$ATI
ATI INC Stock $ati

$ati Overview Financials Valuation SEC Filings Company Website

2024 Q1 Form 10-K Financial Statement

#000162828024006606 Filed on February 23, 2024

Income Statement

Concept	2024 Q1	2023 Q4	2023 Q1
Revenue	$1.043B	$1.064B	$1.038B
YoY Change	0.46%	5.3%	24.46%
Cost Of Revenue	$845.5M	$858.3M	$844.9M
YoY Change	0.07%	4.07%	27.11%
Gross Profit	$197.4M	$205.7M	$193.2M
YoY Change	2.17%	10.77%	14.05%
Gross Profit Margin	18.93%	19.33%	18.61%
Selling, General & Admin	$82.00M	$92.30M	$80.60M
YoY Change	1.74%	20.18%	7.18%
% of Gross Profit	41.54%	44.87%	41.72%
Research & Development
YoY Change
% of Gross Profit
Depreciation & Amortization	$36.00M	$39.50M	$35.10M
YoY Change	2.56%	10.34%	-1.13%
% of Gross Profit	18.24%	19.2%	18.17%
Operating Expenses	$82.00M	$92.30M	$80.60M
YoY Change	1.74%	20.18%	7.18%
Operating Profit	$115.2M	$113.4M	$112.6M
YoY Change	2.31%	4.13%	46.23%
Interest Expense	-$27.00M	-$27.80M	-$20.20M
YoY Change	33.66%	52.75%	-12.93%
% of Operating Profit	-23.44%	-24.51%	-17.94%
Other Income/Expense, Net	$400.0K	-$72.40M	$600.0K
YoY Change	-33.33%	1127.12%	-108.0%
Pretax Income	$85.30M	$8.100M	$76.50M
YoY Change	11.5%	-90.52%	90.77%
Income Tax	$16.90M	-$141.1M	$4.300M
% Of Pretax Income	19.81%	-1741.98%	5.62%
Net Earnings	$66.10M	$145.7M	$70.10M
YoY Change	-5.71%	89.47%	126.86%
Net Earnings / Revenue	6.34%	13.69%	6.75%
Basic Earnings Per Share	$0.52	$1.15	$0.55
Diluted Earnings Per Share	$0.46	$0.99	$0.48
COMMON SHARES
Basic Shares Outstanding	127.8M shares	127.6M shares	128.6M shares
Diluted Shares Outstanding	147.5M shares	150.2M shares	150.1M shares

Balance Sheet

Concept	2024 Q1	2023 Q4	2023 Q1
SHORT-TERM ASSETS
Cash & Short-Term Investments	$394.4M	$743.9M	$196.2M
YoY Change	101.02%	27.38%	-38.05%
Cash & Equivalents	$394.4M	$743.9M	$196.2M
Short-Term Investments
Other Short-Term Assets	$52.80M	$62.20M	$48.00M
YoY Change	10.0%	16.48%	-57.26%
Inventory	$1.285B	$1.248B	$1.294B
Prepaid Expenses
Receivables	$720.5M	$684.1M	$725.6M
Other Receivables	$0.00	$0.00	$0.00
Total Short-Term Assets	$2.518B	$2.738B	$2.316B
YoY Change	8.7%	10.55%	1.34%
LONG-TERM ASSETS
Property, Plant & Equipment	$1.689B	$1.666B	$1.552B
YoY Change	8.83%	7.54%	3.27%
Goodwill	$227.2M	$227.2M	$227.2M
YoY Change	0.0%	0.0%	0.0%
Intangibles
YoY Change
Long-Term Investments
YoY Change
Other Assets	$348.1M	$354.3M	$192.0M
YoY Change	81.3%	83.67%	-1.23%
Total Long-Term Assets	$2.264B	$2.247B	$1.971B
YoY Change	14.88%	14.13%	1.06%
TOTAL ASSETS
Total Short-Term Assets	$2.518B	$2.738B	$2.316B
Total Long-Term Assets	$2.264B	$2.247B	$1.971B
Total Assets	$4.782B	$4.985B	$4.287B
YoY Change	11.54%	12.14%	1.21%
SHORT-TERM LIABILITIES
YoY Change
Accounts Payable	$482.6M	$524.8M	$447.5M
YoY Change	7.84%	-5.15%	12.98%
Accrued Expenses	$225.8M	$256.8M	$201.9M
YoY Change	11.84%	16.83%	-5.43%
Deferred Revenue	$161.6M	$163.6M	$149.7M
YoY Change	7.95%	9.73%	12.3%
Short-Term Debt	$0.00	$0.00	$0.00
YoY Change
Long-Term Debt Due	$27.10M	$31.90M	$24.90M
YoY Change	8.84%	-23.5%	-78.66%
Total Short-Term Liabilities	$897.1M	$977.1M	$824.0M
YoY Change	8.87%	1.37%	-6.06%
LONG-TERM LIABILITIES
Long-Term Debt	$2.146B	$2.148B	$1.702B
YoY Change	26.1%	25.87%	-0.31%
Other Long-Term Liabilities	$156.0M	$379.8M	$193.1M
YoY Change	-19.21%	82.86%	-3.16%
Total Long-Term Liabilities	$156.0M	$2.528B	$193.1M
YoY Change	-19.21%	1116.9%	-3.16%
TOTAL LIABILITIES
Total Short-Term Liabilities	$897.1M	$977.1M	$824.0M
Total Long-Term Liabilities	$156.0M	$2.528B	$193.1M
Total Liabilities	$3.409B	$3.612B	$3.073B
YoY Change	10.93%	9.84%	-10.68%
SHAREHOLDERS EQUITY
Retained Earnings	-$4.000M	-$70.10M	$247.0M
YoY Change	-101.62%	-139.63%	138.42%
Common Stock	$1.717B	$1.710B	$1.688B
YoY Change	1.67%	1.73%	4.52%
Preferred Stock
YoY Change
Treasury Stock (at cost)	$360.1M	$184.0M	$107.8M
YoY Change	234.04%	111.49%	8.12%
Treasury Stock Shares			3.682M shares
Shareholders Equity	$1.264B	$1.373B	$1.097B
YoY Change
Total Liabilities & Shareholders Equity	$4.782B	$4.985B	$4.287B
YoY Change	11.54%	12.14%	1.21%

Cashflow Statement

Concept	2024 Q1	2023 Q4	2023 Q1
OPERATING ACTIVITIES
Net Income	$66.10M	$145.7M	$70.10M
YoY Change	-5.71%	89.47%	126.86%
Depreciation, Depletion And Amortization	$36.00M	$39.50M	$35.10M
YoY Change	2.56%	10.34%	-1.13%
Cash From Operating Activities	-$98.80M	$417.2M	-$285.2M
YoY Change	-65.36%	28.65%	31.31%
INVESTING ACTIVITIES
Capital Expenditures	$65.80M	$53.40M	$60.40M
YoY Change	8.94%	75.66%	-332.31%
Acquisitions
YoY Change
Other Investing Activities	-$1.000M	$3.400M	-$200.0K
YoY Change	400.0%	-27.66%	-80.0%
Cash From Investing Activities	-$63.80M	-$50.00M	-$59.30M
YoY Change	7.59%	94.55%	145.04%
FINANCING ACTIVITIES
Cash Dividend Paid
YoY Change
Common Stock Issuance & Retirement, Net
YoY Change
Debt Paid & Issued, Net
YoY Change
Cash From Financing Activities	-$186.9M	-56.20M	-$43.30M
YoY Change	331.64%	28.6%	-66.59%
NET CHANGE
Cash From Operating Activities	-$98.80M	417.2M	-$285.2M
Cash From Investing Activities	-$63.80M	-50.00M	-$59.30M
Cash From Financing Activities	-$186.9M	-56.20M	-$43.30M
Net Change In Cash	-$349.5M	311.0M	-$387.8M
YoY Change	-9.88%	22.01%	4.53%
FREE CASH FLOW
Cash From Operating Activities	-$98.80M	$417.2M	-$285.2M
Capital Expenditures	$65.80M	$53.40M	$60.40M
Free Cash Flow	-$164.6M	$363.8M	-$345.6M
YoY Change	-52.37%	23.78%	80.75%

