ATI (ATI) 10-Q 31 Oct 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	9 Months Ended
	Sep. 30, 2018	Oct. 19, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Amendment Flag	false
Entity Registrant Name	ALLEGHENY TECHNOLOGIES INCORPORATED
Entity Central Index Key	1,018,963
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		125,684,396
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Entity Public Float			$ 1,900,000,000

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 153.5	$ 141.6
Accounts receivable, net	588.3	545.3
Short-term contract assets	51.6	0
Inventories, net	1,239.8	1,176.1
Prepaid expenses and other current assets	89.2	52.7
Total current assets	2,122.4	1,915.7
Property, plant and equipment, net	2,472.6	2,495.7
Goodwill	536.4	531.4
Other assets	257.6	242.6
Total assets	5,389	5,185.4
Current Liabilities:
Accounts payable	416.1	420.1
Accrued liabilities	228.7	282.4
Short-term contract liabilities	69.2	0
Short-term debt and current portion of long-term debt	16.6	10.1
Total current liabilities	730.6	712.6
Long-term debt	1,535.3	1,530.6
Accrued postretirement benefits	301.1	317.8
Pension liabilities	652.7	697
Deferred income taxes	12.1	9.7
Long-term contract liabilities	7.3	0
Other long-term liabilities	66.7	73.2
Total liabilities	3,305.8	3,340.9
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 September 30, 2018 and December 31, 2017; outstanding-125,684,396 shares at September 30, 2018 and 125,857,197 shares at December 31, 2017	12.7	12.7
Additional paid-in capital	1,608.5	1,596.3
Retained earnings	1,380.9	1,184.3
Treasury stock: 1,010,775 shares at September 30, 2018 and 837,974 shares at December 31, 2017	(30.6)	(26.1)
Accumulated other comprehensive loss, net of tax	(991.3)	(1,027.8)
Total ATI stockholders’ equity	1,980.2	1,739.4
Noncontrolling interests
Noncontrolling interests	103	105.1
Total Equity	2,083.2	1,844.5
Total Liabilities and Equity	$ 5,389	$ 5,185.4

CONSOLIDATED BALANCE SHEETS (PA

CONSOLIDATED BALANCE SHEETS (PARENTHETICAL) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
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	125,684,396	125,857,197
Treasury stock	1,010,775	837,974

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Sales	$ 1,020.2	$ 869.1	$ 3,008.7	$ 2,615.2
Cost of sales	859.8	763.8	2,526	2,260.8
Gross profit	160.4	105.3	482.7	354.4
Selling and administrative expenses	65.5	64.6	195.3	187.5
Impairment of goodwill	0	114.4	0	114.4
Operating income (loss)	94.9	(73.7)	287.4	52.5
Nonoperating retirement benefit expense	(8.4)	(13.6)	(25.5)	(40.9)
Interest expense, net	(24.8)	(34.2)	(75.8)	(102.2)
Other income, net	0.8	0.2	22.4	3.7
Income (loss) before income taxes	62.5	(121.3)	208.5	(86.9)
Income tax provision (benefit)	6.9	(1.9)	16.8	(2)
Net income (loss)	55.6	(119.4)	191.7	(84.9)
Less: Net income attributable to noncontrolling interests	5.1	1.8	10.4	8.7
Net income (loss) attributable to ATI	$ 50.5	$ (121.2)	$ 181.3	$ (93.6)
Basic net income (loss) attributable to ATI per common share (in dollars per share)	$ 0.40	$ (1.12)	$ 1.45	$ (0.87)
Diluted net income (loss) attributable to ATI per common share (in dollars per share)	0.37	(1.12)	1.31	(0.87)
Dividends declared per common share (in dollars per share)	$ 0	$ 0	$ 0	$ 0

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 55.6	$ (119.4)	$ 191.7	$ (84.9)
Currency translation adjustment
Unrealized net change arising during the period	(13.8)	24.2	(16.4)	39
Derivatives
Net derivatives gain (loss) on hedge transactions	(10.8)	9.2	2.4	(1.6)
Reclassification to net income (loss) of net realized gain	(2.6)	(1.2)	(10.3)	(3.5)
Income taxes on derivative transactions	0	4.8	0	(0.2)
Total	(13.4)	3.2	(7.9)	(4.9)
Postretirement benefit plans
Amortization of net actuarial loss	19.2	17.8	57.5	53.6
Amortization to net income (loss) of net prior service credits	(0.7)	(0.4)	(1.9)	(1.2)
Income taxes on postretirement benefit plans	0	(11.1)	0	1.9
Total	18.5	28.5	55.6	50.5
Other comprehensive income (loss), net of tax	(8.7)	55.9	31.3	84.6
Comprehensive income (loss)	46.9	(63.5)	223	(0.3)
Less: Comprehensive income (loss) attributable to noncontrolling interests	(3.9)	6.8	5.2	15.9
Comprehensive income (loss) attributable to ATI	$ 50.8	$ (70.3)	$ 217.8	$ (16.2)

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating Activities:
Net income (loss)	$ 191.7	$ (84.9)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization	117.1	120.7
Deferred taxes	2.8	1.7
Gain on joint venture deconsolidation	(15.9)	0
Impairment of goodwill	0	114.4
Changes in operating assets and liabilities:
Inventories	(137.2)	(64.1)
Accounts receivable	(43)	(73.8)
Accounts payable	71	56.2
Retirement benefits	(10.1)	(117.6)
Accrued liabilities and other	(59.8)	(6.4)
Cash provided by (used in) operating activities	116.6	(53.8)
Investing Activities:
Purchases of property, plant and equipment	(101.3)	(85.3)
Purchases of businesses	(10)	0
Asset disposals and other	2.2	3.2
Cash used in investing activities	(109.1)	(82.1)
Financing Activities:
Borrowings on long-term debt	7.1	8.5
Payments on long-term debt and capital leases	(4.6)	(1.9)
Net borrowings under credit facilities	4	28
Debt issuance costs	0	(0.8)
Dividends paid to noncontrolling interests	(10)	0
Sales to noncontrolling interests	14.4	2.2
Shares repurchased for income tax withholding on share-based compensation and other	(6.5)	(4.8)
Cash provided by financing activities	4.4	31.2
Increase (decrease) in cash and cash equivalents
Increase (decrease) in cash and cash equivalents	11.9	(104.7)
Cash and cash equivalents at beginning of period	141.6	229.6
Cash and cash equivalents at end of period	$ 153.5	$ 124.9

STATEMENTS OF CHANGES IN CONSOL

STATEMENTS OF CHANGES IN CONSOLIDATED EQUITY - USD ($) $ in Millions	Total	[CommonStockMember]	[AdditionalPaidInCapitalMember]	[RetainedEarningsMember]	[TreasuryStockMember]	[AccumulatedOtherComprehensiveIncomeMember]	[NoncontrollingInterestMember]
Total Stockholders' Equity 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	(84.9)			(93.6)			8.7
Other comprehensive income	84.6					77.4	7.2
Dividends to noncontrolling interests	(8)						(8)
Sales of subsidiary shares to noncontrolling interest	2.2						2.2
Employee stock plans	8.8		7.6	(0.9)	2.1
Total Stockholders' Equity at Sep. 30, 2017	1,447.5	11	1,196.4	1,182.6	(25.9)	(1,016.3)	99.7
Total Stockholders' Equity 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	191.7			181.3			10.4
Other comprehensive income	31.3					36.5	(5.2)
Cumulative effect of adoption of new accounting standard	15.5			15.5
Dividends to noncontrolling interests	(10)						(10)
Sales of subsidiary shares to noncontrolling interest	2.7						2.7
Employee stock plans	7.5		12.2	(0.2)	(4.5)
Total Stockholders' Equity at Sep. 30, 2018	$ 2,083.2	$ 12.7	$ 1,608.5	$ 1,380.9	$ (30.6)	$ (991.3)	$ 103

Accounting Policies

Accounting Policies	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Accounting Policies	Accounting Policies The interim consolidated financial statements include the accounts of Allegheny Technologies Incorporated and its subsidiaries. Unless the context requires otherwise, “Allegheny Technologies”, “ATI” and “the Company” refer to Allegheny Technologies Incorporated and its subsidiaries. These unaudited consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles for interim financial information and with the instructions for Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and note disclosures required by U.S. generally accepted accounting principles for complete financial statements. In management’s opinion, all adjustments (which include only normal recurring adjustments) considered necessary for a fair presentation have been included. These unaudited consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in the Company’s 2017 Annual Report on Form 10-K. The results of operations for these interim periods are not necessarily indicative of the operating results for any future period. The December 31, 2017 financial information has been derived from the Company’s audited consolidated financial statements. New Accounting Pronouncements Adopted In January 2018, the Company adopted changes issued by the Financial Accounting Standards Board (FASB) related to revenue recognition with customers. See Note 2 for further explanation related to this adoption, including all newly expanded disclosure requirements. In January 2018, the Company adopted changes issued by the FASB related to changes to the accounting for defined benefit pension and other postretirement benefit expenses. This new guidance requires the disaggregation of the service cost component from the other components of net benefit cost. The service cost component of net benefit cost is to be reported in the same line item on the consolidated statement of operations as other compensation costs arising from services rendered by the pertinent employees, while the other components of net benefit cost are to be presented in the consolidated statement of operations separately, outside a subtotal of operating income. The amendments also provide explicit guidance to allow only the service cost component of net benefit cost to be eligible for capitalization. With this adoption, the change in presentation of net benefit cost in the consolidated statement of operations was applied retrospectively, and the change in capitalization for only service cost was applied prospectively. The Company adopted this new guidance using the practical expedient that permits the use of the amounts disclosed in the retirement benefits footnote for the prior comparative periods as the estimation basis for applying the retrospective presentation requirements. This required accounting change did have a material impact to previously-reported operating income (loss) in the consolidated statement of operations due to the change in presentation of non-service cost expense components. For the third quarter and first nine months of 2017, applying the practical expedient, operating results were higher by $13.6 million and $40.9 million , respectively, with the reclassification of this amount representing the other components of net benefit cost to a newly-created nonoperating retirement benefit expense category. There was no net impact to the reported results before income taxes as a result of this accounting change. This change in presentation of net benefit cost did not affect ATI’s measure of segment operating profit; all defined benefit pension and other postretirement benefit expense attributable to business segment operations remains a component of business segment financial performance. The Company did have a one-time, unfavorable impact of $5.4 million to pre-tax reported results in the first quarter of 2018 upon adoption, primarily affecting the Flat Rolled Products business segment, due to the change limiting only the service cost component of net benefit cost to be capitalizable into inventory. In January 2018, the Company early adopted changes issued by the FASB related to changes to its accounting guidance for derivatives and hedging, which changes both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results. Some changes resulting from this new guidance include the elimination of the concept of recognizing periodic hedge ineffectiveness for cash flow hedges, changes to the recognition and presentation of changes in the fair value of the hedging instrument, enhancement of the ability to use the critical-terms-match method for the cash flow hedge of groups of forecasted transactions when the timing of the hedged transactions does not perfectly match the hedging instrument’s maturity date, and the addition of new disclosure requirements and amendments to existing ones. The Company applied this new guidance to hedging relationships existing on January 1, 2018, the date of adoption. The adoption of these changes did not have a material impact on the Company's financial statements, and disclosures in Note 7 reflect the requirements of this adoption. In August 2018, the FASB issued new accounting guidance for implementation costs incurred in a cloud computing arrangement that is a service contract. This guidance specifies which implementation costs can be capitalized in a hosting arrangement that is a service contract. The guidance aligns the accounting for implementation costs for hosting arrangements, regardless of whether they convey a license to the hosted software. This guidance is required to be adopted either retrospectively or prospectively by the Company beginning in fiscal year 2020 with early adoption permitted, including adoption in any interim period. The Company early adopted this guidance in the third quarter of 2018 on a retrospective basis, which did not have a material impact on the Company’s consolidated financial statements. Pending Accounting Pronouncements In February 2016, the FASB issued new accounting guidance for leases. This new guidance will require that a lessee recognize assets and liabilities on the balance sheet for all leases with a lease term of more than twelve months, with the result being the recognition of a right of use asset and a lease liability. The new lease accounting requirements are effective for ATI’s 2019 fiscal year. In July 2018, the FASB added an additional adoption method, which ATI will use to initially apply the new standard at the adoption date, January 1, 2019. This adoption method recognizes any impact to prior years’ results as a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. The Company is currently in the process of evaluating its existing lease portfolio, including accumulating all of the necessary information required to properly account for the leases under the new standard. In addition, ATI is implementing a company-wide lease management system to assist in the accounting and is evaluating additional changes to its processes and internal controls to ensure the standard’s reporting and disclosure requirements are met. The Company is currently evaluating the impact of the new guidance on its consolidated financial statements. 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 does not plan to 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 August 2018, the FASB issued new disclosure guidance for defined benefit plans, which modified certain required disclosures. This guidance is required to be adopted retrospectively by the Company beginning in fiscal year 2021, with early adoption permitted. The Company plans to early adopt this guidance in the fourth quarter of 2018, which is not expected to have an impact on the Company’s consolidated financial statements other than disclosures.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	Revenue from Contracts with Customers Accounting Policy On January 1, 2018, the Company adopted Accounting Standards Codification Topic 606 (ASC 606), Revenue from Contracts with Customers. This new 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 new 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 that the Company typically has 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. The Company has several customer agreements involving production of parts and components in the High Performance Materials and Components segment that require revenue to be recognized over time in accordance with the new guidance 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. Over-time recognition was a change from the accounting for these products, which was point-in-time prior to the adoption of the new standard. 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. Adoption Method and Impact 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 for several customer agreements, as discussed above, been applied. Contract assets of $49.7 million were recorded, along with a $34.2 million reduction to work-in-process inventory as a result of the ASC 606 adoption using the modified retrospective method. A portion of the cumulative effect impact of over-time revenue recognition related to inventory that is valued utilizing the last-in, first-out (LIFO) costing methodology. As such, an $11.8 million adjustment to the LIFO inventory valuation balance was required, with an equal and offsetting adjustment to net realizable value (NRV) inventory reserves, resulting in no net cumulative effect retained earnings impact for LIFO using the modified retrospective adoption method. See Note 3 for further information on inventory. In addition, as a result of this over-time recognition of these customer agreements, third quarter and first nine months of 2018 sales on the consolidated statement of operations were higher by $1.8 million and lower by $2.5 million , respectively, and cost of sales were higher by $1.1 million and lower by $4.1 million , respectively, as compared to what those amounts would have been under the previous revenue recognition guidance. On the consolidated balance sheet, inventories, net, were $4.1 million higher at September 30, 2018 as compared to what this amount would have been under the previous guidance. Also, $47.1 million of contract assets were recognized on the consolidated balance sheet at September 30, 2018 ( $47.0 million in short-term contract assets and $0.1 million in other long-term assets) related to this over-time revenue recognition. Also, as of January 1, 2018, amounts related largely to cash in advance from customers and progress billings were reclassified on the consolidated balance sheet to contract assets and liabilities in accordance with the new accounting guidance. Such reclassification resulted in a $3.9 million increase in accounts receivable, $28.8 million increase in inventories, net, $44.8 million decrease in accrued liabilities, and $10.7 million decrease in other-long term liabilities on January 1, 2018, with an offsetting increase in contract assets and liabilities ( $3.7 million in short-term contracts assets, $69.7 million in short-term contract liabilities and $22.2 million in other long-term liabilities). 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. As of September 30, 2018 , accounts receivable were higher by $3.7 million , inventories were higher by $14.2 million , accrued liabilities were lower by $46.7 million , and other long-term liabilities were lower by $7.3 million due to these reclassifications to contract assets and liabilities ( $4.6 million in short-term contract assets, $69.2 million short-term contract liabilities and $7.3 million in long-term contract liabilities). Disaggregation of Revenue The Company operates in two business segments; High Performance Materials & Components (HPMC) and Flat Rolled Products (FRP). 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 third quarters and nine months ended September 30, 2018 and 2017 were as follows: (in millions) Third quarter ended September 30, 2018 September 30, 2017 HPMC FRP Total HPMC FRP Total Diversified Global Markets: Aerospace & Defense $ 446.5 $ 52.7 $ 499.2 $ 389.5 $ 38.2 $ 427.7 Oil & Gas 17.9 110.3 128.2 14.3 84.1 98.4 Automotive 2.0 83.0 85.0 2.4 59.3 61.7 Electrical Energy 30.9 29.0 59.9 30.4 18.1 48.5 Medical 44.3 3.6 47.9 41.8 2.7 44.5 Total Key Markets 541.6 278.6 820.2 478.4 202.4 680.8 Food Equipment & Appliances 0.2 58.6 58.8 0.2 54.3 54.5 Construction/Mining 18.5 39.9 58.4 13.5 34.8 48.3 Electronics/Computers/Communications 1.0 40.3 41.3 1.1 41.2 42.3 Other 24.2 17.3 41.5 19.7 23.5 43.2 Total $ 585.5 $ 434.7 $ 1,020.2 $ 512.9 $ 356.2 $ 869.1 (in millions) Nine months ended September 30, 2018 September 30, 2017 HPMC FRP Total HPMC FRP Total Diversified Global Markets: Aerospace & Defense $ 1,311.7 $ 131.9 $ 1,443.6 $ 1,169.7 $ 110.8 $ 1,280.5 Oil & Gas 51.4 362.1 413.5 49.7 240.0 289.7 Automotive 7.4 237.1 244.5 6.4 200.0 206.4 Electrical Energy 101.9 78.4 180.3 84.1 60.1 144.2 Medical 131.5 11.3 142.8 134.2 8.5 142.7 Total Key Markets 1,603.9 820.8 2,424.7 1,444.1 619.4 2,063.5 Food Equipment & Appliances 0.3 181.0 181.3 1.0 167.9 168.9 Construction/Mining 55.1 114.8 169.9 37.6 107.0 144.6 Electronics/Computers/Communications 4.7 105.0 109.7 3.5 104.7 108.2 Other 74.1 49.0 123.1 63.5 66.5 130.0 Total $ 1,738.1 $ 1,270.6 $ 3,008.7 $ 1,549.7 $ 1,065.5 $ 2,615.2 (in millions) Third quarter ended September 30, 2018 September 30, 2017 HPMC FRP Total HPMC FRP Total Primary Geographical Market: United States $ 316.7 $ 290.9 $ 607.6 $ 273.4 $ 233.1 $ 506.5 Europe 173.2 40.5 213.7 164.8 23.8 188.6 Asia 60.9 84.0 144.9 45.1 75.2 120.3 Canada 16.3 7.5 23.8 15.3 5.8 21.1 South America, Middle East and other 18.4 11.8 30.2 14.3 18.3 32.6 Total $ 585.5 $ 434.7 $ 1,020.2 $ 512.9 $ 356.2 $ 869.1 (in millions) Nine months ended September 30, 2018 September 30, 2017 HPMC FRP Total HPMC FRP Total Primary Geographical Market: United States $ 898.6 $ 839.1 $ 1,737.7 $ 820.5 $ 735.2 $ 1,555.7 Europe 565.4 104.3 669.7 502.2 74.4 576.6 Asia 180.7 258.7 439.4 127.3 190.2 317.5 Canada 51.3 29.0 80.3 52.4 21.1 73.5 South America, Middle East and other 42.1 39.5 81.6 47.3 44.6 91.9 Total $ 1,738.1 $ 1,270.6 $ 3,008.7 $ 1,549.7 $ 1,065.5 $ 2,615.2 Comparative information of the Company’s major high-value and standard products based on their percentages of total sales is as follows: Third quarter ended September 30, 2018 September 30, 2017 HPMC FRP Total HPMC FRP Total Diversified Products and Services: High-Value Products Nickel-based alloys and specialty alloys 32 % 29 % 30 % 30 % 27 % 28 % Precision forgings, castings and components 33 % — % 18 % 33 % — % 19 % Titanium and titanium-based alloys 25 % 3 % 16 % 26 % 3 % 17 % Precision and engineered strip — % 34 % 14 % — % 34 % 14 % Zirconium and related alloys 10 % — % 6 % 11 % — % 6 % Total High-Value Products 100 % 66 % 84 % 100 % 64 % 84 % Standard Products Stainless steel sheet — % 20 % 9 % — % 20 % 9 % Specialty stainless sheet — % 9 % 4 % — % 11 % 4 % Stainless steel plate and other — % 5 % 3 % — % 5 % 3 % Total Standard Products — % 34 % 16 % — % 36 % 16 % Total 100 % 100 % 100 % 100 % 100 % 100 % Nine months ended September 30, 2018 September 30, 2017 HPMC FRP Total HPMC FRP Total Diversified Products and Services: High-Value Products Nickel-based alloys and specialty alloys 31 % 29 % 30 % 30 % 23 % 27 % Precision forgings, castings and components 35 % — % 20 % 32 % — % 19 % Titanium and titanium-based alloys 24 % 5 % 15 % 27 % 4 % 17 % Precision and engineered strip — % 32 % 14 % — % 34 % 14 % Zirconium and related alloys 10 % — % 5 % 11 % — % 6 % Total High-Value Products 100 % 66 % 84 % 100 % 61 % 83 % Standard Products Stainless steel sheet — % 20 % 9 % — % 22 % 9 % Specialty stainless sheet — % 10 % 4 % — % 12 % 4 % Stainless steel plate and other — % 4 % 3 % — % 5 % 4 % Total Standard Products — % 34 % 16 % — % 39 % 17 % Total 100 % 100 % 100 % 100 % 100 % 100 % The Company maintains a backlog of confirmed orders totaling $2.17 billion and $1.81 billion at September 30, 2018 and 2017 , respectively. Due to the structure of the Company’s LTAs, 82% of this backlog at September 30, 2018 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. Contract balances As of September 30, 2018 and December 31, 2017 , accounts receivable with customers were $594.5 million and $550.9 million , respectively. The following represents the rollforward of accounts receivable - reserve for doubtful accounts and contract assets and liabilities for the nine months ended September 30, 2018 : (in millions) Accounts Receivable - Reserve for Doubtful Accounts Balance as of January 1, 2018 $ 5.9 Expense to increase the reserve 0.7 Write-off of uncollectible accounts (0.4 ) Balance as of September 30, 2018 $ 6.2 (in millions) Contract Assets Short-term Balance as of January 1, 2018 $ 36.5 Recognized in current year 66.2 Reclassified to accounts receivable (67.9 ) Impairment — Reclassification to/from long-term 16.8 Balance as of September 30, 2018 $ 51.6 Long-term Balance as of January 1, 2018 $ 16.9 Recognized in current year — Reclassified to accounts receivable — Impairment — Reclassification to/from short-term (16.8 ) Balance as of September 30, 2018 $ 0.1 (in millions) Contract Liabilities Short-term Balance as of January 1, 2018 $ 69.7 Recognized in current year 46.9 Amounts in beginning balance reclassified to revenue (40.1 ) Current year amounts reclassified to revenue (23.6 ) Other 1.7 Reclassification to/from long-term 14.6 Balance as of September 30, 2018 $ 69.2 Long-term Balance as of January 1, 2018 $ 22.2 Recognized in current year 0.5 Amounts in beginning balance reclassified to revenue (0.8 ) Current year amounts reclassified to revenue — Other — Reclassification to/from short-term (14.6 ) Balance as of September 30, 2018 $ 7.3 Contract costs for obtaining and fulfilling a contract were $5.2 million as of September 30, 2018 , which are reported in other long-term assets on the consolidated balance sheet. Amortization expense for the three and nine months ended September 30, 2018 of these contract costs was $0.3 million and $0.9 million , respectively.

