52.7	86.8	43.2
Operating Segments | Advanced Alloys & Solutions | Rest of World
Disaggregation of Revenue [Line Items]
Revenue									305.6	241.4	221.2
Operating Segments | Advanced Alloys & Solutions | Aerospace & Defense
Disaggregation of Revenue [Line Items]
Revenue									506.3	402.6	341.1
Operating Segments | Advanced Alloys & Solutions | Energy
Disaggregation of Revenue [Line Items]
Revenue									643.3	646.8	490.7
Operating Segments | Advanced Alloys & Solutions | Automotive
Disaggregation of Revenue [Line Items]
Revenue									286.1	313.9	264.9
Operating Segments | Advanced Alloys & Solutions | Food Equipment & Appliances
Disaggregation of Revenue [Line Items]
Revenue									205.5	244.5	225.6
Operating Segments | Advanced Alloys & Solutions | Construction/Mining
Disaggregation of Revenue [Line Items]
Revenue									152.5	153.3	141.7
Operating Segments | Advanced Alloys & Solutions | Medical
Disaggregation of Revenue [Line Items]
Revenue									87	77.1	101.9
Operating Segments | Advanced Alloys & Solutions | Electronics/Computers/Communications
Disaggregation of Revenue [Line Items]
Revenue									162.7	155.4	150.6
Operating Segments | Advanced Alloys & Solutions | Other
Disaggregation of Revenue [Line Items]
Revenue									100.6	89.9	103.8
External Customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue									4,122.5	4,046.6	3,525.1
External Customers | Operating Segments | High Performance Materials & Components
Disaggregation of Revenue [Line Items]
Revenue									1,978.5	1,963.1	1,704.8
External Customers | Operating Segments | Advanced Alloys & Solutions
Disaggregation of Revenue [Line Items]
Revenue									$ 2,144	$ 2,083.5	$ 1,820.3

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, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	$ 6	$ 5.9	$ 7.3
Expense to increase the reserve	0.2	1.9	0.1
Write-off of uncollectible accounts	(1.6)	(1.8)	(1.5)
Ending Balance	$ 4.6	$ 6	$ 5.9

Revenue from Contracts with C_6

Revenue from Contracts with Customers - Contract Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Contract Assets, Current [Roll Forward]
Balance as of beginning of fiscal year	$ 51.2
Recognized in current year	74.5	$ 92.9
Reclassified to accounts receivable	(79.9)	(95.8)
Impairment	0	0
Reclassification to/from long-term	0	16.8
Divestiture	(7.3)	0
Other	0	0.8
Balance as of period end	38.5	51.2
Contract Assets, Noncurrent [Roll Forward]
Balance as of beginning of fiscal year	0.1
Recognized in current year	0	0
Reclassified to accounts receivable	0	0
Impairment	0	0
Reclassification to/from short-term	0	(16.8)
Balance as of period end	0.1	0.1
Contract Liabilities, Current [Roll Forward]
Balance as of beginning of fiscal year	71.4
Recognized in current year	126.1	76.7
Amounts in beginning balance reclassified to revenue	(49.2)	(49.6)
Current year amounts reclassified to revenue	(76)	(42.7)
Other	1.9	2.7
Reclassification to/from long-term	4.5	14.6
Balance as of period end	78.7	71.4
Contract Liabilities, Noncurrent [Roll Forward]
Balance as of beginning of fiscal year	7.3
Recognized in current year	24.2	0.7
Amounts in beginning balance reclassified to revenue	(1.1)	(1)
Current year amounts reclassified to revenue	0	0
Other	0	0
Reclassification to/from short-term	(4.5)	(14.6)
Balance as of period end	$ 25.9	$ 7.3

Inventories Narrative (Details)

Inventories Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Inventory [Line Items]
LIFO inventory amount	$ 776.1	$ 794.3
Inventory valuation reserves	(104.1)	(88.5)
Effect of LIFO liquidation on income	(1.8)	0.8	$ (4.6)
Inventories, net	1,155.3	1,211.1
Inventory valuation charges due to market-based valuation			$ 17.7
Adjustment from current cost to LIFO cost basis	33.6	2.9
ASU 2014-09 | Transferred over Time
Inventory [Line Items]
Inventories, net		5.4
Net Realizable Value Reserve
Inventory [Line Items]
Inventory valuation reserves	(33.6)	$ (8)
Forged Products
Inventory [Line Items]
Adjustment from current cost to LIFO cost basis	$ 5.2

Inventories Schedule of Invento

Inventories Schedule of Inventory (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Inventory, Gross [Abstract]
Raw materials and supplies	$ 164.9	$ 191.5
Work-in-process	899.6	914.1
Finished goods	161.3	191.1
Total inventories at current cost	1,225.8	1,296.7
Adjustment from current cost to LIFO cost basis	33.6	2.9
Inventory valuation reserves	(104.1)	(88.5)
Progress payments	0	0
Total inventories, net	$ 1,155.3	$ 1,211.1

Inventories Schedule of Inven_2

Inventories Schedule of Inventory Valuation Impact on Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
LIFO benefit (charge)	$ 25.5	$ (28.6)	$ (54.2)
NRV benefit (charge)	(25.6)	27.9	54
Net cost of sales impact	$ (0.1)	$ (0.7)	$ (0.2)

Property, Plant and Equipment_2

Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment Details [Abstract]
Land	$ 34.6	$ 31.5
Buildings	832.7	851.7
Equipment and leasehold improvements	3,671.3	3,622.7
Property plant and equipment, gross	4,538.6	4,505.9
Accumulated depreciation and amortization	(2,088.5)	(2,030.9)
Property, plant and equipment, net	2,450.1	2,475
Construction in progress	177.3	83.7
Depreciation, Depletion and Amortization [Abstract]
Software and other amortization	9.5	10	$ 10
Total depreciation and amortization	151.1	156.4	160.8
Operating Segments
Depreciation, Depletion and Amortization [Abstract]
Depreciation of property, plant and equipment	127.1	131.9	135.2
Software and other amortization	24	24.5	25.6
Total depreciation and amortization	$ 151.1	$ 156.4	$ 160.8

Goodwill and Other Intangible_3

Goodwill and Other Intangible Assets - Goodwill (Details) - USD ($)	Jul. 12, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 03, 2019	Dec. 31, 2016
Goodwill [Line Items]
Goodwill		$ 525,800,000	$ 534,700,000
Period increase (decrease) in goodwill		(8,900,000)
Impairment of goodwill		0	0	$ (114,400,000)
Accumulated goodwill impairment		241,000,000	241,000,000	241,000,000
Addaero Manufacturing [Member]
Goodwill [Line Items]
Goodwill			6,000,000
Payments to Acquire Businesses, Gross	$ 10,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles			$ 2,000,000
High Performance Materials & Components
Goodwill [Line Items]
Goodwill		525,800,000
Impairment of goodwill		0		$ (114,400,000)
Goodwill, Foreign Currency Translation Gain (Loss)		1,500,000
High Performance Materials & Components | First Reporting Unit [Member]
Goodwill [Line Items]
Percentage of fair value in excess of carrying value						12.00%
Forged Products
Goodwill [Line Items]
Goodwill		$ (10,400,000)			$ 10,400,000

Goodwill and Other Intangible_4

Goodwill and Other Intangible Assets - Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets	$ 9.5	$ 10	$ 10
Gross carrying amount	156.2	193.7
Accumulated amortization	(59.9)	(64)
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2020	8
2021	8
2022	8
2023	8
2024	8
Accumulated goodwill impairment	241	241	$ 241
Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	76.8	93.4
Accumulated amortization	(29.7)	(31.9)
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	27	35.7
Accumulated amortization	(9.3)	(10.6)
Trademarks [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	52.4	64.6
Accumulated amortization	(20.9)	$ (21.5)
Cast Products
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Period Increase (Decrease)	(23.8)
Gross carrying amount	33.2
Accumulated amortization	(12.7)
Cast Products, Salem Oregon
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	4.3
Accumulated amortization	$ (1)

Divestitures - Narrative (Detai

Divestitures - Narrative (Details) $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Jul. 22, 2019USD ($)	Jun. 03, 2019USD ($)facility
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of facilities sold | facility							2
Proceeds from sale of business, net of transaction costs			$ 158.1	$ 0	$ 0
Goodwill			525.8	534.7
Gain (loss) on disposal			(1.8)	0	$ 0
Forged Products
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received							$ 37
Proceeds from sale of business, net of transaction costs			33
Goodwill			(10.4)				$ 10.4
Gain (loss) on disposal		$ (7.7)	(8.1)
Prior year revenue from facilities sold				86
Cast Products
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received						$ 127
Proceeds from sale of business, net of transaction costs			125.1
Gain (loss) on disposal	$ 6.2		6.2
Prior year revenue from facilities sold				$ 105
Other asset impairment charges			10.2
Property, Plant and Equipment | Cast Products
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other asset impairment charges			4.5
Right of use assets, operating leases [Member] | Cast Products
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other asset impairment charges			1.4
Right of use assets, finance leases [Member] | Cast Products
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other asset impairment charges			1
Finite-Lived Intangible Assets [Member] | Cast Products
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other asset impairment charges			$ 3.3

Joint Ventures (Details)

Joint Ventures (Details) - USD ($) $ in Millions	3 Months Ended		10 Months Ended	12 Months Ended			34 Months Ended
	Dec. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2020	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Sale to noncontrolling interest				$ 0	$ 14.4	$ 3.7
Gain on joint venture deconsolidation		$ 15.9		0	15.9	0
Cash and cash equivalents	$ 490.8		$ 382	490.8	382	141.6		$ 229.6
Income (loss) from equity method investments				(10.7)	(1)	0
Intercompany notes receivable	0		0	0	0
Undistributed earnings of investees accounted for under equity method	14.5			14.5
Non-cash joint venture impairment charge	11.4			11.4	0	0
Shanghai STAL Precision Stainless Steel Co Ltd [Member]
Schedule of Equity Method Investments [Line Items]
Cash and cash equivalents	22.9			22.9
Next Gen Alloys LLC [Member]
Schedule of Equity Method Investments [Line Items]
Sale to noncontrolling interest					2.7
Cash and cash equivalents	$ 9.9			$ 9.9
Allegheny & Tsingshan Stainless
Schedule of Equity Method Investments [Line Items]
Equity method investment ownership percentage	50.00%			50.00%
Impairment of long-lived assets held-for-use				$ 14.2
Income (loss) from equity method investments				(19.3)	(3.9)
Revenue from related parties				14.6	4.1
Related party accounts receivable	$ 0.1		0.6	0.1	0.6
Due from affiliates, allowance for credit loss	$ 4.3			4.3
Non-cash joint venture impairment charge				$ 11.4
Uniti [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment ownership percentage	50.00%			50.00%
Revenue from related parties				$ 31.3	49.4	38.6
Related party accounts receivable	$ 0.2		1.8	0.2	1.8
Advanced Alloys & Solutions | Allegheny & Tsingshan Stainless
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments				(12.2)
Due from affiliates	36.8		10.5	36.8	10.5
Advanced Alloys & Solutions | Uniti [Member]
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments				1.5	2.9	$ 0.6
Prepaid expenses and other current assets [Member] | Advanced Alloys & Solutions | Allegheny & Tsingshan Stainless
Schedule of Equity Method Investments [Line Items]
Due from affiliates	8.3			8.3
Other Noncurrent Assets [Member] | Advanced Alloys & Solutions | Allegheny & Tsingshan Stainless
Schedule of Equity Method Investments [Line Items]
Due from affiliates	$ 28.5		10.5	$ 28.5	$ 10.5
Allegheny Technologies Inc | Shanghai STAL Precision Stainless Steel Co Ltd [Member]
Schedule of Equity Method Investments [Line Items]
Joint venture ownership percentage	60.00%			60.00%
Allegheny Technologies Inc | Next Gen Alloys LLC [Member]
Schedule of Equity Method Investments [Line Items]
Joint venture ownership percentage	51.00%			51.00%
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	40.00%			40.00%
Allegheny Technologies Inc | VSMPO [Member] | Uniti [Member]
Schedule of Equity Method Investments [Line Items]
Joint venture ownership percentage by unaffiliated entity	50.00%			50.00%
Property, Plant and Equipment | Allegheny & Tsingshan Stainless
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments				$ (7.1)
Tsingshan Group | Allegheny & Tsingshan Stainless
Schedule of Equity Method Investments [Line Items]
Sale to noncontrolling interest			$ 12
Equity method investment ownership percentage	50.00%			50.00%
Forecast [Member] | Tsingshan Group | Allegheny & Tsingshan Stainless
Schedule of Equity Method Investments [Line Items]
Sale to noncontrolling interest							$ 17.5