Facts In Submission

Frame	Concept Type	Concept / XBRL Key	Value	Unit
CY2023	us-gaap	Increase Decrease In Accounts Receivable IncreaseDecreaseInAccountsReceivable	128500000	usd
CY2023	dei	Amendment Flag AmendmentFlag	false
CY2023	dei	Entity Central Index Key EntityCentralIndexKey	0001018963
CY2023	dei	Document Fiscal Year Focus DocumentFiscalYearFocus	2023
CY2023	dei	Document Fiscal Period Focus DocumentFiscalPeriodFocus	FY
CY2022	us-gaap	Accounting Standards Update Extensible List AccountingStandardsUpdateExtensibleList	http://fasb.org/us-gaap/2023#AccountingStandardsUpdate202006Member
CY2023Q4	us-gaap	Operating Lease Right Of Use Asset Statement Of Financial Position Extensible List OperatingLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList	http://fasb.org/us-gaap/2023#OtherAssetsNoncurrent
CY2023Q4	us-gaap	Finance Lease Right Of Use Asset Statement Of Financial Position Extensible List FinanceLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList	http://fasb.org/us-gaap/2023#PropertyPlantAndEquipmentNet
CY2023Q4	us-gaap	Operating Lease Liability Current Statement Of Financial Position Extensible List OperatingLeaseLiabilityCurrentStatementOfFinancialPositionExtensibleList	http://fasb.org/us-gaap/2023#OtherLiabilitiesCurrent
CY2023Q4	us-gaap	Operating Lease Liability Noncurrent Statement Of Financial Position Extensible List OperatingLeaseLiabilityNoncurrentStatementOfFinancialPositionExtensibleList	http://fasb.org/us-gaap/2023#OtherLiabilitiesNoncurrent
CY2023Q4	us-gaap	Finance Lease Liability Current Statement Of Financial Position Extensible List FinanceLeaseLiabilityCurrentStatementOfFinancialPositionExtensibleList	http://fasb.org/us-gaap/2023#DebtCurrent
CY2023Q4	us-gaap	Finance Lease Liability Noncurrent Statement Of Financial Position Extensible List FinanceLeaseLiabilityNoncurrentStatementOfFinancialPositionExtensibleList	http://fasb.org/us-gaap/2023#LongTermDebtAndCapitalLeaseObligations
CY2023Q1	us-gaap	Supplier Finance Program Obligation Current Statement Of Financial Position Extensible Enumeration SupplierFinanceProgramObligationCurrentStatementOfFinancialPositionExtensibleEnumeration	http://fasb.org/us-gaap/2023#AccountsPayableCurrent
CY2023Q4	us-gaap	Supplier Finance Program Obligation Current Statement Of Financial Position Extensible Enumeration SupplierFinanceProgramObligationCurrentStatementOfFinancialPositionExtensibleEnumeration	http://fasb.org/us-gaap/2023#AccountsPayableCurrent
CY2023Q4	us-gaap	Finance Lease Liability Statement Of Financial Position Extensible List FinanceLeaseLiabilityStatementOfFinancialPositionExtensibleList	http://fasb.org/us-gaap/2023#Liabilities
CY2023Q4	us-gaap	Environmental Loss Contingency Current Statement Of Financial Position Extensible Enumeration EnvironmentalLossContingencyCurrentStatementOfFinancialPositionExtensibleEnumeration	http://fasb.org/us-gaap/2023#OtherLiabilitiesCurrent
CY2023	dei	Document Annual Report DocumentAnnualReport	true
CY2023	dei	Document Period End Date DocumentPeriodEndDate	2023-12-31
CY2023	dei	Current Fiscal Year End Date CurrentFiscalYearEndDate	--12-31
CY2023	dei	Document Transition Report DocumentTransitionReport	false
CY2023	dei	Entity File Number EntityFileNumber	1-12001
CY2023	dei	Entity Registrant Name EntityRegistrantName	ATI Inc.
CY2023	dei	Entity Incorporation State Country Code EntityIncorporationStateCountryCode	DE
CY2023	dei	Entity Tax Identification Number EntityTaxIdentificationNumber	25-1792394
CY2023	dei	Entity Address Address Line1 EntityAddressAddressLine1	2021 McKinney Avenue
CY2023	dei	Entity Address City Or Town EntityAddressCityOrTown	Dallas,
CY2023	dei	Entity Address State Or Province EntityAddressStateOrProvince	TX
CY2023	dei	Entity Address Postal Zip Code EntityAddressPostalZipCode	75201
CY2023	dei	City Area Code CityAreaCode	800
CY2023	dei	Local Phone Number LocalPhoneNumber	289-7454
CY2023	dei	Security12b Title Security12bTitle	Common stock, par value $0.10
CY2023	dei	Trading Symbol TradingSymbol	ATI
CY2023	dei	Security Exchange Name SecurityExchangeName	NYSE
CY2023	dei	Entity Well Known Seasoned Issuer EntityWellKnownSeasonedIssuer	Yes
CY2023	dei	Entity Voluntary Filers EntityVoluntaryFilers	No
CY2023	dei	Entity Current Reporting Status EntityCurrentReportingStatus	Yes
CY2023	dei	Entity Interactive Data Current EntityInteractiveDataCurrent	Yes
CY2023	dei	Entity Filer Category EntityFilerCategory	Large Accelerated Filer
CY2023	dei	Entity Small Business EntitySmallBusiness	false
CY2023	dei	Entity Emerging Growth Company EntityEmergingGrowthCompany	false
CY2023	dei	Icfr Auditor Attestation Flag IcfrAuditorAttestationFlag	true
CY2023	dei	Document Fin Stmt Error Correction Flag DocumentFinStmtErrorCorrectionFlag	false
CY2023	dei	Entity Shell Company EntityShellCompany	false
CY2024Q1	dei	Entity Common Stock Shares Outstanding EntityCommonStockSharesOutstanding	127781255	shares
CY2023Q3	dei	Entity Public Float EntityPublicFloat	5700000000	usd
CY2023	us-gaap	Operating Income Loss OperatingIncomeLoss	466400000	usd
CY2023	us-gaap	Operating Income Loss OperatingIncomeLoss	316100000	usd
CY2022	us-gaap	Operating Income Loss OperatingIncomeLoss	117600000	usd
CY2023	dei	Auditor Name AuditorName	Ernst & Young LLP
CY2023	dei	Auditor Location AuditorLocation	Pittsburgh, Pennsylvania
CY2023	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	4173700000	usd
CY2023	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	3836000000	usd
CY2022	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	2799800000	usd
CY2023	us-gaap	Cost Of Goods And Services Sold CostOfGoodsAndServicesSold	3371100000	usd
CY2023	us-gaap	Cost Of Goods And Services Sold CostOfGoodsAndServicesSold	3121800000	usd
CY2022	us-gaap	Cost Of Goods And Services Sold CostOfGoodsAndServicesSold	2466600000	usd
CY2023	us-gaap	Gross Profit GrossProfit	802600000	usd
CY2023	us-gaap	Gross Profit GrossProfit	714200000	usd
CY2022	us-gaap	Gross Profit GrossProfit	333200000	usd
CY2023	us-gaap	Selling General And Administrative Expense SellingGeneralAndAdministrativeExpense	328100000	usd
CY2023	us-gaap	Selling General And Administrative Expense SellingGeneralAndAdministrativeExpense	297500000	usd
CY2022	us-gaap	Selling General And Administrative Expense SellingGeneralAndAdministrativeExpense	226900000	usd
CY2023	ati	Restructuring Settlement And Impairment Provisions Excluding Goodwill Impairment Loss RestructuringSettlementAndImpairmentProvisionsExcludingGoodwillImpairmentLoss	7700000	usd
CY2023	ati	Restructuring Settlement And Impairment Provisions Excluding Goodwill Impairment Loss RestructuringSettlementAndImpairmentProvisionsExcludingGoodwillImpairmentLoss	-4800000	usd
CY2022	ati	Restructuring Settlement And Impairment Provisions Excluding Goodwill Impairment Loss RestructuringSettlementAndImpairmentProvisionsExcludingGoodwillImpairmentLoss	-11300000	usd
CY2023	ati	Gain Loss On Asset And Business Sales Net GainLossOnAssetAndBusinessSalesNet	-400000	usd
CY2023	ati	Gain Loss On Asset And Business Sales Net GainLossOnAssetAndBusinessSalesNet	-105400000	usd
CY2022	ati	Gain Loss On Asset And Business Sales Net GainLossOnAssetAndBusinessSalesNet	0	usd
CY2023	us-gaap	Operating Income Loss OperatingIncomeLoss	466400000	usd
CY2023	us-gaap	Operating Income Loss OperatingIncomeLoss	316100000	usd
CY2022	us-gaap	Operating Income Loss OperatingIncomeLoss	117600000	usd
CY2023	ati	Nonoperatingretirementbenefitexpense Nonoperatingretirementbenefitexpense	79700000	usd
CY2023	ati	Nonoperatingretirementbenefitexpense Nonoperatingretirementbenefitexpense	-138400000	usd
CY2022	ati	Nonoperatingretirementbenefitexpense Nonoperatingretirementbenefitexpense	-260000000.0	usd
CY2023	ati	Interest Expense Net InterestExpenseNet	92800000	usd
CY2023	ati	Interest Expense Net InterestExpenseNet	87400000	usd
CY2022	ati	Interest Expense Net InterestExpenseNet	96900000	usd
CY2023	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	0	usd
CY2023	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	0	usd
CY2022	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	-65500000	usd
CY2023	us-gaap	Other Nonoperating Income Expense OtherNonoperatingIncomeExpense	1300000	usd
CY2023	us-gaap	Other Nonoperating Income Expense OtherNonoperatingIncomeExpense	-12500000	usd
CY2022	us-gaap	Other Nonoperating Income Expense OtherNonoperatingIncomeExpense	18200000	usd
CY2023	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	295200000	usd
CY2023	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	354600000	usd
CY2022	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	233400000	usd
CY2023	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	-128200000	usd
CY2023	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	15500000	usd
CY2022	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	26800000	usd
CY2023	us-gaap	Profit Loss ProfitLoss	423400000	usd
CY2023	us-gaap	Profit Loss ProfitLoss	339100000	usd
CY2022	us-gaap	Profit Loss ProfitLoss	206600000	usd
CY2023	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	12600000	usd
CY2023	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	15600000	usd
CY2022	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	22000000.0	usd
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CY2023	us-gaap	Net Income Loss NetIncomeLoss	323500000	usd
CY2022	us-gaap	Net Income Loss NetIncomeLoss	184600000	usd
CY2023	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.21
CY2023	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	2.54
CY2022	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	1.45
CY2023	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.81
CY2023	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.23
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CY2022	us-gaap	Other Comprehensive Income Foreign Currency Transaction And Translation Gain Loss Arising During Period Net Of Tax OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax	-4600000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Reclassification Adjustment From Aoci Realized Upon Sale Or Liquidation Net Of Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationReclassificationAdjustmentFromAOCIRealizedUponSaleOrLiquidationNetOfTax	0	usd
CY2023	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Reclassification Adjustment From Aoci Realized Upon Sale Or Liquidation Net Of Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationReclassificationAdjustmentFromAOCIRealizedUponSaleOrLiquidationNetOfTax	-20000000.0	usd
CY2022	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Reclassification Adjustment From Aoci Realized Upon Sale Or Liquidation Net Of Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationReclassificationAdjustmentFromAOCIRealizedUponSaleOrLiquidationNetOfTax	0	usd
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CY2023	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Net Of Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax	-23500000	usd
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CY2023	us-gaap	Other Comprehensive Income Loss Cash Flow Hedge Gain Loss Before Reclassification And Tax OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax	53800000	usd
CY2022	us-gaap	Other Comprehensive Income Loss Cash Flow Hedge Gain Loss Before Reclassification And Tax OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax	15500000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Cash Flow Hedge Gain Loss Reclassification Before Tax OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax	-2500000	usd
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CY2022	us-gaap	Other Comprehensive Income Loss Cash Flow Hedge Gain Loss Reclassification Before Tax OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax	11400000	usd
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CY2023	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax	-13200000	usd
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CY2023	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Net Unamortized Gain Loss Arising During Period Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax	54700000	usd
CY2022	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Net Unamortized Gain Loss Arising During Period Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax	8700000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Before Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax	-600000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Before Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax	-500000	usd
CY2022	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Before Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax	-1800000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Finalization Of Pension And Non Pension Postretirement Plan Valuation Before Tax OtherComprehensiveIncomeLossFinalizationOfPensionAndNonPensionPostretirementPlanValuationBeforeTax	1100000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Finalization Of Pension And Non Pension Postretirement Plan Valuation Before Tax OtherComprehensiveIncomeLossFinalizationOfPensionAndNonPensionPostretirementPlanValuationBeforeTax	700000	usd
CY2022	us-gaap	Other Comprehensive Income Loss Finalization Of Pension And Non Pension Postretirement Plan Valuation Before Tax OtherComprehensiveIncomeLossFinalizationOfPensionAndNonPensionPostretirementPlanValuationBeforeTax	-21900000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	-300000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	0	usd
CY2022	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	15500000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-2400000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-68100000	usd
CY2022	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-14400000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-16200000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	55600000	usd
CY2022	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	13900000	usd
CY2023	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	407200000	usd
CY2023	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	394700000	usd
CY2022	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	220500000	usd
CY2023	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	12200000	usd
CY2023	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	-2700000	usd
CY2022	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	26800000	usd
CY2023	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	395000000.0	usd
CY2023	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	397400000	usd
CY2022	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	193700000	usd
CY2023Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	743900000	usd
CY2023Q1	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	584000000.0	usd
CY2023Q4	us-gaap	Accounts Receivable Net Current AccountsReceivableNetCurrent	625000000.0	usd
CY2023Q1	us-gaap	Accounts Receivable Net Current AccountsReceivableNetCurrent	579200000	usd
CY2023Q4	us-gaap	Contract With Customer Asset Net Current ContractWithCustomerAssetNetCurrent	59100000	usd
CY2023Q1	us-gaap	Contract With Customer Asset Net Current ContractWithCustomerAssetNetCurrent	64100000	usd
CY2023Q4	us-gaap	Inventory Net InventoryNet	1247500000	usd
CY2023Q1	us-gaap	Inventory Net InventoryNet	1195700000	usd
CY2023Q4	us-gaap	Other Assets Current OtherAssetsCurrent	62200000	usd
CY2023Q1	us-gaap	Other Assets Current OtherAssetsCurrent	53400000	usd
CY2023Q4	us-gaap	Assets Current AssetsCurrent	2737700000	usd
CY2023Q1	us-gaap	Assets Current AssetsCurrent	2476400000	usd
CY2023Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	1665900000	usd
CY2023Q1	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	1549100000	usd
CY2023Q4	us-gaap	Goodwill Goodwill	227200000	usd
