$ATI
ATI INC Stock $ati

$ati Overview Financials Valuation SEC Filings Company Website

2019 Q4 Form 8-K Financial Statement

#000162828020008258 Filed on May 22, 2020

Income Statement

Concept	2019 Q4	2019	2018 Q4
Revenue	$1.019B	$4.123B	$1.038B
YoY Change	-1.86%	1.88%	14.07%
Cost Of Revenue	$849.3M	$3.485B	$890.3M
YoY Change	-4.61%	2.0%	16.03%
Gross Profit	$169.3M	$638.0M	$147.6M
YoY Change	14.7%	1.22%	3.51%
Gross Profit Margin	16.62%	15.48%	14.22%
Selling, General & Admin	$66.30M	$267.2M	$72.90M
YoY Change	-9.05%	-0.37%	20.5%
% of Gross Profit	39.16%	41.88%	49.39%
Research & Development		$17.80M
YoY Change		-21.59%
% of Gross Profit		2.79%
Depreciation & Amortization	$36.50M	$151.1M	$39.30M
YoY Change	-7.12%	-3.39%	-2.0%
% of Gross Profit	21.56%	23.68%	26.63%
Operating Expenses	$66.30M	$285.0M	$72.90M
YoY Change	-9.05%	-2.03%	20.5%
Operating Profit	$103.0M	$366.3M	$74.70M
YoY Change	37.88%	1.16%	-9.01%
Interest Expense	-$26.10M	-$109.7M	-$25.20M
YoY Change	3.57%	7.55%	-20.25%
% of Operating Profit	-25.34%	-29.95%	-33.73%
Other Income/Expense, Net	-$18.30M	$64.40M	-$10.30M
YoY Change	77.67%	214.15%	-21.37%
Pretax Income	$21.20M	$236.5M	$39.20M
YoY Change	-45.92%	-4.52%	9700.0%
Income Tax	-$38.80M	-$28.50M	-$11.70M
% Of Pretax Income	-183.02%	-12.05%	-29.85%
Net Earnings	$56.50M	$252.5M	$41.10M
YoY Change	37.47%	13.53%	2317.65%
Net Earnings / Revenue	5.55%	6.12%	3.96%
Basic Earnings Per Share	$0.45	$2.01	$0.33
Diluted Earnings Per Share	$0.41	$1.81	$0.30
COMMON SHARES
Basic Shares Outstanding	126.1M shares	125.8M shares	125.7M shares
Diluted Shares Outstanding		146.5M shares

Balance Sheet

Concept	2019 Q4	2019	2018 Q4
SHORT-TERM ASSETS
Cash & Short-Term Investments	$490.8M	$490.8M	$382.0M
YoY Change	28.48%	28.48%	169.77%
Cash & Equivalents	$490.8M		$382.0M
Short-Term Investments		$300.0M
Other Short-Term Assets	$64.30M	$64.30M	$74.60M
YoY Change	-13.81%	-13.81%	41.56%
Inventory	$1.155B	$1.155B	$1.211B
Prepaid Expenses
Receivables	$554.1M	$592.6M	$527.8M
Other Receivables	$0.00	$0.00	$0.00
Total Short-Term Assets	$2.303B	$2.303B	$2.247B
YoY Change	2.51%	2.51%	17.28%
LONG-TERM ASSETS
Property, Plant & Equipment	$2.450B	$2.502B	$2.475B
YoY Change	-1.01%	1.08%	-0.83%
Goodwill	$525.8M		$534.7M
YoY Change	-1.66%		0.62%
Intangibles
YoY Change
Long-Term Investments	$0.00		$0.00
YoY Change
Other Assets	$355.7M	$207.7M	$245.4M
YoY Change	44.95%	79.52%	1.15%
Total Long-Term Assets	$3.332B	$3.332B	$3.255B
YoY Change	2.35%	2.35%	-0.45%
TOTAL ASSETS
Total Short-Term Assets	$2.303B	$2.303B	$2.247B
Total Long-Term Assets	$3.332B	$3.332B	$3.255B
Total Assets	$5.635B	$5.635B	$5.502B
YoY Change	2.41%	2.41%	6.1%
SHORT-TERM LIABILITIES
YoY Change
Accounts Payable	$521.2M	$521.2M	$498.8M
YoY Change	4.49%	4.49%	18.73%
Accrued Expenses	$237.8M	$132.0M	$260.1M
YoY Change	-8.57%	23.25%	-7.9%
Deferred Revenue	$78.70M		$71.40M
YoY Change	10.22%		2.44%
Short-Term Debt	$0.00	$0.00	$0.00
YoY Change
Long-Term Debt Due	$11.50M	$11.50M	$6.600M
YoY Change	74.24%	74.24%	-34.65%
Total Short-Term Liabilities	$849.2M	$849.2M	$836.9M
YoY Change	1.47%	1.47%	17.44%
LONG-TERM LIABILITIES
Long-Term Debt	$1.387B	$1.387B	$1.536B
YoY Change	-9.65%	-9.65%	0.32%
Other Long-Term Liabilities	$160.8M	$1.205B	$89.40M
YoY Change	79.87%	7.1%	22.13%
Total Long-Term Liabilities	$160.8M	$2.592B	$89.40M
YoY Change	79.87%	-2.56%	22.13%
TOTAL LIABILITIES
Total Short-Term Liabilities	$849.2M	$849.2M	$836.9M
Total Long-Term Liabilities	$160.8M	$2.592B	$89.40M
Total Liabilities	$3.441B	$3.545B	$3.510B
YoY Change	-1.96%	-1.98%	5.07%
SHAREHOLDERS EQUITY
Retained Earnings	$1.679B		$1.427B
YoY Change	17.67%		20.5%
Common Stock	$1.631B		$1.628B
YoY Change	0.16%		1.19%
Preferred Stock
YoY Change
Treasury Stock (at cost)	$18.20M		$30.60M
YoY Change	-40.52%		17.24%
Treasury Stock Shares	609.8K shares		1.011M shares
Shareholders Equity	$2.090B	$2.090B	$1.886B
YoY Change
Total Liabilities & Shareholders Equity	$5.635B	$5.635B	$5.502B
YoY Change	2.41%	2.41%	6.1%

Cashflow Statement

Concept	2019 Q4	2019	2018 Q4
OPERATING ACTIVITIES
Net Income	$56.50M	$252.5M	$41.10M
YoY Change	37.47%	13.53%	2317.65%
Depreciation, Depletion And Amortization	$36.50M	$151.1M	$39.30M
YoY Change	-7.12%	-3.39%	-2.0%
Cash From Operating Activities	$240.1M	$230.1M	$276.2M
YoY Change	-13.07%	-41.42%	262.47%
INVESTING ACTIVITIES
Capital Expenditures	-$70.10M	-$168.4M	-$37.90M
YoY Change	84.96%	20.98%	1.34%
Acquisitions		$0.00
YoY Change		-100.0%
Other Investing Activities	$2.400M	$200.0K	$1.900M
YoY Change	26.32%	-115.38%	-2000.0%
Cash From Investing Activities	-$67.70M	$81.70M	-$36.00M
YoY Change	88.06%	-156.31%	-4.0%
FINANCING ACTIVITIES
Cash Dividend Paid
YoY Change
Common Stock Issuance & Retirement, Net		$0.00
YoY Change
Debt Paid & Issued, Net
YoY Change
Cash From Financing Activities	-192.9M	-$203.0M	-11.70M
YoY Change	1548.72%	2680.82%	-46.82%
NET CHANGE