Asset Retirement Obligations (D

Asset Retirement Obligations (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Asset retirement obligation	$ 23.7	$ 23.1	$ 23.5

Asset Retirement Obligations -

Asset Retirement Obligations - Change in Asset Retirement Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Asset Retirement Obligation Disclosure [Abstract]
Balance at beginning of year	$ 23.1	$ 23.5
Accretion expense	0.9	0.8
Payments	(0.3)	(1.2)
Balance at end of year	$ 23.7	$ 23.1

Supplemental Financial Statem_3

Supplemental Financial Statement Information - Cash and Cash Equivalents (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Abstract]
Cash	$ 190.8	$ 264.4
Other short-term investments	300	117.6
Total cash and cash equivalents	$ 490.8	$ 382	$ 141.6	$ 229.6

Supplemental Financial Statem_4

Supplemental Financial Statement Information - Accrued Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Additional Financial Information Disclosure [Abstract]
Accrued salaries, wages and payroll liabilities	$ 94.5	$ 95.8
Accrued interest	$ 25	$ 36.6

Supplemental Financial Statem_5

Supplemental Financial Statement Information - Other Non-operating Income (Expense) (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other Nonoperating Income (Expense) [Abstract]
Rent, royalty income and other income					$ 2.9	$ 3.1	$ 3.5
Gains from disposal of property, plant and equipment, net					90.7	1.3	0.5
Income (loss) from equity method investments					(10.7)	(1)	0
Loss on sale of businesses, net					(1.9)	0	0
Gain on joint venture deconsolidation				$ 15.9	0	15.9	0
Non-cash joint venture impairment charge	$ (11.4)				(11.4)	0	0
Other					0.1	1.2	0
Other income, net					69.7	$ 20.5	$ 4
Gain from sale of certain oil and gas rights		$ 62.4	$ 29.3		$ 91.7

Debt - Schedule of Debt (Detail

Debt - Schedule of Debt (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2016	Feb. 15, 2016	Dec. 31, 2013
Debt Instrument [Line Items]
Debt Issuance Costs, Net		$ 12.3	$ 10.4
Total short-term and long-term debt		1,398.9	1,542.1
Short-term debt and current portion of long-term debt		11.5	6.6
Total long-term debt		$ 1,387.4	$ 1,535.5
Allegheny Technologies $500 million 5.875% Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Debt instrument issuer	[1]	Allegheny Technologies	Allegheny Technologies
Debt instrument interest rate stated percentage					7.875%	5.875%
Debt instrument carrying amount		$ 500	$ 500
Allegheny Technologies $500 million 5.95% Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Debt instrument issuer			Allegheny Technologies
Debt instrument interest rate stated percentage			5.95%
Debt instrument carrying amount		$ 0	$ 500
Allegheny Technologies $350 million 5.875% Senior Notes due 2027
Debt Instrument [Line Items]
Debt instrument issuer		Allegheny Technologies
Debt instrument interest rate stated percentage		5.875%
Debt instrument carrying amount		$ 350	$ 0
Allegheny Technologies $350 million 9.375% Senior Notes due 2019
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage				9.375%
Debt instrument carrying amount				$ 350
Allegheny Technologies, $287.5 million Convertible Senior Notes, 4.75%, Due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument issuer		Allegheny Technologies	Allegheny Technologies
Debt instrument interest rate stated percentage		4.75%	4.75%
Debt instrument carrying amount		$ 287.5	$ 287.5
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	$ 150
Term Loan due 2024
Debt Instrument [Line Items]
Debt instrument issuer		Allegheny Technologies	Allegheny Technologies
Debt instrument interest rate stated percentage		4.21%
Debt instrument carrying amount		$ 100	$ 100
Domestic Bank Group $500 million asset-based credit facility [Member]
Debt Instrument [Line Items]
Debt instrument carrying amount		0	0
Finance leases and other [Member]
Debt Instrument [Line Items]
Debt instrument carrying amount		18.8	15
Foreign credit agreements [Member]
Debt Instrument [Line Items]
Debt instrument carrying amount		$ 4.9	$ 0
Maximum | Allegheny Technologies $500 million 5.875% Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage		7.875%
London Interbank Offered Rate (LIBOR) [Member] | Term Loan due 2024
Debt Instrument [Line Items]
Variable rate spread		2.00%
Revolving Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum | Domestic Bank Group $500 million asset-based credit facility [Member]
Debt Instrument [Line Items]
Variable rate spread		1.25%
Revolving Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum | Domestic Bank Group $500 million asset-based credit facility [Member]
Debt Instrument [Line Items]
Variable rate spread		1.75%
[1]	Bearing interest at 7.875% effective February 15, 2016.

Debt - Narrative (Details)

Debt - Narrative (Details)	Jun. 02, 2016$ / shares	Dec. 31, 2019USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2024USD ($)	Jun. 30, 2020USD ($)	Dec. 31, 2016USD ($)	May 24, 2016USD ($)	Feb. 15, 2016	Dec. 31, 2013
Interest Costs Incurred [Abstract]
Interest expense			$ 104,900,000	$ 102,100,000	$ 134,900,000
Interest costs capitalized			4,700,000	4,100,000	2,600,000
Interest costs paid			105,700,000	102,600,000	133,800,000
Interest income			5,900,000	1,100,000	1,100,000
Long-term Debt, Fiscal Year Maturity [Abstract]
2020		$ 11,500,000	11,500,000
2021		4,800,000	4,800,000
2022		291,500,000	291,500,000
2023		502,700,000	502,700,000
2024		100,700,000	100,700,000
Debt Instrument [Line Items]
Payments of debt issuance costs			5,500,000	0	800,000
Debt extinguishment charge		21,600,000	21,600,000	0	37,000,000
Payment for Debt Extinguishment or Debt Prepayment Cost			20,900,000	0	35,800,000
Write off of Deferred Debt Issuance Cost			$ 700,000		$ 1,200,000
Allegheny Technologies $500 million 5.875% Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage										7.875%	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			2.00%
Debt instrument carrying amount		$ 500,000,000	$ 500,000,000	500,000,000
Allegheny Technologies $500 million 5.875% Senior Notes due 2023 [Member] | Maximum
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage		7.875%	7.875%
Domestic Bank Group $500 million asset-based credit facility [Member]
Debt Instrument [Line Items]
Debt instrument carrying amount		$ 0	$ 0	0
Line of credit facility amount outstanding		$ 35,300,000	$ 35,300,000
Average outstanding amount				$ 43,000,000
Interest rate during period				3.70%
Term Loan due 2024
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage		4.21%	4.21%
Debt instrument carrying amount		$ 100,000,000	$ 100,000,000	$ 100,000,000
Debt Instrument, Prepayment Increments, Minimum			$ 25,000,000
Term Loan due 2024 | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Variable rate spread			2.00%
Allegheny Technologies $500 million 5.95% Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage				5.95%
Debt instrument carrying amount		$ 0	$ 0	$ 500,000,000
Allegheny Technologies, Convertible Senior Notes, 4.75%, Due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage		4.75%	4.75%	4.75%
Debt instrument carrying amount		$ 287,500,000	$ 287,500,000	$ 287,500,000
Allegheny Technologies, Convertible Senior Notes, 4.75%, Due 2022 [Member] | Convertible Debt [Member]
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage		4.75%	4.75%
Long-term debt									$ 287,500,000
Convertible debt conversion rate in shares of stock	0.0692042
Number of equity instruments issuable	19,900,000
Conversion price of convertible notes | $ / shares	$ 14.45
Allegheny Technologies $350 million 9.375% Senior Notes due 2019
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage								9.375%
Debt instrument carrying amount								$ 350,000,000
Allegheny Technologies $350 million 5.875% Senior Notes due 2027
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage		5.875%	5.875%
Proceeds from Issuance of Debt			$ 344,500,000
Debt instrument carrying amount		$ 350,000,000	350,000,000	0
STAL Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit maximum borrowing capacity		20,000,000	20,000,000
Revolving Credit Facility [Member] | Domestic Bank Group $500 million asset-based credit facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Increase to Maximum Borrowing Capacity		100,000,000	100,000,000
Line of credit maximum borrowing capacity		$ 500,000,000	500,000,000
Payments of debt issuance costs			$ 2,200,000	$ 2,100,000
Fixed charge coverage ratio		1	1
Remaining borrowing capacity, percent of minimum borrowing capacity		12.50%	12.50%
Minimum remaining borrowing capacity		$ 62,500,000	$ 62,500,000
Revolving Credit Facility [Member] | Domestic Bank Group $500 million asset-based credit facility [Member] | Minimum | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Variable rate spread			1.25%
Revolving Credit Facility [Member] | Domestic Bank Group $500 million asset-based credit facility [Member] | Minimum | Base Rate [Member]
Debt Instrument [Line Items]
Variable rate spread			0.25%
Revolving Credit Facility [Member] | Domestic Bank Group $500 million asset-based credit facility [Member] | Maximum | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Variable rate spread			1.75%
Revolving Credit Facility [Member] | Domestic Bank Group $500 million asset-based credit facility [Member] | Maximum | Base Rate [Member]
Debt Instrument [Line Items]
Variable rate spread			0.75%
Letter of Credit [Member] | Domestic Bank Group $500 million asset-based credit facility [Member]
Debt Instrument [Line Items]
Line of credit maximum borrowing capacity		200,000,000	$ 200,000,000
Interest Rate Swap [Member] | Term Loan due 2024
Debt Instrument [Line Items]
Derivative notional amount		$ 50,000,000	$ 50,000,000
Forecast [Member] | Delayed-Draw Term Loan [Member]
Debt Instrument [Line Items]
Line of credit maximum borrowing capacity							$ 100,000,000
Forecast [Member] | Revolving Credit Facility [Member] | Domestic Bank Group $500 million asset-based credit facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Increase to Maximum Borrowing Capacity						$ 200,000,000
Allegheny Technologies Inc | STAL Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Joint venture ownership percentage		60.00%	60.00%

Leases - Narrative (Details)

Leases - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2020	Dec. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liabilities				$ 77.7
Operating leases, rent expense	$ 24.4	$ 21.1
Progress payments made on behalf of company, paid				$ 5.3
Progress payments made on behalf of company, scheduled to be paid			$ 8.2
ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset					$ 51.7
Operating lease liabilities					55.6
Operating lease, liability, current					12.5
Operating lease, liability, noncurrent					$ 43.1
Forecast [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lessee, finance lease, lease not yet commenced, right-of-use asset to be recognized			13.5
Lessee, finance lease, lease not yet commenced, liability to be recognized			$ 13.5

Leases - Schedule of Lease Cost

Leases - Schedule of Lease Cost Components (Details) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2019USD ($)
Finance Lease Cost:
Amortization of right of use asset		$ 1.7
Interest on lease liabilities		0.5
Operating lease cost		20.5
Short-term lease cost		3.1
Variable lease cost		0.8
Sublease income		0
Total lease cost		26.6
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from finance leases		0.5
Operating cash flows from operating leases		20.8
Financing cash flows from finance leases		2.4
Right of use assets obtained in exchange for new finance lease liabilities		14.1
Right of use assets obtained in exchange for new operating lease liabilities		$ 35.9
Weighted average remaining lease term - finance leases	4 years	4 years
Weighted average remaining lease term - operating leases	6 years	6 years
Weighted average discount rate - finance leases	5.30%	5.30%
Weighted average discount rate - operating leases	7.00%	7.00%
Operating lease liability, lease renewal reasonably certain	$ 77.7	$ 77.7
Renewal Option Determined As Reasonably Certain
Cash paid for amounts included in the measurement of lease liabilities
Right of use assets obtained in exchange for new operating lease liabilities	10.2
Operating lease liability, lease renewal reasonably certain	$ 10.2	$ 10.2

Leases - Schedule of Operating

Leases - Schedule of Operating Lease Liability Maturities (Details) $ in Millions	Dec. 31, 2019USD ($)
Leases [Abstract]
2020	$ 20
2021	18.2
2022	15.3
2023	11.7
2024	8
2025 and thereafter	24.6
Total undiscounted lease payments	97.8
Present value adjustment	(20.1)
Operating lease liabilities	$ 77.7