CY2023Q1	us-gaap	Goodwill Goodwill	227200000	usd
CY2023Q4	us-gaap	Other Assets Noncurrent OtherAssetsNoncurrent	354300000	usd
CY2023Q1	us-gaap	Other Assets Noncurrent OtherAssetsNoncurrent	192900000	usd
CY2023Q4	us-gaap	Assets Assets	4985100000	usd
CY2023Q1	us-gaap	Assets Assets	4445600000	usd
CY2023Q4	us-gaap	Accounts Payable Current AccountsPayableCurrent	524800000	usd
CY2023Q1	us-gaap	Accounts Payable Current AccountsPayableCurrent	553300000	usd
CY2023Q4	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	163600000	usd
CY2023Q1	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	149100000	usd
CY2023Q4	us-gaap	Debt Current DebtCurrent	31900000	usd
CY2023Q1	us-gaap	Debt Current DebtCurrent	41700000	usd
CY2023Q4	us-gaap	Other Liabilities Current OtherLiabilitiesCurrent	256800000	usd
CY2023Q1	us-gaap	Other Liabilities Current OtherLiabilitiesCurrent	219800000	usd
CY2023Q4	us-gaap	Liabilities Current LiabilitiesCurrent	977100000	usd
CY2023Q1	us-gaap	Liabilities Current LiabilitiesCurrent	963900000	usd
CY2023Q4	us-gaap	Long Term Debt And Capital Lease Obligations LongTermDebtAndCapitalLeaseObligations	2147700000	usd
CY2023Q1	us-gaap	Long Term Debt And Capital Lease Obligations LongTermDebtAndCapitalLeaseObligations	1706300000	usd
CY2023Q4	us-gaap	Other Postretirement Defined Benefit Plan Liabilities Noncurrent OtherPostretirementDefinedBenefitPlanLiabilitiesNoncurrent	175200000	usd
CY2023Q1	us-gaap	Other Postretirement Defined Benefit Plan Liabilities Noncurrent OtherPostretirementDefinedBenefitPlanLiabilitiesNoncurrent	184900000	usd
CY2023Q4	us-gaap	Defined Benefit Pension Plan Liabilities Noncurrent DefinedBenefitPensionPlanLiabilitiesNoncurrent	39700000	usd
CY2023Q1	us-gaap	Defined Benefit Pension Plan Liabilities Noncurrent DefinedBenefitPensionPlanLiabilitiesNoncurrent	225600000	usd
CY2023Q4	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	164900000	usd
CY2023Q1	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	207700000	usd
CY2023Q4	us-gaap	Liabilities Liabilities	3504600000	usd
CY2023Q1	us-gaap	Liabilities Liabilities	3288400000	usd
CY2023Q1	us-gaap	Preferred Stock Par Or Stated Value Per Share PreferredStockParOrStatedValuePerShare	0.10
CY2023Q4	us-gaap	Preferred Stock Par Or Stated Value Per Share PreferredStockParOrStatedValuePerShare	0.10
CY2023Q4	us-gaap	Preferred Stock Shares Authorized PreferredStockSharesAuthorized	50000000	shares
CY2023Q1	us-gaap	Preferred Stock Shares Authorized PreferredStockSharesAuthorized	50000000	shares
CY2023Q1	us-gaap	Preferred Stock Shares Issued PreferredStockSharesIssued	0	shares
CY2023Q4	us-gaap	Preferred Stock Shares Issued PreferredStockSharesIssued	0	shares
CY2023Q4	us-gaap	Preferred Stock Value PreferredStockValue	0	usd
CY2023Q1	us-gaap	Preferred Stock Value PreferredStockValue	0	usd
CY2023Q1	us-gaap	Common Stock Par Or Stated Value Per Share CommonStockParOrStatedValuePerShare	0.10
CY2023Q4	us-gaap	Common Stock Par Or Stated Value Per Share CommonStockParOrStatedValuePerShare	0.10
CY2023Q1	us-gaap	Common Stock Shares Authorized CommonStockSharesAuthorized	500000000	shares
CY2023Q4	us-gaap	Common Stock Shares Authorized CommonStockSharesAuthorized	500000000	shares
CY2023Q4	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	132300971	shares
CY2023Q1	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	131392262	shares
CY2023Q4	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	126879099	shares
CY2023Q1	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	128273042	shares
CY2023Q4	us-gaap	Common Stock Value CommonStockValue	13200000	usd
CY2023Q1	us-gaap	Common Stock Value CommonStockValue	13100000	usd
CY2023Q4	us-gaap	Additional Paid In Capital Common Stock AdditionalPaidInCapitalCommonStock	1697100000	usd
CY2023Q1	us-gaap	Additional Paid In Capital Common Stock AdditionalPaidInCapitalCommonStock	1668100000	usd
CY2023Q4	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	-70100000	usd
CY2023Q1	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	-480900000	usd
CY2023Q4	us-gaap	Treasury Stock Common Shares TreasuryStockCommonShares	5421872	shares
CY2023Q1	us-gaap	Treasury Stock Common Shares TreasuryStockCommonShares	3119220	shares
CY2023Q4	us-gaap	Treasury Stock Value TreasuryStockValue	184000000.0	usd
CY2023Q1	us-gaap	Treasury Stock Value TreasuryStockValue	87000000.0	usd
CY2023Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-83200000	usd
CY2023Q1	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-67400000	usd
CY2023Q4	us-gaap	Stockholders Equity StockholdersEquity	1373000000	usd
CY2023Q1	us-gaap	Stockholders Equity StockholdersEquity	1045900000	usd
CY2023Q4	us-gaap	Minority Interest MinorityInterest	107500000	usd
CY2023Q1	us-gaap	Minority Interest MinorityInterest	111300000	usd
CY2023Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	1480500000	usd
CY2023Q1	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	1157200000	usd
CY2023Q4	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	4985100000	usd
CY2023Q1	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	4445600000	usd
CY2023	us-gaap	Profit Loss ProfitLoss	423400000	usd
CY2023	us-gaap	Profit Loss ProfitLoss	339100000	usd
CY2022	us-gaap	Profit Loss ProfitLoss	206600000	usd
CY2023	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	146100000	usd
CY2023	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	142900000	usd
CY2022	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	143900000	usd
CY2023	us-gaap	Share Based Compensation ShareBasedCompensation	29100000	usd
CY2023	us-gaap	Share Based Compensation ShareBasedCompensation	26000000.0	usd
CY2023	us-gaap	Deferred Income Taxes And Tax Credits DeferredIncomeTaxesAndTaxCredits	-138200000	usd
CY2023	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	0	usd
CY2023	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	0	usd
CY2022	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	-65500000	usd
CY2023	us-gaap	Gain Loss On Sale Of Property Plant Equipment GainLossOnSaleOfPropertyPlantEquipment	600000	usd
CY2023	us-gaap	Gain Loss On Sale Of Property Plant Equipment GainLossOnSaleOfPropertyPlantEquipment	900000	usd
CY2022	us-gaap	Gain Loss On Sale Of Property Plant Equipment GainLossOnSaleOfPropertyPlantEquipment	2900000	usd
CY2023	us-gaap	Gain Loss On Sale Of Business GainLossOnSaleOfBusiness	-600000	usd
CY2023	us-gaap	Gain Loss On Sale Of Business GainLossOnSaleOfBusiness	-112200000	usd
CY2022	us-gaap	Gain Loss On Sale Of Business GainLossOnSaleOfBusiness	13800000	usd
CY2023	us-gaap	Other Asset Impairment Charges OtherAssetImpairmentCharges	3000000.0	usd
CY2023	us-gaap	Other Asset Impairment Charges OtherAssetImpairmentCharges	0	usd
CY2022	us-gaap	Other Asset Impairment Charges OtherAssetImpairmentCharges	0	usd
CY2023	ati	Pension Plan Contributions PensionPlanContributions	-51300000	usd
CY2022	ati	Pension Plan Contributions PensionPlanContributions	-71600000	usd
CY2023	us-gaap	Increase Decrease In Pension And Postretirement Obligations IncreaseDecreaseInPensionAndPostretirementObligations	53800000	usd
CY2023	us-gaap	Increase Decrease In Pension And Postretirement Obligations IncreaseDecreaseInPensionAndPostretirementObligations	-159200000	usd
CY2022	us-gaap	Increase Decrease In Pension And Postretirement Obligations IncreaseDecreaseInPensionAndPostretirementObligations	-261900000	usd
CY2023	us-gaap	Increase Decrease In Accounts Receivable IncreaseDecreaseInAccountsReceivable	46100000	usd
CY2022	us-gaap	Increase Decrease In Accounts Receivable IncreaseDecreaseInAccountsReceivable	126000000.0	usd
CY2023	us-gaap	Increase Decrease In Inventories IncreaseDecreaseInInventories	51800000	usd
CY2023	us-gaap	Increase Decrease In Inventories IncreaseDecreaseInInventories	190800000	usd
CY2022	us-gaap	Increase Decrease In Inventories IncreaseDecreaseInInventories	53900000	usd
CY2023	us-gaap	Increase Decrease In Accounts Payable Trade IncreaseDecreaseInAccountsPayableTrade	-29800000	usd
CY2023	us-gaap	Increase Decrease In Accounts Payable Trade IncreaseDecreaseInAccountsPayableTrade	156100000	usd
CY2022	us-gaap	Increase Decrease In Accounts Payable Trade IncreaseDecreaseInAccountsPayableTrade	88500000	usd
CY2023	us-gaap	Increase Decrease In Accrued Income Taxes Payable IncreaseDecreaseInAccruedIncomeTaxesPayable	-4800000	usd
CY2023	us-gaap	Increase Decrease In Accrued Income Taxes Payable IncreaseDecreaseInAccruedIncomeTaxesPayable	2500000	usd
CY2022	us-gaap	Increase Decrease In Accrued Income Taxes Payable IncreaseDecreaseInAccruedIncomeTaxesPayable	-2600000	usd
CY2023	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	26800000	usd
CY2023	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	23100000	usd
CY2022	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	-22200000	usd
CY2023	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	85900000	usd
CY2023	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	224900000	usd
CY2022	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	16100000	usd
CY2023	us-gaap	Payments To Acquire Productive Assets PaymentsToAcquireProductiveAssets	200700000	usd
CY2023	us-gaap	Payments To Acquire Productive Assets PaymentsToAcquireProductiveAssets	130900000	usd
CY2022	us-gaap	Payments To Acquire Productive Assets PaymentsToAcquireProductiveAssets	152600000	usd
CY2023	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	3800000	usd
CY2023	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	3100000	usd
CY2022	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	20800000	usd
CY2023	ati	Transaction Costs From Sales Of Businesses Net Of Proceeds TransactionCostsFromSalesOfBusinessesNetOfProceeds	-300000	usd
CY2023	ati	Transaction Costs From Sales Of Businesses Net Of Proceeds TransactionCostsFromSalesOfBusinessesNetOfProceeds	300000	usd
CY2022	ati	Transaction Costs From Sales Of Businesses Net Of Proceeds TransactionCostsFromSalesOfBusinessesNetOfProceeds	53100000	usd
CY2023	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	-4000000.0	usd
CY2023	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	-800000	usd
CY2022	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	-1400000	usd
CY2023	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-193200000	usd
CY2023	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-126700000	usd
CY2022	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-77300000	usd
CY2023	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	425000000.0	usd
CY2023	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	0	usd
CY2022	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	675700000	usd
CY2023	us-gaap	Repayments Of Long Term Debt And Capital Securities RepaymentsOfLongTermDebtAndCapitalSecurities	25200000	usd
CY2023	us-gaap	Repayments Of Long Term Debt And Capital Securities RepaymentsOfLongTermDebtAndCapitalSecurities	23100000	usd
CY2022	us-gaap	Repayments Of Long Term Debt And Capital Securities RepaymentsOfLongTermDebtAndCapitalSecurities	515600000	usd
CY2023	us-gaap	Proceeds From Repayments Of Other Debt ProceedsFromRepaymentsOfOtherDebt	-14000000.0	usd
CY2023	us-gaap	Proceeds From Repayments Of Other Debt ProceedsFromRepaymentsOfOtherDebt	-5600000	usd
CY2022	us-gaap	Proceeds From Repayments Of Other Debt ProceedsFromRepaymentsOfOtherDebt	21700000	usd
CY2023	us-gaap	Payments Of Debt Issuance Costs PaymentsOfDebtIssuanceCosts	6200000	usd
CY2023	us-gaap	Payments Of Debt Issuance Costs PaymentsOfDebtIssuanceCosts	0	usd
CY2022	us-gaap	Payments Of Debt Issuance Costs PaymentsOfDebtIssuanceCosts	9500000	usd
CY2023	us-gaap	Payments Of Debt Extinguishment Costs PaymentsOfDebtExtinguishmentCosts	0	usd
CY2023	us-gaap	Payments Of Debt Extinguishment Costs PaymentsOfDebtExtinguishmentCosts	0	usd
CY2022	us-gaap	Payments Of Debt Extinguishment Costs PaymentsOfDebtExtinguishmentCosts	64500000	usd
CY2023	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	85200000	usd
CY2023	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	139900000	usd
CY2022	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	0	usd
CY2023	us-gaap	Proceeds From Minority Shareholders ProceedsFromMinorityShareholders	0	usd
CY2023	us-gaap	Proceeds From Minority Shareholders ProceedsFromMinorityShareholders	6400000	usd
CY2022	us-gaap	Proceeds From Minority Shareholders ProceedsFromMinorityShareholders	0	usd
CY2023	us-gaap	Payments Of Dividends Minority Interest PaymentsOfDividendsMinorityInterest	16000000.0	usd
CY2023	us-gaap	Payments Of Dividends Minority Interest PaymentsOfDividendsMinorityInterest	34000000.0	usd
CY2022	us-gaap	Payments Of Dividends Minority Interest PaymentsOfDividendsMinorityInterest	0	usd
CY2023	us-gaap	Payments For Repurchase Of Other Equity PaymentsForRepurchaseOfOtherEquity	11200000	usd
CY2023	us-gaap	Payments For Repurchase Of Other Equity PaymentsForRepurchaseOfOtherEquity	5700000	usd
CY2022	us-gaap	Payments For Repurchase Of Other Equity PaymentsForRepurchaseOfOtherEquity	4800000	usd
CY2023	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	267200000	usd
CY2023	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	-201900000	usd
CY2022	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	103000000.0	usd
CY2023	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	159900000	usd
CY2023	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	-103700000	usd
CY2022	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	41800000	usd
CY2023Q1	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	584000000.0	usd
CY2022Q1	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	687700000	usd
CY2021Q1	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	645900000	usd
CY2023Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	743900000	usd
CY2023Q1	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	584000000.0	usd
CY2022Q1	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	687700000	usd
CY2022	us-gaap	Profit Loss ProfitLoss	206600000	usd
CY2022	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	13900000	usd
CY2022	ati	Employee Stock Plans EmployeeStockPlans	-16200000	usd
CY2023	us-gaap	Stock Issued During Period Value Conversion Of Convertible Securities StockIssuedDuringPeriodValueConversionOfConvertibleSecurities	-82500000	usd
CY2023	us-gaap	Minority Interest Decrease From Distributions To Noncontrolling Interest Holders MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders	34000000.0	usd
CY2023	us-gaap	Minority Interest Decrease From Redemptions MinorityInterestDecreaseFromRedemptions	-900000	usd
CY2023	ati	Employee Stock Plans EmployeeStockPlans	-20300000	usd
CY2023Q1	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	1157200000	usd
CY2023	us-gaap	Profit Loss ProfitLoss	423400000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-16200000	usd
CY2023	us-gaap	Treasury Stock Value Acquired Cost Method TreasuryStockValueAcquiredCostMethod	85800000	usd
CY2023	us-gaap	Minority Interest Decrease From Distributions To Noncontrolling Interest Holders MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders	16000000.0	usd
CY2023	ati	Employee Stock Plans EmployeeStockPlans	-17900000	usd
CY2023Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	1480500000	usd
CY2023	us-gaap	Fiscal Period FiscalPeriod	<div><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-style:italic;font-weight:700;line-height:107%">Fiscal Year</span></div>The Company follows a 4-4-5 or 5-4-4 fiscal calendar, whereby each fiscal quarter consists of thirteen weeks grouped into two four-week months and one five-week month, and its fiscal year ends on the Sunday closest to December 31. Unless otherwise stated, references to years in this Annual Report on Form 10-K relate to fiscal years, rather than calendar years. Fiscal years 2023, 2022 and 2021 ended on December 31, 2023, January 1, 2023 and January 2, 2022, respectively. All fiscal years presented include 52 weeks of operations. The dates for prior fiscal years have been revised to more precisely reflect the exact day of the year end periods for these fiscal years given our 4-4-5 or 5-4-4 calendar.