Cash From Operating Activities	240.1M	$230.1M	276.2M
Cash From Investing Activities	-67.70M	$81.70M	-36.00M
Cash From Financing Activities	-192.9M	-$203.0M	-11.70M
Net Change In Cash	-20.50M	$108.8M	228.5M
YoY Change	-108.97%	-54.74%	1268.26%
FREE CASH FLOW
Cash From Operating Activities	$240.1M	$230.1M	$276.2M
Capital Expenditures	-$70.10M	-$168.4M	-$37.90M
Free Cash Flow	$310.2M	$398.5M	$314.1M
YoY Change	-1.24%	-25.09%	176.5%

Facts In Submission

Frame	Concept Type	Concept / XBRL Key	Value	Unit
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CY2020Q2	dei	Document Fiscal Period Focus DocumentFiscalPeriodFocus	FY
CY2020Q2	dei	Document Fiscal Year Focus DocumentFiscalYearFocus	2019
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CY2019Q4	us-gaap	Common Stock Shares Authorized CommonStockSharesAuthorized	500000000	shares
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CY2019Q4	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	126695171	shares
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CY2019Q4	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	126085348	shares
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CY2019Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Three FiniteLivedIntangibleAssetsAmortizationExpenseYearThree	8000000	USD
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CY2020Q2	dei	Document Type DocumentType	8-K
CY2019Q4	us-gaap	Preferred Stock Shares Authorized PreferredStockSharesAuthorized	50000000	shares
CY2018Q4	us-gaap	Preferred Stock Shares Issued PreferredStockSharesIssued	0	shares
CY2018Q4	us-gaap	Progress Payments Netted Against Inventory For Long Term Contracts Or Programs ProgressPaymentsNettedAgainstInventoryForLongTermContractsOrPrograms	0	USD
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CY2020Q2	dei	Document Period End Date DocumentPeriodEndDate	2020-05-22
CY2020Q2	dei	Entity Registrant Name EntityRegistrantName	Allegheny Technologies Incorporated
CY2020Q2	dei	Entity Incorporation State Country Code EntityIncorporationStateCountryCode	DE
CY2020Q2	dei	Entity File Number EntityFileNumber	1-12001
CY2020Q2	dei	Entity Tax Identification Number EntityTaxIdentificationNumber	25-1792394
CY2020Q2	dei	Entity Address Address Line1 EntityAddressAddressLine1	1000 Six PPG Place,
CY2020Q2	dei	Entity Address City Or Town EntityAddressCityOrTown	Pittsburgh,
CY2020Q2	dei	Entity Address State Or Province EntityAddressStateOrProvince	PA
CY2020Q2	dei	Entity Address Postal Zip Code EntityAddressPostalZipCode	15222-5479
CY2020Q2	dei	City Area Code CityAreaCode	412
CY2020Q2	dei	Local Phone Number LocalPhoneNumber	394-2800
CY2020Q2	dei	Written Communications WrittenCommunications	false
CY2020Q2	dei	Soliciting Material SolicitingMaterial	false
CY2020Q2	dei	Pre Commencement Tender Offer PreCommencementTenderOffer	false
CY2020Q2	dei	Pre Commencement Issuer Tender Offer PreCommencementIssuerTenderOffer	false
CY2020Q2	dei	Security12b Title Security12bTitle	Common Stock, par value $0.10 per share
CY2020Q2	dei	Trading Symbol TradingSymbol	ATI
CY2020Q2	dei	Security Exchange Name SecurityExchangeName	NYSE
CY2020Q2	dei	Entity Emerging Growth Company EntityEmergingGrowthCompany	false
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CY2019	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	200900000	USD
CY2018	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	124500000	USD
CY2017	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	-6200000	USD
CY2019	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	11200000	USD
CY2018	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	8100000	USD
CY2017	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	19800000	USD
CY2019	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	189700000	USD
CY2018	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	116400000	USD
CY2017	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	-26000000.0	USD
CY2019Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	490800000	USD
CY2018Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	382000000.0	USD
CY2019Q4	us-gaap	Accounts Receivable Net Current AccountsReceivableNetCurrent	554100000	USD
CY2018Q4	us-gaap	Accounts Receivable Net Current AccountsReceivableNetCurrent	527800000	USD
CY2019Q4	us-gaap	Contract With Customer Asset Net Current ContractWithCustomerAssetNetCurrent	38500000	USD
CY2018Q4	us-gaap	Contract With Customer Asset Net Current ContractWithCustomerAssetNetCurrent	51200000	USD
CY2018Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	2475000000.0	USD
CY2018Q4	us-gaap	Assets Current AssetsCurrent	2246700000	USD
CY2019Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	2450100000	USD
CY2018Q4	us-gaap	Accounts Payable Current AccountsPayableCurrent	498800000	USD
CY2019Q4	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	78700000	USD
CY2019Q4	us-gaap	Inventory Net InventoryNet	1155300000	USD