Leases - Schedule of Finance Le

Leases - Schedule of Finance Lease Liability Maturities (Details) $ in Millions	Dec. 31, 2019USD ($)
Leases [Abstract]
2020	$ 4.5
2021	4.2
2022	3.9
2023	2.7
2024	0.7
2025 and thereafter	0
Total undiscounted lease payments	16
Present value adjustment	(1.5)
Finance lease liabilities	$ 14.5

Derivative Financial Instrume_3

Derivative Financial Instruments and Hedging - Narrative (Details) € in Millions, lb in Millions, $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2019USD ($)lb	Dec. 31, 2017USD ($)	Dec. 31, 2015EUR (€)	Dec. 31, 2019EUR (€)
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Percentage of estimated annual nickel requirements		7.00%
Derivative [Line Items]
Tax expense for the recognition of a stranded deferred tax balance arising from deferred tax valuation allowances that was associated with a cash flow hedge portfolio	$ 6
Pre-tax cash flow hedge gain (loss) to be reclassified within twelve months		$ (0.9)
Nickel [Member]
Derivative [Line Items]
Derivative notional amount (in pounds of nickel) | lb		7
Cash Flow Hedging [Member] | Natural gas contracts [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Percentage of forecasted natural gas usage hedged for 2021		50.00%
Percentage Of Forecasted Natural Gas Usage Hedged for 2020		70.00%
Cash Flow Hedging [Member] | Foreign Exchange Forward [Member] | Designated as Hedging Instrument [Member] | Maturity Dates Through 2020 [Member]
Derivative [Line Items]
Derivative notional amount | €					€ 2
Fair Value Hedging [Member] | Foreign Exchange Forward [Member] | Designated as Hedging Instrument [Member] | Maturity Dates Through 2017 [Member]
Derivative [Line Items]
Notional amount of derivatives entered during period | €				€ 244.7
Cost of Sales [Member] | Fair Value Hedging [Member] | Foreign Exchange Forward [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Gain (loss) on derivatives			$ 2.7
Term Loan due 2024
Derivative [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.21%	4.21%			4.21%
Term Loan due 2024 | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative notional amount	$ 50	$ 50

Derivative Financial Instrume_4

Derivative Financial Instruments and Hedging - Schedule of Derivative Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	$ 5.6	$ 3.4
Fair value of derivative liability	7.5	10.4
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	5.6	3
Fair value of derivative liability	7.5	10.4
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	0	0.4
Foreign Exchange Contract [Member] | Designated as Hedging Instrument [Member] | Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liability	0	0.6
Foreign Exchange Contract [Member] | Not Designated as Hedging Instrument [Member] | Prepaid expenses and other current assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	0	0.4
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liability	0.3	0.2
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liability	1.2	0.3
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	4.4	1.2
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	1.2	0.8
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	2.5	6.8
Nickel and other raw material contracts [Member] | Designated as Hedging Instrument [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liability	0	2.1
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	0	0.8
Natural gas contracts [Member] | Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	0	0.2
Natural gas contracts [Member] | Designated as Hedging Instrument [Member] | Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liability	2.5	0.1
Natural gas contracts [Member] | Designated as Hedging Instrument [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liability	$ 1	$ 0.3

Derivative Financial Instrume_5

Derivative Financial Instruments and Hedging - Schedule of Derivative Instruments Gain (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI on Derivatives	$ 9.7	$ (6.4)	$ 14.3
Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI on Derivatives	7.4	(4.9)
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 (Effective Portion)	3.1	8.9
Nickel and other raw material contracts [Member] | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI on Derivatives	11.3	(6.4)
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 (Effective Portion)	3.9	7.7
Natural gas contracts [Member] | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI on Derivatives	(4)	1.5
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 (Effective Portion)	(0.9)	0.4
Foreign Exchange Contract [Member] | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI on Derivatives	1	0.5
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 (Effective Portion)	0.5	1
Interest Rate Swap [Member] | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in OCI on Derivatives	(0.9)	(0.5)
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 (Effective Portion)	$ (0.4)	$ (0.2)

Derivative Financial Instrume_6

Derivative Financial Instruments and Hedging - Schedule of Derivatives Not Designated as Hedging Instruments Gain (Loss) (Details) - Not Designated as Hedging Instrument [Member] € in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2019EUR (€)
Foreign Exchange Forward [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative notional amount | €			€ 0
Foreign Exchange Contract [Member] | Cost of Sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives | $	$ 0.1	$ 0.3

Fair Value of Financial Instr_3

Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
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	$ 490.8	$ 382
Derivative financial instruments: Assets	0	0
Derivative financial instruments: Liabilities	0	0
Debt	1,552.8	1,624.4
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	5.6	3.4
Derivative financial instruments: Liabilities	7.5	10.4
Debt	123.7	115
Total Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	490.8	382
Derivative financial instruments: Assets	5.6	3.4
Derivative financial instruments: Liabilities	7.5	10.4
Debt	1,411.2	1,552.5
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	490.8	382
Derivative financial instruments: Assets	5.6	3.4
Derivative financial instruments: Liabilities	7.5	10.4
Debt	$ 1,676.5	$ 1,739.4

Fair Value Of Financial Instr_4

Fair Value Of Financial Instruments - Narrative (Details)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2016	Feb. 15, 2016	Dec. 31, 2013
Allegheny Technologies $350 million 9.375% Senior Notes due 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument interest rate stated percentage			9.375%
Allegheny Technologies $500 million 5.95% Senior Notes due 2021 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument interest rate stated percentage		5.95%
Allegheny Technologies, 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%	4.75%
Allegheny Technologies $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				7.875%	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] | Allegheny Technologies, 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, 2020	Dec. 31, 2019USD ($)employee	Dec. 31, 2018USD ($)employee	Dec. 31, 2017USD ($)	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Projected Retirement Benefit Expense In Next 12 months		$ 60
Defined Contribution Plan, Cost		$ 44.8	$ 39.9	$ 35.5
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate		4.35%	3.80%	4.35%
Curtailment loss		$ 0	$ 0	$ 0
Employer contributions		0	0
Projected Retirement Benefit Expense In Next 12 months		20
Defined Contribution Plan, Cost		$ 1	$ 1	$ 1.7
Assumed increase in per capita cost of covered benefits in next 12 months		6.00%
Assumed ultimate health care cost trend rate		4.50%
Expected long-term rate of return on assets		4.00%	4.00%	4.00%
Fair value of plan assets		$ 0.1	$ 0.1	$ 0.6
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate		4.40%	3.85%	4.45%
Curtailment loss		$ 0	$ (0.4)	$ 0
Employer contributions		153.4	49.3
Projected Retirement Benefit Expense In Next 12 months		40
Accumulated benefit obligation		$ 2,621.1	$ 2,482.5
Expected long-term rate of return on assets		7.52%	7.75%	7.75%
Actual return on plan assets		15.10%	(4.80%)	16.90%	5.30%	(1.20%)
Fair value of plan assets		$ 1,902.1	$ 1,772.2	$ 2,129.6
Defined Benefit Plan, Weighted Average Life Expectancy		18 years
Pension Benefits [Member] | Global debt securities and cash [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unfunded commitments		$ 46
Pension Benefits [Member] | Private equity [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unfunded commitments		91
Fair value of plan assets		129	137.1
Pension Benefits [Member] | Hedge funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		263.9	258.3
Pension Benefits [Member] | Real estate and other [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unfunded commitments		51
Fair value of plan assets		37.8	52.7
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] | Fair Value, Inputs, Level 3 [Member] | Hedge funds [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] | Real estate and other [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 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected long-term rate of return on assets	7.16%
Pension Benefits [Member] | MultiemployerPlan1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percent of Current Year Contributions to Plan that Company Contributions Exceed			5.00%
Pension Benefits [Member] | Nonqualified and U.K. [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated employer contributions in next 12 months		$ 9
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		1,300
Defined Benefit Plan, Percent Of Employees accruing benefit service		10.00%
Employer contributions		$ 145	$ 40	$ 135
Estimated employer contributions in next 12 months		$ 130
Percentage of total assets		90.00%
Small annuity buy out [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits paid		$ 96	$ 97
Small annuity buy out [Member] | Pension Benefits [Member] | United States
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of participants | employee		1,800	3,700
Percent of U.S. employees as participants		10.00%	17.00%

Retirement Benefits (Details 1)

Retirement Benefits (Details 1) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Cost	$ 44.8	$ 39.9	$ 35.5
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan curtailments	0	0.4
Service cost - benefits earned during the year	12.7	16.4	14.1
Interest cost on benefits earned in prior years	105.5	104.8	116.7
Expected return on plan assets	(131.3)	(157.9)	(146.9)
Amortization of prior service cost (credit)	0.3	0.3	1.3
Amortization of net actuarial loss	73.7	65.9	62.6
Curtailment loss	0	0.4	0
Total retirement benefit expense	60.9	29.9	47.8
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Plan curtailments	0	0
Defined Contribution Plan, Cost	1	1	1.7
Service cost - benefits earned during the year	1.9	2.5	2.4
Interest cost on benefits earned in prior years	14.8	12.7	14.6
Expected return on plan assets	0	0	0
Amortization of prior service cost (credit)	(2.9)	(2.9)	(2.9)
Amortization of net actuarial loss	13.5	10.6	9
Curtailment loss	0	0	0
Total retirement benefit expense	$ 27.3	$ 22.9	$ 23.1

Retirement Benefits (Details 2)

Retirement Benefits (Details 2)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.40%	3.85%	4.45%
Expected long-term rate of return on assets	7.52%	7.75%	7.75%
Pension Benefits [Member] | Minimum
Defined Benefit Plan Disclosure [Line Items]
Rate of increase in future compensation levels	0.50%	0.50%	0.50%
Pension Benefits [Member] | Maximum
Defined Benefit Plan Disclosure [Line Items]
Rate of increase in future compensation levels	1.00%	1.00%	1.00%
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.35%	3.80%	4.35%
Rate of increase in future compensation levels	0.00%	0.00%	0.00%
Expected long-term rate of return on assets	4.00%	4.00%	4.00%

Retirement Benefits (Details 3)

Retirement Benefits (Details 3)	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.40%	4.40%
Pension Benefits [Member] | Minimum
Defined Benefit Plan Disclosure [Line Items]
Rate of increase in future compensation levels	0.50%	0.50%
Pension Benefits [Member] | Maximum
Defined Benefit Plan Disclosure [Line Items]
Rate of increase in future compensation levels	1.00%	1.00%
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.25%	4.35%
Rate of increase in future compensation levels	0.00%	0.00%

Retirement Benefits (Details 4)

Retirement Benefits (Details 4) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	$ 2,497.7	$ 2,829.8
Service cost	12.7	16.4	$ 14.1
Interest cost	105.5	104.8	116.7
Benefits paid	(274.6)	(294.5)
Subsidy paid	0	0
Effect of currency rates	2.8	(4.5)
Net actuarial (gains) losses - discount rate change	266	(150.4)
Net actuarial (gains) losses - other	14.3	(5.7)
Plan curtailments	0	0.4
Plan amendments	9.5	1.4
Benefit obligation at end of year	2,633.9	2,497.7	2,829.8
Other Postretirement Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	359.1	349.9
Service cost	1.9	2.5	2.4
Interest cost	14.8	12.7	14.6
Benefits paid	(37.7)	(36.5)
Subsidy paid	0	0
Effect of currency rates	0	0
Net actuarial (gains) losses - discount rate change	30.5	(17.8)
Net actuarial (gains) losses - other	(18.1)	48.3
Plan curtailments	0	0
Plan amendments	(5.2)	0
Benefit obligation at end of year	$ 345.3	$ 359.1	$ 349.9

Retirement Benefits (Details 5)

Retirement Benefits (Details 5) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	$ 1,772.2	$ 2,129.6
Actual returns on plan assets and plan expenses	248.2	(107.2)
Employer contributions	153.4	49.3
Effect of currency rates	2.9	(5)
Benefits paid	(274.6)	(294.5)
Fair value of plan assets at end of year	1,902.1	1,772.2
Other Postretirement Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	0.1	0.6
Actual returns on plan assets and plan expenses	0	(0.5)
Employer contributions	0	0
Effect of currency rates	0	0
Benefits paid	0	0
Fair value of plan assets at end of year	$ 0.1	$ 0.1

Retirement Benefits (Details 6)

Retirement Benefits (Details 6) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	$ 4.8	$ 9.2
Current liabilities	(5.1)	(4.7)
Noncurrent liabilities	(731.5)	(730)
Total amount recognized	(731.8)	(725.5)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	0	0
Current liabilities	(32.7)	(40.6)
Noncurrent liabilities	(312.5)	(318.4)
Total amount recognized	$ (345.2)	$ (359)