CY2023	us-gaap	Use Of Estimates UseOfEstimates	<div><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-style:italic;font-weight:700;line-height:107%">Risks and Uncertainties and Use of Estimates</span></div>The preparation of consolidated financial statements in conformity with United States generally accepted accounting principles requires management to make estimates and assumptions that affect reported amounts of assets and liabilities at the date of the financial statements, as well as the reported amounts of income and expenses during the reporting period. Actual results could differ from those estimates. Management believes that the estimates are reasonable.
CY2023	us-gaap	Concentration Risk Credit Risk ConcentrationRiskCreditRisk	<div style="margin-top:9pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">The Company markets its products to a diverse customer base, principally throughout the United States. No single customer accounted for more than 10% of sales for any year presented. The major end markets for ATI’s products are customers in the aerospace & defense, energy, automotive, construction and mining, food equipment and appliances, and medical markets.</span></div>
CY2023Q4	dei	Entity Number Of Employees EntityNumberOfEmployees	7300	employee
CY2023	ati	Employees Percent Non U.S. EmployeesPercentNonU.S.	0.15
CY2023	ati	Employees Percent Coveredby Collective Bargaining Agreements EmployeesPercentCoveredbyCollectiveBargainingAgreements	0.35
CY2022Q1	ati	Entity Number Of Employees Covered By Usw Collective Bargaining Agreements Expiring February282021 EntityNumberOfEmployeesCoveredByUSWCollectiveBargainingAgreementsExpiringFebruary282021	1100	employee
CY2023	ati	Nonoperatingretirementbenefitexpense Nonoperatingretirementbenefitexpense	79700000	usd
CY2023	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	295200000	usd
CY2023	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	-128200000	usd
CY2023	us-gaap	Profit Loss ProfitLoss	423400000	usd
CY2023	us-gaap	Net Income Loss NetIncomeLoss	410800000	usd
CY2023	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.21
CY2023	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.81
CY2023	us-gaap	Profit Loss ProfitLoss	423400000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax	-6000000.0	usd
CY2023	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Net Unamortized Gain Loss Arising During Period Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax	-3800000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Finalization Of Pension And Non Pension Postretirement Plan Valuation Before Tax OtherComprehensiveIncomeLossFinalizationOfPensionAndNonPensionPostretirementPlanValuationBeforeTax	1100000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	-300000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-2400000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-16200000	usd
CY2023Q4	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	-70100000	usd
CY2023Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-83200000	usd
CY2023	us-gaap	Profit Loss ProfitLoss	423400000	usd
CY2023	us-gaap	Deferred Income Taxes And Tax Credits DeferredIncomeTaxesAndTaxCredits	-138200000	usd
CY2023	us-gaap	Increase Decrease In Pension And Postretirement Obligations IncreaseDecreaseInPensionAndPostretirementObligations	53800000	usd
CY2023	us-gaap	Profit Loss ProfitLoss	423400000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-16200000	usd
CY2023	ati	Gain Loss On Asset And Business Sales Net GainLossOnAssetAndBusinessSalesNet	-105400000	usd
CY2023	us-gaap	Operating Income Loss OperatingIncomeLoss	316100000	usd
CY2023	ati	Nonoperatingretirementbenefitexpense Nonoperatingretirementbenefitexpense	-138400000	usd
CY2023	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	354600000	usd
CY2023	us-gaap	Profit Loss ProfitLoss	339100000	usd
CY2023	us-gaap	Net Income Loss NetIncomeLoss	323500000	usd
CY2023	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	2.54
CY2023	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.23
CY2023	us-gaap	Profit Loss ProfitLoss	339100000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax	-13200000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Net Unamortized Gain Loss Arising During Period Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax	54700000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Finalization Of Pension And Non Pension Postretirement Plan Valuation Before Tax OtherComprehensiveIncomeLossFinalizationOfPensionAndNonPensionPostretirementPlanValuationBeforeTax	700000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-68100000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	55600000	usd
CY2023Q1	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	-480900000	usd
CY2023Q1	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-67400000	usd
CY2023	us-gaap	Profit Loss ProfitLoss	339100000	usd
CY2023	us-gaap	Gain Loss On Sale Of Business GainLossOnSaleOfBusiness	-112200000	usd
CY2023	us-gaap	Increase Decrease In Pension And Postretirement Obligations IncreaseDecreaseInPensionAndPostretirementObligations	-159200000	usd
CY2023	us-gaap	Profit Loss ProfitLoss	339100000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	55600000	usd
CY2022	ati	Nonoperatingretirementbenefitexpense Nonoperatingretirementbenefitexpense	-260000000.0	usd
CY2022	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	233400000	usd
CY2022	us-gaap	Profit Loss ProfitLoss	206600000	usd
CY2022	us-gaap	Net Income Loss NetIncomeLoss	184600000	usd
CY2022	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	1.45
CY2022	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	1.32
CY2022	us-gaap	Profit Loss ProfitLoss	206600000	usd
CY2022	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax	-13900000	usd
CY2022	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Net Unamortized Gain Loss Arising During Period Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax	8700000	usd
CY2022	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-14400000	usd
CY2022	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	13900000	usd
CY2022Q1	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	-777700000	usd
CY2022Q1	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-141300000	usd
CY2022	us-gaap	Profit Loss ProfitLoss	206600000	usd
CY2022	us-gaap	Increase Decrease In Pension And Postretirement Obligations IncreaseDecreaseInPensionAndPostretirementObligations	-261900000	usd
CY2022	us-gaap	Profit Loss ProfitLoss	206600000	usd
CY2022	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	13900000	usd
CY2023Q4	us-gaap	Allowance For Doubtful Accounts Receivable AllowanceForDoubtfulAccountsReceivable	3200000	usd
CY2023Q1	us-gaap	Allowance For Doubtful Accounts Receivable AllowanceForDoubtfulAccountsReceivable	7700000	usd
CY2023	us-gaap	Research And Development Expense ResearchAndDevelopmentExpense	20700000	usd
CY2023	us-gaap	Research And Development Expense ResearchAndDevelopmentExpense	16300000	usd
CY2022	us-gaap	Research And Development Expense ResearchAndDevelopmentExpense	16500000	usd
CY2023	us-gaap	Research And Development Arrangement Contract To Perform For Others Costs Incurred Gross ResearchAndDevelopmentArrangementContractToPerformForOthersCostsIncurredGross	1400000	usd
CY2023	us-gaap	Research And Development Arrangement Contract To Perform For Others Costs Incurred Gross ResearchAndDevelopmentArrangementContractToPerformForOthersCostsIncurredGross	1400000	usd
CY2022	us-gaap	Research And Development Arrangement Contract To Perform For Others Costs Incurred Gross ResearchAndDevelopmentArrangementContractToPerformForOthersCostsIncurredGross	3500000	usd
CY2023Q4	us-gaap	Revenue Remaining Performance Obligation RevenueRemainingPerformanceObligation	3800000000	usd
CY2023	us-gaap	Number Of Operating Segments NumberOfOperatingSegments	2	segment
CY2023	us-gaap	Number Of Operating Segments NumberOfOperatingSegments	2	segment
CY2023	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	4173700000	usd
CY2023	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	3836000000	usd
CY2022	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	2799800000	usd
CY2023	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	4173700000	usd
CY2023	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	3836000000	usd
CY2022	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	2799800000	usd
CY2023	ati	Revenuefrom Contractwith Customer Excluding Assessed Tax Percentageof Revenue RevenuefromContractwithCustomerExcludingAssessedTaxPercentageofRevenue	1
CY2023	ati	Revenuefrom Contractwith Customer Excluding Assessed Tax Percentageof Revenue RevenuefromContractwithCustomerExcludingAssessedTaxPercentageofRevenue	1
CY2022	ati	Revenuefrom Contractwith Customer Excluding Assessed Tax Percentageof Revenue RevenuefromContractwithCustomerExcludingAssessedTaxPercentageofRevenue	1
CY2023Q1	us-gaap	Revenue Remaining Performance Obligation RevenueRemainingPerformanceObligation	2900000000	usd
CY2022Q1	us-gaap	Revenue Remaining Performance Obligation RevenueRemainingPerformanceObligation	2100000000	usd
CY2023Q4	ati	Revenue Remaining Performance Obligation Current RevenueRemainingPerformanceObligationCurrent	0.70	usd
CY2023Q4	ati	Accountsreceivablewithcustomers Accountsreceivablewithcustomers	628200000	usd
CY2023Q1	ati	Accountsreceivablewithcustomers Accountsreceivablewithcustomers	586900000	usd
CY2021Q1	us-gaap	Allowance For Doubtful Accounts Receivable AllowanceForDoubtfulAccountsReceivable	4300000	usd
CY2022	us-gaap	Provision For Doubtful Accounts ProvisionForDoubtfulAccounts	300000	usd
CY2022	us-gaap	Allowance For Doubtful Accounts Receivable Write Offs AllowanceForDoubtfulAccountsReceivableWriteOffs	800000	usd
CY2022Q1	us-gaap	Allowance For Doubtful Accounts Receivable AllowanceForDoubtfulAccountsReceivable	3800000	usd
CY2023	us-gaap	Provision For Doubtful Accounts ProvisionForDoubtfulAccounts	4600000	usd
CY2023	us-gaap	Allowance For Doubtful Accounts Receivable Write Offs AllowanceForDoubtfulAccountsReceivableWriteOffs	700000	usd
CY2023Q1	us-gaap	Allowance For Doubtful Accounts Receivable AllowanceForDoubtfulAccountsReceivable	7700000	usd
CY2023	us-gaap	Provision For Doubtful Accounts ProvisionForDoubtfulAccounts	100000	usd
CY2023	us-gaap	Allowance For Doubtful Accounts Receivable Write Offs AllowanceForDoubtfulAccountsReceivableWriteOffs	4600000	usd
CY2023Q4	us-gaap	Allowance For Doubtful Accounts Receivable AllowanceForDoubtfulAccountsReceivable	3200000	usd
CY2023Q1	us-gaap	Contract With Customer Asset Net Current ContractWithCustomerAssetNetCurrent	64100000	usd
CY2022Q1	us-gaap	Contract With Customer Asset Net Current ContractWithCustomerAssetNetCurrent	53900000	usd
CY2021Q1	us-gaap	Contract With Customer Asset Net Current ContractWithCustomerAssetNetCurrent	38900000	usd
CY2023	ati	Contractwith Customer Asset Current Period Increase ContractwithCustomerAssetCurrentPeriodIncrease	84100000	usd
CY2023	ati	Contractwith Customer Asset Current Period Increase ContractwithCustomerAssetCurrentPeriodIncrease	105000000.0	usd
CY2022	ati	Contractwith Customer Asset Current Period Increase ContractwithCustomerAssetCurrentPeriodIncrease	93800000	usd
CY2023	ati	Contractwith Customer Asset Current Reclassifiedto Receivable ContractwithCustomerAssetCurrentReclassifiedtoReceivable	89500000	usd
CY2023	ati	Contractwith Customer Asset Current Reclassifiedto Receivable ContractwithCustomerAssetCurrentReclassifiedtoReceivable	88000000.0	usd
CY2022	ati	Contractwith Customer Asset Current Reclassifiedto Receivable ContractwithCustomerAssetCurrentReclassifiedtoReceivable	76200000	usd
CY2023	ati	Contractwith Customer Asset Current Reclassification ContractwithCustomerAssetCurrentReclassification	-400000	usd
CY2023	ati	Contractwith Customer Asset Current Reclassification ContractwithCustomerAssetCurrentReclassification	6800000	usd
CY2022	ati	Contractwith Customer Asset Current Reclassification ContractwithCustomerAssetCurrentReclassification	2600000	usd
CY2023Q4	us-gaap	Contract With Customer Asset Net Current ContractWithCustomerAssetNetCurrent	59100000	usd
CY2023Q1	us-gaap	Contract With Customer Asset Net Current ContractWithCustomerAssetNetCurrent	64100000	usd
CY2022Q1	us-gaap	Contract With Customer Asset Net Current ContractWithCustomerAssetNetCurrent	53900000	usd
CY2023Q1	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	149100000	usd
CY2022Q1	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	116200000	usd
CY2021Q1	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	111800000	usd
CY2023	ati	Contractwith Customer Liability Current Period Increase ContractwithCustomerLiabilityCurrentPeriodIncrease	133400000	usd
CY2023	ati	Contractwith Customer Liability Current Period Increase ContractwithCustomerLiabilityCurrentPeriodIncrease	183100000	usd
CY2022	ati	Contractwith Customer Liability Current Period Increase ContractwithCustomerLiabilityCurrentPeriodIncrease	161500000	usd
CY2023	ati	Contractwith Customer Liability Current Reclassifiedto Revenue ContractwithCustomerLiabilityCurrentReclassifiedtoRevenue	-107900000	usd
CY2023	ati	Contractwith Customer Liability Current Reclassifiedto Revenue ContractwithCustomerLiabilityCurrentReclassifiedtoRevenue	-99800000	usd
CY2022	ati	Contractwith Customer Liability Current Reclassifiedto Revenue ContractwithCustomerLiabilityCurrentReclassifiedtoRevenue	-85100000	usd
CY2023	ati	Contractwith Customer Liability Current Revenue Recognized ContractwithCustomerLiabilityCurrentRevenueRecognized	-40900000	usd
CY2023	ati	Contractwith Customer Liability Current Revenue Recognized ContractwithCustomerLiabilityCurrentRevenueRecognized	-72300000	usd
CY2022	ati	Contractwith Customer Liability Current Revenue Recognized ContractwithCustomerLiabilityCurrentRevenueRecognized	-72900000	usd
CY2023	ati	Contract With Customers Liability Current Divestiture ContractWithCustomersLiabilityCurrentDivestiture	0	usd
CY2023	ati	Contract With Customers Liability Current Divestiture ContractWithCustomersLiabilityCurrentDivestiture	0	usd
CY2022	ati	Contract With Customers Liability Current Divestiture ContractWithCustomersLiabilityCurrentDivestiture	-800000	usd
CY2023	ati	Contractwith Customer Liability Current Other ContractwithCustomerLiabilityCurrentOther	-700000	usd
CY2023	ati	Contractwith Customer Liability Current Other ContractwithCustomerLiabilityCurrentOther	700000	usd
CY2022	ati	Contractwith Customer Liability Current Other ContractwithCustomerLiabilityCurrentOther	100000	usd
CY2023	ati	Contractwith Customer Liability Current Reclassification ContractwithCustomerLiabilityCurrentReclassification	-30600000	usd
CY2023	ati	Contractwith Customer Liability Current Reclassification ContractwithCustomerLiabilityCurrentReclassification	-21200000	usd
CY2022	ati	Contractwith Customer Liability Current Reclassification ContractwithCustomerLiabilityCurrentReclassification	-1600000	usd
CY2023Q4	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	163600000	usd
CY2023Q1	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	149100000	usd
CY2022Q1	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	116200000	usd
CY2023Q1	us-gaap	Contract With Customer Liability Noncurrent ContractWithCustomerLiabilityNoncurrent	66800000	usd
CY2022Q1	us-gaap	Contract With Customer Liability Noncurrent ContractWithCustomerLiabilityNoncurrent	84400000	usd
CY2021Q1	us-gaap	Contract With Customer Liability Noncurrent ContractWithCustomerLiabilityNoncurrent	32000000.0	usd