CY2018Q4	us-gaap	Inventory Net InventoryNet	1211100000	USD
CY2019Q4	us-gaap	Other Assets Current OtherAssetsCurrent	64300000	USD
CY2018Q4	us-gaap	Other Assets Current OtherAssetsCurrent	74600000	USD
CY2019Q4	us-gaap	Assets Current AssetsCurrent	2303000000.0	USD
CY2019Q4	us-gaap	Goodwill Goodwill	525800000	USD
CY2018Q4	us-gaap	Goodwill Goodwill	534700000	USD
CY2019Q4	us-gaap	Other Assets Noncurrent OtherAssetsNoncurrent	355700000	USD
CY2018Q4	us-gaap	Other Assets Noncurrent OtherAssetsNoncurrent	245400000	USD
CY2019Q4	us-gaap	Assets Assets	5634600000	USD
CY2018Q4	us-gaap	Assets Assets	5501800000	USD
CY2019Q4	us-gaap	Accounts Payable Current AccountsPayableCurrent	521200000	USD
CY2018Q4	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	71400000	USD
CY2019Q4	us-gaap	Debt Current DebtCurrent	11500000	USD
CY2018Q4	us-gaap	Debt Current DebtCurrent	6600000	USD
CY2019Q4	us-gaap	Accrued Liabilities Current AccruedLiabilitiesCurrent	237800000	USD
CY2018Q4	us-gaap	Accrued Liabilities Current AccruedLiabilitiesCurrent	260100000	USD
CY2019Q4	us-gaap	Liabilities Current LiabilitiesCurrent	849200000	USD
CY2018Q4	us-gaap	Liabilities Current LiabilitiesCurrent	836900000	USD
CY2019Q4	us-gaap	Long Term Debt And Capital Lease Obligations LongTermDebtAndCapitalLeaseObligations	1387400000	USD
CY2018Q4	us-gaap	Long Term Debt And Capital Lease Obligations LongTermDebtAndCapitalLeaseObligations	1535500000	USD
CY2019Q4	us-gaap	Other Postretirement Defined Benefit Plan Liabilities Noncurrent OtherPostretirementDefinedBenefitPlanLiabilitiesNoncurrent	312500000	USD
CY2018Q4	us-gaap	Other Postretirement Defined Benefit Plan Liabilities Noncurrent OtherPostretirementDefinedBenefitPlanLiabilitiesNoncurrent	318400000	USD
CY2019Q4	us-gaap	Defined Benefit Pension Plan Liabilities Noncurrent DefinedBenefitPensionPlanLiabilitiesNoncurrent	731500000	USD
CY2018Q4	us-gaap	Defined Benefit Pension Plan Liabilities Noncurrent DefinedBenefitPensionPlanLiabilitiesNoncurrent	730000000.0	USD
CY2019Q4	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	160800000	USD
CY2018Q4	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	89400000	USD
CY2019Q4	us-gaap	Liabilities Liabilities	3441400000	USD
CY2018Q4	us-gaap	Liabilities Liabilities	3510200000	USD
CY2019Q4	us-gaap	Preferred Stock Value PreferredStockValue	0	USD
CY2018Q4	us-gaap	Preferred Stock Value PreferredStockValue	0	USD
CY2019Q4	us-gaap	Common Stock Value CommonStockValue	12700000	USD
CY2018Q4	us-gaap	Common Stock Value CommonStockValue	12700000	USD
CY2019Q4	us-gaap	Additional Paid In Capital Common Stock AdditionalPaidInCapitalCommonStock	1618000000.0	USD
CY2018Q4	us-gaap	Additional Paid In Capital Common Stock AdditionalPaidInCapitalCommonStock	1615400000	USD
CY2017	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	160800000	USD
CY2019Q4	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	1679300000	USD
CY2018Q4	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	1422000000.0	USD
CY2019Q4	us-gaap	Treasury Stock Value TreasuryStockValue	18200000	USD
CY2018Q4	us-gaap	Treasury Stock Value TreasuryStockValue	30600000	USD
CY2019Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-1201700000	USD
CY2018Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-1133800000	USD
CY2019Q4	us-gaap	Stockholders Equity StockholdersEquity	2090100000	USD
CY2018Q4	us-gaap	Stockholders Equity StockholdersEquity	1885700000	USD
CY2019Q4	us-gaap	Minority Interest MinorityInterest	103100000	USD
CY2018Q4	us-gaap	Minority Interest MinorityInterest	105900000	USD
CY2019Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	2193200000	USD
CY2018Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	1991600000	USD
CY2019Q4	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	5634600000	USD
CY2018Q4	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	5501800000	USD
CY2019	us-gaap	Profit Loss ProfitLoss	270100000	USD
CY2018	us-gaap	Profit Loss ProfitLoss	236700000	USD
CY2017	us-gaap	Profit Loss ProfitLoss	-79700000	USD
CY2019	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	151100000	USD
CY2018	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	156400000	USD
CY2019	us-gaap	Deferred Income Taxes And Tax Credits DeferredIncomeTaxesAndTaxCredits	-40900000	USD
CY2018	us-gaap	Deferred Income Taxes And Tax Credits DeferredIncomeTaxesAndTaxCredits	2100000	USD
CY2017	us-gaap	Deferred Income Taxes And Tax Credits DeferredIncomeTaxesAndTaxCredits	-1400000	USD
CY2019	us-gaap	Deconsolidation Gain Or Loss Amount DeconsolidationGainOrLossAmount	0	USD
CY2018	us-gaap	Deconsolidation Gain Or Loss Amount DeconsolidationGainOrLossAmount	15900000	USD
CY2017	us-gaap	Deconsolidation Gain Or Loss Amount DeconsolidationGainOrLossAmount	0	USD
CY2019	us-gaap	Goodwill Impairment Loss GoodwillImpairmentLoss	0	USD
CY2018	us-gaap	Goodwill Impairment Loss GoodwillImpairmentLoss	0	USD