Retirement Benefits (Details 7)

Retirement Benefits (Details 7) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Amortization of net actuarial loss	$ 87.2	$ 76.5	$ 71.6
Amortization to net income (loss) of net prior service cost (credits)	(2.6)	(2.6)	(1.6)
Net loss arising during the period	(180.5)	(141.4)	(42.7)
Pension Benefits [Member]
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Beginning of year accumulated other comprehensive loss	(1,470.3)	(1,426.1)
Amortization of net actuarial loss	73.7	65.9
Amortization to net income (loss) of net prior service cost (credits)	0.3	0.3
Net loss arising during the period	(173.4)	(110.4)
End of year accumulated other comprehensive loss	(1,569.7)	(1,470.3)	(1,426.1)
Net change in accumulated other comprehensive loss	(99.4)	(44.2)
Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Beginning of year accumulated other comprehensive loss	(107)	(83.7)
Amortization of net actuarial loss	13.5	10.6
Amortization to net income (loss) of net prior service cost (credits)	(2.9)	(2.9)
Net loss arising during the period	(7.1)	(31)
End of year accumulated other comprehensive loss	(103.5)	(107)	$ (83.7)
Net change in accumulated other comprehensive loss	$ 3.5	$ (23.3)

Retirement Benefits (Details 8)

Retirement Benefits (Details 8) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service (cost) credit	$ (11.2)	$ (2.1)
Net actuarial loss	(1,558.5)	(1,468.2)
Accumulated other comprehensive loss	(1,569.7)	(1,470.3)	$ (1,426.1)
Deferred tax effect	555.7	536.2
Accumulated other comprehensive loss, net of tax	(1,014)	(934.1)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Prior service (cost) credit	11	8.8
Net actuarial loss	(114.5)	(115.8)
Accumulated other comprehensive loss	(103.5)	(107)	$ (83.7)
Deferred tax effect	34.4	35.3
Accumulated other comprehensive loss, net of tax	$ (69.1)	$ (71.7)

Retirement Benefits (Details 9)

Retirement Benefits (Details 9) $ in Millions	Dec. 31, 2019USD ($)
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service cost (credit)	$ (3.2)
Amortization of net actuarial loss	85.3
Amortization of accumulated other comprehensive loss	82.1
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service cost (credit)	0.6
Amortization of net actuarial loss	74.5
Amortization of accumulated other comprehensive loss	75.1
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service cost (credit)	(3.8)
Amortization of net actuarial loss	10.8
Amortization of accumulated other comprehensive loss	$ 7

Retirement Benefits (Details 10

Retirement Benefits (Details 10) - Pension Benefits [Member] - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 2,538.9	$ 2,420.8
Accumulated benefit obligation	2,526.1	2,405.6
Fair value of plan assets	$ 1,802.4	$ 1,686.1

Retirement Benefits (Details 14

Retirement Benefits (Details 14) $ in Millions	Dec. 31, 2019USD ($)
Pension Benefits [Member]
Defined Benefit Plan Expected Future Benefit Payments [Abstract]
2020	$ 174.7
2021	172
2022	170.3
2023	168.3
2024	166
2025-2029	786.5
Other Postretirement Benefits
Defined Benefit Plan Expected Future Benefit Payments [Abstract]
2020	32.8
2021	34.1
2022	31.6
2023	29.4
2024	27.4
2025-2029	110.1
Medicare Part D Subsidy [Abstract]
2020	0.3
2021	0.3
2022	0.2
2023	0.2
2024	0.2
2025-2029	$ 0.7

Retirement Benefits (Details 11

Retirement Benefits (Details 11) - Pension Benefits [Member] - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 1,902.1	$ 1,772.2	$ 2,129.6
NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,455.9	1,189.5
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	274.1	212.2
Significant Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	172.1	370.5
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	443.6	362.9
Equity Securities: Other U.S. equities [Member] | NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	254.7	219.9
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	188.9	143
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	326.1	377.4
Equity Securities: International equities [Member] | NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	299.6	335.7
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	26.5	41.7
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	650.7	493.7
Fixed income and cash equivalents [Member] | NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	419.9	116.9
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	58.7	6.3
Fixed income and cash equivalents [Member] | Significant Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	172.1	370.5
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
Floating rate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	51	90.1
Floating rate [Member] | NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	51	68.9
Floating rate [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	21.2
Floating rate [Member] | Significant Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Floating rate [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	129	137.1
Private equity [Member] | NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	129	137.1
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
Hedge funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	263.9	258.3
Hedge funds [Member] | NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	263.9	258.3
Hedge funds [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
Hedge funds [Member] | Significant Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Hedge funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Real estate and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	37.8	52.7
Real estate and other [Member] | NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	37.8	52.7
Real estate and other [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
Real estate and other [Member] | Significant Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Real estate and other [Member] | 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, 2019
Minimum | Equity Securities: Other U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	.18
Minimum | Global Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	.10
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 | Hedge funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	.10
Minimum | Real estate and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	0
Maximum | Equity Securities: Other U.S. equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	.40
Maximum | Global Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	.3
Maximum | Global debt securities and cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	.4
Maximum | Private equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	.15
Maximum | Hedge funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	.2
Maximum | Real estate and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	0.1

Retirement Benefits (Details 17

Retirement Benefits (Details 17) - Pension Benefits [Member] - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Multiemployer Plan Disclosure [Line Items]
Company Contributions		$ 5.6	$ 5.4	$ 4.5
Steelworkers Western Independent Shops Pension Plan [Member]
Multiemployer Plan Disclosure [Line Items]
Pension Plan Number		001
Pension Protection Act Zone Status		Green	Green
FIP / RP Status Pending / Implemented	[1]	NA
Company Contributions		$ 0.9	$ 0.8	0.6
Surcharge Imposed		No
Expiration Dates of Collective Bargaining Agreements		Feb. 29, 2020
Boilermakers-Blacksmiths National Pension Trust [Member]
Multiemployer Plan Disclosure [Line Items]
Pension Plan Number		001
Pension Protection Act Zone Status		Red	Yellow
FIP / RP Status Pending / Implemented	[1]	Implemented
Company Contributions		$ 2.5	$ 2.5	2.2
Surcharge Imposed		No
Expiration Dates of Collective Bargaining Agreements		Sep. 30, 2026
IAM National Pension Fund [Member]
Multiemployer Plan Disclosure [Line Items]
Pension Plan Number		002
Pension Protection Act Zone Status		Red	Green
FIP / RP Status Pending / Implemented	[1]	Implemented
Company Contributions		$ 2.2	$ 2.1	$ 1.7
Surcharge Imposed		Yes
Expiration Dates of Collective Bargaining Agreements, First Date	[2]	Nov. 14, 2021
Expiration Dates of Collective-Bargaining Agreements, Last Date	[2]	Jul. 14, 2022
[1]	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” zone, is pending or has been implemented as of the end of the plan year that ended in 2019 .
[2]	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 14, 2021 and July 14, 2022.

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		$ (1,133.8)	$ (1,027.8)	$ (1,093.7)
OCI before reclassifications		(136.9)	(132.5)	10.1
Amounts reclassified from AOCI		69	26.5	55.8
Net current-period OCI		(67.9)	(106)	65.9
Ending balance	$ (1,201.7)	(1,201.7)	(1,133.8)	(1,027.8)
Increase (Decrease) in Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance		11.1	17.3	9.7
OCI before reclassifications		(1.3)	(6.2)	7.6
Amounts reclassified from AOCI		0	0	0
Net current-period OCI		(1.3)	(6.2)	7.6
Ending balance	9.8	9.8	11.1	17.3
Tax expense for the recognition of a stranded deferred tax balance arising from deferred tax valuation allowances that was associated with a cash flow hedge portfolio	6
Post- retirement benefit plans [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		(1,005.8)	(954.5)	(965.5)
OCI before reclassifications		(141.6)	(107.2)	(32.5)
Amounts reclassified from AOCI		64.3	55.9	43.5
Net current-period OCI		(77.3)	(51.3)	11
Ending balance	(1,083.1)	(1,083.1)	(1,005.8)	(954.5)
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	0
Currency translation adjustment [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		(73.9)	(53.5)	(85)
OCI before reclassifications		(2.7)	(20.4)	31.5
Amounts reclassified from AOCI		0	0	0
Net current-period OCI		(2.7)	(20.4)	31.5
Ending balance	(76.6)	(76.6)	(73.9)	(53.5)
Increase (Decrease) in Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance		11.1	17.3	9.7
OCI before reclassifications		(1.3)	(6.2)	7.6
Amounts reclassified from AOCI		0	0	0
Net current-period OCI		(1.3)	(6.2)	7.6
Ending balance	9.8	9.8	11.1	17.3
Derivatives [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		(4.8)	9	2.4
OCI before reclassifications		7.4	(4.9)	11.1
Amounts reclassified from AOCI		(3.1)	(8.9)	(4.5)
Net current-period OCI		4.3	(13.8)	6.6
Ending balance	(0.5)	(0.5)	(4.8)	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	0
Accumulated Deferred Tax Asset Valuation Allowance
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		(49.3)	(28.8)	(45.6)
OCI before reclassifications		0	0	0
Amounts reclassified from AOCI		7.8	(20.5)	16.8
Net current-period OCI		7.8	(20.5)	16.8
Ending balance	(41.5)	(41.5)	(49.3)	(28.8)
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	$ 0

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income (Loss) (Details2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization to net income (loss) of net prior service cost (credits)	$ (2.6)	$ (2.6)	$ (1.6)
Amortization of net actuarial loss	87.2	76.5	71.6
Cost of sales	(3,484.7)	(3,416.3)	(3,028.1)
Income (loss) before income taxes	241.6	247.7	(86.5)
Income tax provision (benefit)	(28.5)	11	(6.8)
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 cost (credits)	2.6	2.6	1.6
Amortization of net actuarial loss	(87.2)	(76.5)	(71.6)
Income (loss) before income taxes	(84.6)	(73.9)	(70)
Income tax provision (benefit)	(20.3)	(18)	(26.5)
Income (loss)	(64.3)	(55.9)	(43.5)
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	4.1	11.7	7.2
Income tax provision (benefit)	1	2.8	2.7
Income (loss)	3.1	8.9	4.5
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	5.1	10.2	(3.4)
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	(1.2)	0.5	(5.3)
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	0.7	1.3	15.9
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	$ (0.5)	$ (0.3)	$ 0

Stockholders' Equity (Details)