CY2023	ati	Contractwith Customer Liability Noncurrent Period Increase ContractwithCustomerLiabilityNoncurrentPeriodIncrease	2800000	usd
CY2023	ati	Contractwith Customer Liability Noncurrent Period Increase ContractwithCustomerLiabilityNoncurrentPeriodIncrease	10400000	usd
CY2022	ati	Contractwith Customer Liability Noncurrent Period Increase ContractwithCustomerLiabilityNoncurrentPeriodIncrease	56600000	usd
CY2023	ati	Contractwith Customer Liability Noncurrent Reclassification ContractwithCustomerLiabilityNoncurrentReclassification	30200000	usd
CY2023	ati	Contractwith Customer Liability Noncurrent Reclassification ContractwithCustomerLiabilityNoncurrentReclassification	28000000.0	usd
CY2022	ati	Contractwith Customer Liability Noncurrent Reclassification ContractwithCustomerLiabilityNoncurrentReclassification	4200000	usd
CY2023Q4	us-gaap	Contract With Customer Liability Noncurrent ContractWithCustomerLiabilityNoncurrent	39400000	usd
CY2023Q1	us-gaap	Contract With Customer Liability Noncurrent ContractWithCustomerLiabilityNoncurrent	66800000	usd
CY2022Q1	us-gaap	Contract With Customer Liability Noncurrent ContractWithCustomerLiabilityNoncurrent	84400000	usd
CY2023Q4	us-gaap	Capitalized Contract Cost Net CapitalizedContractCostNet	8100000	usd
CY2023Q1	us-gaap	Capitalized Contract Cost Net CapitalizedContractCostNet	7300000	usd
CY2023	us-gaap	Capitalized Contract Cost Amortization CapitalizedContractCostAmortization	1200000	usd
CY2023	us-gaap	Capitalized Contract Cost Amortization CapitalizedContractCostAmortization	1000000	usd
CY2022	us-gaap	Capitalized Contract Cost Amortization CapitalizedContractCostAmortization	1000000	usd
CY2023Q4	us-gaap	Inventory Raw Materials And Supplies InventoryRawMaterialsAndSupplies	234900000	usd
CY2023Q1	us-gaap	Inventory Raw Materials And Supplies InventoryRawMaterialsAndSupplies	213600000	usd
CY2023Q4	us-gaap	Inventory Work In Process InventoryWorkInProcess	973600000	usd
CY2023Q1	us-gaap	Inventory Work In Process InventoryWorkInProcess	941100000	usd
CY2023Q4	us-gaap	Inventory Finished Goods InventoryFinishedGoods	114500000	usd
CY2023Q1	us-gaap	Inventory Finished Goods InventoryFinishedGoods	111900000	usd
CY2023Q4	us-gaap	Inventory Gross InventoryGross	1323000000	usd
CY2023Q1	us-gaap	Inventory Gross InventoryGross	1266600000	usd
CY2023Q4	us-gaap	Inventory Valuation Reserves InventoryValuationReserves	75500000	usd
CY2023Q1	us-gaap	Inventory Valuation Reserves InventoryValuationReserves	70900000	usd
CY2023Q4	us-gaap	Inventory Net InventoryNet	1247500000	usd
CY2023Q1	us-gaap	Inventory Net InventoryNet	1195700000	usd
CY2023Q4	us-gaap	Land Land	32300000	usd
CY2023Q1	us-gaap	Land Land	31500000	usd
CY2023Q4	us-gaap	Buildings And Improvements Gross BuildingsAndImprovementsGross	692700000	usd
CY2023Q1	us-gaap	Buildings And Improvements Gross BuildingsAndImprovementsGross	601600000	usd
CY2023Q4	us-gaap	Machinery And Equipment Gross MachineryAndEquipmentGross	3024300000	usd
CY2023Q1	us-gaap	Machinery And Equipment Gross MachineryAndEquipmentGross	2895500000	usd
CY2023Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	3749300000	usd
CY2023Q1	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	3528600000	usd
CY2023Q4	us-gaap	Accumulated Depreciation Depletion And Amortization Property Plant And Equipment AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	2083400000	usd
CY2023Q1	us-gaap	Accumulated Depreciation Depletion And Amortization Property Plant And Equipment AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	1979500000	usd
CY2023Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	1665900000	usd
CY2023Q1	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	1549100000	usd
CY2023Q4	us-gaap	Construction In Progress Gross ConstructionInProgressGross	305900000	usd
CY2023Q1	us-gaap	Construction In Progress Gross ConstructionInProgressGross	262100000	usd
CY2023	us-gaap	Capital Expenditures Incurred But Not Yet Paid CapitalExpendituresIncurredButNotYetPaid	41900000	usd
CY2023	us-gaap	Capital Expenditures Incurred But Not Yet Paid CapitalExpendituresIncurredButNotYetPaid	38300000	usd
CY2023Q4	us-gaap	Goodwill Impaired Accumulated Impairment Loss GoodwillImpairedAccumulatedImpairmentLoss	528000000	usd
CY2022Q1	us-gaap	Goodwill Impaired Accumulated Impairment Loss GoodwillImpairedAccumulatedImpairmentLoss	528000000	usd
CY2023Q1	us-gaap	Goodwill Impaired Accumulated Impairment Loss GoodwillImpairedAccumulatedImpairmentLoss	528000000	usd
CY2023Q4	us-gaap	Finite Lived Intangible Assets Gross FiniteLivedIntangibleAssetsGross	134800000	usd
CY2023Q4	us-gaap	Finite Lived Intangible Assets Accumulated Amortization FiniteLivedIntangibleAssetsAccumulatedAmortization	83700000	usd
CY2023Q1	us-gaap	Finite Lived Intangible Assets Gross FiniteLivedIntangibleAssetsGross	134800000	usd
CY2023Q1	us-gaap	Finite Lived Intangible Assets Accumulated Amortization FiniteLivedIntangibleAssetsAccumulatedAmortization	76300000	usd
CY2023	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	7000000	usd
CY2023	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	8000000	usd
CY2022	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	8000000	usd
CY2023Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Two FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo	7000000	usd
CY2023Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Next Twelve Months FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths	7000000	usd
CY2023Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Four FiniteLivedIntangibleAssetsAmortizationExpenseYearFour	7000000	usd
CY2023Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Five FiniteLivedIntangibleAssetsAmortizationExpenseYearFive	7000000	usd
CY2023Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Three FiniteLivedIntangibleAssetsAmortizationExpenseYearThree	7000000	usd
CY2023	ati	Transaction Costs From Sales Of Businesses Net Of Proceeds TransactionCostsFromSalesOfBusinessesNetOfProceeds	300000	usd
CY2023Q4	ati	Retained Earnings Equity Method Undistributed Earnings RetainedEarningsEquityMethodUndistributedEarnings	700000	usd
CY2023Q4	us-gaap	Asset Retirement Obligation AssetRetirementObligation	18300000	usd
CY2023Q1	us-gaap	Asset Retirement Obligation AssetRetirementObligation	17800000	usd
CY2022Q1	us-gaap	Asset Retirement Obligation AssetRetirementObligation	19000000.0	usd
CY2023	us-gaap	Asset Retirement Obligation Accretion Expense AssetRetirementObligationAccretionExpense	700000	usd
CY2023	us-gaap	Asset Retirement Obligation Accretion Expense AssetRetirementObligationAccretionExpense	800000	usd
CY2023	us-gaap	Asset Retirement Obligation Liabilities Settled AssetRetirementObligationLiabilitiesSettled	200000	usd
CY2023	us-gaap	Asset Retirement Obligation Liabilities Settled AssetRetirementObligationLiabilitiesSettled	2000000.0	usd
CY2023Q4	us-gaap	Asset Retirement Obligation AssetRetirementObligation	18300000	usd
CY2023Q1	us-gaap	Asset Retirement Obligation AssetRetirementObligation	17800000	usd
CY2023Q4	us-gaap	Cash Cash	329800000	usd
CY2023Q1	us-gaap	Cash Cash	164900000	usd
CY2023Q4	us-gaap	Money Market Funds At Carrying Value MoneyMarketFundsAtCarryingValue	414100000	usd
CY2023Q1	us-gaap	Money Market Funds At Carrying Value MoneyMarketFundsAtCarryingValue	419100000	usd
CY2023Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	743900000	usd
CY2023Q1	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	584000000.0	usd
CY2023Q4	us-gaap	Employee Related Liabilities Current EmployeeRelatedLiabilitiesCurrent	102300000	usd
CY2023Q1	us-gaap	Employee Related Liabilities Current EmployeeRelatedLiabilitiesCurrent	100800000	usd
CY2023Q4	us-gaap	Interest Payable Current InterestPayableCurrent	23700000	usd
CY2023Q1	us-gaap	Interest Payable Current InterestPayableCurrent	11800000	usd
CY2023	ati	Rent Royalty And Other Income RentRoyaltyAndOtherIncome	2600000	usd
CY2023	ati	Rent Royalty And Other Income RentRoyaltyAndOtherIncome	2300000	usd
CY2022	ati	Rent Royalty And Other Income RentRoyaltyAndOtherIncome	1100000	usd
CY2023	us-gaap	Gain Loss On Disposition Of Assets1 GainLossOnDispositionOfAssets1	300000	usd
CY2023	us-gaap	Gain Loss On Disposition Of Assets1 GainLossOnDispositionOfAssets1	200000	usd
CY2022	us-gaap	Gain Loss On Disposition Of Assets1 GainLossOnDispositionOfAssets1	2900000	usd
CY2023	us-gaap	Income Loss From Equity Method Investments IncomeLossFromEquityMethodInvestments	-1600000	usd
CY2023	us-gaap	Income Loss From Equity Method Investments IncomeLossFromEquityMethodInvestments	12600000	usd
CY2022	us-gaap	Income Loss From Equity Method Investments IncomeLossFromEquityMethodInvestments	100000	usd
CY2023	us-gaap	Disposal Group Not Discontinued Operation Gain Loss On Disposal DisposalGroupNotDiscontinuedOperationGainLossOnDisposal	0	usd
CY2023	us-gaap	Disposal Group Not Discontinued Operation Gain Loss On Disposal DisposalGroupNotDiscontinuedOperationGainLossOnDisposal	0	usd
CY2022	us-gaap	Disposal Group Not Discontinued Operation Gain Loss On Disposal DisposalGroupNotDiscontinuedOperationGainLossOnDisposal	13800000	usd
CY2023	ati	Equity Method Investments Restructuring Credit Charges EquityMethodInvestmentsRestructuringCreditCharges	0	usd
CY2023	ati	Equity Method Investments Restructuring Credit Charges EquityMethodInvestmentsRestructuringCreditCharges	900000	usd
CY2022	ati	Equity Method Investments Restructuring Credit Charges EquityMethodInvestmentsRestructuringCreditCharges	0	usd
CY2023	ati	Other Nonoperating Income Expense Litigation Reserve OtherNonoperatingIncomeExpenseLitigationReserve	0	usd
CY2023	ati	Other Nonoperating Income Expense Litigation Reserve OtherNonoperatingIncomeExpenseLitigationReserve	-28500000	usd
CY2022	ati	Other Nonoperating Income Expense Litigation Reserve OtherNonoperatingIncomeExpenseLitigationReserve	0	usd
CY2023	ati	Other Other Nonoperating Income Expense OtherOtherNonoperatingIncomeExpense	0	usd
CY2023	ati	Other Other Nonoperating Income Expense OtherOtherNonoperatingIncomeExpense	0	usd
CY2022	ati	Other Other Nonoperating Income Expense OtherOtherNonoperatingIncomeExpense	300000	usd
CY2023	us-gaap	Other Nonoperating Income Expense OtherNonoperatingIncomeExpense	1300000	usd
CY2023	us-gaap	Other Nonoperating Income Expense OtherNonoperatingIncomeExpense	-12500000	usd
CY2022	us-gaap	Other Nonoperating Income Expense OtherNonoperatingIncomeExpense	18200000	usd
CY2023Q4	us-gaap	Supplier Finance Program Obligation Current SupplierFinanceProgramObligationCurrent	15600000	usd
CY2023Q1	us-gaap	Supplier Finance Program Obligation Current SupplierFinanceProgramObligationCurrent	23700000	usd
CY2023Q4	us-gaap	Deferred Finance Costs Net DeferredFinanceCostsNet	19600000	usd
CY2023Q1	us-gaap	Deferred Finance Costs Net DeferredFinanceCostsNet	17200000	usd
CY2023Q4	ati	Total Debt TotalDebt	2179600000	usd
CY2023Q1	ati	Total Debt TotalDebt	1748000000	usd
CY2023Q4	us-gaap	Debt Current DebtCurrent	31900000	usd
CY2023Q1	us-gaap	Debt Current DebtCurrent	41700000	usd
CY2023Q4	us-gaap	Long Term Debt And Capital Lease Obligations LongTermDebtAndCapitalLeaseObligations	2147700000	usd
CY2023Q1	us-gaap	Long Term Debt And Capital Lease Obligations LongTermDebtAndCapitalLeaseObligations	1706300000	usd
CY2023	us-gaap	Interest Expense Debt InterestExpenseDebt	105800000	usd
CY2023	us-gaap	Interest Expense Debt InterestExpenseDebt	92100000	usd
CY2022	us-gaap	Interest Expense Debt InterestExpenseDebt	97600000	usd
CY2023	us-gaap	Interest Costs Capitalized InterestCostsCapitalized	13500000	usd
CY2023	us-gaap	Interest Costs Capitalized InterestCostsCapitalized	5100000	usd
CY2022	us-gaap	Interest Costs Capitalized InterestCostsCapitalized	4300000	usd
CY2023	us-gaap	Interest Paid InterestPaid	114700000	usd
CY2023	us-gaap	Interest Paid InterestPaid	92800000	usd
CY2022	us-gaap	Interest Paid InterestPaid	97500000	usd
CY2023	us-gaap	Investment Income Interest InvestmentIncomeInterest	13000000	usd
CY2023	us-gaap	Investment Income Interest InvestmentIncomeInterest	4700000	usd
CY2022	us-gaap	Investment Income Interest InvestmentIncomeInterest	700000	usd
CY2023Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Next Twelve Months LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths	31900000	usd
CY2023Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Two LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo	465300000	usd
CY2023Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Three LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree	18500000	usd
CY2023Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Four LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour	565300000	usd
CY2023Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Five LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive	9600000	usd
CY2022	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	-65500000	usd
CY2022	us-gaap	Payments Of Debt Extinguishment Costs PaymentsOfDebtExtinguishmentCosts	64500000	usd
CY2022	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	-65500000	usd
CY2023	us-gaap	Stock Issued During Period Value Conversion Of Convertible Securities StockIssuedDuringPeriodValueConversionOfConvertibleSecurities	-82500000	usd
CY2023	us-gaap	Stock Issued During Period Shares Conversion Of Convertible Securities StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities	5700000	shares
CY2023	us-gaap	Finance Lease Right Of Use Asset Amortization FinanceLeaseRightOfUseAssetAmortization	10900000	usd
CY2023	us-gaap	Finance Lease Right Of Use Asset Amortization FinanceLeaseRightOfUseAssetAmortization	8900000	usd
CY2022	us-gaap	Finance Lease Right Of Use Asset Amortization FinanceLeaseRightOfUseAssetAmortization	7100000	usd
CY2023	us-gaap	Finance Lease Interest Expense FinanceLeaseInterestExpense	4600000	usd
CY2023	us-gaap	Finance Lease Interest Expense FinanceLeaseInterestExpense	4100000	usd
CY2022	us-gaap	Finance Lease Interest Expense FinanceLeaseInterestExpense	3100000	usd
CY2023	us-gaap	Operating Lease Cost OperatingLeaseCost	17600000	usd
CY2023	us-gaap	Operating Lease Cost OperatingLeaseCost	16400000	usd
CY2022	us-gaap	Operating Lease Cost OperatingLeaseCost	22700000	usd
CY2023	us-gaap	Short Term Lease Cost ShortTermLeaseCost	4500000	usd
CY2023	us-gaap	Short Term Lease Cost ShortTermLeaseCost	2900000	usd
CY2022	us-gaap	Short Term Lease Cost ShortTermLeaseCost	1600000	usd
CY2023	us-gaap	Variable Lease Cost VariableLeaseCost	1000000.0	usd
CY2023	us-gaap	Variable Lease Cost VariableLeaseCost	1000000.0	usd
CY2022	us-gaap	Variable Lease Cost VariableLeaseCost	900000	usd
CY2023	us-gaap	Sublease Income SubleaseIncome	400000	usd
CY2023	us-gaap	Sublease Income SubleaseIncome	0	usd
CY2022	us-gaap	Sublease Income SubleaseIncome	300000	usd
CY2023	us-gaap	Lease Cost LeaseCost	38200000	usd
CY2023	us-gaap	Lease Cost LeaseCost	33300000	usd
CY2022	us-gaap	Lease Cost LeaseCost	35100000	usd
CY2023	us-gaap	Finance Lease Interest Payment On Liability FinanceLeaseInterestPaymentOnLiability	4600000	usd
CY2023	us-gaap	Finance Lease Interest Payment On Liability FinanceLeaseInterestPaymentOnLiability	4100000	usd
CY2022	us-gaap	Finance Lease Interest Payment On Liability FinanceLeaseInterestPaymentOnLiability	3000000.0	usd
CY2023	us-gaap	Operating Lease Payments OperatingLeasePayments	16800000	usd
CY2023	us-gaap	Operating Lease Payments OperatingLeasePayments	17400000	usd
CY2022	us-gaap	Operating Lease Payments OperatingLeasePayments	20000000.0	usd
CY2023	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	24900000	usd
CY2023	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	20900000	usd
CY2022	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	14300000	usd
CY2023	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	54600000	usd
CY2023	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	15300000	usd