CY2017	us-gaap	Goodwill Impairment Loss GoodwillImpairmentLoss	114400000	USD
CY2019	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	-21600000	USD
CY2018	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	0	USD
CY2017	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	-37000000.0	USD
CY2019	us-gaap	Gain Loss On Sale Of Property Plant Equipment GainLossOnSaleOfPropertyPlantEquipment	90600000	USD
CY2018	us-gaap	Gain Loss On Sale Of Property Plant Equipment GainLossOnSaleOfPropertyPlantEquipment	1200000	USD
CY2017	us-gaap	Gain Loss On Sale Of Property Plant Equipment GainLossOnSaleOfPropertyPlantEquipment	500000	USD
CY2019	us-gaap	Disposal Group Not Discontinued Operation Gain Loss On Disposal DisposalGroupNotDiscontinuedOperationGainLossOnDisposal	-1800000	USD
CY2018	us-gaap	Disposal Group Not Discontinued Operation Gain Loss On Disposal DisposalGroupNotDiscontinuedOperationGainLossOnDisposal	0	USD
CY2017	us-gaap	Disposal Group Not Discontinued Operation Gain Loss On Disposal DisposalGroupNotDiscontinuedOperationGainLossOnDisposal	0	USD
CY2019	ati	Other Asset Impairment Charges And Due From Affiliates Allowance For Credit Loss OtherAssetImpairmentChargesAndDueFromAffiliatesAllowanceForCreditLoss	11400000	USD
CY2018	ati	Other Asset Impairment Charges And Due From Affiliates Allowance For Credit Loss OtherAssetImpairmentChargesAndDueFromAffiliatesAllowanceForCreditLoss	0	USD
CY2017	ati	Other Asset Impairment Charges And Due From Affiliates Allowance For Credit Loss OtherAssetImpairmentChargesAndDueFromAffiliatesAllowanceForCreditLoss	0	USD
CY2019	us-gaap	Increase Decrease In Pension And Postretirement Obligations IncreaseDecreaseInPensionAndPostretirementObligations	-103300000	USD
CY2019	us-gaap	Increase Decrease In Accrued Income Taxes Payable IncreaseDecreaseInAccruedIncomeTaxesPayable	4900000	USD
CY2018	us-gaap	Increase Decrease In Accrued Income Taxes Payable IncreaseDecreaseInAccruedIncomeTaxesPayable	1400000	USD
CY2019	us-gaap	Increase Decrease In Inventories IncreaseDecreaseInInventories	-25400000	USD
CY2018	us-gaap	Increase Decrease In Inventories IncreaseDecreaseInInventories	108500000	USD
CY2017	us-gaap	Increase Decrease In Accrued Income Taxes Payable IncreaseDecreaseInAccruedIncomeTaxesPayable	-1900000	USD
CY2019	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	-600000	USD
CY2018	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	15300000	USD
CY2018	us-gaap	Increase Decrease In Pension And Postretirement Obligations IncreaseDecreaseInPensionAndPostretirementObligations	-32600000	USD
CY2017	us-gaap	Increase Decrease In Pension And Postretirement Obligations IncreaseDecreaseInPensionAndPostretirementObligations	-110300000	USD
CY2019	us-gaap	Increase Decrease In Accounts Receivable IncreaseDecreaseInAccountsReceivable	52100000	USD
CY2018	us-gaap	Increase Decrease In Accounts Receivable IncreaseDecreaseInAccountsReceivable	-16000000.0	USD
CY2017	us-gaap	Increase Decrease In Accounts Receivable IncreaseDecreaseInAccountsReceivable	93200000	USD
CY2017	us-gaap	Increase Decrease In Inventories IncreaseDecreaseInInventories	139200000	USD
CY2019	us-gaap	Increase Decrease In Accounts Payable Trade IncreaseDecreaseInAccountsPayableTrade	30100000	USD
CY2018	us-gaap	Increase Decrease In Accounts Payable Trade IncreaseDecreaseInAccountsPayableTrade	153700000	USD
CY2017	us-gaap	Increase Decrease In Accounts Payable Trade IncreaseDecreaseInAccountsPayableTrade	125800000	USD
CY2017	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	-10600000	USD
CY2019	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	230100000	USD
CY2018	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	392800000	USD
CY2017	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	22400000	USD
CY2019	us-gaap	Payments To Acquire Productive Assets PaymentsToAcquireProductiveAssets	168200000	USD
CY2018	us-gaap	Payments To Acquire Productive Assets PaymentsToAcquireProductiveAssets	139200000	USD
CY2017	us-gaap	Payments To Acquire Productive Assets PaymentsToAcquireProductiveAssets	122700000	USD
CY2019	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	92000000.0	USD
CY2018	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	2800000	USD
CY2017	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	2700000	USD
CY2019	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	0	USD
CY2018	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	10000000.0	USD
CY2017	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	0	USD
CY2019	us-gaap	Payments For Proceeds From Businesses And Interest In Affiliates PaymentsForProceedsFromBusinessesAndInterestInAffiliates	-158100000	USD
CY2018	us-gaap	Payments For Proceeds From Businesses And Interest In Affiliates PaymentsForProceedsFromBusinessesAndInterestInAffiliates	0	USD
CY2017	us-gaap	Payments For Proceeds From Businesses And Interest In Affiliates PaymentsForProceedsFromBusinessesAndInterestInAffiliates	0	USD