Inventories

Inventories	9 Months Ended
	Sep. 30, 2018
Inventory Disclosure [Abstract]
Inventories	Inventories Inventories at September 30, 2018 and December 31, 2017 were as follows (in millions): September 30, December 31, Raw materials and supplies $ 204.3 $ 162.8 Work-in-process 929.9 955.5 Finished goods 190.0 165.0 Total inventories at current cost 1,324.2 1,283.3 Adjustment from current cost to LIFO cost basis 1.7 43.1 Inventory valuation reserves (86.1 ) (121.5 ) Progress payments — (28.8 ) Total inventories, net $ 1,239.8 $ 1,176.1 Inventories are stated at the lower of cost (LIFO, first-in, first-out (FIFO), and average cost methods) or market. 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. 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 NRV inventory valuation reserves to adjust carrying value of LIFO inventory to current replacement cost. These NRV reserves were $47.5 million at December 31, 2017 and $6.2 million at September 30, 2018 . Impacts to cost of sales for changes in the LIFO costing methodology and associated NRV inventory reserves were as follows (in millions): Nine months ended September 30, 2018 2017 LIFO benefit (charge) $ (29.5 ) $ (51.5 ) NRV benefit (charge) 29.5 51.3 Net cost of sales impact $ — $ (0.2 ) As a result of the adoption of ASC 606 on revenue recognition on January 1, 2018, progress payments were reclassified on the consolidated balance sheet from inventories to contract liabilities. In addition, a cumulative effect adjustment for the ASC 606 adoption relating to contracts requiring over-time revenue recognition resulted in a $34.2 million reduction to work-in-process inventory at the January 1 adoption date. A portion of that inventory is valued utilizing the LIFO costing methodology. As such, an $11.8 million reduction to the LIFO valuation balance was required, with an offsetting $11.8 million adjustment to the NRV reserve, resulting in no retained earnings impact. See Note 2 for further explanation of the ASC 606 adoption.

Property Plant And Equipment

Property Plant And Equipment	9 Months Ended
	Sep. 30, 2018
Property, Plant and Equipment [Abstract]
Property Plant and Equipment	Property, Plant and Equipment Property, plant and equipment at September 30, 2018 and December 31, 2017 was as follows (in millions): September 30, December 31, Land $ 31.6 $ 31.7 Buildings 851.1 844.5 Equipment and leasehold improvements 3,646.0 3,597.6 4,528.7 4,473.8 Accumulated depreciation and amortization (2,056.1 ) (1,978.1 ) Total property, plant and equipment, net $ 2,472.6 $ 2,495.7 The construction in progress portion of property, plant and equipment at September 30, 2018 was $128.1 million .

Joint Ventures

Joint Ventures	9 Months Ended
	Sep. 30, 2018
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. Majority-Owned Joint Ventures 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 Flat Rolled Products 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 September 30, 2018 were $30.0 million . 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. Cash and cash equivalents held by this joint venture as of September 30, 2018 were $10.4 million . During the first quarter of 2018, the Company received $2.7 million for the sale of noncontrolling interest related to Next Gen Alloys LLC, which is reported as a financing activity on the consolidated statements of cash flows. Equity Method Joint Ventures 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 the first nine months of 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 (DRAP) facility in Midland, PA. ATI provides hot-rolling conversion services to A&T Stainless using the FRP 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 FRP segment results. Following this deconsolidation, ATI accounts for the A&T Stainless joint venture under the equity method of accounting. ATI’s share of the A&T Stainless joint venture results was a $0.3 million loss and $0.2 million of income for the three and nine months ended September 30, 2018 , respectively, which is included in the FRP segment’s operating results, and within other income, net, on the consolidated statements of operations. In late March 2018, ATI filed for an exclusion from the recently enacted Section 232 tariffs on behalf of the A&T Stainless JV, which imports semi-finished stainless slab products from Indonesia. In the absence of an exclusion, these slabs will be subject to the 25% tariff levied on all stainless steel products imported into the United States. The Company continues to work within the U.S. Commerce Department’s Section 232 tariff exclusion request process to secure an exclusion on behalf of the A&T Stainless joint venture. Third quarter 2018 results of A&T Stainless were negatively impacted by these tariffs. 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/(loss) was $0.5 million and $2.3 million for the three and nine months ended September 30, 2018 , respectively, and $(0.1) million and $0.1 million for the three and nine months ended September 30, 2017, respectively, which is included in the FRP segment’s operating results, and within other income, net, in the three and nine months ended September 30, 2018 on the consolidated statements of operations. This equity income is classified in cost of sales for the three and nine months ended September 30, 2017 on the consolidated statements of operations.

Debt

Debt	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Debt	Debt Debt at September 30, 2018 and December 31, 2017 was as follows (in millions): September 30, December 31, Allegheny Technologies 5.875% Notes due 2023 (a) $ 500.0 $ 500.0 Allegheny Technologies 5.95% Notes due 2021 500.0 500.0 Allegheny Technologies 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 2022 100.0 100.0 U.S. revolving credit facility — — Foreign credit facilities 10.0 6.3 Other 15.5 10.0 Debt issuance costs (11.1 ) (13.1 ) Total debt 1,551.9 1,540.7 Short-term debt and current portion of long-term debt 16.6 10.1 Total long-term debt $ 1,535.3 $ 1,530.6 (a) Bearing interest at 7.875% effective February 15, 2016. Revolving Credit Facility The Company has a $500 million Asset Based Lending (ABL) Credit Facility, which is collateralized by the accounts receivable and inventory of the Company’s domestic operations. The ABL facility, which matures in February 2022, includes a $400 million revolving credit facility, a letter of credit sub-facility of up to $200 million , and a $100 million term loan (Term Loan). The Term Loan has an interest rate of 3.0% plus a LIBOR spread and can be prepaid in increments of $50 million if certain minimum liquidity conditions are satisfied. In July 2018, the ABL facility was amended to reduce the Term Loan base interest rate to 2.5% plus a LIBOR spread. In conjunction with this amendment, the Company entered into a $50 million floating-for-fixed interest rate swap which converts half of the Term Loan to a 5.44% fixed interest rate. The swap matures in January 2021. The applicable interest rate for revolving credit borrowings under the ABL facility includes interest rate spreads based on available borrowing capacity that range between 1.75% and 2.25% for LIBOR-based borrowings and between 1.0% and 1.5% for base rate borrowings. The ABL facility contains a financial covenant whereby the Company must maintain a fixed charge coverage ratio of not less than 1.00 : 1.00 after an event of default has occurred and is continuing or if the undrawn availability under the ABL revolving credit portion of the facility is less than the greater of (i) 10% of the then applicable maximum borrowing amount under the revolving credit portion of the ABL and any outstanding Term Loan balance, or (ii) $40.0 million . The Company was in compliance with the fixed charge coverage ratio covenant at September 30, 2018 . Additionally, the Company must demonstrate liquidity, as calculated in accordance with the terms of the ABL facility, of at least $700 million on the date that is 91 days prior to January 15, 2021, the maturity date of the 5.95% Senior Notes due 2021, and that such liquidity is available at all times thereafter until the 5.95% Senior Notes due 2021 are paid in full or refinanced. As of September 30, 2018 , there were no outstanding borrowings under the revolving portion of the ABL facility, and $35.1 million was utilized to support the issuance of letters of credit. Average revolving credit borrowings under the ABL facility for the first nine months of 2018 and 2017 were $56 million and $46 million , respectively, bearing an average annual interest rate of 3.651% and 3.276% , respectively.

Derivative Financial Instrument

Derivative Financial Instruments and Hedging	9 Months Ended
	Sep. 30, 2018
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. In January 2018, the Company early adopted changes issued by the FASB related to accounting guidance for derivatives and hedging, which includes, among other things, the elimination of the concept of recognizing periodic hedge ineffectiveness for cash flow 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 September 30, 2018 , 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 12 million pounds of nickel with hedge dates through 2021. The aggregate notional amount hedged is approximately 12% of a single year’s estimated nickel raw material purchase requirements. At September 30, 2018 , the outstanding financial derivatives used to hedge the Company’s exposure to energy cost volatility included natural gas cost hedges. At September 30, 2018 , the Company hedged approximately 35% of the Company’s forecasted domestic requirements for natural gas for the remainder of 2018, approximately 35% for 2019, and approximately 30% for 2020. 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. At September 30, 2018, the Company held euro forward sales contracts designated as cash flow hedges with a notional value of approximately 16 million euros with maturity dates through May 2019. In addition, the Company may also designate cash balances held in foreign currencies as hedges of forecasted foreign currency transactions. The Company may enter into derivative interest rate contracts to maintain a reasonable balance between fixed- and floating-rate debt. In July 2018, the Company entered into a $50 million floating-for-fixed interest rate swap which converts half of the Term Loan to a 5.44% fixed interest rate. The Company designated the interest rate swap as a cash flow hedge of the Company’s exposure to the variability of the payment of interest on a portion of its Term Loan borrowings. The swap matures in January 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 are substantial and creditworthy commercial banks that are recognized market makers. The Company controls its credit exposure by diversifying across multiple counterparties and by monitoring credit ratings and credit default swap spreads of its counterparties. The Company also enters into master netting agreements with counterparties when possible. The fair values of the Company’s derivative financial instruments are presented below, representing the gross amounts recognized which are not offset by counterparty or by type of item hedged. All fair values for these derivatives were measured using Level 2 information as defined by the accounting standard hierarchy, which includes quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and inputs derived principally from or corroborated by observable market data. (In millions) Asset derivatives Balance sheet location September 30, December 31, Derivatives designated as hedging instruments: Foreign exchange contracts Prepaid expenses and other current assets $ 0.3 $ — Natural gas contacts Prepaid expenses and other current assets 0.3 0.1 Nickel and other raw material contracts Prepaid expenses and other current assets 4.3 10.5 Interest rate swap Other assets 0.1 — Natural gas contracts Other assets 0.1 0.3 Nickel and other raw material contracts Other assets 2.7 5.5 Total derivatives designated as hedging instruments 7.8 16.4 Derivatives not designated as hedging instruments: Foreign exchange contracts Prepaid expenses and other current assets 0.3 0.1 Total derivatives not designated as hedging instruments 0.3 0.1 Total asset derivatives $ 8.1 $ 16.5 Liability derivatives Balance sheet location Derivatives designated as hedging instruments: Interest rate swap Accrued liabilities $ 0.2 $ — Natural gas contracts Accrued liabilities 0.2 0.9 Nickel and other raw material contracts Accrued liabilities 2.9 2.1 Natural gas contracts Other long-term liabilities 0.4 0.3 Nickel and other raw material contracts Other long-term liabilities 1.0 2.2 Total derivatives designated as hedging instruments 4.7 5.5 Total liability derivatives $ 4.7 $ 5.5 For derivative financial instruments that are designated as cash flow hedges, the gain or loss on the derivative is reported as a component of other comprehensive income (OCI) and reclassified into earnings in the same period or periods during which the hedged item affects earnings. For derivative financial instruments that are designated as fair value hedges, changes in the fair value of these derivatives are recognized in current period results and are reported as changes within accrued liabilities and other on the consolidated statements of cash flows. There were no outstanding fair value hedges as of September 30, 2018. 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 effecting results of operations or other comprehensive income, when applicable (see Note 14 for further explanation). Assuming market prices remain constant with those at September 30, 2018 , a pre-tax gain of $1.6 million is expected to be recognized over the next 12 months. Activity with regard to derivatives designated as cash flow hedges for the three and nine month periods ended September 30, 2018 and 2017 was as follows (in millions): Amount of Gain (Loss) Recognized in OCI on Derivatives Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (a) Three months ended September 30, Three months ended September 30, Derivatives in Cash Flow Hedging Relationships 2018 2017 2018 2017 Nickel and other raw material contracts $ (8.0 ) $ 5.6 $ 1.7 $ (0.9 ) Natural gas contracts (0.1 ) — — (0.7 ) Foreign exchange contracts 0.2 0.1 0.4 2.4 Interest rate swap (0.2 ) — (0.1 ) — Total $ (8.1 ) $ 5.7 $ 2.0 $ 0.8 Amount of Gain (Loss) Recognized in OCI on Derivatives Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (a) Nine months ended September 30, Nine months ended September 30, Derivatives in Cash Flow Hedging Relationships 2018 2017 2018 2017 Nickel and other raw material contracts $ 1.3 $ 1.2 $ 7.9 $ (2.5 ) Natural gas contracts 0.1 (2.1 ) (0.4 ) (2.8 ) Foreign exchange contracts 0.7 (0.1 ) 0.4 7.5 Interest rate swap (0.2 ) — (0.1 ) — Total $ 1.9 $ (1.0 ) $ 7.8 $ 2.2 (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. The Company has 10 million euro notional value outstanding as of September 30, 2018 of foreign currency forward contracts not designated as hedges, with maturity dates into the second quarter of 2019. These derivatives that are not designated as hedging instruments were as follows: (In millions) Amount of Gain (Loss) Recognized in Income on Derivatives Three months ended September 30, Nine months ended September 30, Derivatives Not Designated as Hedging Instruments 2018 2017 2018 2017 Foreign exchange contracts $ — $ (0.1 ) $ 0.1 $ (0.7 ) 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.

Fair Value Of Financial Instrum

Fair Value Of Financial Instruments	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value Of Financial Instruments	Fair Value of Financial Instruments The estimated fair value of financial instruments at September 30, 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 $ 153.5 $ 153.5 $ 153.5 $ — Derivative financial instruments: Assets 8.1 8.1 — 8.1 Liabilities 4.7 4.7 — 4.7 Debt (a) 1,563.0 1,945.8 1,820.3 125.5 The estimated fair value of financial instruments at December 31, 2017 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 $ 141.6 $ 141.6 $ 141.6 $ — Derivative financial instruments: Assets 16.5 16.5 — 16.5 Liabilities 5.5 5.5 — 5.5 Debt (a) 1,553.8 1,853.2 1,736.9 116.3 (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 2018 or 2017 . The following methods and assumptions were used by the Company in estimating the fair value of its financial instruments: Cash and cash equivalents: Fair value was 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 Company’s publicly traded debt were based on Level 1 information. The fair values of the other short-term and long-term debt were determined using Level 2 information.

Retirement Benefits

Retirement Benefits	9 Months Ended
	Sep. 30, 2018
Retirement Benefits [Abstract]
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 funds the U.S. pension plans in accordance with the Employee Retirement Income Security Act of 1974, as amended, and the Internal Revenue Code (IRC). 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. For the three month periods ended September 30, 2018 and 2017 , the components of pension and other postretirement benefit expense for the Company’s defined benefit plans included the following (in millions): Pension Benefits Other Postretirement Benefits Three months ended September 30, Three months ended September 30, 2018 2017 2018 2017 Service cost - benefits earned during the year $ 4.1 $ 3.5 $ 0.6 $ 0.6 Interest cost on benefits earned in prior years 26.2 29.2 3.2 3.7 Expected return on plan assets (39.5 ) (36.7 ) — — Amortization of prior service cost (credit) 0.1 0.3 (0.8 ) (0.7 ) Amortization of net actuarial loss 16.5 15.6 2.7 2.2 Total retirement benefit expense $ 7.4 $ 11.9 $ 5.7 $ 5.8 For the nine month periods ended September 30, 2018 and 2017 , the components of pension and other postretirement benefit expense for the Company’s defined benefit plans included the following (in millions): Pension Benefits Other Postretirement Benefits Nine months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 Service cost - benefits earned during the year $ 12.4 $ 10.5 $ 1.8 $ 1.8 Interest cost on benefits earned in prior years 78.5 87.6 9.5 11.0 Expected return on plan assets (118.5 ) (110.1 ) — — Amortization of prior service cost (credit) 0.3 0.9 (2.2 ) (2.1 ) Amortization of net actuarial loss 49.5 46.9 8.0 6.7 Curtailment loss 0.4 — — — Total retirement benefit expense $ 22.6 $ 35.8 $ 17.1 $ 17.4 On June 1, 2018, a new four-year collective bargaining agreement (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. The Company has now completely closed its U.S. defined benefit pension plan to new entrants.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company maintains income tax valuation allowances on its U.S. Federal and state deferred tax assets due to a three year cumulative loss condition, which limits the ability to consider other positive subjective evidence, such as projections of future results, to assess the realizability of deferred tax assets. Results in both 2018 and 2017 include impacts from income taxes that differ from applicable standard tax rates, primarily related to income tax valuation allowances. Third quarter 2018 results included a provision for income taxes of $6.9 million , or 11.0% of income before income taxes, primarily related to income taxes on non-U.S. operations. The overall income tax provision for the third quarter 2018 includes discrete adjustments of $0.9 million of tax expense resulting from tax expense related to uncertain tax positions, impact of change in tax rates and tax calculations for entities excluded from the annual effective tax rate. The third quarter 2017 benefit for income taxes was $1.9 million , which included $0.3 million of discrete tax benefits. The Company continues to account for impacts of the Tax Cuts and Jobs Act (Tax Act) as estimated amounts, pending further information and analysis, which includes final tax return filings, analysis of foreign earnings and profits (E&P), and interpretive Internal Revenue Service (IRS) guidance. The Company estimated the impact of the Tax Act as part of the 2017 year-end financial statements. Additional IRS guidance and IRC elections have been published, which have aided in refining the initial estimate related to the tax on the mandatory repatriation of foreign earnings, otherwise known as the “transition tax”. The transition tax is a tax on certain previously untaxed accumulated and current E&P of the Company’s foreign subsidiaries. The Company was able to reasonably estimate the transition tax and recorded an initial provisional transition tax liability of $0 as of December 31, 2017. The initial estimate was approximately $100 million of federal taxable income on the mandatory deemed repatriation of foreign E&P, for which the Company planned to utilize a portion of its federal net operating loss (NOL) deferred tax asset to fully offset the estimated transition tax liability of $35 million . On the basis of revised E&P computations that were calculated during the second quarter of 2018, as well as further IRS guidance issued during this 2018 period, the Company recognized an additional measurement-period adjustment of $5.9 million related to the transition tax liability, with a corresponding adjustment of $5.9 million to income tax expense during the nine months ended September 30, 2018. This was based on the Company’s updated untaxed foreign E&P estimate of $97.5 million , resulting in a transition tax liability of $34.1 million . The Company’s current strategy is to make an election to not utilize NOLs to offset the transition tax liability, and instead utilize available tax credits of $28.2 million , resulting in a remaining transition tax liability of $5.9 million . Due to final regulations not being issued, the accounting for this item is not yet complete. The Company expects to complete the accounting within the prescribed one-year measurement period from the Tax Act enactment date. The transition tax liability is payable over eight years under the IRC, and the first installment payment of $0.5 million was paid in April 2018. The adoption of this strategy would preserve $97.5 million federal NOL tax attributes that the Company expects it will be able to utilize before expiration, while using tax credits that would potentially expire due to utilization limitations. The overall impact on the Company’s deferred tax assets as of December 31, 2017 is zero due to the net valuation allowance position. Changes to certain deferred tax assets and the valuation allowance at December 31, 2017 as a result of the Company’s expected use of tax credits to meet a portion of the transition tax were as follows (in millions): Deferred Income Tax Assets Estimate Refinement Originally Reported Change Net operating loss tax carryovers $ 357.0 $ 336.1 $ 20.9 Tax credits $ 62.4 $ 92.6 $ (30.2 ) Gross deferred income tax assets $ 733.6 $ 742.9 $ (9.3 ) Valuation allowance (264.7 ) (274.0 ) 9.3 Total deferred income tax assets $ 468.9 $ 468.9 $ — The utilization of the tax credits of $28.2 million does not match the change in the deferred tax asset amount due to the refinement of the transition tax calculation. Discrete tax benefits of $5.8 million were recognized in the first nine months of 2018 relating to valuation allowance releases resulting from the acceptance of net operating loss carryback claims and amendments of historical tax returns due to changes in estimated tax credit utilization resulting from recently-issued IRS guidance. For the nine months of 2018, the provision for income taxes was $16.8 million , or 8.1% , compared to a benefit for income taxes of $2.0 million , for the comparable 2017 period. The first nine months of 2018 included discrete tax expense of $0.9 million , while the comparable 2017 period included discrete tax benefits of $7.0 million , largely for the effects of amending tax returns for prior periods in certain domestic jurisdictions.