Stockholders' Equity (Details)	Nov. 07, 2017$ / sharesshares	Feb. 28, 2019shares	Feb. 28, 2018shares	Feb. 28, 2017shares	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015shares	Dec. 31, 2014shares
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]
Shares issued	17,000,000
Price per share of shares issued (in dollars per share) | $ / shares	$ 24
Issuance of common stock | $						$ 0	$ 0	$ 397,800,000
Granted (shares)						396,000	290,000	378,000
Common stock shares available for future awards						4,100,000
Shares vested						681,000	540,000	591,000
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)					756,000	1,055,000	1,320,000	1,852,000
Granted (shares)						396,000	290,000	378,000
Vested (shares)						(681,000)	(540,000)	(591,000)
Forfeited (shares)						(14,000)	(15,000)	(319,000)
Nonvested end of the year (shares)						756,000	1,055,000	1,320,000	1,852,000
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					$ 24,200,000	$ 28,300,000	$ 32,500,000	$ 51,500,000
Granted (in dollars per share) | $ / shares						10,800,000	7,800,000	7,100,000
Vested (in dollars per share) | $ / shares						(14,500,000)	(11,700,000)	(16,900,000)
Forfeited (in dollars per share) | $ / shares						(400,000)	(300,000)	(9,200,000)
Ending balance (in dollars per share) | $ / shares						$ 24,200,000	$ 28,300,000	$ 32,500,000	$ 51,500,000
Retained Earnings Note Disclosure [Abstract]
Undistributed earnings of investees accounted for under equity method | $						$ 14,500,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Income target attainment measurement period						3 years
Restricted stock and RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense | $						$ 9,800,000	$ 9,700,000	$ 9,800,000
Unrecognized compensation expense | $						$ 5,900,000
Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Forfeited (shares)						(48,598)	(21,848)	(67,521)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Granted (in dollars per share) | $ / shares						$ 14,700,000	$ 12,900,000	$ 12,400,000
Forfeited (in dollars per share) | $ / shares						$ (1,100,000)	$ (500,000)	$ (1,000,000)
2016 LTIP [Member] | Restricted Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vested		175,287	178,335	190,421
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Vested (shares)		(175,287)	(178,335)	(190,421)
2017 RSU [Member] | Restricted Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (shares)								320,808
Shares vested		102,188	102,279
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Granted (shares)								320,808
Vested (shares)		(102,188)	(102,279)
2018 RSU [Member] | Restricted Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (shares)							253,393
Shares vested		83,312
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Granted (shares)							253,393
Vested (shares)		(83,312)
2019 RSU [Member] | Restricted Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (shares)						345,400
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Granted (shares)						345,400
Long-Term Shareholder Value (LTSV) 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of performance metric expected to be obtained								60.00%
Shares vested								73,734
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Vested (shares)								(73,734)
Forfeited (shares)								(49,148)
Long-Term Shareholder Value (LTSV) 2015 [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Income target attainment measurement period						3 years
PRSP 2012 [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vested				166,929
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Vested (shares)				(166,929)
Forfeited (shares)											(171,083)
PRSP 2013 [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vested			233,896
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Vested (shares)			(233,896)
Forfeited (shares)										(244,899)
PRSP 2014 [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vested		207,751
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Vested (shares)		(207,751)
Forfeited (shares)									(214,571)
PRSP 2015 [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vested								126,585
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Vested (shares)								(126,585)
Forfeited (shares)								(196,196)
PSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Adjustment percentage						20.00%	20.00%
PSU [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance measurement period						3 years
Share based compensation expense | $						$ 14,600,000	$ 11,400,000	$ 3,800,000
Common stock shares available for future awards						1,800,000
Unrecognized compensation expense | $						$ 12,900,000
TSR Modifier [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance measurement period							3 years
TSR and TSRP Awards [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense | $								$ 3,600,000
2016 PSU [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vested							329,897
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Vested (shares)							(329,897)
2017 PSU [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (shares)								589,980
Shares vested						669,898
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Granted (shares)								589,980
Vested (shares)						(669,898)
2018 PSU [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (shares)							456,318
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Granted (shares)							456,318
2019 PSU [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (shares)						479,364
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Granted (shares)						479,364
Minimum | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period						3 years
Minimum | PSU [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected compensation cost | $						$ 0
Minimum | TSR and TSRP Awards [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award multiplier								0
Minimum | 2017 PSU [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Attainment level range (percent)						25.00%
Minimum | 2018 and 2019 PSU [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Attainment level range (percent)						25.00%
Maximum | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period						5 years
Maximum | PSU [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected compensation cost | $						$ 51,000,000
Maximum | TSR and TSRP Awards [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award multiplier								2
Maximum | 2017 PSU [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Attainment level range (percent)						150.00%
Maximum | 2018 and 2019 PSU [Member] | Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Attainment level range (percent)						200.00%
Forecast [Member] | Restricted stock and RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense | $					$ 4,600,000
Forecast [Member] | PSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense | $					$ 7,700,000
Domestic Bank Group $500 million asset-based credit facility [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Debt instrument carrying amount | $						$ 0	$ 0
Allegheny Technologies $350 million 9.375% Senior Notes due 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Debt instrument carrying amount | $									$ 350,000,000
Debt instrument interest rate stated percentage									9.375%
Revolving Credit Facility [Member] | Domestic Bank Group $500 million asset-based credit facility [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Debt covenant, line of credit facility remaining borrowing capacity after dividends, upper threshold | $						$ 150,000,000
Debt covenant, line of credit facility remaining borrowing capacity after dividends as percent of maximum borrowing capacity, upper threshold						30.00%
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						15.00%
Fixed charge coverage ratio						1

Income Taxes Income by Region (

Income Taxes Income by Region (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
U.S.	$ 190.2	$ 190.8	$ (119.8)
Non-U.S.	51.4	56.9	33.3
Income (loss) before income taxes	$ 241.6	$ 247.7	$ (86.5)

Schedule of Income Tax Provisio

Schedule of Income Tax Provision (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Components Of Income Tax Expense Benefit Continuing Operations Abstract
Current: Federal	$ 2.2	$ 1	$ (0.8)
Current: State	0.2	(0.8)	(1.3)
Current: Foreign	8.1	10.1	6.2
Total Current	10.5	10.3	4.1
Deferred: Federal	(4.6)	1.3	2.4
Deferred: State	(40.4)	(0.5)	(14.4)
Deferred: Foreign	6	(0.1)	1.1
Total Deferred	(39)	0.7	(10.9)
Income tax provision (benefit)	$ (28.5)	$ 11	$ (6.8)

Reconciliation of Federal Tax R

Reconciliation of Federal Tax Rate to Effective Tax Rate (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Taxes computed at the federal rate	$ 50.7	$ 52	$ (30.3)
Goodwill impairment	0	0	36.6
State and local income taxes, net of federal tax benefit	0.3	(0.5)	0
Valuation allowance	(90.1)	(48)	(14.5)
Repatriation of foreign earnings (GILTI starting in 2018)	3.5	5.4	14.2
Restructuring	4.2	0	0
Impact of U.S. tax reform	0	5.9	(4.1)
Foreign earnings taxed at different rate	2.7	3.2	(3.5)
Adjustment to prior years’ taxes	0	(5.8)	(5.2)
Withholding taxes	2.7	2.7	2.2
Preferential tax rate	(4.1)	(4.8)	(3.7)
Other	1.6	0.9	1.5
Income tax provision (benefit)	$ (28.5)	$ 11	$ (6.8)

Narrative (Details)

Narrative (Details) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2015year	Dec. 31, 2016USD ($)
NOL and Tax Credit Carryforwards [Line Items]
Income tax penalties and interest accrued	$ 2.7	$ 2.7	$ 2.7
Foreign earnings inclusion, Global Intangible Low-Taxed Income (GILTI)		16.8	25.7
Repatriation of foreign earnings (GILTI starting in 2018)		3.5	5.4	$ 14.2
Estimate of federal limit on deductible interest expense		24
Restructuring		4.2	0	0
Benefit from re-measurement of indefinite lived deferred tax liabilities				2.6
Benefit from decrease in deferred tax asset valuation allowance				1.5
Number of years in cumulative loss profit position | year					3
Valuation allowance		(90.1)	(48)	(14.5)
Income (loss) before income taxes		241.6	247.7	(86.5)
Income from continuing operations before income taxes, domestic		190.2	190.8	(119.8)
Valuation allowance decrease due to change in judgment on the realizability of deferred tax assets	(41.9)	(45.1)
Accumulated other comprehensive loss, net of tax	1,201.7	1,201.7	1,133.8	1,027.8		$ 1,093.7
Tax expense for the recognition of a stranded deferred tax balance arising from deferred tax valuation allowances that was associated with a cash flow hedge portfolio	6
Transition tax expense			5.9
Impact of U.S. tax reform		0	5.9	(4.1)
Total deferred income tax assets	537.9	537.9	478.8
Net operating loss tax carryovers	264.4	264.4	307.5
Income tax refunds received		9.2	1.6	7.1
Deferred taxes for foreign withholding taxes	3.5	3.5
Unrecognized tax benefits classified within deferred taxes as a reduction of net operating loss carryforwards	11.5	11.5	12.1	11.7
Unrecognized tax benefits that would impact effective tax rate	3	3
Unrecognized tax benefits that will be recognized within 12 months of year end	2	2
Federal and State Deferred Tax Assets
NOL and Tax Credit Carryforwards [Line Items]
Valuation allowance			(46.3)
Accumulated Deferred Tax Asset Valuation Allowance
NOL and Tax Credit Carryforwards [Line Items]
Accumulated other comprehensive loss, net of tax	41.5	41.5	49.3	$ 28.8		$ 45.6
State [Member]
NOL and Tax Credit Carryforwards [Line Items]
Tax credit carryforwards	$ 11	$ 11
Tax Cuts and Jobs Act, Transition Tax Liability
NOL and Tax Credit Carryforwards [Line Items]
Tax credit carryforwards			$ 28.2

Changes In Deferred Tax Assets

Changes In Deferred Tax Assets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Tax Credit Carryforward [Line Items]
Net operating loss tax carryovers	$ 264.4	$ 307.5
Tax credits	42.6	49.7
Gross deferred income tax assets	632.4	673.6
Valuation allowance	(94.5)	(194.8)
Total deferred income tax assets	$ 537.9	$ 478.8

Schedule of Deferred Tax Assets

Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Deferred income tax assets
Pensions	$ 155.5	$ 159.4
Postretirement benefits other than pensions	83.8	87.3
Net operating loss tax carryovers	264.4	307.5
Tax credits	42.6	49.7
Other items	86.1	69.7
Gross deferred income tax assets	632.4	673.6
Valuation allowance for deferred tax assets	(94.5)	(194.8)
Total deferred income tax assets	537.9	478.8
Deferred income tax liabilities
Bases of property, plant and equipment	364.2	371.5
Inventory valuation	65.5	67.1
Bases of amortizable intangible assets	23.7	29.9
Other items	27	14.5
Total deferred tax liabilities	480.4	483
Net deferred tax asset	$ 57.5
Net deferred tax (liability)		$ (4.2)

Schedule of Income Taxes Paid a

Schedule of Income Taxes Paid and Refunded (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes Paid, Net [Abstract]
Income Taxes Paid	$ 15.1	$ 9.7	$ 10.4
Income tax refunds received	(9.2)	(1.6)	(7.1)
Income Taxes Paid (Received), Net, Total	$ 5.9	$ 8.1	$ 3.3

Income Taxes NOL and Tax Credit

Income Taxes NOL and Tax Credit Carryforwards (Details) $ in Millions	Dec. 31, 2019USD ($)
United States
NOL and Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	$ 766
State [Member]
NOL and Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	136
Tax credit carryforwards	11
United Kingdom
NOL and Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	23
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	30
Tax credit carryforwards	3
Within 5 years [Member] | United Kingdom
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	766
Within 5-20 years [Member] | State [Member]
NOL and Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	106
Tax credit carryforwards	8
Within 5-20 years [Member] | United Kingdom
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	30
Foreign Tax Credits [Member] | Within 5 years [Member] | United States
NOL and Tax Credit Carryforwards [Line Items]
Tax credit carryforwards	7
Foreign Tax Credits [Member] | Within 5-20 years [Member] | United States
NOL and Tax Credit Carryforwards [Line Items]
Tax credit carryforwards	23
Research Tax Credit Carryforward [Member] | United States
NOL and Tax Credit Carryforwards [Line Items]
Tax credit carryforwards	2
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	2
Economic Zone Credit [Member] | Poland [Member]
NOL and Tax Credit Carryforwards [Line Items]
Tax credit carryforwards	2
Economic Zone Credit [Member] | Within 5 years [Member] | Poland [Member]
NOL and Tax Credit Carryforwards [Line Items]
Tax credit carryforwards	0
Economic Zone Credit [Member] | Within 5-20 years [Member] | Poland [Member]
NOL and Tax Credit Carryforwards [Line Items]
Tax credit carryforwards	$ 2

Schedule of Changes in Unrecogn

Schedule of Changes in Unrecognized Income Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Uncertainties [Abstract]
Unrecognized tax benefits classified within deferred taxes as a reduction of net operating loss carryforwards				$ 11.5	$ 12.1	$ 11.7
Reconciliation Of Unrecognized Tax Benefits Excluding Amounts Pertaining To Examined Tax Returns Roll Forward
Increases in prior period tax positions	$ 0	$ 0	$ 0
Decreases in prior period tax positions	0	(0.1)	(0.7)
Increases in current period tax positions	0.9	0.7	0.7
Unrecognized tax benefits	14.4	14.7	14.7	14.4	14.7	$ 14.7	$ 22.7
Expiration of the statute of limitations	(1.2)	(0.6)	(0.4)
Settlements	0	0	(7.6)
Ending balance	$ 14.4	$ 14.7	$ 14.7
Income tax penalties and interest accrued				2.7	$ 2.7
Unrecognized tax benefits that would impact effective tax rate				3
Unrecognized tax benefits that will be recognized within 12 months of year end				$ 2