CY2019	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	200000	USD
CY2018	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	-1300000	USD
CY2017	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	-400000	USD
CY2019	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	81700000	USD
CY2018	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-145100000	USD
CY2017	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-119600000	USD
CY2019	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	350000000.0	USD
CY2018	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	7100000	USD
CY2017	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	8500000	USD
CY2019	us-gaap	Repayments Of Long Term Debt And Capital Securities RepaymentsOfLongTermDebtAndCapitalSecurities	507600000	USD
CY2018	us-gaap	Payments Of Dividends Minority Interest PaymentsOfDividendsMinorityInterest	10000000.0	USD
CY2018	us-gaap	Repayments Of Long Term Debt And Capital Securities RepaymentsOfLongTermDebtAndCapitalSecurities	6400000	USD
CY2017	us-gaap	Repayments Of Long Term Debt And Capital Securities RepaymentsOfLongTermDebtAndCapitalSecurities	353000000.0	USD
CY2019	us-gaap	Proceeds From Repayments Of Other Debt ProceedsFromRepaymentsOfOtherDebt	4900000	USD
CY2018	us-gaap	Proceeds From Repayments Of Other Debt ProceedsFromRepaymentsOfOtherDebt	-5900000	USD
CY2017	us-gaap	Proceeds From Repayments Of Other Debt ProceedsFromRepaymentsOfOtherDebt	1600000	USD
CY2019	us-gaap	Payments Of Debt Issuance Costs PaymentsOfDebtIssuanceCosts	5500000	USD
CY2018	us-gaap	Payments Of Debt Issuance Costs PaymentsOfDebtIssuanceCosts	0	USD
CY2017	us-gaap	Payments Of Debt Issuance Costs PaymentsOfDebtIssuanceCosts	800000	USD
CY2019	us-gaap	Payments Of Debt Extinguishment Costs PaymentsOfDebtExtinguishmentCosts	20900000	USD
CY2018	us-gaap	Payments Of Debt Extinguishment Costs PaymentsOfDebtExtinguishmentCosts	0	USD
CY2017	us-gaap	Payments Of Debt Extinguishment Costs PaymentsOfDebtExtinguishmentCosts	35800000	USD
CY2019	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	0	USD
CY2018	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	0	USD
CY2017	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	397800000	USD
CY2019	us-gaap	Payments Of Dividends Minority Interest PaymentsOfDividendsMinorityInterest	14000000.0	USD
CY2017	us-gaap	Payments Of Dividends Minority Interest PaymentsOfDividendsMinorityInterest	8000000.0	USD
CY2019	us-gaap	Proceeds From Minority Shareholders ProceedsFromMinorityShareholders	0	USD
CY2018	us-gaap	Proceeds From Minority Shareholders ProceedsFromMinorityShareholders	14400000	USD
CY2017	us-gaap	Proceeds From Minority Shareholders ProceedsFromMinorityShareholders	3700000	USD
CY2019	us-gaap	Payments For Repurchase Of Other Equity PaymentsForRepurchaseOfOtherEquity	9900000	USD
CY2018	us-gaap	Payments For Repurchase Of Other Equity PaymentsForRepurchaseOfOtherEquity	6500000	USD
CY2017	us-gaap	Payments For Repurchase Of Other Equity PaymentsForRepurchaseOfOtherEquity	4800000	USD
CY2019	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	-203000000.0	USD
CY2018	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	-7300000	USD
CY2017	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	9200000	USD
CY2019	us-gaap	Cash And Cash Equivalents Period Increase Decrease CashAndCashEquivalentsPeriodIncreaseDecrease	108800000	USD
CY2018	us-gaap	Cash And Cash Equivalents Period Increase Decrease CashAndCashEquivalentsPeriodIncreaseDecrease	240400000	USD
CY2017	us-gaap	Cash And Cash Equivalents Period Increase Decrease CashAndCashEquivalentsPeriodIncreaseDecrease	-88000000.0	USD
CY2018Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	382000000.0	USD
CY2017Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	141600000	USD
CY2016Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	229600000	USD
CY2019Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	490800000	USD
CY2018Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	382000000.0	USD
CY2017Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	141600000	USD
CY2016Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	1444800000	USD
CY2017	us-gaap	Profit Loss ProfitLoss	-79700000	USD
CY2017	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	73500000	USD
CY2017	us-gaap	Stock Issued During Period Value New Issues StockIssuedDuringPeriodValueNewIssues	397800000	USD
CY2017	us-gaap	Minority Interest Decrease From Distributions To Noncontrolling Interest Holders MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders	8000000.0	USD
CY2017Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	1844500000	USD
CY2018	us-gaap	Profit Loss ProfitLoss	236700000	USD
CY2019	ati	Employee Stock Plans EmployeeStockPlans	-14700000	USD
CY2019Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	2193200000	USD