Business Segments

Business Segments	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
Business Segments	Business Segments The Company operates in two business segments: High Performance Materials & Components and Flat Rolled Products. The measure of segment operating profit, which is used to analyze the performance and results of the business segments, 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, restructuring and asset impairment charges, and non-operating gains and losses. Management believes segment operating profit, as defined, provides an appropriate measure of controllable operating results at the business segment level. Following is certain financial information with respect to the Company’s business segments for the periods indicated (in millions): Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 Total sales: High Performance Materials & Components $ 615.2 $ 526.3 $ 1,806.3 $ 1,593.3 Flat Rolled Products 452.5 372.3 1,330.9 1,118.5 1,067.7 898.6 3,137.2 2,711.8 Intersegment sales: High Performance Materials & Components 29.7 13.4 68.2 43.6 Flat Rolled Products 17.8 16.1 60.3 53.0 47.5 29.5 128.5 96.6 Sales to external customers: High Performance Materials & Components 585.5 512.9 1,738.1 1,549.7 Flat Rolled Products 434.7 356.2 1,270.6 1,065.5 $ 1,020.2 $ 869.1 $ 3,008.7 $ 2,615.2 Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 Operating profit: High Performance Materials & Components $ 76.0 $ 61.7 $ 259.4 $ 180.6 Flat Rolled Products 29.5 (7.3 ) 66.5 14.6 Total operating profit 105.5 54.4 325.9 195.2 LIFO and net realizable value reserves — (0.1 ) — (0.2 ) Corporate expenses (14.8 ) (14.8 ) (40.9 ) (36.9 ) Closed operations and other expenses (3.4 ) (12.2 ) (16.6 ) (28.4 ) Impairment of goodwill — (114.4 ) — (114.4 ) Gain on joint venture deconsolidation (See Note 5) — — 15.9 — Interest expense, net (24.8 ) (34.2 ) (75.8 ) (102.2 ) Income before income taxes $ 62.5 $ (121.3 ) $ 208.5 $ (86.9 ) Closed operations and other expenses were lower in the third quarter of 2018 , compared to the prior year period, primarily due to lower carrying costs for closed facilities, mainly related to property taxes and insurance expenses for the Rowley, UT and Midland, PA locations, compared to the prior year period. On a year to date basis, closed operations and other expenses were lower in 2018 primary due to foreign currency remeasurement gains compared to remeasurement losses in 2017 from the Company’s European Treasury Center operation as well as lower carrying costs for closed facilities. The reduction in interest expense compared to the prior year period is due to the redemption of the Company’s previously outstanding 9.375% Senior Notes due 2019 in the fourth quarter of 2017. During the third quarter of 2017, the Company recorded a $114.4 million goodwill impairment charge to write-off all the goodwill assigned to ATI Cast Products, a titanium investment casting business in the HPMC segment. This goodwill impairment charge was excluded from 2017 HPMC business segment results. On July 12, 2018, the Company acquired the assets of Addaero Manufacturing (Addaero) for $10 million of cash consideration. Addaero is a leader in metal alloy-based additive manufacturing for the aerospace and defense industries, located in New Britain, CT. Management expects the acquisition to expand the Company’s capabilities to provide comprehensive customer solutions ranging from the design of parts for additive manufacturing to the production of ready-to-install components. The acquisition of Addaero is another building block in the strategy to enhance ATI’s full specialty materials capabilities to provide end customers with finished products. This business is reported as part of the HPMC segment from the date of the acquisition. The purchase price allocation includes 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.

Per Share Information

Per Share Information	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Per Share Information	Per Share Information The following table sets forth the computation of basic and diluted income (loss) per common share: Three months ended Nine months ended (In millions, except per share amounts) September 30, September 30, 2018 2017 2018 2017 Numerator: Numerator for basic income (loss) per common share – Net income (loss) attributable to ATI $ 50.5 $ (121.2 ) $ 181.3 $ (93.6 ) Effect of dilutive securities: 4.75% Convertible Senior Notes due 2022 3.2 — 9.6 — Numerator for diluted income (loss) per common share – Net income (loss) attributable to ATI after assumed conversions $ 53.7 $ (121.2 ) $ 190.9 $ (93.6 ) Denominator: Denominator for basic net income (loss) per common share – weighted average shares 125.2 107.7 125.1 107.7 Effect of dilutive securities: Share-based compensation 0.9 — 0.7 — 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 146.0 107.7 145.7 107.7 Basic net income (loss) attributable to ATI per common share $ 0.40 $ (1.12 ) $ 1.45 $ (0.87 ) Diluted net income (loss) attributable to ATI per common share $ 0.37 $ (1.12 ) $ 1.31 $ (0.87 ) Common stock that would be issuable upon the assumed conversion of the 4.75% Convertible Senior Notes due 2022 and other option equivalents and contingently issuable shares are excluded from the computation of contingently issuable shares, and therefore, from the denominator for diluted earnings per share, if the effect of inclusion is anti-dilutive. There were no anti-dilutive shares for the three and nine month periods ended September 30, 2018 . There were 20.9 million and 20.7 million anti-dilutive shares for the three and nine month periods ended September 30, 2017, respectively.

Financial Information for Subsi

Financial Information for Subsidiary and Guarantor Parent	9 Months Ended
	Sep. 30, 2018
Condensed Financial Information Disclosure [Abstract]
Financial Information for Subsidiary and Guarantor Parent	Financial Information for Subsidiary and Guarantor Parent The payment obligations under the $150 million 6.95% debentures due 2025 issued by Allegheny Ludlum, LLC (the “Subsidiary”) are fully and unconditionally guaranteed by Allegheny Technologies Incorporated (the “Guarantor Parent”). In accordance with positions established by the 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 ATI Pension Plan, the Company’s U.S. qualified defined benefit pension plan (the “Plan”) which covers 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 Plan assets or liabilities, or the related deferred taxes and valuation allowances. The Plan 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 September 30, 2018 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Assets: Cash and cash equivalents $ 1.1 $ 6.8 $ 145.6 $ — $ 153.5 Accounts receivable, net — 156.4 431.9 — 588.3 Intercompany notes receivable — — 3,913.5 (3,913.5 ) — Short-term contract assets — — 51.6 — 51.6 Inventories, net — 238.6 1,001.2 — 1,239.8 Prepaid expenses and other current assets 14.7 38.4 36.1 — 89.2 Total current assets 15.8 440.2 5,579.9 (3,913.5 ) 2,122.4 Property, plant and equipment, net 0.7 1,551.6 920.3 — 2,472.6 Goodwill — — 536.4 — 536.4 Intercompany notes receivable — — 200.0 (200.0 ) — Investment in subsidiaries 6,131.9 37.7 — (6,169.6 ) — Other assets 34.1 40.5 183.0 — 257.6 Total assets $ 6,182.5 $ 2,070.0 $ 7,419.6 $ (10,283.1 ) $ 5,389.0 Liabilities and stockholders’ equity: Accounts payable $ 4.6 $ 153.4 $ 258.1 $ — $ 416.1 Accrued liabilities 37.3 68.8 122.6 — 228.7 Intercompany notes payable 2,144.5 1,769.0 — (3,913.5 ) — Short-term contract liabilities — 30.7 38.5 — 69.2 Short-term debt and current portion of long-term debt 0.2 0.8 15.6 — 16.6 Total current liabilities 2,186.6 2,022.7 434.8 (3,913.5 ) 730.6 Long-term debt 1,277.5 152.0 105.8 — 1,535.3 Intercompany notes payable — 200.0 — (200.0 ) — Accrued postretirement benefits — 243.8 57.3 — 301.1 Pension liabilities 602.0 3.9 46.8 — 652.7 Deferred income taxes 12.1 — — — 12.1 Long-term contract liabilities — — 7.3 — 7.3 Other long-term liabilities 21.1 17.5 28.1 — 66.7 Total liabilities 4,099.3 2,639.9 680.1 (4,113.5 ) 3,305.8 Total stockholders’ equity (deficit) 2,083.2 (569.9 ) 6,739.5 (6,169.6 ) 2,083.2 Total liabilities and stockholders’ equity $ 6,182.5 $ 2,070.0 $ 7,419.6 $ (10,283.1 ) $ 5,389.0 Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Operations and Comprehensive Income For the three months ended September 30, 2018 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Sales $ — $ 357.4 $ 662.8 $ — $ 1,020.2 Cost of sales 3.7 316.3 539.8 — 859.8 Gross profit (loss) (3.7 ) 41.1 123.0 — 160.4 Selling and administrative expenses 24.9 7.3 33.3 — 65.5 Operating income (loss) (28.6 ) 33.8 89.7 — 94.9 Nonoperating retirement benefit expense (3.1 ) (4.9 ) (0.4 ) — (8.4 ) Interest income (expense), net (34.9 ) (29.5 ) 39.6 — (24.8 ) Other income (loss) including equity in income of unconsolidated subsidiaries 129.1 0.4 (0.1 ) (128.6 ) 0.8 Income (loss) before income tax provision (benefit) 62.5 (0.2 ) 128.8 (128.6 ) 62.5 Income tax provision (benefit) 6.9 1.4 21.2 (22.6 ) 6.9 Net income (loss) 55.6 (1.6 ) 107.6 (106.0 ) 55.6 Less: Net income attributable to noncontrolling interests — — 5.1 — 5.1 Net income (loss) attributable to ATI $ 55.6 $ (1.6 ) $ 102.5 $ (106.0 ) $ 50.5 Comprehensive income (loss) attributable to ATI $ 46.9 $ 0.9 $ 97.9 $ (94.9 ) $ 50.8 Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Operations and Comprehensive Income For the nine months ended September 30, 2018 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Sales $ — $ 1,047.0 $ 1,961.7 $ — $ 3,008.7 Cost of sales 11.7 962.8 1,551.5 — 2,526.0 Gross profit (loss) (11.7 ) 84.2 410.2 — 482.7 Selling and administrative expenses 73.0 25.2 97.1 — 195.3 Operating income (loss) (84.7 ) 59.0 313.1 — 287.4 Nonoperating retirement benefit expense (9.7 ) (14.6 ) (1.2 ) — (25.5 ) Interest income (expense), net (102.1 ) (83.3 ) 109.6 — (75.8 ) Other income (loss) including equity in income of unconsolidated subsidiaries 405.0 19.5 0.6 (402.7 ) 22.4 Income (loss) before income tax provision (benefit) 208.5 (19.4 ) 422.1 (402.7 ) 208.5 Income tax provision (benefit) 16.8 (2.9 ) 66.3 (63.4 ) 16.8 Net income (loss) 191.7 (16.5 ) 355.8 (339.3 ) 191.7 Less: Net income attributable to noncontrolling interests — — 10.4 — 10.4 Net income (loss) attributable to ATI $ 191.7 $ (16.5 ) $ 345.4 $ (339.3 ) $ 181.3 Comprehensive income (loss) attributable to ATI $ 223.0 $ (9.3 ) $ 334.7 $ (330.6 ) $ 217.8 Condensed Statements of Cash Flows For the nine months ended September 30, 2018 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Cash flows provided by (used in) operating activities $ (102.9 ) $ (126.7 ) $ 361.2 $ (15.0 ) $ 116.6 Investing Activities: Purchases of property, plant and equipment (1.4 ) (19.2 ) (80.7 ) — (101.3 ) Net receipts/(payments) on intercompany activity — — (236.0 ) 236.0 — Purchases of businesses — — (10.0 ) — (10.0 ) Asset disposals and other 0.8 1.3 0.1 — 2.2 Cash flows provided by (used in) investing activities (0.6 ) (17.9 ) (326.6 ) 236.0 (109.1 ) Financing Activities: Borrowings on long-term debt — — 7.1 — 7.1 Payments on long-term debt and capital leases (0.2 ) (0.6 ) (3.8 ) — (4.6 ) Net borrowings under credit facilities — — 4.0 — 4.0 Net receipts/(payments) on intercompany activity 109.2 126.8 — (236.0 ) — Dividends paid to stockholders — — (15.0 ) 15.0 — Dividends paid to noncontrolling interests — — (10.0 ) — (10.0 ) Sales to 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 102.5 137.9 (15.0 ) (221.0 ) 4.4 Increase (decrease) in cash and cash equivalents $ (1.0 ) $ (6.7 ) $ 19.6 $ — $ 11.9 Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Balance Sheets December 31, 2017 Guarantor Non-guarantor (In millions) Parent Subsidiary Subsidiaries Eliminations Consolidated Assets: Cash and cash equivalents $ 2.1 $ 13.5 $ 126.0 $ — $ 141.6 Accounts receivable, net 0.2 141.6 403.5 — 545.3 Intercompany notes receivable — — 3,505.6 (3,505.6 ) — Inventories, net — 207.9 968.2 — 1,176.1 Prepaid expenses and other current assets 6.6 4.5 41.6 — 52.7 Total current assets 8.9 367.5 5,044.9 (3,505.6 ) 1,915.7 Property, plant and equipment, net 0.9 1,581.6 913.2 — 2,495.7 Goodwill — — 531.4 — 531.4 Intercompany notes receivable — — 200.0 (200.0 ) — Investment in subsidiaries 5,645.6 37.7 — (5,683.3 ) — Other assets 25.4 18.0 199.2 — 242.6 Total assets $ 5,680.8 $ 2,004.8 $ 6,888.7 $ (9,388.9 ) $ 5,185.4 Liabilities and stockholders’ equity: Accounts payable $ 3.0 $ 180.3 $ 236.8 $ — $ 420.1 Accrued liabilities 54.1 88.5 139.8 — 282.4 Intercompany notes payable 1,836.5 1,669.1 — (3,505.6 ) — Short-term debt and current portion of long-term debt 0.3 0.6 9.2 — 10.1 Total current liabilities 1,893.9 1,938.5 385.8 (3,505.6 ) 712.6 Long-term debt 1,275.7 150.7 104.2 — 1,530.6 Intercompany notes payable — 200.0 — (200.0 ) — Accrued postretirement benefits — 250.2 67.6 — 317.8 Pension liabilities 644.3 4.4 48.3 — 697.0 Deferred income taxes 9.7 — — — 9.7 Other long-term liabilities 12.7 17.2 43.3 — 73.2 Total liabilities 3,836.3 2,561.0 649.2 (3,705.6 ) 3,340.9 Total stockholders’ equity (deficit) 1,844.5 (556.2 ) 6,239.5 (5,683.3 ) 1,844.5 Total liabilities and stockholders’ equity $ 5,680.8 $ 2,004.8 $ 6,888.7 $ (9,388.9 ) $ 5,185.4 Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Operations and Comprehensive Income For the three months ended September 30, 2017 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Sales $ — $ 287.9 $ 581.2 $ — $ 869.1 Cost of sales 3.4 279.3 481.1 — 763.8 Gross profit (loss) (3.4 ) 8.6 100.1 — 105.3 Selling and administrative expenses 24.8 8.4 31.4 — 64.6 Impairment of goodwill — — 114.4 — 114.4 Operating income (loss) (28.2 ) 0.2 (45.7 ) — (73.7 ) Nonoperating retirement benefit expense (8.0 ) (4.7 ) (0.9 ) — (13.6 ) Interest income (expense), net (40.1 ) (22.9 ) 28.8 — (34.2 ) Other income (loss) including equity in income of unconsolidated subsidiaries (45.0 ) 0.3 (0.1 ) 45.0 0.2 Income (loss) before income tax provision (benefit) (121.3 ) (27.1 ) (17.9 ) 45.0 (121.3 ) Income tax provision (benefit) (1.9 ) (8.6 ) 28.3 (19.7 ) (1.9 ) Net income (loss) (119.4 ) (18.5 ) (46.2 ) 64.7 (119.4 ) Less: Net income attributable to noncontrolling interests — — 1.8 — 1.8 Net income (loss) attributable to ATI $ (119.4 ) $ (18.5 ) $ (48.0 ) $ 64.7 $ (121.2 ) Comprehensive income (loss) attributable to ATI $ (63.5 ) $ (15.5 ) $ (28.5 ) $ 37.2 $ (70.3 ) Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Operations and Comprehensive Income For the nine months ended September 30, 2017 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Sales $ — $ 866.3 $ 1,748.9 $ — $ 2,615.2 Cost of sales 12.5 809.0 1,439.3 — 2,260.8 Gross profit (loss) (12.5 ) 57.3 309.6 — 354.4 Selling and administrative expenses 66.8 26.5 94.2 — 187.5 Impairment of goodwill — — 114.4 — 114.4 Operating income (loss) (79.3 ) 30.8 101.0 — 52.5 Nonoperating retirement benefit expense (24.2 ) (14.0 ) (2.7 ) — (40.9 ) Interest income (expense), net (118.4 ) (66.6 ) 82.8 — (102.2 ) Other income (loss) including equity in income of unconsolidated subsidiaries 135.0 1.1 2.6 (135.0 ) 3.7 Income (loss) before income tax provision (benefit) (86.9 ) (48.7 ) 183.7 (135.0 ) (86.9 ) Income tax provision (benefit) (2.0 ) (16.3 ) 97.4 (81.1 ) (2.0 ) Net income (loss) (84.9 ) (32.4 ) 86.3 (53.9 ) (84.9 ) Less: Net income attributable to noncontrolling interests — — 8.7 — 8.7 Net income (loss) attributable to ATI $ (84.9 ) $ (32.4 ) $ 77.6 $ (53.9 ) $ (93.6 ) Comprehensive income (loss) attributable to ATI $ (0.3 ) $ (27.1 ) $ 109.9 $ (98.7 ) $ (16.2 ) Condensed Statements of Cash Flows For the nine months ended September 30, 2017 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Cash flows provided by (used in) operating activities $ (84.2 ) $ (83.1 ) $ 113.5 $ — $ (53.8 ) Investing Activities: Purchases of property, plant and equipment (0.5 ) (27.4 ) (57.4 ) — (85.3 ) Net receipts/(payments) on intercompany activity — — (205.1 ) 205.1 — Asset disposals and other — 0.1 3.1 — 3.2 Cash flows provided by (used in) investing activities (0.5 ) (27.3 ) (259.4 ) 205.1 (82.1 ) Financing Activities: Borrowings on long-term debt — — 8.5 — 8.5 Payments on long-term debt and capital leases (0.3 ) (0.2 ) (1.4 ) — (1.9 ) Net borrowings under credit facilities — — 28.0 — 28.0 Debt issuance costs — — (0.8 ) — (0.8 ) Net receipts/(payments) on intercompany activity 89.6 115.5 — (205.1 ) — Sale to noncontrolling interests — — 2.2 — 2.2 Shares repurchased for income tax withholding on share-based compensation (4.8 ) — — — (4.8 ) Cash flows provided by (used in) financing activities 84.5 115.3 36.5 (205.1 ) 31.2 Increase (decrease) in cash and cash equivalents $ (0.2 ) $ 4.9 $ (109.4 ) $ — $ (104.7 )

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) The changes in accumulated other comprehensive income (loss) (AOCI) by component, net of tax, for the three month period ended September 30, 2018 were as follows (in millions): Post- retirement benefit plans Currency translation adjustment Unrealized holding gains on securities Derivatives Deferred Tax Asset Valuation Allowance Total Attributable to ATI: Balance, June 30, 2018 $ (926.2 ) $ (59.9 ) $ — $ 13.2 $ (18.7 ) $ (991.6 ) OCI before reclassifications — (4.8 ) — (8.1 ) — (12.9 ) Amounts reclassified from AOCI (a) 14.0 (b) — (b) — (c) (2.0 ) (d) 1.2 13.2 Net current-period OCI 14.0 (4.8 ) — (10.1 ) 1.2 0.3 Balance, September 30, 2018 $ (912.2 ) $ (64.7 ) $ — $ 3.1 $ (17.5 ) $ (991.3 ) Attributable to noncontrolling interests: Balance, June 30, 2018 $ — $ 21.1 $ — $ — $ — $ 21.1 OCI before reclassifications — (9.0 ) — — — (9.0 ) Amounts reclassified from AOCI — (b) — — — — — Net current-period OCI — (9.0 ) — — — (9.0 ) Balance, September 30, 2018 $ — $ 12.1 $ — $ — $ — $ 12.1 The changes in AOCI by component, net of tax, for the nine month period ended September 30, 2018 were as follows (in millions): Post- retirement benefit plans Currency translation adjustment Unrealized holding gains on securities Derivatives Deferred Tax Asset Valuation Allowance Total Attributable to ATI: Balance, December 31, 2017 $ (954.5 ) $ (53.5 ) $ — $ 9.0 $ (28.8 ) $ (1,027.8 ) OCI before reclassifications — (11.2 ) — 1.9 — (9.3 ) Amounts reclassified from AOCI (a) 42.3 (b) — (b) — (c) (7.8 ) (d) 11.3 45.8 Net current-period OCI 42.3 (11.2 ) — (5.9 ) 11.3 36.5 Balance, September 30, 2018 $ (912.2 ) $ (64.7 ) $ — $ 3.1 $ (17.5 ) $ (991.3 ) Attributable to noncontrolling interests: Balance, December 31, 2017 $ — $ 17.3 $ — $ — $ — $ 17.3 OCI before reclassifications — (5.2 ) — — — (5.2 ) Amounts reclassified from AOCI — (b) — — — — — Net current-period OCI — (5.2 ) — — — (5.2 ) Balance, September 30, 2018 $ — $ 12.1 $ — $ — $ — $ 12.1 (a) Amounts were included in net periodic benefit cost for pension and other postretirement benefit plans (see Note 9). (b) No amounts were reclassified to earnings. (c) 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 7). (d) Represents the net change in deferred tax asset valuation allowances on changes in AOCI balances between the balance sheet dates. The changes in AOCI by component, net of tax, for the three month period ended September 30, 2017 were as follows (in millions): Post- retirement benefit plans Currency translation adjustment Unrealized holding gains on securities Derivatives Deferred Tax Asset Valuation Allowance Total Attributable to ATI: Balance, June 30, 2017 $ (943.5 ) $ (72.4 ) $ — $ (5.7 ) $ (45.6 ) $ (1,067.2 ) OCI before reclassifications — 19.2 — 5.7 — 24.9 Amounts reclassified from AOCI (a) 10.5 (b) — (b) — (c) (0.8 ) 16.3 26.0 Net current-period OCI 10.5 19.2 — 4.9 16.3 50.9 Balance, September 30, 2017 $ (933.0 ) $ (53.2 ) $ — $ (0.8 ) $ (29.3 ) $ (1,016.3 ) Attributable to noncontrolling interests: Balance, June 30, 2017 $ — $ 11.9 $ — $ — $ — $ 11.9 OCI before reclassifications — 5.0 — — — 5.0 Amounts reclassified from AOCI — (b) — — — — — Net current-period OCI — 5.0 — — — $ 5.0 Balance, September 30, 2017 $ — $ 16.9 $ — $ — $ — $ 16.9 The changes in AOCI by component, net of tax, for the nine month period ended September 30, 2017 were as follows (in millions): Post- retirement benefit plans Currency translation adjustment Unrealized holding gains on securities 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 — 31.8 — (1.0 ) — 30.8 Amounts reclassified from AOCI (a) 32.5 (b) — (b) — (c) (2.2 ) 16.3 46.6 Net current-period OCI 32.5 31.8 — (3.2 ) 16.3 77.4 Balance, September 30, 2017 $ (933.0 ) $ (53.2 ) $ — $ (0.8 ) $ (29.3 ) $ (1,016.3 ) Attributable to noncontrolling interests: Balance, December 31, 2016 $ — $ 9.7 $ — $ — $ — $ 9.7 OCI before reclassifications — 7.2 — — — 7.2 Amounts reclassified from AOCI — (b) — — — — — Net current-period OCI — 7.2 — — — $ 7.2 Balance, September 30, 2017 $ — $ 16.9 $ — $ — $ — $ 16.9 (a) Amounts were included in net periodic benefit cost for pension and other postretirement benefit plans (see Note 9). (b) No amounts were reclassified to earnings. (c) Amounts related to the effective portion of the derivatives are included in cost of goods sold in the period or periods the hedged item affects earnings (see Note 7). 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, resulting from the Company’s three year cumulative loss position. 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 three and nine month periods ended September 30, 2018 and 2017 were as follows: Amount reclassified from AOCI Details about AOCI Components (In millions) Three months ended September 30, 2018 Three months ended September 30, 2017 Nine months ended September 30, 2018 Nine months ended September 30, 2017 Affected line item in the statements of operations Postretirement benefit plans Prior service credit $ 0.7 $ 0.4 $ 1.9 $ 1.2 (a) Actuarial losses (19.2 ) (17.8 ) (57.5 ) (53.6 ) (a) (18.5 ) (17.4 ) (55.6 ) (52.4 ) (c) Total before tax (4.5 ) (6.9 ) (13.3 ) (19.9 ) Tax provision (benefit) (d) $ (14.0 ) $ (10.5 ) $ (42.3 ) $ (32.5 ) Net of tax Derivatives Nickel and other raw material contracts $ 2.2 $ (1.5 ) $ 10.4 $ (4.0 ) (b) Natural gas contracts — (1.1 ) (0.5 ) (4.5 ) (b) Foreign exchange contracts 0.5 3.8 0.5 12.0 (b) Interest rate swap (0.1 ) — (0.1 ) — (b) 2.6 1.2 10.3 3.5 (c) Total before tax 0.6 0.4 2.5 1.3 Tax provision (benefit) (d) $ 2.0 $ 0.8 $ 7.8 $ 2.2 Net of tax (a) Amounts are reported in nonoperating retirement benefit expense (see Note 9). (b) 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 7). (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 allowance, when applicable.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies 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 September 30, 2018 , the Company’s reserves for environmental remediation obligations totaled approximately $15 million , of which $9 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; $11 million for formerly owned or operated sites for which the Company has remediation or indemnification obligations; and $1 million for owned or controlled sites at which Company operations have been discontinued. 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. The Company continues to evaluate whether it may be able to recover a portion of past and 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 costs for recorded 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. See Note 20. Commitments and Contingencies to the Company’s consolidated financial statements in the Company’s Annual Report on Form 10-K for its fiscal year ended December 31, 2017 for a discussion of legal proceedings affecting the Company. A number of other lawsuits, claims and proceedings have been or may be asserted against the Company relating to the conduct of its currently and formerly owned businesses, including those pertaining to product liability, environmental, health and safety matters and occupational disease (including as each relates to alleged asbestos exposure), as well as patent infringement, commercial, government contracting, construction, employment, employee and retiree benefits, taxes, environmental, and stockholder and corporate governance matters. While the outcome of litigation cannot be predicted with certainty, and some of these lawsuits, claims or proceedings may be determined adversely to the Company, management does not believe that the disposition of any such pending matters is likely to have a material adverse effect on the Company’s financial condition or liquidity, although the resolution in any reporting period of one or more of these matters could have a material adverse effect on the Company’s consolidated results of operations for that period.