Business Segments - Narrative (

Business Segments - Narrative (Details) $ in Millions	3 Months Ended			12 Months Ended
	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Dec. 31, 2019USD ($)employeesegment	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016
Segment Reporting Information [Line Items]
Gain on asset sales, net				$ 89.8	$ 0	$ 0
Restructuring and other charges	$ 4.5			$ 4.5	0	0
Number of Reportable Segments | segment				2,000,000
Restructuring charges				$ 4.5	0	0
Income (loss) from equity method investments				(10.7)	(1)	0
Total international sales				1,667.9	1,698.4	1,454.5
Sales by U.S. operations to foreign countries				1,262.6	1,303.8	1,078.6
LIFO-related net realizable value charge	(33.6)			(33.6)	(2.9)
Inventory valuation reserves	$ 104.1			104.1	88.5
Closed operations and other expenses				25.5	21.6	34
Gain (Loss) on Disposition of Oil and Gas and Timber Property		$ 62.4	$ 29.3	91.7
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal				$ (1.8)	0	0
Advanced Alloys & Solutions
Segment Reporting Information [Line Items]
Restructuring and Related Cost, Expected Number of Positions Eliminated | employee				70
Allegheny & Tsingshan Stainless
Segment Reporting Information [Line Items]
Equity method investment ownership percentage	50.00%			50.00%
Revenue from related parties				$ 14.6	4.1
Income (loss) from equity method investments				(19.3)	(3.9)
Allegheny & Tsingshan Stainless | Advanced Alloys & Solutions
Segment Reporting Information [Line Items]
Income (loss) from equity method investments				$ (12.2)
Uniti [Member]
Segment Reporting Information [Line Items]
Equity method investment ownership percentage	50.00%			50.00%
Revenue from related parties				$ 31.3	49.4	38.6
Uniti [Member] | Advanced Alloys & Solutions
Segment Reporting Information [Line Items]
Income (loss) from equity method investments				$ 1.5	$ 2.9	$ 0.6
Aerospace & Defense Market Concentration Risk [Member] | Revenue Benchmark [Member] | High Performance Materials & Components
Segment Reporting Information [Line Items]
Percentage of sales				80.00%
Energy and Aerospace & Defense Market Concentration [Member] | Revenue Benchmark [Member] | Advanced Alloys & Solutions
Segment Reporting Information [Line Items]
Percentage of sales				50.00%
Allegheny Technologies $350 million 9.375% Senior Notes due 2019
Segment Reporting Information [Line Items]
Debt Instrument, Interest Rate, Stated Percentage							9.375%
Cast Products
Segment Reporting Information [Line Items]
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal		$ 6.2		$ 6.2
Forged Products
Segment Reporting Information [Line Items]
LIFO-related net realizable value charge	$ (5.2)			(5.2)
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal			$ (7.7)	$ (8.1)
Allegheny Technologies Inc | STAL Precision Stainless Steel Company Limited [Member]
Segment Reporting Information [Line Items]
Joint venture ownership percentage	60.00%			60.00%
Allegheny Technologies Inc | Uniti [Member] | VSMPO [Member]
Segment Reporting Information [Line Items]
Joint venture ownership percentage by unaffiliated entity	50.00%			50.00%

Business Segments (Details)

Business Segments (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Sales	$ 1,018.6	$ 1,018.7	$ 1,080.4	$ 1,004.8	$ 1,037.9	$ 1,020.2	$ 1,009.5	$ 979	$ 4,122.5	$ 4,046.6	$ 3,525.1
Operating Segments
Segment Reporting Information [Line Items]
Sales									4,446.4	4,341.6	3,758
Operating Segments | Intersegment Sales [Member]
Segment Reporting Information [Line Items]
Sales									323.9	295	232.9
Operating Segments | External Sales [Member]
Segment Reporting Information [Line Items]
Sales									4,122.5	4,046.6	3,525.1
Operating Segments | High Performance Materials & Components
Segment Reporting Information [Line Items]
Sales									2,054.2	2,039.2	1,751.1
Operating Segments | High Performance Materials & Components | Intersegment Sales [Member]
Segment Reporting Information [Line Items]
Sales									75.7	76.1	46.3
Operating Segments | High Performance Materials & Components | External Sales [Member]
Segment Reporting Information [Line Items]
Sales									1,978.5	1,963.1	1,704.8
Operating Segments | Advanced Alloys & Solutions
Segment Reporting Information [Line Items]
Sales									2,392.2	2,302.4	2,006.9
Operating Segments | Advanced Alloys & Solutions | Intersegment Sales [Member]
Segment Reporting Information [Line Items]
Sales									248.2	218.9	186.6
Operating Segments | Advanced Alloys & Solutions | External Sales [Member]
Segment Reporting Information [Line Items]
Sales									$ 2,144	$ 2,083.5	$ 1,820.3

Business Segments (Details8)

Business Segments (Details8) - USD ($)	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Inventory valuation reserves	$ 104,100,000		$ 104,100,000	$ 88,500,000
Segment Operating Profit Loss			380,700,000	413,200,000	$ 283,400,000
LIFO and net realizable value reserves			(100,000)	(700,000)	(200,000)
Corporate expenses			(66,800,000)	(58,100,000)	(50,500,000)
Closed operations and other expenses			(25,500,000)	(21,600,000)	(34,000,000)
Restructuring and other charges	(4,500,000)		(4,500,000)	0	0
Impairment of goodwill			0	0	(114,400,000)
Debt extinguishment charge	(21,600,000)		(21,600,000)	0	(37,000,000)
Gain on joint venture deconsolidation		$ 15,900,000	0	15,900,000	0
Non-cash joint venture impairment charge	$ (11,400,000)		(11,400,000)	0	0
Gain on asset sales, net			89,800,000	0	0
Interest expense, net			(99,000,000)	(101,000,000)	(133,800,000)
Income (loss) before income taxes			241,600,000	247,700,000	(86,500,000)
High Performance Materials & Components
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Impairment of goodwill			0		(114,400,000)
Operating Segments | High Performance Materials & Components
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Segment Operating Profit Loss			271,600,000	269,700,000	191,400,000
Operating Segments | Advanced Alloys & Solutions
Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items]
Segment Operating Profit Loss			$ 109,100,000	$ 143,500,000	$ 92,000,000

Business Segments (Details2)

Business Segments (Details2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Other Significant Reconciling Item [Line Items]
Depreciation and amortization	$ 151.1	$ 156.4	$ 160.8
Capital expenditures	168.2	139.2	122.7
Operating Segments
Segment Reporting Other Significant Reconciling Item [Line Items]
Depreciation and amortization	151.1	156.4	160.8
Capital expenditures	168.2	139.2	122.7
Operating Segments | High Performance Materials & Components
Segment Reporting Other Significant Reconciling Item [Line Items]
Depreciation and amortization	84.7	90.6	91.5
Capital expenditures	119.9	71.7	52.7
Operating Segments | Advanced Alloys & Solutions
Segment Reporting Other Significant Reconciling Item [Line Items]
Depreciation and amortization	63.5	62.9	63.4
Capital expenditures	47.4	64.5	69.1
Operating Segments | Corporate [Member]
Segment Reporting Other Significant Reconciling Item [Line Items]
Depreciation and amortization	2.9	2.9	5.9
Capital expenditures	$ 0.9	$ 3	$ 0.9

Business Segments (Details3)

Business Segments (Details3) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Asset Reconciling Item [Line Items]
Identifiable Assets	$ 5,634.6	$ 5,501.8	$ 5,185.4
Deferred taxes	537.9	478.8
High Performance Materials & Components
Segment Reporting Asset Reconciling Item [Line Items]
Identifiable Assets	2,324.6	2,400.7	2,329.9
Advanced Alloys & Solutions
Segment Reporting Asset Reconciling Item [Line Items]
Identifiable Assets	2,621.1	2,590.4	2,550.8
Discontinued Operations [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Identifiable Assets	0	0	0.2
Corporate, Non-Segment [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Deferred taxes	64.5	8.7	7.6
Corporate: Cash and cash equivalents and other [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Identifiable Assets	$ 624.4	$ 502	$ 296.9

Business Segments (Details4)

Business Segments (Details4) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Long-Lived Assets [Line Items]
Sales	$ 1,018.6	$ 1,018.7	$ 1,080.4	$ 1,004.8	$ 1,037.9	$ 1,020.2	$ 1,009.5	$ 979	$ 4,122.5	$ 4,046.6	$ 3,525.1
Identifiable Assets	$ 5,634.6				$ 5,501.8				$ 5,634.6	$ 5,501.8	$ 5,185.4
Percent of total	100.00%				100.00%				100.00%	100.00%	100.00%
United States
Long-Lived Assets [Line Items]
Sales									$ 2,454.6	$ 2,348.1	$ 2,070.6
Identifiable Assets	$ 4,956.4				$ 4,859.1				$ 4,956.4	$ 4,859.1	$ 4,547.7
Percent of total	88.00%				88.00%				88.00%	88.00%	88.00%
China
Long-Lived Assets [Line Items]
Sales									$ 355.6	$ 320	$ 265.6
Identifiable Assets	$ 288.1				$ 287.3				$ 288.1	$ 287.3	$ 276
Percent of total	5.00%				5.00%				5.00%	5.00%	5.00%
United Kingdom
Long-Lived Assets [Line Items]
Sales									$ 173.8	$ 242.1	$ 231.6
Identifiable Assets	$ 141.3				$ 136.7				$ 141.3	$ 136.7	$ 122.7
Percent of total	3.00%				3.00%				3.00%	3.00%	2.00%
Germany
Long-Lived Assets [Line Items]
Sales									$ 219.3	$ 247.2	$ 217.1
France
Long-Lived Assets [Line Items]
Sales									155.5	183.6	165.6
Japan
Long-Lived Assets [Line Items]
Sales									147.7	214.9	131.7
Other [Member]
Long-Lived Assets [Line Items]
Identifiable Assets	$ 248.8				$ 218.7				$ 248.8	$ 218.7	$ 239
Percent of total	4.00%				4.00%				4.00%	4.00%	5.00%

Restructuring Costs (Details)

Restructuring Costs (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 4.5	$ 0	$ 0
Restructuring and other charges	$ 4.5	$ 4.5	$ 0	$ 0

Per Share Information (Details)

Per Share Information (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share Reconciliation [Abstract]
Net income (loss)									$ 257.6	$ 222.4	$ (91.9)
Effect of dilutive securities: Convertible Senior Notes									12.8	12.9	0
Numerator for diluted net income (loss) per common share - Income (loss) attributable to ATI after assumed conversions									$ 270.4	$ 235.3	$ (91.9)
Denominator for basic net income (loss) per common share - weighted average shares (shares)	126.1	126.1	126.1	125.8	125.7	125.7	125.7	125.7	125.8	125.2	110.1
Effect of dilutive securities: Share-based compensation									0.8	0.8	0
Effect of dilutive securities: Convertible Senior Notes									19.9	19.9	0
Denominator for diluted net income (loss) per common share—adjusted weighted average shares and assumed conversions									146.5	145.9	110.1
Basic income (loss) attributable to ATI per common share (in dollars per share)									$ 2.05	$ 1.78	$ (0.83)
Diluted income (loss) attributable to ATI per common share (in dollars per share)									$ 1.85	$ 1.61	$ (0.83)
Anti-dilutive securities excluded from computation of earnings per share amount									0	0	20.8
Allegheny Technologies, Convertible Senior Notes, 4.75%, Due 2022 [Member]
Earnings Per Share Reconciliation [Abstract]
Debt instrument interest rate stated percentage	4.75%				4.75%				4.75%	4.75%
Convertible Debt [Member] | Allegheny Technologies, Convertible Senior Notes, 4.75%, Due 2022 [Member]
Earnings Per Share Reconciliation [Abstract]
Debt instrument interest rate stated percentage	4.75%								4.75%

Financial Information for Sub_3

Financial Information for Subsidiary and Guarantor Parent - Narrative (Details) - Allegheny Ludlum 6.95% Debentures due 2025 [Member] - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Condensed Financial Statements, Captions [Line Items]
Debt instrument carrying amount	$ 150	$ 150
Debt instrument interest rate stated percentage	6.95%	6.95%