CY2017	us-gaap	Noncontrolling Interest Increase From Sale Of Parent Equity Interest NoncontrollingInterestIncreaseFromSaleOfParentEquityInterest	3700000	USD
CY2017	ati	Employee Stock Plans EmployeeStockPlans	-12400000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-112200000	USD
CY2018	us-gaap	Cumulative Effect On Retained Earnings Net Of Tax1 CumulativeEffectOnRetainedEarningsNetOfTax1	15500000	USD
CY2018	us-gaap	Minority Interest Decrease From Distributions To Noncontrolling Interest Holders MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders	10000000.0	USD
CY2018	us-gaap	Noncontrolling Interest Increase From Sale Of Parent Equity Interest NoncontrollingInterestIncreaseFromSaleOfParentEquityInterest	2700000	USD
CY2018	ati	Employee Stock Plans EmployeeStockPlans	-14400000	USD
CY2018Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	1991600000	USD
CY2019	us-gaap	Profit Loss ProfitLoss	270100000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-69200000	USD
CY2019	us-gaap	Minority Interest Decrease From Distributions To Noncontrolling Interest Holders MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders	14000000.0	USD
CY2019	us-gaap	Use Of Estimates UseOfEstimates	<div style="line-height:120%;padding-top:12px;font-size:10pt;"><span style="font-family:inherit;font-size:10pt;font-style:italic;font-weight:bold;">Risks and Uncertainties and Use of Estimates</span></div><div style="line-height:120%;padding-top:12px;font-size:10pt;"><span style="font-family:inherit;font-size:10pt;">The preparation of consolidated financial statements in conformity with United States generally accepted accounting principles requires management to make estimates and assumptions that affect reported amounts of assets and liabilities at the date of the financial statements, as well as the reported amounts of income and expenses during the reporting period. Actual results could differ from those estimates. Management believes that the estimates are reasonable. Certain prior year amounts have been reclassified in order to conform with the </span><span style="font-family:inherit;font-size:10pt;">2019</span><span style="font-family:inherit;font-size:10pt;"> presentation.</span></div>
CY2019	us-gaap	Concentration Risk Credit Risk ConcentrationRiskCreditRisk	<div style="line-height:120%;padding-top:12px;font-size:10pt;"><span style="font-family:inherit;font-size:10pt;">The Company markets its products to a diverse customer base, principally throughout the United States. No single customer accounted for more than 10% of sales for any year presented. The major end markets for the ATI’s products are customers in the aerospace & defense, energy, automotive, construction and mining, food equipment and appliances, and medical markets.</span></div>
CY2019Q4	dei	Entity Number Of Employees EntityNumberOfEmployees	8100	employee
CY2019	ati	Employees Percent Non U.S. EmployeesPercentNonU.S.	0.17
CY2019	ati	Employees Percent Coveredby Collective Bargaining Agreements EmployeesPercentCoveredbyCollectiveBargainingAgreements	0.40
CY2019Q4	ati	Entity Number Of Employees Covered By Usw Collective Bargaining Agreements Expiring February292020 EntityNumberOfEmployeesCoveredByUSWCollectiveBargainingAgreementsExpiringFebruary292020	1500	employee
CY2019Q4	us-gaap	Allowance For Doubtful Accounts Receivable AllowanceForDoubtfulAccountsReceivable	4600000	USD
CY2018Q4	us-gaap	Allowance For Doubtful Accounts Receivable AllowanceForDoubtfulAccountsReceivable	6000000.0	USD
CY2019	us-gaap	Research And Development Expense ResearchAndDevelopmentExpense	17800000	USD
CY2018	us-gaap	Research And Development Expense ResearchAndDevelopmentExpense	22700000	USD
CY2017	us-gaap	Research And Development Expense ResearchAndDevelopmentExpense	13300000	USD
CY2019	us-gaap	Research And Development Arrangement Contract To Perform For Others Costs Incurred Gross ResearchAndDevelopmentArrangementContractToPerformForOthersCostsIncurredGross	2400000	USD
CY2018	us-gaap	Research And Development Arrangement Contract To Perform For Others Costs Incurred Gross ResearchAndDevelopmentArrangementContractToPerformForOthersCostsIncurredGross	2200000	USD
CY2017	us-gaap	Research And Development Arrangement Contract To Perform For Others Costs Incurred Gross ResearchAndDevelopmentArrangementContractToPerformForOthersCostsIncurredGross	1400000	USD