CY2022	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	58900000	usd
CY2023	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	25800000	usd
CY2023	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	18000000.0	usd
CY2022	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	4800000	usd
CY2023Q4	us-gaap	Finance Lease Weighted Average Remaining Lease Term1 FinanceLeaseWeightedAverageRemainingLeaseTerm1	P4Y
CY2023Q1	us-gaap	Finance Lease Weighted Average Remaining Lease Term1 FinanceLeaseWeightedAverageRemainingLeaseTerm1	P4Y
CY2022Q1	us-gaap	Finance Lease Weighted Average Remaining Lease Term1 FinanceLeaseWeightedAverageRemainingLeaseTerm1	P5Y
CY2023Q4	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P7Y
CY2023Q1	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P6Y
CY2022Q1	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P5Y
CY2023Q4	us-gaap	Finance Lease Weighted Average Discount Rate Percent FinanceLeaseWeightedAverageDiscountRatePercent	0.054
CY2023Q1	us-gaap	Finance Lease Weighted Average Discount Rate Percent FinanceLeaseWeightedAverageDiscountRatePercent	0.056
CY2022Q1	us-gaap	Finance Lease Weighted Average Discount Rate Percent FinanceLeaseWeightedAverageDiscountRatePercent	0.052
CY2023Q4	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.071
CY2023Q1	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.068
CY2022Q1	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.065
CY2023Q4	us-gaap	Lessee Operating Lease Liability Payments Due Next Twelve Months LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths	17000000.0	usd
CY2023Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Two LesseeOperatingLeaseLiabilityPaymentsDueYearTwo	14400000	usd
CY2023Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Three LesseeOperatingLeaseLiabilityPaymentsDueYearThree	13200000	usd
CY2023Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Four LesseeOperatingLeaseLiabilityPaymentsDueYearFour	10400000	usd
CY2023Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Five LesseeOperatingLeaseLiabilityPaymentsDueYearFive	8200000	usd
CY2023Q4	us-gaap	Lessee Operating Lease Liability Payments Due After Year Five LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive	24900000	usd
CY2023Q4	us-gaap	Lessee Operating Lease Liability Payments Due LesseeOperatingLeaseLiabilityPaymentsDue	88100000	usd
CY2023Q4	us-gaap	Lessee Operating Lease Liability Undiscounted Excess Amount LesseeOperatingLeaseLiabilityUndiscountedExcessAmount	19400000	usd
CY2023Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	68700000	usd
CY2023Q4	us-gaap	Finance Lease Liability Payments Due Next Twelve Months FinanceLeaseLiabilityPaymentsDueNextTwelveMonths	32400000	usd
CY2023Q4	us-gaap	Finance Lease Liability Payments Due Year Two FinanceLeaseLiabilityPaymentsDueYearTwo	27800000	usd
CY2023Q4	us-gaap	Finance Lease Liability Payments Due Year Three FinanceLeaseLiabilityPaymentsDueYearThree	20800000	usd
CY2023Q4	us-gaap	Finance Lease Liability Payments Due Year Four FinanceLeaseLiabilityPaymentsDueYearFour	16900000	usd
CY2023Q4	us-gaap	Finance Lease Liability Payments Due Year Five FinanceLeaseLiabilityPaymentsDueYearFive	10500000	usd
CY2023Q4	us-gaap	Finance Lease Liability Payments Due After Year Five FinanceLeaseLiabilityPaymentsDueAfterYearFive	9100000	usd
CY2023Q4	us-gaap	Finance Lease Liability Payments Due FinanceLeaseLiabilityPaymentsDue	117500000	usd
CY2023Q4	us-gaap	Finance Lease Liability Undiscounted Excess Amount FinanceLeaseLiabilityUndiscountedExcessAmount	15300000	usd
CY2023Q4	us-gaap	Finance Lease Liability FinanceLeaseLiability	102200000	usd
CY2023Q4	ati	Progress Payments Made On Behalf Of Company Paid ProgressPaymentsMadeOnBehalfOfCompanyPaid	28400000	usd
CY2024Q1	ati	Progress Payments Made On Behalf Of Company Scheduled To Be Paid ProgressPaymentsMadeOnBehalfOfCompanyScheduledToBePaid	39700000	usd
CY2024Q1	ati	Lessee Finance Lease Lease Not Yet Commenced Liability To Be Recognized LesseeFinanceLeaseLeaseNotYetCommencedLiabilityToBeRecognized	68100000	usd
CY2024Q1	ati	Lessee Finance Lease Lease Not Yet Commenced Right Of Use Asset To Be Recognized LesseeFinanceLeaseLeaseNotYetCommencedRightOfUseAssetToBeRecognized	68100000	usd
CY2023	us-gaap	Proceeds From Sale Of Other Property Plant And Equipment ProceedsFromSaleOfOtherPropertyPlantAndEquipment	2800000	usd
CY2023	us-gaap	Proceeds From Sale Of Other Property Plant And Equipment ProceedsFromSaleOfOtherPropertyPlantAndEquipment	1800000	usd
CY2022	us-gaap	Proceeds From Sale Of Other Property Plant And Equipment ProceedsFromSaleOfOtherPropertyPlantAndEquipment	16200000	usd
CY2023	ati	Percentage Of Raw Material Usage Hedged PercentageOfRawMaterialUsageHedged	0.06
CY2023Q4	us-gaap	Derivative Fair Value Of Derivative Asset DerivativeFairValueOfDerivativeAsset	900000	usd
CY2023Q1	us-gaap	Derivative Fair Value Of Derivative Asset DerivativeFairValueOfDerivativeAsset	18000000.0	usd
CY2023Q4	us-gaap	Derivative Fair Value Of Derivative Liability DerivativeFairValueOfDerivativeLiability	14200000	usd
CY2023Q1	us-gaap	Derivative Fair Value Of Derivative Liability DerivativeFairValueOfDerivativeLiability	4600000	usd
CY2023	us-gaap	Cash Flow Hedge Gain Loss To Be Reclassified Within Twelve Months CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths	-12300000	usd
CY2023	ati	Derivative Asset Statement Of Financial Position Extensible Enumeration Not Disclosed Flag DerivativeAssetStatementOfFinancialPositionExtensibleEnumerationNotDisclosedFlag	Assets
CY2023	ati	Derivative Liability Statement Of Financial Position Extensible Enumeration Not Disclosed Flag DerivativeLiabilityStatementOfFinancialPositionExtensibleEnumerationNotDisclosedFlag	Liabilities
CY2023Q4	ati	Transfer Of Defined Benefit Pension Plan Percentage TransferOfDefinedBenefitPensionPlanPercentage	0.85
CY2023Q4	ati	Number Of Us Retirees And Beneficiaries Transferred NumberOfUSRetireesAndBeneficiariesTransferred	8200	usretireeandbeneficiary
CY2023Q4	ati	Number Of Us Retirees And Beneficiaries NumberOfUSRetireesAndBeneficiaries	1980	usretireeandbeneficiary
CY2023	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	38800000	usd
CY2023	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	31100000	usd
CY2022	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	20400000	usd
CY2023Q4	ati	Number Of Us Retirees And Beneficiaries Transferred NumberOfUSRetireesAndBeneficiariesTransferred	8200	usretireeandbeneficiary
CY2023Q4	ati	Number Of Us Retirees And Beneficiaries Transferred NumberOfUSRetireesAndBeneficiariesTransferred	8200	usretireeandbeneficiary
CY2023	ati	Projected Retirement Benefit Expense In Next Year ProjectedRetirementBenefitExpenseInNextYear	21000000	usd
CY2023Q4	us-gaap	Defined Benefit Plan Expected Amortization Of Prior Service Cost Credit Next Fiscal Year DefinedBenefitPlanExpectedAmortizationOfPriorServiceCostCreditNextFiscalYear	-500000	usd
CY2023Q4	us-gaap	Defined Benefit Plan Expected Amortization Of Gain Loss Next Fiscal Year DefinedBenefitPlanExpectedAmortizationOfGainLossNextFiscalYear	-5300000	usd
CY2023Q4	us-gaap	Defined Benefit Plan Expected Amortization Next Fiscal Year DefinedBenefitPlanExpectedAmortizationNextFiscalYear	4800000	usd
CY2021Q1	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-1223600000	usd
CY2022	us-gaap	Other Comprehensive Income Loss Before Reclassifications Net Of Tax OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax	8900000	usd
CY2022	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	-200000	usd
CY2022	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	1082300000	usd
CY2022Q1	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-141300000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Before Reclassifications Net Of Tax OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax	57100000	usd
CY2023	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	-16800000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	73900000	usd
CY2023Q1	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-67400000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Before Reclassifications Net Of Tax OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax	-23000000.0	usd
CY2023	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	-7200000	usd
CY2023	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	-15800000	usd
CY2023Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-83200000	usd
CY2021Q1	ati	Accumulated Other Comprehensive Income Loss Netof Tax Attributableto Noncontrolling Interest AccumulatedOtherComprehensiveIncomeLossNetofTaxAttributabletoNoncontrollingInterest	21200000	usd
CY2022	ati	Other Comprehensive Income Lossbefore Reclassifications Netof Tax Attributableto Noncontrolling Interest OtherComprehensiveIncomeLossbeforeReclassificationsNetofTaxAttributabletoNoncontrollingInterest	4800000	usd
CY2022	ati	Reclassificationfrom Accumulated Other Comprehensive Income Current Period Netof Tax Attributableto Noncontrolling Interest ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetofTaxAttributabletoNoncontrollingInterest	0	usd
CY2022	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Noncontrolling Interest OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest	4800000	usd
CY2022Q1	ati	Accumulated Other Comprehensive Income Loss Netof Tax Attributableto Noncontrolling Interest AccumulatedOtherComprehensiveIncomeLossNetofTaxAttributabletoNoncontrollingInterest	26000000.0	usd
CY2023	ati	Other Comprehensive Income Lossbefore Reclassifications Netof Tax Attributableto Noncontrolling Interest OtherComprehensiveIncomeLossbeforeReclassificationsNetofTaxAttributabletoNoncontrollingInterest	-18300000	usd
CY2023	ati	Reclassificationfrom Accumulated Other Comprehensive Income Current Period Netof Tax Attributableto Noncontrolling Interest ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetofTaxAttributabletoNoncontrollingInterest	0	usd
CY2023	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Noncontrolling Interest OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest	-18300000	usd
CY2023Q1	ati	Accumulated Other Comprehensive Income Loss Netof Tax Attributableto Noncontrolling Interest AccumulatedOtherComprehensiveIncomeLossNetofTaxAttributabletoNoncontrollingInterest	7700000	usd
CY2023	ati	Other Comprehensive Income Lossbefore Reclassifications Netof Tax Attributableto Noncontrolling Interest OtherComprehensiveIncomeLossbeforeReclassificationsNetofTaxAttributabletoNoncontrollingInterest	-400000	usd
CY2023	ati	Reclassificationfrom Accumulated Other Comprehensive Income Current Period Netof Tax Attributableto Noncontrolling Interest ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetofTaxAttributabletoNoncontrollingInterest	0	usd
CY2023	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Noncontrolling Interest OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest	-400000	usd
CY2023Q4	ati	Accumulated Other Comprehensive Income Loss Netof Tax Attributableto Noncontrolling Interest AccumulatedOtherComprehensiveIncomeLossNetofTaxAttributabletoNoncontrollingInterest	7300000	usd
CY2022	us-gaap	Other Comprehensive Income Finalization Of Pension And Non Pension Postretirement Plan Valuation Tax OtherComprehensiveIncomeFinalizationOfPensionAndNonPensionPostretirementPlanValuationTax	6400000	usd
CY2023Q4	us-gaap	Preferred Stock Shares Issued PreferredStockSharesIssued	0	shares
CY2023Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant	5400000	shares
CY2023	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	258200000	usd
CY2023	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	394300000	usd
CY2022	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	168700000	usd
CY2023	us-gaap	Income Loss From Continuing Operations Before Income Taxes Foreign IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign	37000000.0	usd
CY2023	us-gaap	Income Loss From Continuing Operations Before Income Taxes Foreign IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign	-39700000	usd
CY2022	us-gaap	Income Loss From Continuing Operations Before Income Taxes Foreign IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign	64700000	usd
CY2023	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	295200000	usd
CY2023	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	354600000	usd
CY2022	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	233400000	usd
CY2023	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	3000000.0	usd
CY2023	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	5000000.0	usd
CY2022	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	700000	usd
CY2023	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	500000	usd
CY2023	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	3700000	usd
CY2022	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	-300000	usd
CY2023	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	7800000	usd
CY2023	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	10000000.0	usd
CY2022	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	9400000	usd
CY2023	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	11300000	usd
CY2023	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	18700000	usd
CY2022	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	9800000	usd
CY2023	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	-96100000	usd
CY2023	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	-3300000	usd
CY2022	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	18600000	usd
CY2023	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	-42500000	usd
CY2023	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	200000	usd
CY2022	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	-900000	usd
CY2023	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	-900000	usd
CY2023	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	-100000	usd
CY2022	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	-700000	usd
CY2023	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	-139500000	usd
CY2023	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	-3200000	usd
CY2022	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	17000000.0	usd
CY2023	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	-128200000	usd
CY2023	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	15500000	usd
CY2022	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	26800000	usd
CY2023	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	62000000.0	usd
CY2023	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	74500000	usd
CY2022	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	49000000.0	usd
CY2023	us-gaap	Income Tax Reconciliation Nondeductible Expense Impairment Losses IncomeTaxReconciliationNondeductibleExpenseImpairmentLosses	0	usd
CY2023	us-gaap	Income Tax Reconciliation Nondeductible Expense Impairment Losses IncomeTaxReconciliationNondeductibleExpenseImpairmentLosses	0	usd
CY2022	us-gaap	Income Tax Reconciliation Nondeductible Expense Impairment Losses IncomeTaxReconciliationNondeductibleExpenseImpairmentLosses	2600000	usd
CY2023	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	1200000	usd
CY2023	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	2900000	usd
CY2022	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	400000	usd
CY2023	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	-198800000	usd
CY2023	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	-84400000	usd
CY2022	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	-29200000	usd
CY2023	us-gaap	Effective Income Tax Rate Reconciliation Gilti Amount EffectiveIncomeTaxRateReconciliationGiltiAmount	5000000.0	usd
CY2023	us-gaap	Effective Income Tax Rate Reconciliation Gilti Amount EffectiveIncomeTaxRateReconciliationGiltiAmount	0	usd