Financial Information for Sub_4

Financial Information for Subsidiary and Guarantor Parent (B.S.) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	$ 490.8	$ 382		$ 141.6	$ 229.6
Accounts receivable, net	554.1	527.8
Intercompany notes receivable	0	0
Short-term contract assets	38.5	51.2	$ 36.5
Inventories, net	1,155.3	1,211.1
Prepaid expenses and other current assets	64.3	74.6
Total Current Assets	2,303	2,246.7
Property, plant and equipment, net	2,450.1	2,475
Goodwill	525.8	534.7
Intercompany notes receivable	0	0
Investments in subsidiaries	0	0
Other assets	355.7	245.4
Total Assets	5,634.6	5,501.8		5,185.4
Accounts payable	521.2	498.8
Intercompany notes payable	0	0
Short-term contract liabilities	78.7	71.4	69.7
Short-term debt and current portion of long-term debt	11.5	6.6
Other current liabilities	237.8	260.1
Total Current Liabilities	849.2	836.9
Long-term debt	1,387.4	1,535.5
Intercompany notes payable	0	0
Accrued postretirement benefits	312.5	318.4
Pension liabilities	731.5	730
Long-term contract liabilities	25.9	7.3	$ 22.2
Other long-term liabilities	160.8	89.4
Total Liabilities	3,441.4	3,510.2
Total Stockholders’ Equity	2,193.2	1,991.6		$ 1,844.5	$ 1,444.8
Total Liabilities and Stockholders’ Equity	5,634.6	5,501.8
Legal Entities [Member] | Guarantor Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	0.3	0.1
Accounts receivable, net	0	0
Intercompany notes receivable	0	0
Short-term contract assets	0	0
Inventories, net	0	0
Prepaid expenses and other current assets	5.6	12.9
Total Current Assets	5.9	13
Property, plant and equipment, net	6.5	1.7
Goodwill	0	0
Intercompany notes receivable	0	0
Investments in subsidiaries	6,434.3	6,096.4
Other assets	98.3	35.6
Total Assets	6,545	6,146.7
Accounts payable	4.6	3.3
Intercompany notes payable	2,457.1	2,102.8
Short-term contract liabilities	0	0
Short-term debt and current portion of long-term debt	1.4	0.2
Other current liabilities	51.5	59.1
Total Current Liabilities	2,514.6	2,165.4
Long-term debt	1,130.1	1,278.8
Intercompany notes payable	0	0
Accrued postretirement benefits	0	0
Pension liabilities	678.8	681.6
Other long-term liabilities	28.3	29.3
Total Liabilities	4,351.8	4,155.1
Total Stockholders’ Equity	2,193.2	1,991.6
Total Liabilities and Stockholders’ Equity	6,545	6,146.7
Legal Entities [Member] | Subsidiary [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	4.2	10.8
Accounts receivable, net	123.7	126.3
Intercompany notes receivable	0	0
Short-term contract assets	0	0
Inventories, net	213	216.1
Prepaid expenses and other current assets	18.5	29.3
Total Current Assets	359.4	382.5
Property, plant and equipment, net	1,539.3	1,548.4
Goodwill	0	0
Intercompany notes receivable	0	0
Investments in subsidiaries	37.7	37.7
Other assets	83.1	30.7
Total Assets	2,019.5	1,999.3
Accounts payable	184	177.5
Intercompany notes payable	1,945.7	1,866
Short-term contract liabilities	26.4	33
Short-term debt and current portion of long-term debt	0.2	0.7
Other current liabilities	68.1	71.7
Total Current Liabilities	2,224.4	2,148.9
Long-term debt	150.4	151.8
Intercompany notes payable	200	200
Accrued postretirement benefits	261.2	259.2
Pension liabilities	3.8	4
Other long-term liabilities	44.1	17.6
Total Liabilities	2,883.9	2,781.5
Total Stockholders’ Equity	(864.4)	(782.2)
Total Liabilities and Stockholders’ Equity	2,019.5	1,999.3
Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	486.3	371.1
Accounts receivable, net	430.4	401.5
Intercompany notes receivable	4,402.8	3,968.8
Short-term contract assets	38.5	51.2
Inventories, net	942.3	995
Prepaid expenses and other current assets	40.2	32.4
Total Current Assets	6,340.5	5,820
Property, plant and equipment, net	904.3	924.9
Goodwill	525.8	534.7
Intercompany notes receivable	200	200
Investments in subsidiaries	0	0
Other assets	174.3	179.1
Total Assets	8,144.9	7,658.7
Accounts payable	332.6	318
Intercompany notes payable	0	0
Short-term contract liabilities	52.3	38.4
Short-term debt and current portion of long-term debt	9.9	5.7
Other current liabilities	118.2	129.3
Total Current Liabilities	513	491.4
Long-term debt	106.9	104.9
Intercompany notes payable	0	0
Accrued postretirement benefits	51.3	59.2
Pension liabilities	48.9	44.4
Other long-term liabilities	88.4	42.5
Total Liabilities	808.5	742.4
Total Stockholders’ Equity	7,336.4	6,916.3
Total Liabilities and Stockholders’ Equity	8,144.9	7,658.7
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	0	0
Accounts receivable, net	0	0
Intercompany notes receivable	(4,402.8)	(3,968.8)
Short-term contract assets	0	0
Inventories, net	0	0
Prepaid expenses and other current assets	0	0
Total Current Assets	(4,402.8)	(3,968.8)
Property, plant and equipment, net	0	0
Goodwill	0	0
Intercompany notes receivable	(200)	(200)
Investments in subsidiaries	(6,472)	(6,134.1)
Other assets	0	0
Total Assets	(11,074.8)	(10,302.9)
Accounts payable	0	0
Intercompany notes payable	(4,402.8)	(3,968.8)
Short-term contract liabilities	0	0
Short-term debt and current portion of long-term debt	0	0
Other current liabilities	0	0
Total Current Liabilities	(4,402.8)	(3,968.8)
Long-term debt	0	0
Intercompany notes payable	(200)	(200)
Accrued postretirement benefits	0	0
Pension liabilities	0	0
Other long-term liabilities	0	0
Total Liabilities	(4,602.8)	(4,168.8)
Total Stockholders’ Equity	(6,472)	(6,134.1)
Total Liabilities and Stockholders’ Equity	$ (11,074.8)	$ (10,302.9)

Financial Information for Sub_5

Financial Information for Subsidiary and Guarantor Parent (I.S.) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Sales	$ 1,018.6	$ 1,018.7	$ 1,080.4	$ 1,004.8	$ 1,037.9	$ 1,020.2	$ 1,009.5	$ 979	$ 4,122.5	$ 4,046.6	$ 3,525.1
Cost of sales									3,484.7	3,416.3	3,028.1
Gross profit	169.3	159.7	177.7	131.1	147.6	160.4	173.7	148.6	637.8	630.3	497
Selling and administrative expenses									267.2	268.2	248
Restructuring charges									4.5	0	0
Impairment of goodwill									0	0	114.4
Operating income									366.1	362.1	134.6
Nonoperating retirement benefit expense									(73.6)	(33.9)	(54.3)
Interest expense, net									(99)	(101)	(133.8)
Debt extinguishment charge	(21.6)								(21.6)	0	(37)
Other income (expense) including equity in income of unconsolidated subsidiaries									69.7	20.5	4
Income (loss) before income taxes									241.6	247.7	(86.5)
Income tax provision (benefit)									(28.5)	11	(6.8)
Net income (loss)	60	115.3	78.5	16.3	45	55.6	75.6	60.5	270.1	236.7	(79.7)
Less: Net income attributable to noncontrolling interests									12.5	14.3	12.2
Net income (loss) attributable to ATI	$ 56.5	$ 111	$ 75.1	$ 15	$ 41.1	$ 50.5	$ 72.8	$ 58	257.6	222.4	(91.9)
Legal Entities [Member] | Guarantor Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Sales									0	0	0
Cost of sales									13.5	16.6	14.6
Gross profit									(13.5)	(16.6)	(14.6)
Selling and administrative expenses									116.5	101.7	86.6
Restructuring charges									4.5
Impairment of goodwill											0
Operating income									(134.5)	(118.3)	(101.2)
Nonoperating retirement benefit expense									(47.5)	(12.7)	(32.2)
Interest expense, net									(148.2)	(138.8)	(155.8)
Debt extinguishment charge									(21.6)		(37)
Other income (expense) including equity in income of unconsolidated subsidiaries									593.4	517.5	239.7
Income (loss) before income taxes									241.6	247.7	(86.5)
Income tax provision (benefit)									(28.5)	11	(6.8)
Net income (loss)									270.1	236.7	(79.7)
Less: Net income attributable to noncontrolling interests									0	0	0
Net income (loss) attributable to ATI									270.1	236.7	(79.7)
Legal Entities [Member] | Subsidiary [Member]
Condensed Financial Statements, Captions [Line Items]
Sales									1,429	1,410.3	1,178.9
Cost of sales									1,302.8	1,302.4	1,085.5
Gross profit									126.2	107.9	93.4
Selling and administrative expenses									33.2	34.2	36.9
Restructuring charges									0
Impairment of goodwill											0
Operating income									93	73.7	56.5
Nonoperating retirement benefit expense									(24.7)	(19.5)	(18.7)
Interest expense, net									(131.6)	(114.6)	(90)
Debt extinguishment charge									0		0
Other income (expense) including equity in income of unconsolidated subsidiaries									(22)	16.8	1.6
Income (loss) before income taxes									(85.3)	(43.6)	(50.6)
Income tax provision (benefit)									(18.3)	(8.7)	(16.6)
Net income (loss)									(67)	(34.9)	(34)
Less: Net income attributable to noncontrolling interests									0	0	0
Net income (loss) attributable to ATI									(67)	(34.9)	(34)
Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Sales									2,693.5	2,636.3	2,346.2
Cost of sales									2,168.4	2,097.3	1,928
Gross profit									525.1	539	418.2
Selling and administrative expenses									117.5	132.3	124.5
Restructuring charges									0
Impairment of goodwill											114.4
Operating income									407.6	406.7	179.3
Nonoperating retirement benefit expense									(1.4)	(1.7)	(3.4)
Interest expense, net									180.8	152.4	112
Debt extinguishment charge									0		0
Other income (expense) including equity in income of unconsolidated subsidiaries									90.2	0.8	2.4
Income (loss) before income taxes									677.2	558.2	290.3
Income tax provision (benefit)									115.6	83.9	131.4
Net income (loss)									561.6	474.3	158.9
Less: Net income attributable to noncontrolling interests									12.5	14.3	12.2
Net income (loss) attributable to ATI									549.1	460	146.7
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Sales									0	0	0
Cost of sales									0	0	0
Gross profit									0	0	0
Selling and administrative expenses									0	0	0
Restructuring charges									0
Impairment of goodwill											0
Operating income									0	0	0
Nonoperating retirement benefit expense									0	0	0
Interest expense, net									0	0	0
Debt extinguishment charge									0		0
Other income (expense) including equity in income of unconsolidated subsidiaries									(591.9)	(514.6)	(239.7)
Income (loss) before income taxes									(591.9)	(514.6)	(239.7)
Income tax provision (benefit)									(97.3)	(75.2)	(114.8)
Net income (loss)									(494.6)	(439.4)	(124.9)
Less: Net income attributable to noncontrolling interests									0	0	0
Net income (loss) attributable to ATI									$ (494.6)	$ (439.4)	$ (124.9)

Financial Information for Sub_6

Financial Information for Subsidiary and Guarantor Parent (Comp Inc.) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	$ 60	$ 115.3	$ 78.5	$ 16.3	$ 45	$ 55.6	$ 75.6	$ 60.5	$ 270.1	$ 236.7	$ (79.7)
Currency translation adjustment arising during the period									(4)	(26.6)	39.1
Net derivative gain (loss) on hedge transactions									10.3	(18.1)	7.1
Pension and postretirement benefits									(75.5)	(67.5)	27.3
Other comprehensive income (loss), net of tax									(69.2)	(112.2)	73.5
Comprehensive income (loss)									200.9	124.5	(6.2)
Less: Comprehensive income attributable to noncontrolling interest									11.2	8.1	19.8
Comprehensive income (loss) attributable to ATI									189.7	116.4	(26)
Legal Entities [Member] | Guarantor Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)									270.1	236.7	(79.7)
Currency translation adjustment arising during the period									(4)	(26.6)	39.1
Net derivative gain (loss) on hedge transactions									10.3	(18.1)	7.1
Pension and postretirement benefits									(75.5)	(67.5)	27.3
Other comprehensive income (loss), net of tax									(69.2)	(112.2)	73.5
Comprehensive income (loss)									200.9	124.5	(6.2)
Less: Comprehensive income attributable to noncontrolling interest									0	0	0
Comprehensive income (loss) attributable to ATI									200.9	124.5	(6.2)
Legal Entities [Member] | Subsidiary [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)									(67)	(34.9)	(34)
Currency translation adjustment arising during the period									0	0	0
Net derivative gain (loss) on hedge transactions									0	0	0
Pension and postretirement benefits									3.8	(19.1)	(5.8)
Other comprehensive income (loss), net of tax									3.8	(19.1)	(5.8)
Comprehensive income (loss)									(63.2)	(54)	(39.8)
Less: Comprehensive income attributable to noncontrolling interest									0	0	0
Comprehensive income (loss) attributable to ATI									(63.2)	(54)	(39.8)
Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)									561.6	474.3	158.9
Currency translation adjustment arising during the period									(4)	(26.6)	39.1
Net derivative gain (loss) on hedge transactions									0	0	0
Pension and postretirement benefits									(15.2)	0.7	(10.7)
Other comprehensive income (loss), net of tax									(19.2)	(25.9)	28.4
Comprehensive income (loss)									542.4	448.4	187.3
Less: Comprehensive income attributable to noncontrolling interest									11.2	8.1	19.8
Comprehensive income (loss) attributable to ATI									531.2	440.3	167.5
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)									(494.6)	(439.4)	(124.9)
Currency translation adjustment arising during the period									4	26.6	(39.1)
Net derivative gain (loss) on hedge transactions									0	0	0
Pension and postretirement benefits									11.4	18.4	16.5
Other comprehensive income (loss), net of tax									15.4	45	(22.6)
Comprehensive income (loss)									(479.2)	(394.4)	(147.5)
Less: Comprehensive income attributable to noncontrolling interest									0	0	0
Comprehensive income (loss) attributable to ATI									$ (479.2)	$ (394.4)	$ (147.5)