CY2019	us-gaap	Description Of New Accounting Pronouncements Not Yet Adopted DescriptionOfNewAccountingPronouncementsNotYetAdopted	<div style="line-height:120%;padding-top:12px;font-size:10pt;"><span style="font-family:inherit;font-size:10pt;font-weight:bold;">Pending Accounting Pronouncements</span></div><div style="line-height:120%;text-align:left;font-size:10pt;"><span style="font-family:inherit;font-size:10pt;"><br/></span></div><div style="line-height:120%;text-align:left;font-size:10pt;"><span style="font-family:inherit;font-size:10pt;">In August 2018, the FASB issued new disclosure guidance on fair value measurement. This new guidance modifies the disclosure requirements on fair value measurements, including removal and modifications of various current disclosures as well as some additional disclosure requirements for Level 3 fair value measurements. Some of these disclosure changes must be applied prospectively while others retrospectively depending on requirement. This guidance is required to be adopted by the Company beginning in fiscal year 2020, with early adoption permitted. The Company did not early adopt this guidance. The adoption of these changes is not expected to have an impact on the Company’s consolidated financial statements other than disclosures. </span></div><div style="line-height:120%;text-align:left;font-size:10pt;"><span style="font-family:inherit;font-size:10pt;"><br/></span></div><div style="line-height:120%;text-align:left;font-size:10pt;"><span style="font-family:inherit;font-size:10pt;">In June 2016, the FASB added a new impairment model (known as the current expected credit loss (CECL) model) that is based on expected losses rather than incurred losses. Under the new guidance, an entity recognizes as an allowance its estimate of expected credit losses. The CECL model applies to trade receivables, other receivables, contract assets and most debt instruments. The CECL model does not have a minimum threshold for recognition of impairment losses, and entities will need to measure expected credit losses on assets that have a low risk of loss. This guidance was adopted by the Company in fiscal year 2020 without significant impact to the consolidated financial statements.</span></div><div style="line-height:120%;text-align:left;font-size:10pt;"><span style="font-family:inherit;font-size:10pt;"><br/></span></div><div style="line-height:120%;text-align:left;font-size:10pt;"><span style="font-family:inherit;font-size:10pt;">In December 2019, the FASB issued new guidance to simplify the accounting for income taxes. The areas for simplification in the guidance involve the removal of certain exceptions to the general principals in the current guidance, including intraperiod allocation and the calculation of income taxes in an interim period when a year to date loss exceeds the anticipated loss for the year. The new guidance also simplifies the accounting for income taxes in the area of franchise taxes. This new guidance is effective for the Company in fiscal year 2021, with early adoption permitted. This guidance was early adopted by the Company in fiscal year 2020 without significant impact to the consolidated financial statements.</span></div>
CY2019	us-gaap	Number Of Operating Segments NumberOfOperatingSegments	2	segment
CY2019	us-gaap	Number Of Operating Segments NumberOfOperatingSegments	2	segment
CY2019	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	4122500000	USD
CY2018	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	4046600000	USD
CY2017	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	3525100000	USD
CY2019	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	4122500000	USD
CY2018	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	4046600000	USD
CY2017	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	3525100000	USD
CY2019	ati	Revenuefrom Contractwith Customer Excluding Assessed Tax Percentageof Revenue RevenuefromContractwithCustomerExcludingAssessedTaxPercentageofRevenue	1
CY2018	ati	Revenuefrom Contractwith Customer Excluding Assessed Tax Percentageof Revenue RevenuefromContractwithCustomerExcludingAssessedTaxPercentageofRevenue	1
CY2017	ati	Revenuefrom Contractwith Customer Excluding Assessed Tax Percentageof Revenue RevenuefromContractwithCustomerExcludingAssessedTaxPercentageofRevenue	1
CY2019Q4	us-gaap	Revenue Remaining Performance Obligation RevenueRemainingPerformanceObligation	2300000000	USD
CY2018Q4	us-gaap	Revenue Remaining Performance Obligation RevenueRemainingPerformanceObligation	2200000000	USD
CY2017Q4	us-gaap	Revenue Remaining Performance Obligation RevenueRemainingPerformanceObligation	2100000000	USD
CY2019Q4	ati	Revenue Remaining Performance Obligation Current RevenueRemainingPerformanceObligationCurrent	0.81	USD
CY2019Q4	ati	Accountsreceivablewithcustomers Accountsreceivablewithcustomers	558700000	USD
CY2018Q4	ati	Accountsreceivablewithcustomers Accountsreceivablewithcustomers	533800000	USD
CY2016Q4	us-gaap	Allowance For Doubtful Accounts Receivable AllowanceForDoubtfulAccountsReceivable	7300000	USD
CY2017	us-gaap	Provision For Doubtful Accounts ProvisionForDoubtfulAccounts	100000	USD
CY2017	us-gaap	Allowance For Doubtful Accounts Receivable Write Offs AllowanceForDoubtfulAccountsReceivableWriteOffs	1500000	USD
CY2017Q4	us-gaap	Allowance For Doubtful Accounts Receivable AllowanceForDoubtfulAccountsReceivable	5900000	USD