CY2022	us-gaap	Effective Income Tax Rate Reconciliation Gilti Amount EffectiveIncomeTaxRateReconciliationGiltiAmount	2000000.0	usd
CY2023	us-gaap	Income Tax Reconciliation Disposition Of Business IncomeTaxReconciliationDispositionOfBusiness	0	usd
CY2023	us-gaap	Income Tax Reconciliation Disposition Of Business IncomeTaxReconciliationDispositionOfBusiness	23000000.0	usd
CY2022	us-gaap	Income Tax Reconciliation Disposition Of Business IncomeTaxReconciliationDispositionOfBusiness	0	usd
CY2023	ati	Effective Income Tax Rate Reconciliation Recognition Of Stranded Deferred Tax Balance EffectiveIncomeTaxRateReconciliationRecognitionOfStrandedDeferredTaxBalance	0	usd
CY2023	ati	Effective Income Tax Rate Reconciliation Recognition Of Stranded Deferred Tax Balance EffectiveIncomeTaxRateReconciliationRecognitionOfStrandedDeferredTaxBalance	0	usd
CY2022	ati	Effective Income Tax Rate Reconciliation Recognition Of Stranded Deferred Tax Balance EffectiveIncomeTaxRateReconciliationRecognitionOfStrandedDeferredTaxBalance	3900000	usd
CY2023	us-gaap	Income Tax Reconciliation Foreign Income Tax Rate Differential IncomeTaxReconciliationForeignIncomeTaxRateDifferential	2700000	usd
CY2023	us-gaap	Income Tax Reconciliation Foreign Income Tax Rate Differential IncomeTaxReconciliationForeignIncomeTaxRateDifferential	3200000	usd
CY2022	us-gaap	Income Tax Reconciliation Foreign Income Tax Rate Differential IncomeTaxReconciliationForeignIncomeTaxRateDifferential	3000000.0	usd
CY2023	ati	Effective Income Tax Rate Reconciliation Withholding Taxes EffectiveIncomeTaxRateReconciliationWithholdingTaxes	4800000	usd
CY2023	ati	Effective Income Tax Rate Reconciliation Withholding Taxes EffectiveIncomeTaxRateReconciliationWithholdingTaxes	2600000	usd
CY2022	ati	Effective Income Tax Rate Reconciliation Withholding Taxes EffectiveIncomeTaxRateReconciliationWithholdingTaxes	3400000	usd
CY2023	us-gaap	Income Tax Reconciliation Tax Holidays IncomeTaxReconciliationTaxHolidays	3600000	usd
CY2023	us-gaap	Income Tax Reconciliation Tax Holidays IncomeTaxReconciliationTaxHolidays	4900000	usd
CY2022	us-gaap	Income Tax Reconciliation Tax Holidays IncomeTaxReconciliationTaxHolidays	6200000	usd
CY2023	us-gaap	Income Tax Reconciliation Other Reconciling Items IncomeTaxReconciliationOtherReconcilingItems	-1500000	usd
CY2023	us-gaap	Income Tax Reconciliation Other Reconciling Items IncomeTaxReconciliationOtherReconcilingItems	-1400000	usd
CY2022	us-gaap	Income Tax Reconciliation Other Reconciling Items IncomeTaxReconciliationOtherReconcilingItems	-2100000	usd
CY2023	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	-128200000	usd
CY2023	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	15500000	usd
CY2022	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	26800000	usd
CY2023Q4	ati	Valuation Allowance Benefit Related Toat Is Ability To Utilize Projections For Future Income ValuationAllowanceBenefitRelatedTOATIsAbilityToUtilizeProjectionsForFutureIncome	-140300000	usd
CY2023	us-gaap	Income Tax Reconciliation Disposition Of Business IncomeTaxReconciliationDispositionOfBusiness	23000000	usd
CY2022Q1	ati	Discrete Tax Effects Related To Postretirement Medical Benefits Settlement Gain Portion Within Valuation Allowance DiscreteTaxEffectsRelatedToPostretirementMedicalBenefitsSettlementGainPortionWithinValuationAllowance	11600000	usd
CY2022	ati	Effective Income Tax Rate Reconciliation Recognition Of Stranded Deferred Tax Balance EffectiveIncomeTaxRateReconciliationRecognitionOfStrandedDeferredTaxBalance	3900000	usd
CY2022Q1	ati	Discrete Tax Effects Related To Postretirement Medical Benefits Settlement Gain Portion Within Valuation Allowance DiscreteTaxEffectsRelatedToPostretirementMedicalBenefitsSettlementGainPortionWithinValuationAllowance	11600000	usd
CY2022Q1	ati	Valuation Allowance Deferred Tax Asset Additional Requirement Following Reduction Of Deferred Tax Liabilities In Aoci ValuationAllowanceDeferredTaxAssetAdditionalRequirementFollowingReductionOfDeferredTaxLiabilitiesInAOCI	5200000	usd
CY2022	us-gaap	Other Comprehensive Income Finalization Of Pension And Non Pension Postretirement Plan Valuation Tax OtherComprehensiveIncomeFinalizationOfPensionAndNonPensionPostretirementPlanValuationTax	6400000	usd
CY2022	us-gaap	Income Tax Reconciliation Nondeductible Expense Impairment Losses IncomeTaxReconciliationNondeductibleExpenseImpairmentLosses	2600000	usd
CY2023Q4	us-gaap	Deferred Tax Assets Operating Loss Carryforwards DeferredTaxAssetsOperatingLossCarryforwards	133000000.0	usd
CY2023Q1	us-gaap	Deferred Tax Assets Operating Loss Carryforwards DeferredTaxAssetsOperatingLossCarryforwards	184100000	usd
CY2023Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Pensions DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensions	2200000	usd
CY2023Q1	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Pensions DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensions	51700000	usd
CY2023Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Postretirement Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPostretirementBenefits	48500000	usd
CY2023Q1	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Postretirement Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPostretirementBenefits	51500000	usd
CY2023Q4	us-gaap	Deferred Tax Assets Tax Credit Carryforwards DeferredTaxAssetsTaxCreditCarryforwards	43500000	usd
CY2023Q1	us-gaap	Deferred Tax Assets Tax Credit Carryforwards DeferredTaxAssetsTaxCreditCarryforwards	42000000.0	usd
CY2023Q4	us-gaap	Deferred Tax Assets Tax Credit Carryforwards Research DeferredTaxAssetsTaxCreditCarryforwardsResearch	20700000	usd
CY2023Q1	us-gaap	Deferred Tax Assets Tax Credit Carryforwards Research DeferredTaxAssetsTaxCreditCarryforwardsResearch	7400000	usd
CY2023Q4	us-gaap	Deferred Tax Assets Inventory DeferredTaxAssetsInventory	1100000	usd
CY2023Q1	us-gaap	Deferred Tax Assets Inventory DeferredTaxAssetsInventory	0	usd
CY2023Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	107500000	usd
CY2023Q1	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	95600000	usd
CY2023Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	356500000	usd
CY2023Q1	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	432300000	usd
CY2023Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	60300000	usd
CY2023Q1	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	266900000	usd
CY2023Q4	us-gaap	Deferred Tax Assets Net DeferredTaxAssetsNet	296200000	usd
CY2023Q1	us-gaap	Deferred Tax Assets Net DeferredTaxAssetsNet	165400000	usd
CY2023Q4	us-gaap	Deferred Tax Liabilities Property Plant And Equipment DeferredTaxLiabilitiesPropertyPlantAndEquipment	124800000	usd
CY2023Q1	us-gaap	Deferred Tax Liabilities Property Plant And Equipment DeferredTaxLiabilitiesPropertyPlantAndEquipment	122200000	usd
CY2023Q4	ati	Deferred Tax Liabilities Inventory DeferredTaxLiabilitiesInventory	0	usd
CY2023Q1	ati	Deferred Tax Liabilities Inventory DeferredTaxLiabilitiesInventory	17100000	usd
CY2023Q4	us-gaap	Deferred Tax Liabilities Goodwill And Intangible Assets DeferredTaxLiabilitiesGoodwillAndIntangibleAssets	14900000	usd
CY2023Q1	us-gaap	Deferred Tax Liabilities Goodwill And Intangible Assets DeferredTaxLiabilitiesGoodwillAndIntangibleAssets	16400000	usd
CY2023Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	25500000	usd
CY2023Q1	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	23000000.0	usd
CY2023Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	165200000	usd
CY2023Q1	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	178700000	usd
CY2023Q4	us-gaap	Deferred Tax Assets Liabilities Net DeferredTaxAssetsLiabilitiesNet	131000000.0	usd
CY2023Q1	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	13300000	usd
CY2023	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	-198800000	usd
CY2023	us-gaap	Income Taxes Paid IncomeTaxesPaid	16700000	usd
CY2023	us-gaap	Income Taxes Paid IncomeTaxesPaid	18900000	usd
CY2022	us-gaap	Income Taxes Paid IncomeTaxesPaid	14200000	usd
CY2023	us-gaap	Proceeds From Income Tax Refunds ProceedsFromIncomeTaxRefunds	900000	usd
CY2023	us-gaap	Proceeds From Income Tax Refunds ProceedsFromIncomeTaxRefunds	400000	usd
CY2022	us-gaap	Proceeds From Income Tax Refunds ProceedsFromIncomeTaxRefunds	600000	usd
CY2023	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	15800000	usd
CY2023	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	18500000	usd
CY2022	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	13600000	usd
CY2023Q4	us-gaap	Deferred Tax Liabilities Undistributed Foreign Earnings DeferredTaxLiabilitiesUndistributedForeignEarnings	7700000	usd
CY2023Q1	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	9100000	usd
CY2022Q1	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	14200000	usd
CY2021Q1	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	15200000	usd
CY2023	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	1200000	usd
CY2023	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	0	usd
CY2022	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	0	usd
CY2023	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions	0	usd
CY2023	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions	3300000	usd
CY2022	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions	0	usd
CY2023	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	0	usd
CY2023	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	0	usd
CY2022	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	300000	usd
CY2023	us-gaap	Unrecognized Tax Benefits Reductions Resulting From Lapse Of Applicable Statute Of Limitations UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations	1400000	usd
CY2023	us-gaap	Unrecognized Tax Benefits Reductions Resulting From Lapse Of Applicable Statute Of Limitations UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations	1800000	usd
CY2022	us-gaap	Unrecognized Tax Benefits Reductions Resulting From Lapse Of Applicable Statute Of Limitations UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations	1300000	usd
CY2023Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	8900000	usd
CY2023Q1	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	9100000	usd
CY2022Q1	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	14200000	usd
CY2023Q4	ati	Unrecognized Tax Benefits Reductionof Operating Loss Carryforwards UnrecognizedTaxBenefitsReductionofOperatingLossCarryforwards	7200000	usd
CY2023Q1	ati	Unrecognized Tax Benefits Reductionof Operating Loss Carryforwards UnrecognizedTaxBenefitsReductionofOperatingLossCarryforwards	7800000	usd
CY2022Q1	ati	Unrecognized Tax Benefits Reductionof Operating Loss Carryforwards UnrecognizedTaxBenefitsReductionofOperatingLossCarryforwards	12300000	usd
CY2023Q4	us-gaap	Unrecognized Tax Benefits That Would Impact Effective Tax Rate UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate	1700000	usd
CY2023Q4	us-gaap	Significant Change In Unrecognized Tax Benefits Is Reasonably Possible Amount Of Unrecorded Benefit SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleAmountOfUnrecordedBenefit	500000	usd
CY2023Q4	us-gaap	Unrecognized Tax Benefits Income Tax Penalties And Interest Accrued UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued	1300000	usd
CY2023Q1	us-gaap	Unrecognized Tax Benefits Income Tax Penalties And Interest Accrued UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued	1400000	usd
CY2023	ati	Revenue From International Sales RevenueFromInternationalSales	1922900000	usd
CY2023	ati	Revenue From International Sales RevenueFromInternationalSales	1617400000	usd
CY2022	ati	Revenue From International Sales RevenueFromInternationalSales	1264900000	usd
CY2023	ati	Entity Wide Disclosure On Geographic Areas Revenue From External Foreign Customers Attributed To Entitys Country Of Domicile EntityWideDisclosureOnGeographicAreasRevenueFromExternalForeignCustomersAttributedToEntitysCountryOfDomicile	1498700000	usd
CY2023	ati	Entity Wide Disclosure On Geographic Areas Revenue From External Foreign Customers Attributed To Entitys Country Of Domicile EntityWideDisclosureOnGeographicAreasRevenueFromExternalForeignCustomersAttributedToEntitysCountryOfDomicile	1217900000	usd
CY2022	ati	Entity Wide Disclosure On Geographic Areas Revenue From External Foreign Customers Attributed To Entitys Country Of Domicile EntityWideDisclosureOnGeographicAreasRevenueFromExternalForeignCustomersAttributedToEntitysCountryOfDomicile	846300000	usd
CY2023	ati	Segment Earnings Before Income Taxes Depreciation Amortization Ebitda SegmentEarningsBeforeIncomeTaxesDepreciationAmortizationEBITDA	710200000	usd
CY2023	ati	Segment Earnings Before Income Taxes Depreciation Amortization Ebitda SegmentEarningsBeforeIncomeTaxesDepreciationAmortizationEBITDA	678700000	usd
CY2022	ati	Segment Earnings Before Income Taxes Depreciation Amortization Ebitda SegmentEarningsBeforeIncomeTaxesDepreciationAmortizationEBITDA	417100000	usd
CY2023	ati	Corporate Expenses CorporateExpenses	62300000	usd
CY2023	ati	Corporate Expenses CorporateExpenses	60300000	usd
CY2022	ati	Corporate Expenses CorporateExpenses	53700000	usd
CY2023	ati	Other Expense OtherExpense	13300000	usd
CY2023	ati	Other Expense OtherExpense	5600000	usd
CY2022	ati	Other Expense OtherExpense	-3100000	usd
CY2023	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	146100000	usd
CY2023	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	142900000	usd
CY2022	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	143900000	usd
CY2023	ati	Interest Expense Net InterestExpenseNet	92800000	usd
CY2023	ati	Interest Expense Net InterestExpenseNet	87400000	usd
CY2022	ati	Interest Expense Net InterestExpenseNet	96900000	usd
CY2023	ati	Restructuringandothercharges Restructuringandothercharges	31400000	usd
CY2023	ati	Restructuringandothercharges Restructuringandothercharges	23700000	usd
CY2022	ati	Restructuringandothercharges Restructuringandothercharges	-10500000	usd
CY2023	ati	Strike Related Costs StrikeRelatedCosts	0	usd
CY2023	ati	Strike Related Costs StrikeRelatedCosts	0	usd
CY2022	ati	Strike Related Costs StrikeRelatedCosts	63200000	usd
CY2023	ati	Defined Benefit Plan Net Periodic Benefit Cost Credit Settlement Gain Loss Statement Of Income Or Comprehensive Income Extensible List Not Disclosed Flag DefinedBenefitPlanNetPeriodicBenefitCostCreditSettlementGainLossStatementOfIncomeOrComprehensiveIncomeExtensibleListNotDisclosedFlag	Retirement benefit settlement gain (loss) (See Note 14)
CY2023	ati	Defined Benefit Plan Net Periodic Benefit Cost Credit Settlement Gain Loss Statement Of Income Or Comprehensive Income Extensible List Not Disclosed Flag DefinedBenefitPlanNetPeriodicBenefitCostCreditSettlementGainLossStatementOfIncomeOrComprehensiveIncomeExtensibleListNotDisclosedFlag	Retirement benefit settlement gain (loss) (See Note 14)
CY2022	ati	Defined Benefit Plan Net Periodic Benefit Cost Credit Settlement Gain Loss Statement Of Income Or Comprehensive Income Extensible List Not Disclosed Flag DefinedBenefitPlanNetPeriodicBenefitCostCreditSettlementGainLossStatementOfIncomeOrComprehensiveIncomeExtensibleListNotDisclosedFlag	Retirement benefit settlement gain (loss) (See Note 14)
CY2023	us-gaap	Defined Benefit Plan Recognized Net Gain Loss Due To Settlements1 DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1	-41700000	usd
CY2023	us-gaap	Defined Benefit Plan Recognized Net Gain Loss Due To Settlements1 DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1	0	usd
CY2022	us-gaap	Defined Benefit Plan Recognized Net Gain Loss Due To Settlements1 DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1	64900000	usd
CY2023	ati	Defined Benefit Plan Net Periodic Benefit Cost Credit Immediate Recognition Of Actuarial Gain Loss Statement Of Income Or Comprehensive Income Extensible List Not Disclosed Flag DefinedBenefitPlanNetPeriodicBenefitCostCreditImmediateRecognitionOfActuarialGainLossStatementOfIncomeOrComprehensiveIncomeExtensibleListNotDisclosedFlag	Pension remeasurement gain (loss) (See Note 14)