Financial Information for Sub_7

Financial Information for Subsidiary and Guarantor Parent (Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Cash flows provided by (used in) operating activities	$ 230.1	$ 392.8	$ 22.4
Purchases of property, plant and equipment	(168.2)	(139.2)	(122.7)
Net receipts (payments) on intercompany activity	0	0	0
Proceeds from disposal of property, plant and equipment	92	2.8	2.7
Purchases of businesses	0	(10)	0
Proceeds from sale of business, net of transaction costs	158.1	0	0
Other	(0.2)	1.3	0.4
Cash flows provided by (used in) investing activities	81.7	(145.1)	(119.6)
Borrowings on long-term debt	350	7.1	8.5
Payments on long-term debt and finance leases	(507.6)	(6.4)	(353)
Net borrowings (payments) under credit facilities	4.9	(5.9)	1.6
Debt issuance costs	(5.5)	0	(0.8)
Debt extinguishment charge	(20.9)	0	(35.8)
Net receipts (payments) on intercompany activity	0	0	0
Issuance of common stock	0	0	397.8
Dividends paid to stockholders	0	0	0
Dividends paid to noncontrolling interests	(14)	(10)	(8)
Sale to noncontrolling interest	0	14.4	3.7
Shares repurchased for income tax withholding on share-based compensation	(9.9)	(6.5)	(4.8)
Cash (used in) provided by financing activities	(203)	(7.3)	9.2
Increase (decrease) in cash and cash equivalents	108.8	240.4	(88)
Legal Entities [Member] | Guarantor Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Cash flows provided by (used in) operating activities	16.1	(107)	(78.8)
Purchases of property, plant and equipment	(0.7)	(2.1)	(0.9)
Net receipts (payments) on intercompany activity	0	0	0
Proceeds from disposal of property, plant and equipment	0	0	0
Purchases of businesses		0
Proceeds from sale of business, net of transaction costs	0
Other	(0.2)	1.3	0
Cash flows provided by (used in) investing activities	(0.9)	(0.8)	(0.9)
Borrowings on long-term debt	350	0	0
Payments on long-term debt and finance leases	(500.7)	(0.2)	(350.4)
Net borrowings (payments) under credit facilities	0	0	0
Debt issuance costs	(5.5)		0
Debt extinguishment charge	(20.9)		(35.8)
Net receipts (payments) on intercompany activity	172	112.5	72.7
Issuance of common stock			397.8
Dividends paid to stockholders	0	0	0
Dividends paid to noncontrolling interests	0	0	0
Sale to noncontrolling interest		0	0
Shares repurchased for income tax withholding on share-based compensation	(9.9)	(6.5)	(4.8)
Cash (used in) provided by financing activities	(15)	105.8	79.5
Increase (decrease) in cash and cash equivalents	0.2	(2)	(0.2)
Legal Entities [Member] | Subsidiary [Member]
Condensed Financial Statements, Captions [Line Items]
Cash flows provided by (used in) operating activities	(109.1)	(223.9)	(101.5)
Purchases of property, plant and equipment	(33.4)	(26.2)	(38.5)
Net receipts (payments) on intercompany activity	0	0	0
Proceeds from disposal of property, plant and equipment	0.1	2.6	0.1
Purchases of businesses		0
Proceeds from sale of business, net of transaction costs	0
Other	0	0	0
Cash flows provided by (used in) investing activities	(33.3)	(23.6)	(38.4)
Borrowings on long-term debt	0	0	0
Payments on long-term debt and finance leases	(0.2)	(0.9)	(0.3)
Net borrowings (payments) under credit facilities	0	0	0
Debt issuance costs	0		0
Debt extinguishment charge	0		0
Net receipts (payments) on intercompany activity	136	234	151.2
Issuance of common stock			0
Dividends paid to stockholders	0	0	0
Dividends paid to noncontrolling interests	0	0	0
Sale to noncontrolling interest		11.7	0
Shares repurchased for income tax withholding on share-based compensation	0	0	0
Cash (used in) provided by financing activities	135.8	244.8	150.9
Increase (decrease) in cash and cash equivalents	(6.6)	(2.7)	11
Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Cash flows provided by (used in) operating activities	344.1	738.7	214.7
Purchases of property, plant and equipment	(134.1)	(110.9)	(83.3)
Net receipts (payments) on intercompany activity	(308)	(346.5)	(223.9)
Proceeds from disposal of property, plant and equipment	91.9	0.2	2.6
Purchases of businesses		(10)
Proceeds from sale of business, net of transaction costs	158.1
Other	0	0	0.4
Cash flows provided by (used in) investing activities	(192.1)	(467.2)	(304.2)
Borrowings on long-term debt	0	7.1	8.5
Payments on long-term debt and finance leases	(6.7)	(5.3)	(2.3)
Net borrowings (payments) under credit facilities	4.9	(5.9)	1.6
Debt issuance costs	0		(0.8)
Debt extinguishment charge	0		0
Net receipts (payments) on intercompany activity	0	0	0
Issuance of common stock			0
Dividends paid to stockholders	(21)	(15)	(12)
Dividends paid to noncontrolling interests	(14)	(10)	(8)
Sale to noncontrolling interest		2.7	3.7
Shares repurchased for income tax withholding on share-based compensation	0	0	0
Cash (used in) provided by financing activities	(36.8)	(26.4)	(9.3)
Increase (decrease) in cash and cash equivalents	115.2	245.1	(98.8)
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Cash flows provided by (used in) operating activities	(21)	(15)	(12)
Purchases of property, plant and equipment	0	0	0
Net receipts (payments) on intercompany activity	308	346.5	223.9
Proceeds from disposal of property, plant and equipment	0	0	0
Purchases of businesses		0
Proceeds from sale of business, net of transaction costs	0
Other	0	0	0
Cash flows provided by (used in) investing activities	308	346.5	223.9
Borrowings on long-term debt	0	0	0
Payments on long-term debt and finance leases	0	0	0
Net borrowings (payments) under credit facilities	0	0	0
Debt issuance costs	0		0
Debt extinguishment charge	0		0
Net receipts (payments) on intercompany activity	(308)	(346.5)	(223.9)
Issuance of common stock			0
Dividends paid to stockholders	21	15	12
Dividends paid to noncontrolling interests	0	0	0
Sale to noncontrolling interest		0	0
Shares repurchased for income tax withholding on share-based compensation	0	0	0
Cash (used in) provided by financing activities	(287)	(331.5)	(211.9)
Increase (decrease) in cash and cash equivalents	$ 0	$ 0	$ 0

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Millions	Dec. 31, 2019USD ($)
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Purchase obligation, property, plant, and equipment	$ 116.5
Accrual for Environmental Loss Contingencies [Abstract]
Accrual for environmental remediation obligations	18
Accrued environmental loss contingencies recorded in other current liabilities	7
Components of Environmental Loss Accrual [Abstract]
Federal Superfund and comparable state-managed sites	3
Formerly owned or operated sites	13
Owned or controlled sites at which Company operations have been discontinued	1
Environmental Remediation Obligation For Ongoing Operations	1
Reasonably possible amount by which current matters may exceed reserves	$ 16

Selected Quarterly Financial _3

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Sales	$ 1,018.6	$ 1,018.7	$ 1,080.4	$ 1,004.8	$ 1,037.9	$ 1,020.2	$ 1,009.5	$ 979	$ 4,122.5	$ 4,046.6	$ 3,525.1
Gross profit	169.3	159.7	177.7	131.1	147.6	160.4	173.7	148.6	637.8	630.3	497
Net income (loss)	60	115.3	78.5	16.3	45	55.6	75.6	60.5	270.1	236.7	(79.7)
Net income attributable to ATI	$ 56.5	$ 111	$ 75.1	$ 15	$ 41.1	$ 50.5	$ 72.8	$ 58	$ 257.6	$ 222.4	$ (91.9)
Basic income (loss) attributable to ATI per common share (in dollars per share)									$ 2.05	$ 1.78	$ (0.83)
Basic net income (loss) attributable to ATI per common share (in dollars per share)	$ 0.45	$ 0.88	$ 0.60	$ 0.12	$ 0.33	$ 0.40	$ 0.58	$ 0.46	2.05	1.78	(0.83)
Diluted income (loss) attributable to ATI per common share (in dollars per share)									1.85	1.61	(0.83)
Diluted net income (loss) attributable to ATI per common share (in dollars per share)	$ 0.41	$ 0.78	$ 0.54	$ 0.12	$ 0.30	$ 0.37	$ 0.52	$ 0.42	$ 1.85	$ 1.61	$ (0.83)
Average shares outstanding (shares)	126.1	126.1	126.1	125.8	125.7	125.7	125.7	125.7	125.8	125.2	110.1

Selected Quarterly Financial _4

Selected Quarterly Financial Data (Unaudited) - Narrative (Details) - USD ($) shares in Millions, $ in Millions	Nov. 07, 2017	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Unusual Or Infrequent Item [Line Items]
Gain (Loss) on Disposition of Oil and Gas and Timber Property			$ 62.4	$ 29.3		$ 91.7
Gain (Loss) On Disposition Of Oil And Gas And Timber Property, Net Of Tax			60.5	27.3
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal						(1.8)	$ 0	$ 0
Restructuring and other charges		$ (4.5)				(4.5)	0	0
Restructuring And Other Charges, Net Of Tax		(4.3)
Gain on joint venture deconsolidation					$ 15.9	0	15.9	0
Deconsolidation, Gain (Loss), Amount, Net of tax					$ 14.7
NRV charge						25.6	(27.9)	(54)
Impairment of goodwill						0	0	114.4
Debt extinguishment charge		(21.6)				(21.6)	0	(37)
Debt extinguishment charge, net of tax		(20.5)
Non-cash joint venture impairment charge		(11.4)				(11.4)	$ 0	$ 0
Non-cash joint venture impairment charge, net of tax		(10.8)
Valuation allowance decrease due to change in judgment on the realizability of deferred tax assets		$ 41.9				45.1
Shares issued	17
Allegheny Technologies $350 million 9.375% Senior Notes due 2019
Unusual Or Infrequent Item [Line Items]
Debt instrument carrying amount									$ 350
Debt Instrument, Interest Rate, Stated Percentage									9.375%
Allegheny & Tsingshan Stainless
Unusual Or Infrequent Item [Line Items]
Non-cash joint venture impairment charge						$ (11.4)
Equity method investment ownership percentage		50.00%				50.00%
Forged Products
Unusual Or Infrequent Item [Line Items]
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal				(7.7)		$ (8.1)
Disposal Group, Not Discontinued Operation, Gain (Loss) On Disposal, Net Of Tax				$ (7.2)
Cast Products
Unusual Or Infrequent Item [Line Items]
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal			6.2			$ 6.2
Disposal Group, Not Discontinued Operation, Gain (Loss) On Disposal, Net Of Tax			$ 6
Tsingshan Group | Allegheny & Tsingshan Stainless
Unusual Or Infrequent Item [Line Items]
Equity method investment ownership percentage		50.00%				50.00%