Accounting Policies (Policies)

Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Basis Of Accounting	The interim consolidated financial statements include the accounts of Allegheny Technologies Incorporated and its subsidiaries. Unless the context requires otherwise, “Allegheny Technologies”, “ATI” and “the Company” refer to Allegheny Technologies Incorporated and its subsidiaries. These unaudited consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles for interim financial information and with the instructions for Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and note disclosures required by U.S. generally accepted accounting principles for complete financial statements. In management’s opinion, all adjustments (which include only normal recurring adjustments) considered necessary for a fair presentation have been included. These unaudited consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in the Company’s 2017 Annual Report on Form 10-K. The results of operations for these interim periods are not necessarily indicative of the operating results for any future period. The December 31, 2017 financial information has been derived from the Company’s audited consolidated financial statements.
New Accounting Pronouncements Adopted	New Accounting Pronouncements Adopted In January 2018, the Company adopted changes issued by the Financial Accounting Standards Board (FASB) related to revenue recognition with customers. See Note 2 for further explanation related to this adoption, including all newly expanded disclosure requirements. In January 2018, the Company adopted changes issued by the FASB related to changes to the accounting for defined benefit pension and other postretirement benefit expenses. This new guidance requires the disaggregation of the service cost component from the other components of net benefit cost. The service cost component of net benefit cost is to be reported in the same line item on the consolidated statement of operations as other compensation costs arising from services rendered by the pertinent employees, while the other components of net benefit cost are to be presented in the consolidated statement of operations separately, outside a subtotal of operating income. The amendments also provide explicit guidance to allow only the service cost component of net benefit cost to be eligible for capitalization. With this adoption, the change in presentation of net benefit cost in the consolidated statement of operations was applied retrospectively, and the change in capitalization for only service cost was applied prospectively. The Company adopted this new guidance using the practical expedient that permits the use of the amounts disclosed in the retirement benefits footnote for the prior comparative periods as the estimation basis for applying the retrospective presentation requirements. This required accounting change did have a material impact to previously-reported operating income (loss) in the consolidated statement of operations due to the change in presentation of non-service cost expense components. For the third quarter and first nine months of 2017, applying the practical expedient, operating results were higher by $13.6 million and $40.9 million , respectively, with the reclassification of this amount representing the other components of net benefit cost to a newly-created nonoperating retirement benefit expense category. There was no net impact to the reported results before income taxes as a result of this accounting change. This change in presentation of net benefit cost did not affect ATI’s measure of segment operating profit; all defined benefit pension and other postretirement benefit expense attributable to business segment operations remains a component of business segment financial performance. The Company did have a one-time, unfavorable impact of $5.4 million to pre-tax reported results in the first quarter of 2018 upon adoption, primarily affecting the Flat Rolled Products business segment, due to the change limiting only the service cost component of net benefit cost to be capitalizable into inventory. In January 2018, the Company early adopted changes issued by the FASB related to changes to its accounting guidance for derivatives and hedging, which changes both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results. Some changes resulting from this new guidance include the elimination of the concept of recognizing periodic hedge ineffectiveness for cash flow hedges, changes to the recognition and presentation of changes in the fair value of the hedging instrument, enhancement of the ability to use the critical-terms-match method for the cash flow hedge of groups of forecasted transactions when the timing of the hedged transactions does not perfectly match the hedging instrument’s maturity date, and the addition of new disclosure requirements and amendments to existing ones. The Company applied this new guidance to hedging relationships existing on January 1, 2018, the date of adoption. The adoption of these changes did not have a material impact on the Company's financial statements, and disclosures in Note 7 reflect the requirements of this adoption. In August 2018, the FASB issued new accounting guidance for implementation costs incurred in a cloud computing arrangement that is a service contract. This guidance specifies which implementation costs can be capitalized in a hosting arrangement that is a service contract. The guidance aligns the accounting for implementation costs for hosting arrangements, regardless of whether they convey a license to the hosted software. This guidance is required to be adopted either retrospectively or prospectively by the Company beginning in fiscal year 2020 with early adoption permitted, including adoption in any interim period. The Company early adopted this guidance in the third quarter of 2018 on a retrospective basis, which did not have a material impact on the Company’s consolidated financial statements.
New Accounting Pronouncements Not Yet Adopted	Pending Accounting Pronouncements In February 2016, the FASB issued new accounting guidance for leases. This new guidance will require that a lessee recognize assets and liabilities on the balance sheet for all leases with a lease term of more than twelve months, with the result being the recognition of a right of use asset and a lease liability. The new lease accounting requirements are effective for ATI’s 2019 fiscal year. In July 2018, the FASB added an additional adoption method, which ATI will use to initially apply the new standard at the adoption date, January 1, 2019. This adoption method recognizes any impact to prior years’ results as a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. The Company is currently in the process of evaluating its existing lease portfolio, including accumulating all of the necessary information required to properly account for the leases under the new standard. In addition, ATI is implementing a company-wide lease management system to assist in the accounting and is evaluating additional changes to its processes and internal controls to ensure the standard’s reporting and disclosure requirements are met. The Company is currently evaluating the impact of the new guidance on its consolidated financial statements. 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 does not plan to 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 August 2018, the FASB issued new disclosure guidance for defined benefit plans, which modified certain required disclosures. This guidance is required to be adopted retrospectively by the Company beginning in fiscal year 2021, with early adoption permitted. The Company plans to early adopt this guidance in the fourth quarter of 2018, which is not expected to have an impact on the Company’s consolidated financial statements other than disclosures.
Revenue from Contracts with Customers	On January 1, 2018, the Company adopted Accounting Standards Codification Topic 606 (ASC 606), Revenue from Contracts with Customers. This new 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 new 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 that the Company typically has 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. The Company has several customer agreements involving production of parts and components in the High Performance Materials and Components segment that require revenue to be recognized over time in accordance with the new guidance 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. Over-time recognition was a change from the accounting for these products, which was point-in-time prior to the adoption of the new standard. 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.
Inventory	Inventories are stated at the lower of cost (LIFO, first-in, first-out (FIFO), and average cost methods) or market. 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. 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 NRV inventory valuation reserves to adjust carrying value of LIFO inventory to current replacement cost.
Derivatives	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. In January 2018, the Company early adopted changes issued by the FASB related to accounting guidance for derivatives and hedging, which includes, among other things, the elimination of the concept of recognizing periodic hedge ineffectiveness for cash flow 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 September 30, 2018 , 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 12 million pounds of nickel with hedge dates through 2021. The aggregate notional amount hedged is approximately 12% of a single year’s estimated nickel raw material purchase requirements. At September 30, 2018 , the outstanding financial derivatives used to hedge the Company’s exposure to energy cost volatility included natural gas cost hedges. At September 30, 2018 , the Company hedged approximately 35% of the Company’s forecasted domestic requirements for natural gas for the remainder of 2018, approximately 35% for 2019, and approximately 30% for 2020. 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. At September 30, 2018, the Company held euro forward sales contracts designated as cash flow hedges with a notional value of approximately 16 million euros with maturity dates through May 2019. In addition, the Company may also designate cash balances held in foreign currencies as hedges of forecasted foreign currency transactions. The Company may enter into derivative interest rate contracts to maintain a reasonable balance between fixed- and floating-rate debt. In July 2018, the Company entered into a $50 million floating-for-fixed interest rate swap which converts half of the Term Loan to a 5.44% fixed interest rate. The Company designated the interest rate swap as a cash flow hedge of the Company’s exposure to the variability of the payment of interest on a portion of its Term Loan borrowings. The swap matures in January 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 are 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. For derivative financial instruments that are designated as cash flow hedges, the gain or loss on the derivative is reported as a component of other comprehensive income (OCI) and reclassified into earnings in the same period or periods during which the hedged item affects earnings. For derivative financial instruments that are designated as fair value hedges, changes in the fair value of these derivatives are recognized in current period results and are reported as changes within accrued liabilities and other on the consolidated statements of cash flows. There were no outstanding fair value hedges as of September 30, 2018. 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 effecting results of operations or other comprehensive income, when applicable (see Note 14 for further explanation).
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 funds the U.S. pension plans in accordance with the Employee Retirement Income Security Act of 1974, as amended, and the Internal Revenue Code (IRC). 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.
Commitments And Contingencies	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.

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	9 Months Ended
	Sep. 30, 2018
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 third quarters and nine months ended September 30, 2018 and 2017 were as follows: (in millions) Third quarter ended September 30, 2018 September 30, 2017 HPMC FRP Total HPMC FRP Total Diversified Global Markets: Aerospace & Defense $ 446.5 $ 52.7 $ 499.2 $ 389.5 $ 38.2 $ 427.7 Oil & Gas 17.9 110.3 128.2 14.3 84.1 98.4 Automotive 2.0 83.0 85.0 2.4 59.3 61.7 Electrical Energy 30.9 29.0 59.9 30.4 18.1 48.5 Medical 44.3 3.6 47.9 41.8 2.7 44.5 Total Key Markets 541.6 278.6 820.2 478.4 202.4 680.8 Food Equipment & Appliances 0.2 58.6 58.8 0.2 54.3 54.5 Construction/Mining 18.5 39.9 58.4 13.5 34.8 48.3 Electronics/Computers/Communications 1.0 40.3 41.3 1.1 41.2 42.3 Other 24.2 17.3 41.5 19.7 23.5 43.2 Total $ 585.5 $ 434.7 $ 1,020.2 $ 512.9 $ 356.2 $ 869.1 (in millions) Nine months ended September 30, 2018 September 30, 2017 HPMC FRP Total HPMC FRP Total Diversified Global Markets: Aerospace & Defense $ 1,311.7 $ 131.9 $ 1,443.6 $ 1,169.7 $ 110.8 $ 1,280.5 Oil & Gas 51.4 362.1 413.5 49.7 240.0 289.7 Automotive 7.4 237.1 244.5 6.4 200.0 206.4 Electrical Energy 101.9 78.4 180.3 84.1 60.1 144.2 Medical 131.5 11.3 142.8 134.2 8.5 142.7 Total Key Markets 1,603.9 820.8 2,424.7 1,444.1 619.4 2,063.5 Food Equipment & Appliances 0.3 181.0 181.3 1.0 167.9 168.9 Construction/Mining 55.1 114.8 169.9 37.6 107.0 144.6 Electronics/Computers/Communications 4.7 105.0 109.7 3.5 104.7 108.2 Other 74.1 49.0 123.1 63.5 66.5 130.0 Total $ 1,738.1 $ 1,270.6 $ 3,008.7 $ 1,549.7 $ 1,065.5 $ 2,615.2 (in millions) Third quarter ended September 30, 2018 September 30, 2017 HPMC FRP Total HPMC FRP Total Primary Geographical Market: United States $ 316.7 $ 290.9 $ 607.6 $ 273.4 $ 233.1 $ 506.5 Europe 173.2 40.5 213.7 164.8 23.8 188.6 Asia 60.9 84.0 144.9 45.1 75.2 120.3 Canada 16.3 7.5 23.8 15.3 5.8 21.1 South America, Middle East and other 18.4 11.8 30.2 14.3 18.3 32.6 Total $ 585.5 $ 434.7 $ 1,020.2 $ 512.9 $ 356.2 $ 869.1 (in millions) Nine months ended September 30, 2018 September 30, 2017 HPMC FRP Total HPMC FRP Total Primary Geographical Market: United States $ 898.6 $ 839.1 $ 1,737.7 $ 820.5 $ 735.2 $ 1,555.7 Europe 565.4 104.3 669.7 502.2 74.4 576.6 Asia 180.7 258.7 439.4 127.3 190.2 317.5 Canada 51.3 29.0 80.3 52.4 21.1 73.5 South America, Middle East and other 42.1 39.5 81.6 47.3 44.6 91.9 Total $ 1,738.1 $ 1,270.6 $ 3,008.7 $ 1,549.7 $ 1,065.5 $ 2,615.2 Comparative information of the Company’s major high-value and standard products based on their percentages of total sales is as follows: Third quarter ended September 30, 2018 September 30, 2017 HPMC FRP Total HPMC FRP Total Diversified Products and Services: High-Value Products Nickel-based alloys and specialty alloys 32 % 29 % 30 % 30 % 27 % 28 % Precision forgings, castings and components 33 % — % 18 % 33 % — % 19 % Titanium and titanium-based alloys 25 % 3 % 16 % 26 % 3 % 17 % Precision and engineered strip — % 34 % 14 % — % 34 % 14 % Zirconium and related alloys 10 % — % 6 % 11 % — % 6 % Total High-Value Products 100 % 66 % 84 % 100 % 64 % 84 % Standard Products Stainless steel sheet — % 20 % 9 % — % 20 % 9 % Specialty stainless sheet — % 9 % 4 % — % 11 % 4 % Stainless steel plate and other — % 5 % 3 % — % 5 % 3 % Total Standard Products — % 34 % 16 % — % 36 % 16 % Total 100 % 100 % 100 % 100 % 100 % 100 % Nine months ended September 30, 2018 September 30, 2017 HPMC FRP Total HPMC FRP Total Diversified Products and Services: High-Value Products Nickel-based alloys and specialty alloys 31 % 29 % 30 % 30 % 23 % 27 % Precision forgings, castings and components 35 % — % 20 % 32 % — % 19 % Titanium and titanium-based alloys 24 % 5 % 15 % 27 % 4 % 17 % Precision and engineered strip — % 32 % 14 % — % 34 % 14 % Zirconium and related alloys 10 % — % 5 % 11 % — % 6 % Total High-Value Products 100 % 66 % 84 % 100 % 61 % 83 % Standard Products Stainless steel sheet — % 20 % 9 % — % 22 % 9 % Specialty stainless sheet — % 10 % 4 % — % 12 % 4 % Stainless steel plate and other — % 4 % 3 % — % 5 % 4 % Total Standard Products — % 34 % 16 % — % 39 % 17 % Total 100 % 100 % 100 % 100 % 100 % 100 %
Schedule of Accounts Receivable - Reserve for Doubtful Accounts	(in millions) Accounts Receivable - Reserve for Doubtful Accounts Balance as of January 1, 2018 $ 5.9 Expense to increase the reserve 0.7 Write-off of uncollectible accounts (0.4 ) Balance as of September 30, 2018 $ 6.2
Schedule of Contract Assets and Liabilities	(in millions) Contract Assets Short-term Balance as of January 1, 2018 $ 36.5 Recognized in current year 66.2 Reclassified to accounts receivable (67.9 ) Impairment — Reclassification to/from long-term 16.8 Balance as of September 30, 2018 $ 51.6 Long-term Balance as of January 1, 2018 $ 16.9 Recognized in current year — Reclassified to accounts receivable — Impairment — Reclassification to/from short-term (16.8 ) Balance as of September 30, 2018 $ 0.1 (in millions) Contract Liabilities Short-term Balance as of January 1, 2018 $ 69.7 Recognized in current year 46.9 Amounts in beginning balance reclassified to revenue (40.1 ) Current year amounts reclassified to revenue (23.6 ) Other 1.7 Reclassification to/from long-term 14.6 Balance as of September 30, 2018 $ 69.2 Long-term Balance as of January 1, 2018 $ 22.2 Recognized in current year 0.5 Amounts in beginning balance reclassified to revenue (0.8 ) Current year amounts reclassified to revenue — Other — Reclassification to/from short-term (14.6 ) Balance as of September 30, 2018 $ 7.3

Inventories (Tables)

Inventories (Tables)	9 Months Ended
	Sep. 30, 2018
Inventory Disclosure [Abstract]
Schedule of Inventories	Inventories at September 30, 2018 and December 31, 2017 were as follows (in millions): September 30, December 31, Raw materials and supplies $ 204.3 $ 162.8 Work-in-process 929.9 955.5 Finished goods 190.0 165.0 Total inventories at current cost 1,324.2 1,283.3 Adjustment from current cost to LIFO cost basis 1.7 43.1 Inventory valuation reserves (86.1 ) (121.5 ) Progress payments — (28.8 ) Total inventories, net $ 1,239.8 $ 1,176.1
Schedule of Inventory Valuation Impact on Income	Impacts to cost of sales for changes in the LIFO costing methodology and associated NRV inventory reserves were as follows (in millions): Nine months ended September 30, 2018 2017 LIFO benefit (charge) $ (29.5 ) $ (51.5 ) NRV benefit (charge) 29.5 51.3 Net cost of sales impact $ — $ (0.2 )

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	9 Months Ended
	Sep. 30, 2018
Property, Plant and Equipment [Abstract]
Property Plant And Equipment	Property, plant and equipment at September 30, 2018 and December 31, 2017 was as follows (in millions): September 30, December 31, Land $ 31.6 $ 31.7 Buildings 851.1 844.5 Equipment and leasehold improvements 3,646.0 3,597.6 4,528.7 4,473.8 Accumulated depreciation and amortization (2,056.1 ) (1,978.1 ) Total property, plant and equipment, net $ 2,472.6 $ 2,495.7

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Schedule of Debt Instruments	Debt at September 30, 2018 and December 31, 2017 was as follows (in millions): September 30, December 31, Allegheny Technologies 5.875% Notes due 2023 (a) $ 500.0 $ 500.0 Allegheny Technologies 5.95% Notes due 2021 500.0 500.0 Allegheny Technologies 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 2022 100.0 100.0 U.S. revolving credit facility — — Foreign credit facilities 10.0 6.3 Other 15.5 10.0 Debt issuance costs (11.1 ) (13.1 ) Total debt 1,551.9 1,540.7 Short-term debt and current portion of long-term debt 16.6 10.1 Total long-term debt $ 1,535.3 $ 1,530.6 (a) Bearing interest at 7.875% effective February 15, 2016.

Derivative Financial Instrume_2

Derivative Financial Instruments and Hedging (Tables)	9 Months Ended
	Sep. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule Of Derivative Instruments In Statement Of Financial Position Fair Value	The fair values of the Company’s derivative financial instruments are presented below, representing the gross amounts recognized which are not offset by counterparty or by type of item hedged. All fair values for these derivatives were measured using Level 2 information as defined by the accounting standard hierarchy, which includes quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and inputs derived principally from or corroborated by observable market data. (In millions) Asset derivatives Balance sheet location September 30, December 31, Derivatives designated as hedging instruments: Foreign exchange contracts Prepaid expenses and other current assets $ 0.3 $ — Natural gas contacts Prepaid expenses and other current assets 0.3 0.1 Nickel and other raw material contracts Prepaid expenses and other current assets 4.3 10.5 Interest rate swap Other assets 0.1 — Natural gas contracts Other assets 0.1 0.3 Nickel and other raw material contracts Other assets 2.7 5.5 Total derivatives designated as hedging instruments 7.8 16.4 Derivatives not designated as hedging instruments: Foreign exchange contracts Prepaid expenses and other current assets 0.3 0.1 Total derivatives not designated as hedging instruments 0.3 0.1 Total asset derivatives $ 8.1 $ 16.5 Liability derivatives Balance sheet location Derivatives designated as hedging instruments: Interest rate swap Accrued liabilities $ 0.2 $ — Natural gas contracts Accrued liabilities 0.2 0.9 Nickel and other raw material contracts Accrued liabilities 2.9 2.1 Natural gas contracts Other long-term liabilities 0.4 0.3 Nickel and other raw material contracts Other long-term liabilities 1.0 2.2 Total derivatives designated as hedging instruments 4.7 5.5 Total liability derivatives $ 4.7 $ 5.5
Schedule Of Derivative Instruments Gain Loss In Statement Of Financial Performance	Activity with regard to derivatives designated as cash flow hedges for the three and nine month periods ended September 30, 2018 and 2017 was as follows (in millions): Amount of Gain (Loss) Recognized in OCI on Derivatives Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (a) Three months ended September 30, Three months ended September 30, Derivatives in Cash Flow Hedging Relationships 2018 2017 2018 2017 Nickel and other raw material contracts $ (8.0 ) $ 5.6 $ 1.7 $ (0.9 ) Natural gas contracts (0.1 ) — — (0.7 ) Foreign exchange contracts 0.2 0.1 0.4 2.4 Interest rate swap (0.2 ) — (0.1 ) — Total $ (8.1 ) $ 5.7 $ 2.0 $ 0.8 Amount of Gain (Loss) Recognized in OCI on Derivatives Amount of Gain (Loss) Reclassified from Accumulated OCI into Income (a) Nine months ended September 30, Nine months ended September 30, Derivatives in Cash Flow Hedging Relationships 2018 2017 2018 2017 Nickel and other raw material contracts $ 1.3 $ 1.2 $ 7.9 $ (2.5 ) Natural gas contracts 0.1 (2.1 ) (0.4 ) (2.8 ) Foreign exchange contracts 0.7 (0.1 ) 0.4 7.5 Interest rate swap (0.2 ) — (0.1 ) — Total $ 1.9 $ (1.0 ) $ 7.8 $ 2.2 (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 Derivative Instruments Not Designated as Hedging Instruments	These derivatives that are not designated as hedging instruments were as follows: (In millions) Amount of Gain (Loss) Recognized in Income on Derivatives Three months ended September 30, Nine months ended September 30, Derivatives Not Designated as Hedging Instruments 2018 2017 2018 2017 Foreign exchange contracts $ — $ (0.1 ) $ 0.1 $ (0.7 )

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value By Balance Sheet Grouping	The estimated fair value of financial instruments at September 30, 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 $ 153.5 $ 153.5 $ 153.5 $ — Derivative financial instruments: Assets 8.1 8.1 — 8.1 Liabilities 4.7 4.7 — 4.7 Debt (a) 1,563.0 1,945.8 1,820.3 125.5 The estimated fair value of financial instruments at December 31, 2017 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 $ 141.6 $ 141.6 $ 141.6 $ — Derivative financial instruments: Assets 16.5 16.5 — 16.5 Liabilities 5.5 5.5 — 5.5 Debt (a) 1,553.8 1,853.2 1,736.9 116.3 (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.