CY2023	ati	Defined Benefit Plan Net Periodic Benefit Cost Credit Immediate Recognition Of Actuarial Gain Loss Statement Of Income Or Comprehensive Income Extensible List Not Disclosed Flag DefinedBenefitPlanNetPeriodicBenefitCostCreditImmediateRecognitionOfActuarialGainLossStatementOfIncomeOrComprehensiveIncomeExtensibleListNotDisclosedFlag	Pension remeasurement gain (loss) (See Note 14)
CY2022	ati	Defined Benefit Plan Net Periodic Benefit Cost Credit Immediate Recognition Of Actuarial Gain Loss Statement Of Income Or Comprehensive Income Extensible List Not Disclosed Flag DefinedBenefitPlanNetPeriodicBenefitCostCreditImmediateRecognitionOfActuarialGainLossStatementOfIncomeOrComprehensiveIncomeExtensibleListNotDisclosedFlag	Pension remeasurement gain (loss) (See Note 14)
CY2023	us-gaap	Defined Benefit Plan Actuarial Gain Loss Immediate Recognition As Component In Net Periodic Benefit Cost Credit DefinedBenefitPlanActuarialGainLossImmediateRecognitionAsComponentInNetPeriodicBenefitCostCredit	-26800000	usd
CY2023	us-gaap	Defined Benefit Plan Actuarial Gain Loss Immediate Recognition As Component In Net Periodic Benefit Cost Credit DefinedBenefitPlanActuarialGainLossImmediateRecognitionAsComponentInNetPeriodicBenefitCostCredit	100300000	usd
CY2022	us-gaap	Defined Benefit Plan Actuarial Gain Loss Immediate Recognition As Component In Net Periodic Benefit Cost Credit DefinedBenefitPlanActuarialGainLossImmediateRecognitionAsComponentInNetPeriodicBenefitCostCredit	147200000	usd
CY2023	ati	Equity Method Investments Restructuring Credit Charges EquityMethodInvestmentsRestructuringCreditCharges	0	usd
CY2023	ati	Equity Method Investments Restructuring Credit Charges EquityMethodInvestmentsRestructuringCreditCharges	900000	usd
CY2022	ati	Equity Method Investments Restructuring Credit Charges EquityMethodInvestmentsRestructuringCreditCharges	0	usd
CY2023	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	0	usd
CY2023	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	0	usd
CY2022	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	-65500000	usd
CY2023	us-gaap	Gain Loss On Sales Of Assets And Asset Impairment Charges GainLossOnSalesOfAssetsAndAssetImpairmentCharges	-600000	usd
CY2023	us-gaap	Gain Loss On Sales Of Assets And Asset Impairment Charges GainLossOnSalesOfAssetsAndAssetImpairmentCharges	-105400000	usd
CY2022	us-gaap	Gain Loss On Sales Of Assets And Asset Impairment Charges GainLossOnSalesOfAssetsAndAssetImpairmentCharges	13800000	usd
CY2023	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	295200000	usd
CY2023	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	354600000	usd
CY2022	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	233400000	usd
CY2023	ati	Income From Government Assistance Cares Act IncomeFromGovernmentAssistanceCARESAct	34000000	usd
CY2022	ati	Strike Related Costs StrikeRelatedCosts	63200000	usd
CY2023	us-gaap	Gain Loss On Sales Of Assets And Asset Impairment Charges GainLossOnSalesOfAssetsAndAssetImpairmentCharges	-600000	usd
CY2023	ati	Transaction Costs From Sales Of Businesses Net Of Proceeds TransactionCostsFromSalesOfBusinessesNetOfProceeds	-300000	usd
CY2022	us-gaap	Gain Loss On Sales Of Assets And Asset Impairment Charges GainLossOnSalesOfAssetsAndAssetImpairmentCharges	13800000	usd
CY2023Q4	us-gaap	Assets Assets	4985100000	usd
CY2023Q1	us-gaap	Assets Assets	4445600000	usd
CY2022Q1	us-gaap	Assets Assets	4285200000	usd
CY2023Q4	us-gaap	Assets Assets	4985100000	usd
CY2023Q4	ati	Entity Wide Disclosure On Geographic Areas Total Assets Attributed To Individual Countries Percentage Amount EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount	1
CY2023Q1	us-gaap	Assets Assets	4445600000	usd
CY2023Q1	ati	Entity Wide Disclosure On Geographic Areas Total Assets Attributed To Individual Countries Percentage Amount EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount	1
CY2022Q1	us-gaap	Assets Assets	4285200000	usd
CY2022Q1	ati	Entity Wide Disclosure On Geographic Areas Total Assets Attributed To Individual Countries Percentage Amount EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount	1
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CY2023	ati	Restructuring Settlement And Impairment Provisions Excluding Goodwill Impairment Loss RestructuringSettlementAndImpairmentProvisionsExcludingGoodwillImpairmentLoss	7700000	usd
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CY2023	us-gaap	Restructuring And Related Cost Expected Number Of Positions Eliminated RestructuringAndRelatedCostExpectedNumberOfPositionsEliminated	110	employee
CY2023	ati	Restructuringandothercharges Restructuringandothercharges	23700000	usd
CY2023	ati	Other Nonoperating Income Expense Litigation Reserve OtherNonoperatingIncomeExpenseLitigationReserve	-28500000	usd
CY2023	ati	Restructuring Settlement And Impairment Provisions Excluding Goodwill Impairment Loss RestructuringSettlementAndImpairmentProvisionsExcludingGoodwillImpairmentLoss	-4800000	usd
CY2022	ati	Restructuringandothercharges Restructuringandothercharges	-10500000	usd
CY2022	ati	Restructuring Settlement And Impairment Provisions Excluding Goodwill Impairment Loss RestructuringSettlementAndImpairmentProvisionsExcludingGoodwillImpairmentLoss	-11300000	usd
CY2022	us-gaap	Inventory Write Down InventoryWriteDown	800000	usd
CY2023	us-gaap	Income Loss From Continuing Operations IncomeLossFromContinuingOperations	410800000	usd
CY2023	us-gaap	Income Loss From Continuing Operations IncomeLossFromContinuingOperations	323500000	usd
CY2022	us-gaap	Income Loss From Continuing Operations IncomeLossFromContinuingOperations	184600000	usd
CY2023	us-gaap	Net Income Loss Available To Common Stockholders Diluted NetIncomeLossAvailableToCommonStockholdersDiluted	421400000	usd
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CY2022	us-gaap	Net Income Loss Available To Common Stockholders Diluted NetIncomeLossAvailableToCommonStockholdersDiluted	200800000	usd
CY2023	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	128100000	shares
CY2023	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	127500000	shares
CY2022	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	127100000	shares
CY2023	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	3100000	shares
CY2023	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	2100000	shares
CY2022	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	1000000.0	shares
CY2023	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	150000000.0	shares
CY2023	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	151200000	shares
CY2022	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	152700000	shares
CY2023	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	3.21
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CY2022	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	1.32
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CY2022	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	0	shares
CY2023	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	0	shares
CY2022Q1	us-gaap	Stock Repurchase Program Authorized Amount1 StockRepurchaseProgramAuthorizedAmount1	150000000	usd
CY2023Q2	us-gaap	Stock Repurchase Program Authorized Amount1 StockRepurchaseProgramAuthorizedAmount1	75000000	usd
CY2023	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	85200000	usd
CY2023	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired	2000000	shares
CY2023	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	139900000	usd
CY2023	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired	5200000	shares
CY2022Q1	us-gaap	Stock Repurchase Program Authorized Amount1 StockRepurchaseProgramAuthorizedAmount1	150000000	usd
CY2023Q4	us-gaap	Stock Repurchase Program Authorized Amount1 StockRepurchaseProgramAuthorizedAmount1	150000000	usd
CY2023Q4	us-gaap	Unrecorded Unconditional Purchase Obligation Balance Sheet Amount UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount	86100000	usd
CY2023Q4	us-gaap	Accrual For Environmental Loss Contingencies AccrualForEnvironmentalLossContingencies	13000000	usd
CY2023Q4	us-gaap	Accrued Environmental Loss Contingencies Current AccruedEnvironmentalLossContingenciesCurrent	7000000	usd
CY2023	ati	Environmental Loss Contingency Statement Of Financial Position Extensible Enumeration Not Disclosed Flag EnvironmentalLossContingencyStatementOfFinancialPositionExtensibleEnumerationNotDisclosedFlag	other
CY2023Q4	ati	Environmental Remediation Obligation Federal Superfund Sites EnvironmentalRemediationObligationFederalSuperfundSites	3000000	usd
CY2023Q4	ati	Environmental Remediation Obligation For Formerly Owned Sites EnvironmentalRemediationObligationForFormerlyOwnedSites	7000000	usd
CY2023Q4	ati	Environmental Remediation Obligation For Owned Or Controlled Sites With Closed Operations EnvironmentalRemediationObligationForOwnedOrControlledSitesWithClosedOperations	2000000	usd
CY2023Q4	ati	Environmental Remediation Obligation For Owned Or Controlled Sites With Ongoing Operations EnvironmentalRemediationObligationForOwnedOrControlledSitesWithOngoingOperations	1000000	usd
CY2023Q4	us-gaap	Loss Contingency Range Of Possible Loss Portion Not Accrued LossContingencyRangeOfPossibleLossPortionNotAccrued	17000000	usd
CY2023	ati	Other Nonoperating Income Expense Litigation Reserve OtherNonoperatingIncomeExpenseLitigationReserve	-28500000	usd
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CY2023Q4	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	1064000000	usd
CY2023Q2	us-gaap	Operating Income Loss OperatingIncomeLoss	112600000	usd
CY2023Q3	us-gaap	Operating Income Loss OperatingIncomeLoss	120300000	usd
CY2023Q4	us-gaap	Operating Income Loss OperatingIncomeLoss	125200000	usd
CY2023Q4	us-gaap	Operating Income Loss OperatingIncomeLoss	108300000	usd
CY2023Q2	us-gaap	Profit Loss ProfitLoss	86600000	usd
CY2023Q3	us-gaap	Profit Loss ProfitLoss	93500000	usd
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CY2023Q4	us-gaap	Profit Loss ProfitLoss	149200000	usd
CY2023Q2	us-gaap	Net Income Loss NetIncomeLoss	84500000	usd
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CY2023Q4	us-gaap	Net Income Loss NetIncomeLoss	90200000	usd
CY2023Q4	us-gaap	Net Income Loss NetIncomeLoss	145700000	usd
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CY2023Q1	us-gaap	Profit Loss ProfitLoss	197300000	usd
CY2022Q2	us-gaap	Net Income Loss NetIncomeLoss	46900000	usd
CY2022Q3	us-gaap	Net Income Loss NetIncomeLoss	6700000	usd
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CY2022Q3	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.05
CY2022Q4	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.59
CY2023Q2	ati	Restructuring And Other Credits Charges Net Of Tax RestructuringAndOtherCreditsChargesNetOfTax	1100000	usd
CY2023Q3	ati	Restructuring And Other Charges Credits RestructuringAndOtherChargesCredits	10600000	usd
CY2023Q3	ati	Restructuring And Other Credits Charges Net Of Tax RestructuringAndOtherCreditsChargesNetOfTax	10200000	usd
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CY2022Q3	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.05
CY2022Q4	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.53
CY2023Q1	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	1.30
CY2023Q2	ati	Restructuring And Other Charges Credits RestructuringAndOtherChargesCredits	1200000	usd
CY2023Q4	ati	Restructuring And Other Charges Credits RestructuringAndOtherChargesCredits	4200000	usd
CY2023Q4	ati	Restructuring And Other Credits Charges Net Of Tax RestructuringAndOtherCreditsChargesNetOfTax	4000000	usd
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CY2022Q2	ati	Restructuring And Other Credits Charges Net Of Tax RestructuringAndOtherCreditsChargesNetOfTax	25800000	usd
CY2023Q4	ati	Restructuring And Other Credits Charges Net Of Tax RestructuringAndOtherCreditsChargesNetOfTax	84700000	usd
CY2023Q4	ati	Valuation Allowance Benefit Related Toat Is Ability To Utilize Projections For Future Income ValuationAllowanceBenefitRelatedTOATIsAbilityToUtilizeProjectionsForFutureIncome	-140300000	usd
CY2022Q2	ati	Restructuring And Other Charges Credits RestructuringAndOtherChargesCredits	25800000	usd
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CY2022Q2	us-gaap	Restructuring Charges RestructuringCharges	-1100000	usd
CY2022Q3	ati	Restructuring And Other Charges Credits RestructuringAndOtherChargesCredits	85800000	usd
CY2022Q3	ati	Restructuring And Other Credits Charges Net Of Tax RestructuringAndOtherCreditsChargesNetOfTax	85900000	usd
CY2022Q3	us-gaap	Restructuring Charges RestructuringCharges	-1300000	usd
CY2022Q4	ati	Restructuring And Other Charges Credits RestructuringAndOtherChargesCredits	17300000	usd
CY2022Q4	ati	Restructuring And Other Credits Charges Net Of Tax RestructuringAndOtherCreditsChargesNetOfTax	16300000	usd
CY2022Q4	ati	Other Nonoperating Income Expense Litigation Reserve OtherNonoperatingIncomeExpenseLitigationReserve	-19900000	usd
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CY2023Q2	us-gaap	Profit Loss ProfitLoss	86600000	usd
CY2023Q2	us-gaap	Net Income Loss NetIncomeLoss	84500000	usd
CY2023Q2	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.66
CY2023Q2	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.58
CY2023Q3	us-gaap	Profit Loss ProfitLoss	93500000	usd
CY2023Q3	us-gaap	Net Income Loss NetIncomeLoss	90400000	usd
CY2023Q3	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.70
CY2023Q3	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.62
CY2023Q4	us-gaap	Profit Loss ProfitLoss	94100000	usd
CY2023Q4	us-gaap	Net Income Loss NetIncomeLoss	90200000	usd
CY2023Q4	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.70
CY2023Q4	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.62
CY2023Q4	us-gaap	Profit Loss ProfitLoss	149200000	usd
CY2023Q4	us-gaap	Net Income Loss NetIncomeLoss	145700000	usd
CY2023Q4	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	1.15
CY2023Q4	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.99
CY2022Q2	us-gaap	Profit Loss ProfitLoss	51200000	usd
CY2022Q2	us-gaap	Net Income Loss NetIncomeLoss	46900000	usd
CY2022Q2	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.37
CY2022Q2	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.33
CY2022Q3	us-gaap	Operating Income Loss OperatingIncomeLoss	17200000	usd
CY2022Q3	us-gaap	Profit Loss ProfitLoss	10400000	usd
CY2022Q3	us-gaap	Net Income Loss NetIncomeLoss	6700000	usd
CY2022Q3	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.05
CY2022Q3	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.05
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CY2022Q4	us-gaap	Net Income Loss NetIncomeLoss	76900000	usd
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CY2022Q4	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.53
CY2023Q1	us-gaap	Profit Loss ProfitLoss	197300000	usd
CY2023Q1	us-gaap	Net Income Loss NetIncomeLoss	193000000.0	usd
CY2023Q1	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	1.49
CY2023Q1	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	1.30
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CY2023Q4	ecd	Non Rule10b51 Arr Trmntd Flag NonRule10b51ArrTrmntdFlag	false
CY2023	dei	Auditor Firm AuditorFirmId	42

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$ATI
ATI INC Stock $ati

2024 Q1 Form 10-K Financial Statement

#000162828024006606 Filed on February 23, 2024

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$ATI ATI INC Stock $ati

2024 Q1 Form 10-K Financial Statement

#000162828024006606 Filed on February 23, 2024

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$ATI
ATI INC Stock $ati