Retirement Benefits (Tables)

Retirement Benefits (Tables)	9 Months Ended
	Sep. 30, 2018
Retirement Benefits [Abstract]
Schedule Of Defined Benefit Plans Disclosures [Table Text Block]	For the three month periods ended September 30, 2018 and 2017 , the components of pension and other postretirement benefit expense for the Company’s defined benefit plans included the following (in millions): Pension Benefits Other Postretirement Benefits Three months ended September 30, Three months ended September 30, 2018 2017 2018 2017 Service cost - benefits earned during the year $ 4.1 $ 3.5 $ 0.6 $ 0.6 Interest cost on benefits earned in prior years 26.2 29.2 3.2 3.7 Expected return on plan assets (39.5 ) (36.7 ) — — Amortization of prior service cost (credit) 0.1 0.3 (0.8 ) (0.7 ) Amortization of net actuarial loss 16.5 15.6 2.7 2.2 Total retirement benefit expense $ 7.4 $ 11.9 $ 5.7 $ 5.8 For the nine month periods ended September 30, 2018 and 2017 , the components of pension and other postretirement benefit expense for the Company’s defined benefit plans included the following (in millions): Pension Benefits Other Postretirement Benefits Nine months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 Service cost - benefits earned during the year $ 12.4 $ 10.5 $ 1.8 $ 1.8 Interest cost on benefits earned in prior years 78.5 87.6 9.5 11.0 Expected return on plan assets (118.5 ) (110.1 ) — — Amortization of prior service cost (credit) 0.3 0.9 (2.2 ) (2.1 ) Amortization of net actuarial loss 49.5 46.9 8.0 6.7 Curtailment loss 0.4 — — — Total retirement benefit expense $ 22.6 $ 35.8 $ 17.1 $ 17.4

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Schedule of Changes in Deferred Tax Assets	Changes to certain deferred tax assets and the valuation allowance at December 31, 2017 as a result of the Company’s expected use of tax credits to meet a portion of the transition tax were as follows (in millions): Deferred Income Tax Assets Estimate Refinement Originally Reported Change Net operating loss tax carryovers $ 357.0 $ 336.1 $ 20.9 Tax credits $ 62.4 $ 92.6 $ (30.2 ) Gross deferred income tax assets $ 733.6 $ 742.9 $ (9.3 ) Valuation allowance (264.7 ) (274.0 ) 9.3 Total deferred income tax assets $ 468.9 $ 468.9 $ —

Business Segments (Tables)

Business Segments (Tables)	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
Schedule Of Segment Reporting Information By Segment	Following is certain financial information with respect to the Company’s business segments for the periods indicated (in millions): Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 Total sales: High Performance Materials & Components $ 615.2 $ 526.3 $ 1,806.3 $ 1,593.3 Flat Rolled Products 452.5 372.3 1,330.9 1,118.5 1,067.7 898.6 3,137.2 2,711.8 Intersegment sales: High Performance Materials & Components 29.7 13.4 68.2 43.6 Flat Rolled Products 17.8 16.1 60.3 53.0 47.5 29.5 128.5 96.6 Sales to external customers: High Performance Materials & Components 585.5 512.9 1,738.1 1,549.7 Flat Rolled Products 434.7 356.2 1,270.6 1,065.5 $ 1,020.2 $ 869.1 $ 3,008.7 $ 2,615.2 Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 Operating profit: High Performance Materials & Components $ 76.0 $ 61.7 $ 259.4 $ 180.6 Flat Rolled Products 29.5 (7.3 ) 66.5 14.6 Total operating profit 105.5 54.4 325.9 195.2 LIFO and net realizable value reserves — (0.1 ) — (0.2 ) Corporate expenses (14.8 ) (14.8 ) (40.9 ) (36.9 ) Closed operations and other expenses (3.4 ) (12.2 ) (16.6 ) (28.4 ) Impairment of goodwill — (114.4 ) — (114.4 ) Gain on joint venture deconsolidation (See Note 5) — — 15.9 — Interest expense, net (24.8 ) (34.2 ) (75.8 ) (102.2 ) Income before income taxes $ 62.5 $ (121.3 ) $ 208.5 $ (86.9 )

Per Share Information (Tables)

Per Share Information (Tables)	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Schedule Of Earnings Per Share Diluted By Common Class	The following table sets forth the computation of basic and diluted income (loss) per common share: Three months ended Nine months ended (In millions, except per share amounts) September 30, September 30, 2018 2017 2018 2017 Numerator: Numerator for basic income (loss) per common share – Net income (loss) attributable to ATI $ 50.5 $ (121.2 ) $ 181.3 $ (93.6 ) Effect of dilutive securities: 4.75% Convertible Senior Notes due 2022 3.2 — 9.6 — Numerator for diluted income (loss) per common share – Net income (loss) attributable to ATI after assumed conversions $ 53.7 $ (121.2 ) $ 190.9 $ (93.6 ) Denominator: Denominator for basic net income (loss) per common share – weighted average shares 125.2 107.7 125.1 107.7 Effect of dilutive securities: Share-based compensation 0.9 — 0.7 — 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 146.0 107.7 145.7 107.7 Basic net income (loss) attributable to ATI per common share $ 0.40 $ (1.12 ) $ 1.45 $ (0.87 ) Diluted net income (loss) attributable to ATI per common share $ 0.37 $ (1.12 ) $ 1.31 $ (0.87 )

Financial Information for Sub_2

Financial Information for Subsidiary and Guarantor Parent (Tables)	9 Months Ended
	Sep. 30, 2018
Condensed Statement of Income Captions [Line Items]
Balance Sheets	Balance Sheets September 30, 2018 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Assets: Cash and cash equivalents $ 1.1 $ 6.8 $ 145.6 $ — $ 153.5 Accounts receivable, net — 156.4 431.9 — 588.3 Intercompany notes receivable — — 3,913.5 (3,913.5 ) — Short-term contract assets — — 51.6 — 51.6 Inventories, net — 238.6 1,001.2 — 1,239.8 Prepaid expenses and other current assets 14.7 38.4 36.1 — 89.2 Total current assets 15.8 440.2 5,579.9 (3,913.5 ) 2,122.4 Property, plant and equipment, net 0.7 1,551.6 920.3 — 2,472.6 Goodwill — — 536.4 — 536.4 Intercompany notes receivable — — 200.0 (200.0 ) — Investment in subsidiaries 6,131.9 37.7 — (6,169.6 ) — Other assets 34.1 40.5 183.0 — 257.6 Total assets $ 6,182.5 $ 2,070.0 $ 7,419.6 $ (10,283.1 ) $ 5,389.0 Liabilities and stockholders’ equity: Accounts payable $ 4.6 $ 153.4 $ 258.1 $ — $ 416.1 Accrued liabilities 37.3 68.8 122.6 — 228.7 Intercompany notes payable 2,144.5 1,769.0 — (3,913.5 ) — Short-term contract liabilities — 30.7 38.5 — 69.2 Short-term debt and current portion of long-term debt 0.2 0.8 15.6 — 16.6 Total current liabilities 2,186.6 2,022.7 434.8 (3,913.5 ) 730.6 Long-term debt 1,277.5 152.0 105.8 — 1,535.3 Intercompany notes payable — 200.0 — (200.0 ) — Accrued postretirement benefits — 243.8 57.3 — 301.1 Pension liabilities 602.0 3.9 46.8 — 652.7 Deferred income taxes 12.1 — — — 12.1 Long-term contract liabilities — — 7.3 — 7.3 Other long-term liabilities 21.1 17.5 28.1 — 66.7 Total liabilities 4,099.3 2,639.9 680.1 (4,113.5 ) 3,305.8 Total stockholders’ equity (deficit) 2,083.2 (569.9 ) 6,739.5 (6,169.6 ) 2,083.2 Total liabilities and stockholders’ equity $ 6,182.5 $ 2,070.0 $ 7,419.6 $ (10,283.1 ) $ 5,389.0 Balance Sheets December 31, 2017 Guarantor Non-guarantor (In millions) Parent Subsidiary Subsidiaries Eliminations Consolidated Assets: Cash and cash equivalents $ 2.1 $ 13.5 $ 126.0 $ — $ 141.6 Accounts receivable, net 0.2 141.6 403.5 — 545.3 Intercompany notes receivable — — 3,505.6 (3,505.6 ) — Inventories, net — 207.9 968.2 — 1,176.1 Prepaid expenses and other current assets 6.6 4.5 41.6 — 52.7 Total current assets 8.9 367.5 5,044.9 (3,505.6 ) 1,915.7 Property, plant and equipment, net 0.9 1,581.6 913.2 — 2,495.7 Goodwill — — 531.4 — 531.4 Intercompany notes receivable — — 200.0 (200.0 ) — Investment in subsidiaries 5,645.6 37.7 — (5,683.3 ) — Other assets 25.4 18.0 199.2 — 242.6 Total assets $ 5,680.8 $ 2,004.8 $ 6,888.7 $ (9,388.9 ) $ 5,185.4 Liabilities and stockholders’ equity: Accounts payable $ 3.0 $ 180.3 $ 236.8 $ — $ 420.1 Accrued liabilities 54.1 88.5 139.8 — 282.4 Intercompany notes payable 1,836.5 1,669.1 — (3,505.6 ) — Short-term debt and current portion of long-term debt 0.3 0.6 9.2 — 10.1 Total current liabilities 1,893.9 1,938.5 385.8 (3,505.6 ) 712.6 Long-term debt 1,275.7 150.7 104.2 — 1,530.6 Intercompany notes payable — 200.0 — (200.0 ) — Accrued postretirement benefits — 250.2 67.6 — 317.8 Pension liabilities 644.3 4.4 48.3 — 697.0 Deferred income taxes 9.7 — — — 9.7 Other long-term liabilities 12.7 17.2 43.3 — 73.2 Total liabilities 3,836.3 2,561.0 649.2 (3,705.6 ) 3,340.9 Total stockholders’ equity (deficit) 1,844.5 (556.2 ) 6,239.5 (5,683.3 ) 1,844.5 Total liabilities and stockholders’ equity $ 5,680.8 $ 2,004.8 $ 6,888.7 $ (9,388.9 ) $ 5,185.4
Statements of Operations and Comprehensive Income	Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Operations and Comprehensive Income For the three months ended September 30, 2018 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Sales $ — $ 357.4 $ 662.8 $ — $ 1,020.2 Cost of sales 3.7 316.3 539.8 — 859.8 Gross profit (loss) (3.7 ) 41.1 123.0 — 160.4 Selling and administrative expenses 24.9 7.3 33.3 — 65.5 Operating income (loss) (28.6 ) 33.8 89.7 — 94.9 Nonoperating retirement benefit expense (3.1 ) (4.9 ) (0.4 ) — (8.4 ) Interest income (expense), net (34.9 ) (29.5 ) 39.6 — (24.8 ) Other income (loss) including equity in income of unconsolidated subsidiaries 129.1 0.4 (0.1 ) (128.6 ) 0.8 Income (loss) before income tax provision (benefit) 62.5 (0.2 ) 128.8 (128.6 ) 62.5 Income tax provision (benefit) 6.9 1.4 21.2 (22.6 ) 6.9 Net income (loss) 55.6 (1.6 ) 107.6 (106.0 ) 55.6 Less: Net income attributable to noncontrolling interests — — 5.1 — 5.1 Net income (loss) attributable to ATI $ 55.6 $ (1.6 ) $ 102.5 $ (106.0 ) $ 50.5 Comprehensive income (loss) attributable to ATI $ 46.9 $ 0.9 $ 97.9 $ (94.9 ) $ 50.8 Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Operations and Comprehensive Income For the nine months ended September 30, 2018 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Sales $ — $ 1,047.0 $ 1,961.7 $ — $ 3,008.7 Cost of sales 11.7 962.8 1,551.5 — 2,526.0 Gross profit (loss) (11.7 ) 84.2 410.2 — 482.7 Selling and administrative expenses 73.0 25.2 97.1 — 195.3 Operating income (loss) (84.7 ) 59.0 313.1 — 287.4 Nonoperating retirement benefit expense (9.7 ) (14.6 ) (1.2 ) — (25.5 ) Interest income (expense), net (102.1 ) (83.3 ) 109.6 — (75.8 ) Other income (loss) including equity in income of unconsolidated subsidiaries 405.0 19.5 0.6 (402.7 ) 22.4 Income (loss) before income tax provision (benefit) 208.5 (19.4 ) 422.1 (402.7 ) 208.5 Income tax provision (benefit) 16.8 (2.9 ) 66.3 (63.4 ) 16.8 Net income (loss) 191.7 (16.5 ) 355.8 (339.3 ) 191.7 Less: Net income attributable to noncontrolling interests — — 10.4 — 10.4 Net income (loss) attributable to ATI $ 191.7 $ (16.5 ) $ 345.4 $ (339.3 ) $ 181.3 Comprehensive income (loss) attributable to ATI $ 223.0 $ (9.3 ) $ 334.7 $ (330.6 ) $ 217.8 Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Operations and Comprehensive Income For the three months ended September 30, 2017 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Sales $ — $ 287.9 $ 581.2 $ — $ 869.1 Cost of sales 3.4 279.3 481.1 — 763.8 Gross profit (loss) (3.4 ) 8.6 100.1 — 105.3 Selling and administrative expenses 24.8 8.4 31.4 — 64.6 Impairment of goodwill — — 114.4 — 114.4 Operating income (loss) (28.2 ) 0.2 (45.7 ) — (73.7 ) Nonoperating retirement benefit expense (8.0 ) (4.7 ) (0.9 ) — (13.6 ) Interest income (expense), net (40.1 ) (22.9 ) 28.8 — (34.2 ) Other income (loss) including equity in income of unconsolidated subsidiaries (45.0 ) 0.3 (0.1 ) 45.0 0.2 Income (loss) before income tax provision (benefit) (121.3 ) (27.1 ) (17.9 ) 45.0 (121.3 ) Income tax provision (benefit) (1.9 ) (8.6 ) 28.3 (19.7 ) (1.9 ) Net income (loss) (119.4 ) (18.5 ) (46.2 ) 64.7 (119.4 ) Less: Net income attributable to noncontrolling interests — — 1.8 — 1.8 Net income (loss) attributable to ATI $ (119.4 ) $ (18.5 ) $ (48.0 ) $ 64.7 $ (121.2 ) Comprehensive income (loss) attributable to ATI $ (63.5 ) $ (15.5 ) $ (28.5 ) $ 37.2 $ (70.3 ) Allegheny Technologies Incorporated Financial Information for Subsidiary and Guarantor Parent Statements of Operations and Comprehensive Income For the nine months ended September 30, 2017 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Sales $ — $ 866.3 $ 1,748.9 $ — $ 2,615.2 Cost of sales 12.5 809.0 1,439.3 — 2,260.8 Gross profit (loss) (12.5 ) 57.3 309.6 — 354.4 Selling and administrative expenses 66.8 26.5 94.2 — 187.5 Impairment of goodwill — — 114.4 — 114.4 Operating income (loss) (79.3 ) 30.8 101.0 — 52.5 Nonoperating retirement benefit expense (24.2 ) (14.0 ) (2.7 ) — (40.9 ) Interest income (expense), net (118.4 ) (66.6 ) 82.8 — (102.2 ) Other income (loss) including equity in income of unconsolidated subsidiaries 135.0 1.1 2.6 (135.0 ) 3.7 Income (loss) before income tax provision (benefit) (86.9 ) (48.7 ) 183.7 (135.0 ) (86.9 ) Income tax provision (benefit) (2.0 ) (16.3 ) 97.4 (81.1 ) (2.0 ) Net income (loss) (84.9 ) (32.4 ) 86.3 (53.9 ) (84.9 ) Less: Net income attributable to noncontrolling interests — — 8.7 — 8.7 Net income (loss) attributable to ATI $ (84.9 ) $ (32.4 ) $ 77.6 $ (53.9 ) $ (93.6 ) Comprehensive income (loss) attributable to ATI $ (0.3 ) $ (27.1 ) $ 109.9 $ (98.7 ) $ (16.2 )
Condensed Statements of Cash Flows	Condensed Statements of Cash Flows For the nine months ended September 30, 2018 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Cash flows provided by (used in) operating activities $ (102.9 ) $ (126.7 ) $ 361.2 $ (15.0 ) $ 116.6 Investing Activities: Purchases of property, plant and equipment (1.4 ) (19.2 ) (80.7 ) — (101.3 ) Net receipts/(payments) on intercompany activity — — (236.0 ) 236.0 — Purchases of businesses — — (10.0 ) — (10.0 ) Asset disposals and other 0.8 1.3 0.1 — 2.2 Cash flows provided by (used in) investing activities (0.6 ) (17.9 ) (326.6 ) 236.0 (109.1 ) Financing Activities: Borrowings on long-term debt — — 7.1 — 7.1 Payments on long-term debt and capital leases (0.2 ) (0.6 ) (3.8 ) — (4.6 ) Net borrowings under credit facilities — — 4.0 — 4.0 Net receipts/(payments) on intercompany activity 109.2 126.8 — (236.0 ) — Dividends paid to stockholders — — (15.0 ) 15.0 — Dividends paid to noncontrolling interests — — (10.0 ) — (10.0 ) Sales to 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 102.5 137.9 (15.0 ) (221.0 ) 4.4 Increase (decrease) in cash and cash equivalents $ (1.0 ) $ (6.7 ) $ 19.6 $ — $ 11.9 Condensed Statements of Cash Flows For the nine months ended September 30, 2017 (In millions) Guarantor Parent Subsidiary Non-guarantor Subsidiaries Eliminations Consolidated Cash flows provided by (used in) operating activities $ (84.2 ) $ (83.1 ) $ 113.5 $ — $ (53.8 ) Investing Activities: Purchases of property, plant and equipment (0.5 ) (27.4 ) (57.4 ) — (85.3 ) Net receipts/(payments) on intercompany activity — — (205.1 ) 205.1 — Asset disposals and other — 0.1 3.1 — 3.2 Cash flows provided by (used in) investing activities (0.5 ) (27.3 ) (259.4 ) 205.1 (82.1 ) Financing Activities: Borrowings on long-term debt — — 8.5 — 8.5 Payments on long-term debt and capital leases (0.3 ) (0.2 ) (1.4 ) — (1.9 ) Net borrowings under credit facilities — — 28.0 — 28.0 Debt issuance costs — — (0.8 ) — (0.8 ) Net receipts/(payments) on intercompany activity 89.6 115.5 — (205.1 ) — Sale to noncontrolling interests — — 2.2 — 2.2 Shares repurchased for income tax withholding on share-based compensation (4.8 ) — — — (4.8 ) Cash flows provided by (used in) financing activities 84.5 115.3 36.5 (205.1 ) 31.2 Increase (decrease) in cash and cash equivalents $ (0.2 ) $ 4.9 $ (109.4 ) $ — $ (104.7 )

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Schedule Of Accumulated Other Comprehensive Income Loss	The changes in accumulated other comprehensive income (loss) (AOCI) by component, net of tax, for the three month period ended September 30, 2018 were as follows (in millions): Post- retirement benefit plans Currency translation adjustment Unrealized holding gains on securities Derivatives Deferred Tax Asset Valuation Allowance Total Attributable to ATI: Balance, June 30, 2018 $ (926.2 ) $ (59.9 ) $ — $ 13.2 $ (18.7 ) $ (991.6 ) OCI before reclassifications — (4.8 ) — (8.1 ) — (12.9 ) Amounts reclassified from AOCI (a) 14.0 (b) — (b) — (c) (2.0 ) (d) 1.2 13.2 Net current-period OCI 14.0 (4.8 ) — (10.1 ) 1.2 0.3 Balance, September 30, 2018 $ (912.2 ) $ (64.7 ) $ — $ 3.1 $ (17.5 ) $ (991.3 ) Attributable to noncontrolling interests: Balance, June 30, 2018 $ — $ 21.1 $ — $ — $ — $ 21.1 OCI before reclassifications — (9.0 ) — — — (9.0 ) Amounts reclassified from AOCI — (b) — — — — — Net current-period OCI — (9.0 ) — — — (9.0 ) Balance, September 30, 2018 $ — $ 12.1 $ — $ — $ — $ 12.1 The changes in AOCI by component, net of tax, for the nine month period ended September 30, 2018 were as follows (in millions): Post- retirement benefit plans Currency translation adjustment Unrealized holding gains on securities Derivatives Deferred Tax Asset Valuation Allowance Total Attributable to ATI: Balance, December 31, 2017 $ (954.5 ) $ (53.5 ) $ — $ 9.0 $ (28.8 ) $ (1,027.8 ) OCI before reclassifications — (11.2 ) — 1.9 — (9.3 ) Amounts reclassified from AOCI (a) 42.3 (b) — (b) — (c) (7.8 ) (d) 11.3 45.8 Net current-period OCI 42.3 (11.2 ) — (5.9 ) 11.3 36.5 Balance, September 30, 2018 $ (912.2 ) $ (64.7 ) $ — $ 3.1 $ (17.5 ) $ (991.3 ) Attributable to noncontrolling interests: Balance, December 31, 2017 $ — $ 17.3 $ — $ — $ — $ 17.3 OCI before reclassifications — (5.2 ) — — — (5.2 ) Amounts reclassified from AOCI — (b) — — — — — Net current-period OCI — (5.2 ) — — — (5.2 ) Balance, September 30, 2018 $ — $ 12.1 $ — $ — $ — $ 12.1 (a) Amounts were included in net periodic benefit cost for pension and other postretirement benefit plans (see Note 9). (b) No amounts were reclassified to earnings. (c) 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 7). (d) Represents the net change in deferred tax asset valuation allowances on changes in AOCI balances between the balance sheet dates. The changes in AOCI by component, net of tax, for the three month period ended September 30, 2017 were as follows (in millions): Post- retirement benefit plans Currency translation adjustment Unrealized holding gains on securities Derivatives Deferred Tax Asset Valuation Allowance Total Attributable to ATI: Balance, June 30, 2017 $ (943.5 ) $ (72.4 ) $ — $ (5.7 ) $ (45.6 ) $ (1,067.2 ) OCI before reclassifications — 19.2 — 5.7 — 24.9 Amounts reclassified from AOCI (a) 10.5 (b) — (b) — (c) (0.8 ) 16.3 26.0 Net current-period OCI 10.5 19.2 — 4.9 16.3 50.9 Balance, September 30, 2017 $ (933.0 ) $ (53.2 ) $ — $ (0.8 ) $ (29.3 ) $ (1,016.3 ) Attributable to noncontrolling interests: Balance, June 30, 2017 $ — $ 11.9 $ — $ — $ — $ 11.9 OCI before reclassifications — 5.0 — — — 5.0 Amounts reclassified from AOCI — (b) — — — — — Net current-period OCI — 5.0 — — — $ 5.0 Balance, September 30, 2017 $ — $ 16.9 $ — $ — $ — $ 16.9 The changes in AOCI by component, net of tax, for the nine month period ended September 30, 2017 were as follows (in millions): Post- retirement benefit plans Currency translation adjustment Unrealized holding gains on securities 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 — 31.8 — (1.0 ) — 30.8 Amounts reclassified from AOCI (a) 32.5 (b) — (b) — (c) (2.2 ) 16.3 46.6 Net current-period OCI 32.5 31.8 — (3.2 ) 16.3 77.4 Balance, September 30, 2017 $ (933.0 ) $ (53.2 ) $ — $ (0.8 ) $ (29.3 ) $ (1,016.3 ) Attributable to noncontrolling interests: Balance, December 31, 2016 $ — $ 9.7 $ — $ — $ — $ 9.7 OCI before reclassifications — 7.2 — — — 7.2 Amounts reclassified from AOCI — (b) — — — — — Net current-period OCI — 7.2 — — — $ 7.2 Balance, September 30, 2017 $ — $ 16.9 $ — $ — $ — $ 16.9 (a) Amounts were included in net periodic benefit cost for pension and other postretirement benefit plans (see Note 9). (b) No amounts were reclassified to earnings. (c) Amounts related to the effective portion of the derivatives are included in cost of goods sold in the period or periods the hedged item affects earnings (see Note 7).
Reclassification out of Accumulated Other Comprehensive Income	Reclassifications out of AOCI for the three and nine month periods ended September 30, 2018 and 2017 were as follows: Amount reclassified from AOCI Details about AOCI Components (In millions) Three months ended September 30, 2018 Three months ended September 30, 2017 Nine months ended September 30, 2018 Nine months ended September 30, 2017 Affected line item in the statements of operations Postretirement benefit plans Prior service credit $ 0.7 $ 0.4 $ 1.9 $ 1.2 (a) Actuarial losses (19.2 ) (17.8 ) (57.5 ) (53.6 ) (a) (18.5 ) (17.4 ) (55.6 ) (52.4 ) (c) Total before tax (4.5 ) (6.9 ) (13.3 ) (19.9 ) Tax provision (benefit) (d) $ (14.0 ) $ (10.5 ) $ (42.3 ) $ (32.5 ) Net of tax Derivatives Nickel and other raw material contracts $ 2.2 $ (1.5 ) $ 10.4 $ (4.0 ) (b) Natural gas contracts — (1.1 ) (0.5 ) (4.5 ) (b) Foreign exchange contracts 0.5 3.8 0.5 12.0 (b) Interest rate swap (0.1 ) — (0.1 ) — (b) 2.6 1.2 10.3 3.5 (c) Total before tax 0.6 0.4 2.5 1.3 Tax provision (benefit) (d) $ 2.0 $ 0.8 $ 7.8 $ 2.2 Net of tax (a) Amounts are reported in nonoperating retirement benefit expense (see Note 9). (b) 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 7). (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 allowance, when applicable.

Accounting Policies (Accounting

Accounting Policies (Accounting Pronouncements) (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impact of new accounting principle on prior period operating income	$ 94.9		$ (73.7)	$ 287.4	$ 52.5
Unfavorable impact on pre-tax operating results	$ (62.5)		121.3	$ (208.5)	86.9
Accounting Standards Update 2017-07 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impact of new accounting principle on prior period operating income			$ 13.6		$ 40.9
Unfavorable impact on pre-tax operating results		$ 5.4

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Narrative (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)segment	Sep. 30, 2017USD ($)	Jan. 01, 2018USD ($)	Dec. 31, 2017USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Inventories, net	$ 1,239,800,000		$ 1,239,800,000			$ 1,176,100,000
Adjustment from current cost to LIFO cost basis	(1,700,000)		(1,700,000)			(43,100,000)
Sales	1,020,200,000	$ 869,100,000	3,008,700,000	$ 2,615,200,000
Cost of sales	859,800,000	763,800,000	2,526,000,000	2,260,800,000
Short-term contract assets	51,600,000		51,600,000		$ 36,500,000	0
Long-term contract assets	100,000		100,000		16,900,000
Accrued liabilities	228,700,000		228,700,000			282,400,000
Other long-term liabilities	66,700,000		66,700,000			73,200,000
Short-term contract liabilities	69,200,000		69,200,000		69,700,000	0
Long-term contract liabilities	7,300,000		$ 7,300,000		22,200,000	0
Number of business segments | segment			2
Revenue, Performance Obligation [Abstract]
Confirmed order backlog	2,170,000,000	$ 1,810,000,000	$ 2,170,000,000	$ 1,810,000,000
Confirmed orders with current performance obligations	0.82		0.82
Accounts receivable with customers	594,500,000		594,500,000			$ 550,900,000
Contract costs for obtaining and fulfilling contracts	5,200,000		5,200,000
Amortization of contract costs	300,000		900,000
ASU 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Inventories, net	14,200,000		14,200,000		28,800,000
Adjustment from current cost to LIFO cost basis					11,800,000
Short-term contract assets	4,600,000		4,600,000		3,700,000
Increase in accounts receivable	3,700,000		3,700,000		3,900,000
Accrued liabilities	(46,700,000)		(46,700,000)		(44,800,000)
Other long-term liabilities	(7,300,000)		(7,300,000)		(10,700,000)
Short-term contract liabilities	69,200,000		69,200,000		69,700,000
Long-term contract liabilities	7,300,000		7,300,000		22,200,000
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	47,100,000		47,100,000		49,700,000
Inventories, net	4,100,000		4,100,000		$ (34,200,000)
Sales	1,800,000		(2,500,000)
Cost of sales	1,100,000		(4,100,000)
Short-term contract assets	47,000,000		47,000,000
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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 1,020.2	$ 869.1	$ 3,008.7	$ 2,615.2
Percent of total revenue	100.00%	100.00%	100.00%	100.00%
Total High-Value Products
Disaggregation of Revenue [Line Items]
Percent of total revenue	84.00%	84.00%	84.00%	83.00%
Nickel-based alloys and specialty alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	30.00%	28.00%	30.00%	27.00%
Precision forgings, castings and components
Disaggregation of Revenue [Line Items]
Percent of total revenue	18.00%	19.00%	20.00%	19.00%
Titanium and titanium-based alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	16.00%	17.00%	15.00%	17.00%
Precision and engineered strip
Disaggregation of Revenue [Line Items]
Percent of total revenue	14.00%	14.00%	14.00%	14.00%
Zirconium and related alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	6.00%	6.00%	5.00%	6.00%
Total Standard Products
Disaggregation of Revenue [Line Items]
Percent of total revenue	16.00%	16.00%	16.00%	17.00%
Stainless steel sheet
Disaggregation of Revenue [Line Items]
Percent of total revenue	9.00%	9.00%	9.00%	9.00%
Specialty stainless sheet
Disaggregation of Revenue [Line Items]
Percent of total revenue	4.00%	4.00%	4.00%	4.00%
Stainless steel plate and other
Disaggregation of Revenue [Line Items]
Percent of total revenue	3.00%	3.00%	3.00%	4.00%
United States
Disaggregation of Revenue [Line Items]
Revenue	$ 607.6	$ 506.5	$ 1,737.7	$ 1,555.7
Europe
Disaggregation of Revenue [Line Items]
Revenue	213.7	188.6	669.7	576.6
Asia
Disaggregation of Revenue [Line Items]
Revenue	144.9	120.3	439.4	317.5
Canada
Disaggregation of Revenue [Line Items]
Revenue	23.8	21.1	80.3	73.5
South America, Middle East and other
Disaggregation of Revenue [Line Items]
Revenue	30.2	32.6	81.6	91.9
Total Key Markets
Disaggregation of Revenue [Line Items]
Revenue	820.2	680.8	2,424.7	2,063.5
Aerospace & Defense
Disaggregation of Revenue [Line Items]
Revenue	499.2	427.7	1,443.6	1,280.5
Oil & Gas
Disaggregation of Revenue [Line Items]
Revenue	128.2	98.4	413.5	289.7
Automotive
Disaggregation of Revenue [Line Items]
Revenue	85	61.7	244.5	206.4
Electrical Energy
Disaggregation of Revenue [Line Items]
Revenue	59.9	48.5	180.3	144.2
Medical
Disaggregation of Revenue [Line Items]
Revenue	47.9	44.5	142.8	142.7
Food Equipment & Appliances
Disaggregation of Revenue [Line Items]
Revenue	58.8	54.5	181.3	168.9
Construction/Mining
Disaggregation of Revenue [Line Items]
Revenue	58.4	48.3	169.9	144.6
Electronics/Computers/Communications
Disaggregation of Revenue [Line Items]
Revenue	41.3	42.3	109.7	108.2
Other
Disaggregation of Revenue [Line Items]
Revenue	41.5	43.2	123.1	130
Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,067.7	898.6	3,137.2	2,711.8
Operating Segments | High Performance Materials & Components
Disaggregation of Revenue [Line Items]
Revenue	$ 615.2	$ 526.3	$ 1,806.3	$ 1,593.3
Percent of total revenue	100.00%	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%	100.00%
Operating Segments | High Performance Materials & Components | Nickel-based alloys and specialty alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	32.00%	30.00%	31.00%	30.00%
Operating Segments | High Performance Materials & Components | Precision forgings, castings and components
Disaggregation of Revenue [Line Items]
Percent of total revenue	33.00%	33.00%	35.00%	32.00%
Operating Segments | High Performance Materials & Components | Titanium and titanium-based alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	25.00%	26.00%	24.00%	27.00%
Operating Segments | High Performance Materials & Components | Precision and engineered strip
Disaggregation of Revenue [Line Items]
Percent of total revenue	0.00%	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	10.00%	11.00%	10.00%	11.00%
Operating Segments | High Performance Materials & Components | Total Standard Products
Disaggregation of Revenue [Line Items]
Percent of total revenue	0.00%	0.00%	0.00%	0.00%
Operating Segments | High Performance Materials & Components | Stainless steel sheet
Disaggregation of Revenue [Line Items]
Percent of total revenue	0.00%	0.00%	0.00%	0.00%
Operating Segments | High Performance Materials & Components | Specialty stainless sheet
Disaggregation of Revenue [Line Items]
Percent of total revenue	0.00%	0.00%	0.00%	0.00%
Operating Segments | High Performance Materials & Components | Stainless steel plate and other
Disaggregation of Revenue [Line Items]
Percent of total revenue	0.00%	0.00%	0.00%	0.00%
Operating Segments | High Performance Materials & Components | United States
Disaggregation of Revenue [Line Items]
Revenue	$ 316.7	$ 273.4	$ 898.6	$ 820.5
Operating Segments | High Performance Materials & Components | Europe
Disaggregation of Revenue [Line Items]
Revenue	173.2	164.8	565.4	502.2
Operating Segments | High Performance Materials & Components | Asia
Disaggregation of Revenue [Line Items]
Revenue	60.9	45.1	180.7	127.3
Operating Segments | High Performance Materials & Components | Canada
Disaggregation of Revenue [Line Items]
Revenue	16.3	15.3	51.3	52.4
Operating Segments | High Performance Materials & Components | South America, Middle East and other
Disaggregation of Revenue [Line Items]
Revenue	18.4	14.3	42.1	47.3
Operating Segments | High Performance Materials & Components | Total Key Markets
Disaggregation of Revenue [Line Items]
Revenue	541.6	478.4	1,603.9	1,444.1
Operating Segments | High Performance Materials & Components | Aerospace & Defense
Disaggregation of Revenue [Line Items]
Revenue	446.5	389.5	1,311.7	1,169.7
Operating Segments | High Performance Materials & Components | Oil & Gas
Disaggregation of Revenue [Line Items]
Revenue	17.9	14.3	51.4	49.7
Operating Segments | High Performance Materials & Components | Automotive
Disaggregation of Revenue [Line Items]
Revenue	2	2.4	7.4	6.4
Operating Segments | High Performance Materials & Components | Electrical Energy
Disaggregation of Revenue [Line Items]
Revenue	30.9	30.4	101.9	84.1
Operating Segments | High Performance Materials & Components | Medical
Disaggregation of Revenue [Line Items]
Revenue	44.3	41.8	131.5	134.2
Operating Segments | High Performance Materials & Components | Food Equipment & Appliances
Disaggregation of Revenue [Line Items]
Revenue	0.2	0.2	0.3	1
Operating Segments | High Performance Materials & Components | Construction/Mining
Disaggregation of Revenue [Line Items]
Revenue	18.5	13.5	55.1	37.6
Operating Segments | High Performance Materials & Components | Electronics/Computers/Communications
Disaggregation of Revenue [Line Items]
Revenue	1	1.1	4.7	3.5
Operating Segments | High Performance Materials & Components | Other
Disaggregation of Revenue [Line Items]
Revenue	24.2	19.7	74.1	63.5
Operating Segments | Flat Rolled Products
Disaggregation of Revenue [Line Items]
Revenue	$ 452.5	$ 372.3	$ 1,330.9	$ 1,118.5
Percent of total revenue	100.00%	100.00%	100.00%	100.00%
Operating Segments | Flat Rolled Products | Total High-Value Products
Disaggregation of Revenue [Line Items]
Percent of total revenue	66.00%	64.00%	66.00%	61.00%
Operating Segments | Flat Rolled Products | Nickel-based alloys and specialty alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	29.00%	27.00%	29.00%	23.00%
Operating Segments | Flat Rolled Products | Precision forgings, castings and components
Disaggregation of Revenue [Line Items]
Percent of total revenue	0.00%	0.00%	0.00%	0.00%
Operating Segments | Flat Rolled Products | Titanium and titanium-based alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	3.00%	3.00%	5.00%	4.00%
Operating Segments | Flat Rolled Products | Precision and engineered strip
Disaggregation of Revenue [Line Items]
Percent of total revenue	34.00%	34.00%	32.00%	34.00%
Operating Segments | Flat Rolled Products | Zirconium and related alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	0.00%	0.00%	0.00%	0.00%
Operating Segments | Flat Rolled Products | Total Standard Products
Disaggregation of Revenue [Line Items]
Percent of total revenue	34.00%	36.00%	34.00%	39.00%
Operating Segments | Flat Rolled Products | Stainless steel sheet
Disaggregation of Revenue [Line Items]
Percent of total revenue	20.00%	20.00%	20.00%	22.00%
Operating Segments | Flat Rolled Products | Specialty stainless sheet
Disaggregation of Revenue [Line Items]
Percent of total revenue	9.00%	11.00%	10.00%	12.00%
Operating Segments | Flat Rolled Products | Stainless steel plate and other
Disaggregation of Revenue [Line Items]
Percent of total revenue	5.00%	5.00%	4.00%	5.00%
Operating Segments | Flat Rolled Products | United States
Disaggregation of Revenue [Line Items]
Revenue	$ 290.9	$ 233.1	$ 839.1	$ 735.2
Operating Segments | Flat Rolled Products | Europe
Disaggregation of Revenue [Line Items]
Revenue	40.5	23.8	104.3	74.4
Operating Segments | Flat Rolled Products | Asia
Disaggregation of Revenue [Line Items]
Revenue	84	75.2	258.7	190.2
Operating Segments | Flat Rolled Products | Canada
Disaggregation of Revenue [Line Items]
Revenue	7.5	5.8	29	21.1
Operating Segments | Flat Rolled Products | South America, Middle East and other
Disaggregation of Revenue [Line Items]
Revenue	11.8	18.3	39.5	44.6
Operating Segments | Flat Rolled Products | Total Key Markets
Disaggregation of Revenue [Line Items]
Revenue	278.6	202.4	820.8	619.4
Operating Segments | Flat Rolled Products | Aerospace & Defense
Disaggregation of Revenue [Line Items]
Revenue	52.7	38.2	131.9	110.8
Operating Segments | Flat Rolled Products | Oil & Gas
Disaggregation of Revenue [Line Items]
Revenue	110.3	84.1	362.1	240
Operating Segments | Flat Rolled Products | Automotive
Disaggregation of Revenue [Line Items]
Revenue	83	59.3	237.1	200
Operating Segments | Flat Rolled Products | Electrical Energy
Disaggregation of Revenue [Line Items]
Revenue	29	18.1	78.4	60.1
Operating Segments | Flat Rolled Products | Medical
Disaggregation of Revenue [Line Items]
Revenue	3.6	2.7	11.3	8.5
Operating Segments | Flat Rolled Products | Food Equipment & Appliances
Disaggregation of Revenue [Line Items]
Revenue	58.6	54.3	181	167.9
Operating Segments | Flat Rolled Products | Construction/Mining
Disaggregation of Revenue [Line Items]
Revenue	39.9	34.8	114.8	107
Operating Segments | Flat Rolled Products | Electronics/Computers/Communications
Disaggregation of Revenue [Line Items]
Revenue	40.3	41.2	105	104.7
Operating Segments | Flat Rolled Products | Other
Disaggregation of Revenue [Line Items]
Revenue	17.3	23.5	49	66.5
External Customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,020.2	869.1	3,008.7	2,615.2
External Customers | Operating Segments | High Performance Materials & Components
Disaggregation of Revenue [Line Items]
Revenue	585.5	512.9	1,738.1	1,549.7
External Customers | Operating Segments | Flat Rolled Products
Disaggregation of Revenue [Line Items]
Revenue	$ 434.7	$ 356.2	$ 1,270.6	$ 1,065.5

Revenue from Contracts with C_5

Revenue from Contracts with Customers - Accounts Receivable Reserve for Doubtful Accounts (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance as of January 1, 2018	$ 5.9
Expense to increase the reserve	0.7
Write-off of uncollectible accounts	(0.4)
Balance as of September 30, 2018	$ 6.2

Revenue from Contracts with C_6

Revenue from Contracts with Customers - Contract Assets and Liabilities (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)
Contract Assets, Current [Roll Forward]
Balance as of January 1, 2018	$ 0
Recognized in current year	66.2
Reclassified to accounts receivable	(67.9)
Impairment	0
Reclassification to/from long-term	16.8
Balance as of September 30, 2018	51.6
Contract Assets, Noncurrent [Roll Forward]
Recognized in current year	0
Reclassified to accounts receivable	0
Impairment	0
Reclassification to/from short-term	(16.8)
Balance as of September 30, 2018	0.1
Contract Liabilities, Current [Roll Forward]
Balance as of January 1, 2018	0
Recognized in current year	46.9
Amounts in beginning balance reclassified to revenue	(40.1)
Current year amounts reclassified to revenue	(23.6)
Other	1.7
Reclassification to/from long-term	14.6
Balance as of September 30, 2018	69.2
Contract Liabilities, Noncurrent [Roll Forward]
Balance as of January 1, 2018	0
Recognized in current year	0.5
Amounts in beginning balance reclassified to revenue	(0.8)
Current year amounts reclassified to revenue	0
Other	0
Reclassification to/from short-term	(14.6)
Balance as of September 30, 2018	$ 7.3

Inventories (Details)

Inventories (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Inventory [Line Items]
Raw materials and supplies	$ 204.3		$ 204.3			$ 162.8
Work-in-process	929.9		929.9			955.5
Finished goods	190		190			165
Total inventories at current cost	1,324.2		1,324.2			1,283.3
Adjustment from current cost to LIFO cost basis	1.7		1.7			43.1
Inventory valuation reserves	(86.1)		(86.1)			(121.5)
Progress payments	0		0			(28.8)
Total inventories, net	1,239.8		1,239.8			1,176.1
LIFO benefit (charge)			(29.5)	$ (51.5)
NRV benefit (charge)			29.5	51.3
Net cost of sales impact	0	$ (0.1)	0	$ (0.2)
ASU 2014-09
Inventory [Line Items]
Adjustment from current cost to LIFO cost basis					$ (11.8)
Inventory valuation reserves					11.8
Total inventories, net	14.2		14.2		28.8
Net Realizable Value Reserve [Member]
Inventory [Line Items]
Inventory valuation reserves	(6.2)		(6.2)			$ (47.5)
Revenue Recognized Over-time | ASU 2014-09
Inventory [Line Items]
Total inventories, net	$ 4.1		$ 4.1		$ (34.2)

Property, Plant and Equipment_2

Property, Plant and Equipment (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Land	$ 31.6	$ 31.7
Buildings	851.1	844.5
Equipment and leasehold improvements	3,646	3,597.6
Property Plant And Equipment, gross	4,528.7	4,473.8
Accumulated depreciation and amortization	(2,056.1)	(1,978.1)
Total property, plant and equipment, net	2,472.6	$ 2,495.7
Construction in progress	$ 128.1

Joint Ventures (Details)

Joint Ventures (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended		24 Months Ended
	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2019	Dec. 31, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Cash and cash equivalents	$ 153.5		$ 124.9	$ 153.5	$ 124.9		$ 141.6	$ 229.6
Sales to noncontrolling interests				14.4	2.2
Gain on joint venture deconsolidation (See Note 5)	$ 0		0	$ 15.9	0
Next Gen Alloys LLC
Schedule of Equity Method Investments [Line Items]
Joint venture ownership percentage	51.00%			51.00%
Cash and cash equivalents	$ 10.4			$ 10.4
Sales to noncontrolling interests		$ 2.7
Allegheny & Tsingshan Stainless
Schedule of Equity Method Investments [Line Items]
Sales to noncontrolling interests				$ 12
Equity method investment ownership percentage	50.00%			50.00%
Uniti
Schedule of Equity Method Investments [Line Items]
Equity method investment ownership percentage	50.00%			50.00%
Tsingshan Group | Allegheny & Tsingshan Stainless
Schedule of Equity Method Investments [Line Items]
Joint venture ownership percentage by unaffiliated entity	50.00%			50.00%
VSMPO | Uniti
Schedule of Equity Method Investments [Line Items]
Joint venture ownership percentage by unaffiliated entity	50.00%			50.00%
Flat Rolled Products | Shanghai STAL Precision Stainless Steel Co Ltd
Schedule of Equity Method Investments [Line Items]
Joint venture ownership percentage	60.00%			60.00%
Cash and cash equivalents	$ 30			$ 30
Flat Rolled Products | Allegheny & Tsingshan Stainless
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments	(0.3)			0.2
Flat Rolled Products | Uniti
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments	$ 0.5		$ (0.1)	$ 2.3	$ 0.1
Flat Rolled Products | China Baowu Steel Group Corporation Limited | Shanghai STAL Precision Stainless Steel Co Ltd
Schedule of Equity Method Investments [Line Items]
Joint venture ownership percentage by unaffiliated entity	40.00%			40.00%
Forecast | Allegheny & Tsingshan Stainless
Schedule of Equity Method Investments [Line Items]
Sales to noncontrolling interests						$ 17.5

Debt Schedule of Debt (Details)

Debt Schedule of Debt (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2018	Dec. 31, 2017	Jul. 31, 2018	Feb. 15, 2016	Dec. 31, 2013
Debt Instrument [Line Items]
Debt Issuance Costs, Net		$ 11.1	$ 13.1
Total Debt		1,551.9	1,540.7
Short-term debt and current portion of long-term debt		16.6	10.1
Long-term debt		1,535.3	1,530.6
Allegheny Technologies, Convertible Senior Notes, 4.75%, Due 2022
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 287.5	$ 287.5
Debt Instrument, Issuer		Allegheny Technologies
Debt Instrument, Maturity Date		Jul. 1, 2022	Jul. 1, 2022
Interest rate		4.75%	4.75%
Allegheny Technologies 5.875% Notes due 2023 (a)
Debt Instrument [Line Items]
Long-term Debt, Gross	[1]	$ 500	$ 500
Debt Instrument, Issuer		Allegheny Technologies
Debt Instrument, Maturity Date		Aug. 15, 2023	Aug. 15, 2023
Interest rate		7.875%	7.875%		7.875%	5.875%
Allegheny Technologies 5.95% Notes due 2021
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 500	$ 500
Debt Instrument, Issuer		Allegheny Technologies
Debt Instrument, Maturity Date		Jan. 15, 2021	Jan. 15, 2021
Interest rate		5.95%	5.95%
Allegheny Ludlum 6.95% debentures due 2025
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 150	$ 150
Debt Instrument, Issuer		Allegheny Ludlum
Debt Instrument, Maturity Date		Dec. 15, 2025	Dec. 15, 2025
Interest rate		6.95%	6.95%
2022 Term Loan
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 100	$ 100
Debt Instrument, Issuer		Allegheny Technologies
Debt Instrument, Maturity Date		Feb. 28, 2022	Feb. 28, 2022
Interest rate				5.44%
Domestic Bank Group $400 million asset-based credit facility
Debt Instrument [Line Items]
Short-term Debt		$ 0	$ 0
Foreign credit facilities
Debt Instrument [Line Items]
Short-term Debt		10	6.3
Other
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 15.5	$ 10
[1]	Bearing interest at 7.875% effective February 15, 2016.

Debt Narrative (Details)

Debt Narrative (Details)		1 Months Ended	9 Months Ended
		Jul. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)	Feb. 15, 2016	Dec. 31, 2013
Allegheny Technologies 5.875% Notes due 2023 (a)
Debt Instrument [Line Items]
Interest rate			7.875%		7.875%	7.875%	5.875%
Outstanding borrowings	[1]		$ 500,000,000		$ 500,000,000
Asset-based lending credit facility
Debt Instrument [Line Items]
Maximum borrowing capacity			500,000,000
Domestic Bank Group $400 million asset-based credit facility
Debt Instrument [Line Items]
Short-term Debt			0		0
Amount utilized to support the issuance of letters of credit			35,100,000
Average borrowings during period			$ 56,000,000	$ 46,000,000
Interest rate during period			3.651%	3.276%
Domestic Bank Group $400 million asset-based credit facility | Revolving credit facility
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 400,000,000
Minimum fixed charge coverage ratio allowed in event of default			1
Percentage of borrowing capacity unavailable due to fixed charge coverage ratio covenant			10.00%
Borrowing capacity unavailable due to fixed charge coverage ratio covenant			$ 40,000,000
Minimum required liquidity number of days prior to maturity of Senior Notes			91 days
Domestic Bank Group $400 million asset-based credit facility | Revolving credit facility | Minimum | LIBOR based borrowings
Debt Instrument [Line Items]
Variable interest rate (percentage)			1.75%
Domestic Bank Group $400 million asset-based credit facility | Revolving credit facility | Minimum | Base rate borrowings
Debt Instrument [Line Items]
Variable interest rate (percentage)			1.00%
Domestic Bank Group $400 million asset-based credit facility | Revolving credit facility | Maximum | LIBOR based borrowings
Debt Instrument [Line Items]
Variable interest rate (percentage)			2.25%
Domestic Bank Group $400 million asset-based credit facility | Revolving credit facility | Maximum | Base rate borrowings
Debt Instrument [Line Items]
Variable interest rate (percentage)			1.50%
Domestic Bank Group $400 million asset-based credit facility | Letter of credit sub-facility
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 200,000,000
2022 Term Loan
Debt Instrument [Line Items]
Interest rate		5.44%
Minimum prepayment increments allowed			50,000,000
Outstanding borrowings			$ 100,000,000		$ 100,000,000
2022 Term Loan | Interest Rate Swap
Debt Instrument [Line Items]
Notional amount of derivative		$ 50,000,000
2022 Term Loan | LIBOR based borrowings
Debt Instrument [Line Items]
Variable interest rate (percentage)		2.50%	3.00%
Allegheny Technologies, Convertible Senior Notes, 4.75%, Due 2022
Debt Instrument [Line Items]
Interest rate			4.75%		4.75%
Outstanding borrowings			$ 287,500,000		$ 287,500,000
Allegheny Technologies 5.95% Notes due 2021
Debt Instrument [Line Items]
Interest rate			5.95%		5.95%
Outstanding borrowings			$ 500,000,000		$ 500,000,000
Allegheny Technologies 5.95% Notes due 2021 | Revolving credit facility
Debt Instrument [Line Items]
Minimum required liquidity prior to maturity of Senior Notes			$ 700,000,000
[1]	Bearing interest at 7.875% effective February 15, 2016.

Derivative Financial Instrume_3

Derivative Financial Instruments and Hedging (Details) € in Millions, lb in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)lb	Sep. 30, 2017USD ($)	Sep. 30, 2018EUR (€)	Jul. 31, 2018USD ($)
Derivative Instruments Gain Loss [Line Items]
Percentage of estimated annual nickel requirements			12.00%
Percentage Of Forecasted Natural Gas Usage Hedged for 2018			35.00%
Percentage Of Forecasted Natural Gas Usage Hedged for 2019			35.00%
Percentage of Forecasted Natural Gas Usage Hedged for 2020			30.00%
Net derivatives gain (loss) on hedge transactions	$ (10.8)	$ 9.2	$ 2.4	$ (1.6)
Reclassification of Cash Flow Hedge Gain (Loss) [Abstract]
Cash Flow Hedge Gain (Loss) To Be Reclassified Within Twelve Months			1.6
Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Net derivatives gain (loss) on hedge transactions	(8.1)	5.7	1.9	(1)
Cost of Sales and Interest Expense [Member] | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Reclassified From Accumulated OCI Into Income Effective Portion Net	2		$ 7.8
Cost Of Sales | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Reclassified From Accumulated OCI Into Income Effective Portion Net		0.8		2.2
Nickel
Derivative Instruments Gain Loss [Line Items]
Notional amount of nickel hedge (in pounds of nickel) | lb			12
Interest Rate Swap | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Net derivatives gain (loss) on hedge transactions	(0.2)	0	$ (0.2)	0
Interest Rate Swap | Interest Expense [Member] | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Reclassified From Accumulated OCI Into Income Effective Portion Net	(0.1)	0	(0.1)	0
Nickel and other raw material contracts | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Net derivatives gain (loss) on hedge transactions	(8)	5.6	1.3	1.2
Nickel and other raw material contracts | Cost Of Sales | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Reclassified From Accumulated OCI Into Income Effective Portion Net	1.7	(0.9)	7.9	(2.5)
Natural gas contracts | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Net derivatives gain (loss) on hedge transactions	(0.1)	0	0.1	(2.1)
Natural gas contracts | Cost Of Sales | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Reclassified From Accumulated OCI Into Income Effective Portion Net	0	(0.7)	(0.4)	(2.8)
Foreign exchange contracts | Other Comprehensive Income (Loss) [Member] | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Net derivatives gain (loss) on hedge transactions	0.2	0.1	0.7	(0.1)
Foreign exchange contracts | Cost Of Sales | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Reclassified From Accumulated OCI Into Income Effective Portion Net	0.4	2.4	0.4	7.5
Designated as Hedging Instrument | Foreign exchange forward | Maturity Dates Through 2019 [Member] | Cash Flow Hedging
Derivative Instruments Gain Loss [Line Items]
Notional amount of derivative | €					€ 16
Not Designated as Hedging Instrument | Foreign exchange forward | Maturity Dates Through 2019 [Member]
Derivative Instruments Gain Loss [Line Items]
Notional amount of derivative | €					€ 10
Not Designated as Hedging Instrument | Foreign exchange contracts | Cost Of Sales
Derivative Instruments Gain Loss [Line Items]
Derivative Instruments Gain Loss Recognized In Income Net	$ 0	$ (0.1)	$ 0.1	$ (0.7)
2022 Term Loan
Derivative Instruments Gain Loss [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						5.44%
2022 Term Loan | Interest Rate Swap
Derivative Instruments Gain Loss [Line Items]
Notional amount of derivative						$ 50

Derivative Financial Instrume_4

Derivative Financial Instruments and Hedging (Details2) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	$ 8.1	$ 16.5
Derivative Fair Value Of Derivative Liability	4.7	5.5
Designated as Hedging Instrument
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	7.8	16.4
Derivative Fair Value Of Derivative Liability	4.7	5.5
Designated as Hedging Instrument | Nickel and other raw material contracts | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	4.3	10.5
Designated as Hedging Instrument | Nickel and other raw material contracts | Other assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	2.7	5.5
Designated as Hedging Instrument | Nickel and other raw material contracts | Accrued liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	2.9	2.1
Designated as Hedging Instrument | Nickel and other raw material contracts | Other long-term liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	1	2.2
Designated as Hedging Instrument | Interest Rate Swap | Other assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	0.1	0
Designated as Hedging Instrument | Interest Rate Swap | Accrued liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	0.2	0
Designated as Hedging Instrument | Natural gas contracts | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	0.3	0.1
Designated as Hedging Instrument | Natural gas contracts | Other assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	0.1	0.3
Designated as Hedging Instrument | Natural gas contracts | Accrued liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	0.2	0.9
Designated as Hedging Instrument | Natural gas contracts | Other long-term liabilities
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Liability	0.4	0.3
Designated as Hedging Instrument | Foreign exchange contracts | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	0.3	0
Not Designated as Hedging Instrument
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	0.3	0.1
Not Designated as Hedging Instrument | Foreign exchange contracts | Prepaid expenses and other current assets
Derivatives Fair Value [Line Items]
Derivative Fair Value Of Derivative Asset	$ 0.3	$ 0.1

Fair Value of Financial Instr_3

Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Carrying Value Reported Amount Fair Value Disclosure
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 153.5	$ 141.6
Derivative financial instruments, Assets	8.1	16.5
Derivative Financial Instruments, liabilities	4.7	5.5
Debt	1,563	1,553.8
Estimate Of Fair Value Fair Value Disclosure
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	153.5	141.6
Derivative financial instruments, Assets	8.1	16.5
Derivative Financial Instruments, liabilities	4.7	5.5
Debt	1,945.8	1,853.2
Estimate Of Fair Value Fair Value Disclosure | Fair Value Inputs Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	153.5	141.6
Derivative financial instruments, Assets	0	0
Derivative Financial Instruments, liabilities	0	0
Debt	1,820.3	1,736.9
Estimate Of Fair Value Fair Value Disclosure | Fair Value Inputs Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Derivative financial instruments, Assets	8.1	16.5
Derivative Financial Instruments, liabilities	4.7	5.5
Debt	$ 125.5	$ 116.3

Retirement Benefits (Details1)

Retirement Benefits (Details1) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Plans Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefits earned during the year	$ 4.1	$ 3.5	$ 12.4	$ 10.5
Interest cost on benefits earned in prior years	26.2	29.2	78.5	87.6
Expected return on plan assets	(39.5)	(36.7)	(118.5)	(110.1)
Amortization of prior service cost (credit)	0.1	0.3	0.3	0.9
Amortization of net actuarial loss	16.5	15.6	49.5	46.9
Curtailment loss			0.4	0
Total retirement benefit expense	7.4	11.9	22.6	35.8
Other Postretirement Benefit Plan, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefits earned during the year	0.6	0.6	1.8	1.8
Interest cost on benefits earned in prior years	3.2	3.7	9.5	11
Expected return on plan assets	0	0	0	0
Amortization of prior service cost (credit)	(0.8)	(0.7)	(2.2)	(2.1)
Amortization of net actuarial loss	2.7	2.2	8	6.7
Curtailment loss			0	0
Total retirement benefit expense	$ 5.7	$ 5.8	$ 17.1	$ 17.4

Retirement Benefits Narrative (

Retirement Benefits Narrative (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Pension Plans Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Curtailment loss	$ (0.4)	$ 0
Other Postretirement Benefit Plan, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Curtailment loss	$ 0	$ 0

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Apr. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Investments, Owned, Federal Income Tax Note [Line Items]
Income tax (provision) benefit		$ (6,900,000)	$ 1,900,000	$ (16,800,000)	$ 2,000,000
Transition tax expense				5,900,000		$ 0
Discrete tax benefit related to amending tax returns for prior periods				5,800,000
Federal taxable income on the mandatory deemed repatriation of foreign E&P				97,500,000		100,000,000
Transition tax liability		$ 34,100,000		34,100,000		$ 35,000,000
Adjustment to transition tax liability				$ 5,900,000
Payment of transition tax liability	$ 500,000
Effective income tax rate		11.00%		8.10%
Discrete tax benefits (expense)		$ (900,000)	$ 300,000	$ (900,000)	$ 7,000,000
Tax Cuts and Jobs Act, Transition Tax Liability [Member]
Investments, Owned, Federal Income Tax Note [Line Items]
Tax credit carryforward utilized		28,200,000		28,200,000
Federal | Tax Cuts and Jobs Act, Transition Tax Liability [Member]
Investments, Owned, Federal Income Tax Note [Line Items]
NOL tax attributes preserved		$ 97,500,000		$ 97,500,000

Income Taxes - Changes in Defer

Income Taxes - Changes in Deferred Tax Assets (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Tax Credit Carryforward [Line Items]
Net operating loss tax carryovers	$ 357	$ 336.1
Tax credits	62.4	92.6
Gross deferred income tax assets	733.6	742.9
Valuation allowance	(264.7)	(274)
Total deferred income tax assets	468.9	$ 468.9
Change
Tax Credit Carryforward [Line Items]
Net operating loss tax carryovers	20.9
Tax credits	(30.2)
Gross deferred income tax assets	(9.3)
Valuation allowance	9.3
Total deferred income tax assets	$ 0

Business Segments (Details)

Business Segments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Sales	$ 1,020.2	$ 869.1	$ 3,008.7	$ 2,615.2
Operating profit (loss)	105.5	54.4	325.9	195.2
LIFO and net realizable value reserves	0	(0.1)	0	(0.2)
Corporate expenses	(14.8)	(14.8)	(40.9)	(36.9)
Closed operations and other expenses	(3.4)	(12.2)	(16.6)	(28.4)
Impairment of goodwill	0	(114.4)	0	(114.4)
Gain on joint venture deconsolidation (See Note 5)	0	0	15.9	0
Interest expense, net	(24.8)	(34.2)	(75.8)	(102.2)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	62.5	(121.3)	208.5	(86.9)
Operating Segments
Segment Reporting Information [Line Items]
Sales	1,067.7	898.6	3,137.2	2,711.8
Operating Segments | High Performance Materials & Components
Segment Reporting Information [Line Items]
Sales	615.2	526.3	1,806.3	1,593.3
Operating profit (loss)	76	61.7	259.4	180.6
Operating Segments | Flat Rolled Products
Segment Reporting Information [Line Items]
Sales	452.5	372.3	1,330.9	1,118.5
Operating profit (loss)	29.5	(7.3)	66.5	14.6
Internal Customers | Operating Segments
Segment Reporting Information [Line Items]
Sales	47.5	29.5	128.5	96.6
Internal Customers | Operating Segments | High Performance Materials & Components
Segment Reporting Information [Line Items]
Sales	29.7	13.4	68.2	43.6
Internal Customers | Operating Segments | Flat Rolled Products
Segment Reporting Information [Line Items]
Sales	17.8	16.1	60.3	53
External Customers | Operating Segments
Segment Reporting Information [Line Items]
Sales	1,020.2	869.1	3,008.7	2,615.2
External Customers | Operating Segments | High Performance Materials & Components
Segment Reporting Information [Line Items]
Sales	585.5	512.9	1,738.1	1,549.7
External Customers | Operating Segments | Flat Rolled Products
Segment Reporting Information [Line Items]
Sales	$ 434.7	$ 356.2	$ 1,270.6	$ 1,065.5

Business Segments - Additional

Business Segments - Additional Information (Details) $ in Millions	Jul. 12, 2018USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)segment	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Restructuring Cost and Reserve [Line Items]
Number of business segments | segment				2
Impairment of goodwill		$ 0	$ 114.4	$ 0	$ 114.4
Goodwill		536.4		536.4		$ 531.4
Allegheny Technologies, Senior Notes, 9.375, Due 2019 [Member]
Restructuring Cost and Reserve [Line Items]
Interest rate			9.375%		9.375%
Addaero Manufacturing [Member]
Restructuring Cost and Reserve [Line Items]
Payments to Acquire Businesses, Gross	$ 10
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles		2		2
Goodwill		$ 6		$ 6

Per Share Information (Details)

Per Share Information (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Earnings Per Share Reconciliation [Abstract]
Net income (loss) attributable to ATI	$ 50.5	$ (121.2)	$ 181.3	$ (93.6)
4.75% Convertible Senor Notes due 2022	3.2	0	9.6	0
Net income (loss) attributable to ATI after assumed conversions	$ 53.7	$ (121.2)	$ 190.9	$ (93.6)
Denominator for basic net income (loss) per common share – weighted average shares	125.2	107.7	125.1	107.7
Share-based compensation	0.9	0	0.7	0
Effective of dilutive securities: 4.75% Convertible Senior Notes due 2022	19.9	0	19.9	0
Denominator for diluted net income (loss) per common share – adjusted weighted average shares and assumed conversions	146	107.7	145.7	107.7
Basic net income (loss) attributable to ATI per common share (in dollars per share)	$ 0.40	$ (1.12)	$ 1.45	$ (0.87)
Diluted net income (loss) attributable to ATI per common share (in dollars per share)	$ 0.37	$ (1.12)	$ 1.31	$ (0.87)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share Amount	0	20.9	0	20.7
Allegheny Technologies, Convertible Senior Notes, 4.75%, Due 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Interest rate	4.75%		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 - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 150	$ 150
Interest rate	6.95%	6.95%

Financial Information for Sub_4

Financial Information for Subsidiary and Guarantor Parent (B.S.) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
ASSETS
Cash and cash equivalents	$ 153.5		$ 141.6	$ 124.9	$ 229.6
Accounts receivable, net	588.3		545.3
Intercompany notes receivable	0		0
Short-term contract assets	51.6	$ 36.5	0
Inventories, net	1,239.8		1,176.1
Prepaid expenses and other current assets	89.2		52.7
Total current assets	2,122.4		1,915.7
Property, plant and equipment, net	2,472.6		2,495.7
Goodwill	536.4		531.4
Intercompany notes receivable	0		0
Long-term contract assets	0.1	16.9
Investment in subsidiaries	0		0
Other assets	257.6		242.6
Total assets	5,389		5,185.4
LIABILITIES AND EQUITY
Accounts payable	416.1		420.1
Accrued liabilities	228.7		282.4
Intercompany notes payable	0		0
Short-term contract liabilities	69.2	69.7	0
Short-term debt and current portion of long-term debt	16.6		10.1
Total current liabilities	730.6		712.6
Long-term debt	1,535.3		1,530.6
Intercompany notes payable	0		0
Accrued postretirement benefits	301.1		317.8
Pension liabilities	652.7		697
Deferred income taxes	12.1		9.7
Long-term contract liabilities	7.3	$ 22.2	0
Other long-term liabilities	66.7		73.2
Total liabilities	3,305.8		3,340.9
Total stockholders’ equity	2,083.2		1,844.5	$ 1,447.5	$ 1,444.8
Total Liabilities and Equity	5,389		5,185.4
Reportable Legal Entities | Parent Company
ASSETS
Cash and cash equivalents	1.1		2.1
Accounts receivable, net	0		0.2
Intercompany notes receivable	0		0
Short-term contract assets	0
Inventories, net	0		0
Prepaid expenses and other current assets	14.7		6.6
Total current assets	15.8		8.9
Property, plant and equipment, net	0.7		0.9
Goodwill	0		0
Intercompany notes receivable	0		0
Investment in subsidiaries	6,131.9		5,645.6
Other assets	34.1		25.4
Total assets	6,182.5		5,680.8
LIABILITIES AND EQUITY
Accounts payable	4.6		3
Accrued liabilities	37.3		54.1
Intercompany notes payable	2,144.5		1,836.5
Short-term contract liabilities	0
Short-term debt and current portion of long-term debt	0.2		0.3
Total current liabilities	2,186.6		1,893.9
Long-term debt	1,277.5		1,275.7
Intercompany notes payable	0		0
Accrued postretirement benefits	0		0
Pension liabilities	602		644.3
Deferred income taxes	12.1		9.7
Long-term contract liabilities	0
Other long-term liabilities	21.1		12.7
Total liabilities	4,099.3		3,836.3
Total stockholders’ equity	2,083.2		1,844.5
Total Liabilities and Equity	6,182.5		5,680.8
Reportable Legal Entities | Subsidiary
ASSETS
Cash and cash equivalents	6.8		13.5
Accounts receivable, net	156.4		141.6
Intercompany notes receivable	0		0
Short-term contract assets	0
Inventories, net	238.6		207.9
Prepaid expenses and other current assets	38.4		4.5
Total current assets	440.2		367.5
Property, plant and equipment, net	1,551.6		1,581.6
Goodwill	0		0
Intercompany notes receivable	0		0
Investment in subsidiaries	37.7		37.7
Other assets	40.5		18
Total assets	2,070		2,004.8
LIABILITIES AND EQUITY
Accounts payable	153.4		180.3
Accrued liabilities	68.8		88.5
Intercompany notes payable	1,769		1,669.1
Short-term contract liabilities	30.7
Short-term debt and current portion of long-term debt	0.8		0.6
Total current liabilities	2,022.7		1,938.5
Long-term debt	152		150.7
Intercompany notes payable	200		200
Accrued postretirement benefits	243.8		250.2
Pension liabilities	3.9		4.4
Deferred income taxes	0		0
Long-term contract liabilities	0
Other long-term liabilities	17.5		17.2
Total liabilities	2,639.9		2,561
Total stockholders’ equity	(569.9)		(556.2)
Total Liabilities and Equity	2,070		2,004.8
Reportable Legal Entities | NonGuarantor Subsidiaries
ASSETS
Cash and cash equivalents	145.6		126
Accounts receivable, net	431.9		403.5
Intercompany notes receivable	3,913.5		3,505.6
Short-term contract assets	51.6
Inventories, net	1,001.2		968.2
Prepaid expenses and other current assets	36.1		41.6
Total current assets	5,579.9		5,044.9
Property, plant and equipment, net	920.3		913.2
Goodwill	536.4		531.4
Intercompany notes receivable	200		200
Investment in subsidiaries	0		0
Other assets	183		199.2
Total assets	7,419.6		6,888.7
LIABILITIES AND EQUITY
Accounts payable	258.1		236.8
Accrued liabilities	122.6		139.8
Intercompany notes payable	0		0
Short-term contract liabilities	38.5
Short-term debt and current portion of long-term debt	15.6		9.2
Total current liabilities	434.8		385.8
Long-term debt	105.8		104.2
Intercompany notes payable	0		0
Accrued postretirement benefits	57.3		67.6
Pension liabilities	46.8		48.3
Deferred income taxes	0		0
Long-term contract liabilities	7.3
Other long-term liabilities	28.1		43.3
Total liabilities	680.1		649.2
Total stockholders’ equity	6,739.5		6,239.5
Total Liabilities and Equity	7,419.6		6,888.7
Eliminations
ASSETS
Cash and cash equivalents	0		0
Accounts receivable, net	0		0
Intercompany notes receivable	(3,913.5)		(3,505.6)
Short-term contract assets	0
Inventories, net	0		0
Prepaid expenses and other current assets	0		0
Total current assets	(3,913.5)		(3,505.6)
Property, plant and equipment, net	0		0
Goodwill	0		0
Intercompany notes receivable	(200)		(200)
Investment in subsidiaries	(6,169.6)		(5,683.3)
Other assets	0		0
Total assets	(10,283.1)		(9,388.9)
LIABILITIES AND EQUITY
Accounts payable	0		0
Accrued liabilities	0		0
Intercompany notes payable	(3,913.5)		(3,505.6)
Short-term contract liabilities	0
Short-term debt and current portion of long-term debt	0		0
Total current liabilities	(3,913.5)		(3,505.6)
Long-term debt	0		0
Intercompany notes payable	(200)		(200)
Accrued postretirement benefits	0		0
Pension liabilities	0		0
Deferred income taxes	0		0
Long-term contract liabilities	0
Other long-term liabilities	0		0
Total liabilities	(4,113.5)		(3,705.6)
Total stockholders’ equity	(6,169.6)		(5,683.3)
Total Liabilities and Equity	$ (10,283.1)		$ (9,388.9)

Financial Information for Sub_5

Financial Information for Subsidiary and Guarantor Parent (I.S.) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Sales	$ 1,020.2	$ 869.1	$ 3,008.7	$ 2,615.2
Cost of sales	859.8	763.8	2,526	2,260.8
Gross profit (loss)	160.4	105.3	482.7	354.4
Selling and administrative expenses	65.5	64.6	195.3	187.5
Impairment of goodwill	0	114.4	0	114.4
Operating income (loss)	94.9	(73.7)	287.4	52.5
Nonoperating retirement benefit expense	(8.4)	(13.6)	(25.5)	(40.9)
Interest income (expense), net	(24.8)	(34.2)	(75.8)	(102.2)
Other income (loss) including equity in income of unconsolidated subsidiaries	0.8	0.2	22.4	3.7
Income (loss) before income tax provision (benefit)	62.5	(121.3)	208.5	(86.9)
Income tax provision (benefit)	6.9	(1.9)	16.8	(2)
Net income (loss)	55.6	(119.4)	191.7	(84.9)
Less: Net income attributable to noncontrolling interests	5.1	1.8	10.4	8.7
Net income (loss) attributable to ATI	50.5	(121.2)	181.3	(93.6)
Comprehensive income (loss) attributable to ATI	50.8	(70.3)	217.8	(16.2)
Reportable Legal Entities | Parent Company
Income Statement [Abstract]
Sales	0	0	0	0
Cost of sales	3.7	3.4	11.7	12.5
Gross profit (loss)	(3.7)	(3.4)	(11.7)	(12.5)
Selling and administrative expenses	24.9	24.8	73	66.8
Impairment of goodwill		0		0
Operating income (loss)	(28.6)	(28.2)	(84.7)	(79.3)
Nonoperating retirement benefit expense	(3.1)	(8)	(9.7)	(24.2)
Interest income (expense), net	(34.9)	(40.1)	(102.1)	(118.4)
Other income (loss) including equity in income of unconsolidated subsidiaries	129.1	(45)	405	135
Income (loss) before income tax provision (benefit)	62.5	(121.3)	208.5	(86.9)
Income tax provision (benefit)	6.9	(1.9)	16.8	(2)
Net income (loss)	55.6	(119.4)	191.7	(84.9)
Less: Net income attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to ATI	55.6	(119.4)	191.7	(84.9)
Comprehensive income (loss) attributable to ATI	46.9	(63.5)	223	(0.3)
Reportable Legal Entities | Subsidiary
Income Statement [Abstract]
Sales	357.4	287.9	1,047	866.3
Cost of sales	316.3	279.3	962.8	809
Gross profit (loss)	41.1	8.6	84.2	57.3
Selling and administrative expenses	7.3	8.4	25.2	26.5
Impairment of goodwill		0		0
Operating income (loss)	33.8	0.2	59	30.8
Nonoperating retirement benefit expense	(4.9)	(4.7)	(14.6)	(14)
Interest income (expense), net	(29.5)	(22.9)	(83.3)	(66.6)
Other income (loss) including equity in income of unconsolidated subsidiaries	0.4	0.3	19.5	1.1
Income (loss) before income tax provision (benefit)	(0.2)	(27.1)	(19.4)	(48.7)
Income tax provision (benefit)	1.4	(8.6)	(2.9)	(16.3)
Net income (loss)	(1.6)	(18.5)	(16.5)	(32.4)
Less: Net income attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to ATI	(1.6)	(18.5)	(16.5)	(32.4)
Comprehensive income (loss) attributable to ATI	0.9	(15.5)	(9.3)	(27.1)
Reportable Legal Entities | NonGuarantor Subsidiaries
Income Statement [Abstract]
Sales	662.8	581.2	1,961.7	1,748.9
Cost of sales	539.8	481.1	1,551.5	1,439.3
Gross profit (loss)	123	100.1	410.2	309.6
Selling and administrative expenses	33.3	31.4	97.1	94.2
Impairment of goodwill		114.4		114.4
Operating income (loss)	89.7	(45.7)	313.1	101
Nonoperating retirement benefit expense	(0.4)	(0.9)	(1.2)	(2.7)
Interest income (expense), net	39.6	28.8	109.6	82.8
Other income (loss) including equity in income of unconsolidated subsidiaries	(0.1)	(0.1)	0.6	2.6
Income (loss) before income tax provision (benefit)	128.8	(17.9)	422.1	183.7
Income tax provision (benefit)	21.2	28.3	66.3	97.4
Net income (loss)	107.6	(46.2)	355.8	86.3
Less: Net income attributable to noncontrolling interests	5.1	1.8	10.4	8.7
Net income (loss) attributable to ATI	102.5	(48)	345.4	77.6
Comprehensive income (loss) attributable to ATI	97.9	(28.5)	334.7	109.9
Eliminations
Income Statement [Abstract]
Sales	0	0	0	0
Cost of sales	0	0	0	0
Gross profit (loss)	0	0	0	0
Selling and administrative expenses	0	0	0	0
Impairment of goodwill		0		0
Operating income (loss)	0	0	0	0
Nonoperating retirement benefit expense	0	0	0	0
Interest income (expense), net	0	0	0	0
Other income (loss) including equity in income of unconsolidated subsidiaries	(128.6)	45	(402.7)	(135)
Income (loss) before income tax provision (benefit)	(128.6)	45	(402.7)	(135)
Income tax provision (benefit)	(22.6)	(19.7)	(63.4)	(81.1)
Net income (loss)	(106)	64.7	(339.3)	(53.9)
Less: Net income attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to ATI	(106)	64.7	(339.3)	(53.9)
Comprehensive income (loss) attributable to ATI	$ (94.9)	$ 37.2	$ (330.6)	$ (98.7)

Financial Information for Sub_6

Financial Information for Subsidiary and Guarantor Parent (Cash Flow) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Statement of Cash Flows
Cash flows provided by (used in) operating activities	$ 116.6	$ (53.8)
Investing Activities:
Purchases of property, plant and equipment	(101.3)	(85.3)
Net receipts/(payments) on intercompany activity	0	0
Purchases of businesses	(10)	0
Asset disposals and other	2.2	3.2
Cash used in investing activities	(109.1)	(82.1)
Financing Activities:
Borrowings on long-term debt	7.1	8.5
Payments on long-term debt and capital leases	(4.6)	(1.9)
Net borrowings under credit facilities	4	28
Debt issuance costs	0	(0.8)
Net receipts/(payments) on intercompany activity	0	0
Dividends paid to stockholders	0
Dividends paid to noncontrolling interests	(10)	0
Sales to noncontrolling interests	14.4	2.2
Shares repurchased for income tax withholding on share-based compensation and other	(6.5)	(4.8)
Cash provided by financing activities	4.4	31.2
Increase (decrease) in cash and cash equivalents	11.9	(104.7)
Reportable Legal Entities | Parent Company
Statement of Cash Flows
Cash flows provided by (used in) operating activities	(102.9)	(84.2)
Investing Activities:
Purchases of property, plant and equipment	(1.4)	(0.5)
Net receipts/(payments) on intercompany activity	0	0
Purchases of businesses	0
Asset disposals and other	0.8	0
Cash used in investing activities	(0.6)	(0.5)
Financing Activities:
Borrowings on long-term debt	0	0
Payments on long-term debt and capital leases	(0.2)	(0.3)
Net borrowings under credit facilities	0	0
Debt issuance costs		0
Net receipts/(payments) on intercompany activity	109.2	89.6
Dividends paid to stockholders	0
Dividends paid to noncontrolling interests	0
Sales to noncontrolling interests	0	0
Shares repurchased for income tax withholding on share-based compensation and other	(6.5)	(4.8)
Cash provided by financing activities	102.5	84.5
Increase (decrease) in cash and cash equivalents	(1)	(0.2)
Reportable Legal Entities | Subsidiary
Statement of Cash Flows
Cash flows provided by (used in) operating activities	(126.7)	(83.1)
Investing Activities:
Purchases of property, plant and equipment	(19.2)	(27.4)
Net receipts/(payments) on intercompany activity	0	0
Purchases of businesses	0
Asset disposals and other	1.3	0.1
Cash used in investing activities	(17.9)	(27.3)
Financing Activities:
Borrowings on long-term debt	0	0
Payments on long-term debt and capital leases	(0.6)	(0.2)
Net borrowings under credit facilities	0	0
Debt issuance costs		0
Net receipts/(payments) on intercompany activity	126.8	115.5
Dividends paid to stockholders	0
Dividends paid to noncontrolling interests	0
Sales to noncontrolling interests	11.7	0
Shares repurchased for income tax withholding on share-based compensation and other	0	0
Cash provided by financing activities	137.9	115.3
Increase (decrease) in cash and cash equivalents	(6.7)	4.9
Reportable Legal Entities | NonGuarantor Subsidiaries
Statement of Cash Flows
Cash flows provided by (used in) operating activities	361.2	113.5
Investing Activities:
Purchases of property, plant and equipment	(80.7)	(57.4)
Net receipts/(payments) on intercompany activity	(236)	(205.1)
Purchases of businesses	(10)
Asset disposals and other	0.1	3.1
Cash used in investing activities	(326.6)	(259.4)
Financing Activities:
Borrowings on long-term debt	7.1	8.5
Payments on long-term debt and capital leases	(3.8)	(1.4)
Net borrowings under credit facilities	4	28
Debt issuance costs		(0.8)
Net receipts/(payments) on intercompany activity	0	0
Dividends paid to stockholders	(15)
Dividends paid to noncontrolling interests	(10)
Sales to noncontrolling interests	2.7	2.2
Shares repurchased for income tax withholding on share-based compensation and other	0	0
Cash provided by financing activities	(15)	36.5
Increase (decrease) in cash and cash equivalents	19.6	(109.4)
Eliminations
Statement of Cash Flows
Cash flows provided by (used in) operating activities	(15)	0
Investing Activities:
Purchases of property, plant and equipment	0	0
Net receipts/(payments) on intercompany activity	236	205.1
Purchases of businesses	0
Asset disposals and other	0	0
Cash used in investing activities	236	205.1
Financing Activities:
Borrowings on long-term debt	0	0
Payments on long-term debt and capital leases	0	0
Net borrowings under credit facilities	0	0
Debt issuance costs		0
Net receipts/(payments) on intercompany activity	(236)	(205.1)
Dividends paid to stockholders	15
Dividends paid to noncontrolling interests	0
Sales to noncontrolling interests	0	0
Shares repurchased for income tax withholding on share-based compensation and other	0	0
Cash provided by financing activities	(221)	(205.1)
Increase (decrease) in cash and cash equivalents	$ 0	$ 0

Financial Information for Sub_7

Financial Information for Subsidiary and Guarantor Parent (Changes) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Current assets	$ 2,122.4		$ 1,915.7
Assets	5,389		5,185.4
Current liabilities	730.6		712.6
Liabilities	3,305.8		3,340.9
Stockholders' equity	2,083.2	$ 1,447.5	$ 1,844.5	$ 1,444.8
Cash flows provided by (used in) operating activities	116.6	(53.8)
Net Cash Provided by (Used in) Investing Activities	(109.1)	(82.1)
Cash provided by financing activities	$ 4.4	$ 31.2

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ (991.6)		$ (1,067.2)		$ (1,027.8)		$ (1,093.7)
OCI before reclassifications	(12.9)		24.9		(9.3)		30.8
Amounts reclassified from AOCI	13.2		26		45.8		46.6
Net current-period OCI	0.3		50.9		36.5		77.4
Ending balance	(991.3)		(1,016.3)		(991.3)		(1,016.3)
Increase (Decrease) in Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance	21.1		11.9		17.3		9.7
OCI before reclassifications	(9)		5		(5.2)		7.2
Amounts reclassified from AOCI	0		0		0		0
Net current-period OCI	(9)		5		(5.2)		7.2
Ending balance	12.1		16.9		12.1		16.9
Post- retirement benefit plans [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(926.2)		(943.5)		(954.5)		(965.5)
OCI before reclassifications	0		0		0		0
Amounts reclassified from AOCI	14	[1]	10.5	[2]	42.3	[1]	32.5	[2]
Net current-period OCI	14		10.5		42.3		32.5
Ending balance	(912.2)		(933)		(912.2)		(933)
Increase (Decrease) in Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance	0		0		0		0
OCI before reclassifications	0		0		0		0
Amounts reclassified from AOCI	0		0		0		0
Net current-period OCI	0		0		0		0
Ending balance	0		0		0		0
Currency translation adjustment [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(59.9)		(72.4)		(53.5)		(85)
OCI before reclassifications	(4.8)		19.2		(11.2)		31.8
Amounts reclassified from AOCI	0	[3]	0	[4]	0	[3]	0	[4]
Net current-period OCI	(4.8)		19.2		(11.2)		31.8
Ending balance	(64.7)		(53.2)		(64.7)		(53.2)
Increase (Decrease) in Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance	21.1		11.9		17.3		9.7
OCI before reclassifications	(9)		5		(5.2)		7.2
Amounts reclassified from AOCI	0	[3]	0	[4]	0	[3]	0	[4]
Net current-period OCI	(9)		5		(5.2)		7.2
Ending balance	12.1		16.9		12.1		16.9
Unrealized holding gains on securities [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	0		0		0		0
OCI before reclassifications	0		0		0		0
Amounts reclassified from AOCI	0	[3]	0	[4]	0	[3]	0	[4]
Net current-period OCI	0		0		0		0
Ending balance	0		0		0		0
Increase (Decrease) in Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance	0		0		0		0
OCI before reclassifications	0		0		0		0
Amounts reclassified from AOCI	0		0		0		0
Net current-period OCI	0		0		0		0
Ending balance	0		0		0		0
Derivatives [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	13.2		(5.7)		9		2.4
OCI before reclassifications	(8.1)		5.7		1.9		(1)
Amounts reclassified from AOCI	(2)	[5]	(0.8)	[6]	(7.8)	[5]	(2.2)	[6]
Net current-period OCI	(10.1)		4.9		(5.9)		(3.2)
Ending balance	3.1		(0.8)		3.1		(0.8)
Increase (Decrease) in Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance	0		0		0		0
OCI before reclassifications	0		0		0		0
Amounts reclassified from AOCI	0		0		0		0
Net current-period OCI	0		0		0		0
Ending balance	0		0		0		0
Accumulated Deferred Tax Asset Valuation Allowance [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(18.7)		(45.6)		(28.8)		(45.6)
OCI before reclassifications	0		0		0		0
Amounts reclassified from AOCI	1.2	[7]	16.3		11.3	[7]	16.3
Net current-period OCI	1.2		16.3		11.3		16.3
Ending balance	(17.5)		(29.3)		(17.5)		(29.3)
Increase (Decrease) in Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance	0		0		0		0
OCI before reclassifications	0		0		0		0
Amounts reclassified from AOCI	0		0		0		0
Net current-period OCI	0		0		0		0
Ending balance	$ 0		$ 0		$ 0		$ 0
[1]	Amounts were included in net periodic benefit cost for pension and other postretirement benefit plans (see Note 9).
[2]	Amounts were included in net periodic benefit cost for pension and other postretirement benefit plans (see Note 9).
[3]	No amounts were reclassified to earnings.
[4]	No amounts were reclassified to earnings.
[5]	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 7).
[6]	Amounts related to the effective portion of the derivatives are included in cost of goods sold in the period or periods the hedged item affects earnings (see Note 7).
[7]	Represents the net change in deferred tax asset valuation allowances on changes in AOCI balances between the balance sheet dates.

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income (Loss) (Details 2) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization to net income (loss) of net prior service credits		$ (0.7)	$ (0.4)	$ (1.9)	$ (1.2)
Amount reclassified from AOCI, Postretirement benefit plans, Actuarial losses		19.2	17.8	57.5	53.6
Income (loss) before income tax provision (benefit)		62.5	(121.3)	208.5	(86.9)
Income tax provision (benefit)		6.9	(1.9)	16.8	(2)
Cost of sales		(859.8)	(763.8)	(2,526)	(2,260.8)
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 credits	[1]	0.7	0.4	1.9	1.2
Amount reclassified from AOCI, Postretirement benefit plans, Actuarial losses	[1]	(19.2)	(17.8)	(57.5)	(53.6)
Income (loss) before income tax provision (benefit)	[2]	(18.5)	(17.4)	(55.6)	(52.4)
Income tax provision (benefit)	[3]	(4.5)	(6.9)	(13.3)	(19.9)
Net income (loss)		(14)	(10.5)	(42.3)	(32.5)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income tax provision (benefit)	[2]	2.6	1.2	10.3	3.5
Income tax provision (benefit)	[3]	0.6	0.4	2.5	1.3
Net income (loss)		2	0.8	7.8	2.2
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member] | Nickel and other raw material contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of sales	[4]	2.2	(1.5)	10.4	(4)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member] | Natural gas contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of sales	[4]	0	(1.1)	(0.5)	(4.5)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member] | Foreign exchange contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of sales	[4]	0.5	3.8	0.5	12
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member] | Interest Rate Swap
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	[4]	$ (0.1)	$ 0	$ (0.1)	$ 0
[1]	Amounts are reported in nonoperating retirement benefit expense (see Note 9).
[2]	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.
[3]	These amounts exclude the impact of any deferred tax asset valuation allowance, when applicable.
[4]	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 7).

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Millions	Sep. 30, 2018USD ($)
Components of Environmental Loss Accrual [Abstract]
Accrual For Environmental Loss Contingencies	$ 15
Accrued Environmental Loss Contingencies Current	9
Federal Superfund and comparable state-managed sites	3
Formerly owned or operated sites	11
Owned or controlled sites at which Company operations have been discontinued	1
Maximum
Loss Contingency, Estimate [Abstract]
Loss contingency maximum possible loss	$ 16