CY2018	us-gaap	Provision For Doubtful Accounts ProvisionForDoubtfulAccounts	1900000	USD
CY2018	us-gaap	Allowance For Doubtful Accounts Receivable Write Offs AllowanceForDoubtfulAccountsReceivableWriteOffs	1800000	USD
CY2018Q4	us-gaap	Allowance For Doubtful Accounts Receivable AllowanceForDoubtfulAccountsReceivable	6000000.0	USD
CY2019	us-gaap	Provision For Doubtful Accounts ProvisionForDoubtfulAccounts	200000	USD
CY2019	us-gaap	Allowance For Doubtful Accounts Receivable Write Offs AllowanceForDoubtfulAccountsReceivableWriteOffs	1600000	USD
CY2019Q4	us-gaap	Allowance For Doubtful Accounts Receivable AllowanceForDoubtfulAccountsReceivable	4600000	USD
CY2018Q4	us-gaap	Contract With Customer Asset Net Current ContractWithCustomerAssetNetCurrent	51200000	USD
CY2018Q1	us-gaap	Contract With Customer Asset Net Current ContractWithCustomerAssetNetCurrent	36500000	USD
CY2019	ati	Contractwith Customer Asset Current Period Increase ContractwithCustomerAssetCurrentPeriodIncrease	74500000	USD
CY2018	ati	Contractwith Customer Asset Current Period Increase ContractwithCustomerAssetCurrentPeriodIncrease	92900000	USD
CY2019	ati	Contractwith Customer Asset Current Reclassifiedto Receivable ContractwithCustomerAssetCurrentReclassifiedtoReceivable	79900000	USD
CY2018	ati	Contractwith Customer Asset Current Reclassifiedto Receivable ContractwithCustomerAssetCurrentReclassifiedtoReceivable	95800000	USD
CY2019	ati	Contractwith Customer Asset Current Impairment ContractwithCustomerAssetCurrentImpairment	0	USD
CY2018	ati	Contractwith Customer Asset Current Impairment ContractwithCustomerAssetCurrentImpairment	0	USD
CY2019	ati	Contractwith Customer Asset Current Reclassification ContractwithCustomerAssetCurrentReclassification	0	USD
CY2018	ati	Contractwith Customer Asset Current Reclassification ContractwithCustomerAssetCurrentReclassification	-16800000	USD
CY2019	ati	Contractwithcustomer Asset Current Divestiture ContractwithcustomerAssetCurrentDivestiture	7300000	USD
CY2018	ati	Contractwithcustomer Asset Current Divestiture ContractwithcustomerAssetCurrentDivestiture	0	USD
CY2019	ati	Contract With Customer Asset Current Other ContractWithCustomerAssetCurrentOther	0	USD
CY2018	ati	Contract With Customer Asset Current Other ContractWithCustomerAssetCurrentOther	800000	USD
CY2019Q4	us-gaap	Contract With Customer Asset Net Current ContractWithCustomerAssetNetCurrent	38500000	USD
CY2018Q4	us-gaap	Contract With Customer Asset Net Current ContractWithCustomerAssetNetCurrent	51200000	USD
CY2018Q4	us-gaap	Contract With Customer Asset Net Noncurrent ContractWithCustomerAssetNetNoncurrent	100000	USD
CY2018Q1	us-gaap	Contract With Customer Asset Net Noncurrent ContractWithCustomerAssetNetNoncurrent	16900000	USD
CY2019	ati	Contractwith Customer Asset Nocurrent Period Increase ContractwithCustomerAssetNocurrentPeriodIncrease	0	USD
CY2018	ati	Contractwith Customer Asset Nocurrent Period Increase ContractwithCustomerAssetNocurrentPeriodIncrease	0	USD
CY2019	ati	Contractwith Customer Asset Noncurrent Reclassifiedto Receivable ContractwithCustomerAssetNoncurrentReclassifiedtoReceivable	0	USD
CY2018	ati	Contractwith Customer Asset Noncurrent Reclassifiedto Receivable ContractwithCustomerAssetNoncurrentReclassifiedtoReceivable	0	USD
CY2019	ati	Contractwith Customer Asset Noncurrent Impairment ContractwithCustomerAssetNoncurrentImpairment	0	USD
CY2019	ati	Contractwith Customer Asset Noncurrent Reclassification ContractwithCustomerAssetNoncurrentReclassification	0	USD
CY2018	ati	Contractwith Customer Asset Noncurrent Reclassification ContractwithCustomerAssetNoncurrentReclassification	16800000	USD
CY2018	ati	Contractwith Customer Asset Noncurrent Impairment ContractwithCustomerAssetNoncurrentImpairment	0	USD
CY2018Q4	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	71400000	USD
CY2018Q1	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	69700000	USD
CY2018Q4	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	71400000	USD
CY2019Q4	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	78700000	USD
CY2019Q4	us-gaap	Contract With Customer Asset Net Noncurrent ContractWithCustomerAssetNetNoncurrent	100000	USD
CY2018Q4	us-gaap	Contract With Customer Asset Net Noncurrent ContractWithCustomerAssetNetNoncurrent	100000	USD
CY2019	ati	Contractwith Customer Liability Current Period Increase ContractwithCustomerLiabilityCurrentPeriodIncrease	126100000	USD
CY2018	ati	Contractwith Customer Liability Current Period Increase ContractwithCustomerLiabilityCurrentPeriodIncrease	76700000	USD
CY2019	ati	Contractwith Customer Liability Current Reclassifiedto Revenue ContractwithCustomerLiabilityCurrentReclassifiedtoRevenue	-49200000	USD
CY2018	ati	Contractwith Customer Liability Current Reclassifiedto Revenue ContractwithCustomerLiabilityCurrentReclassifiedtoRevenue	-49600000	USD
CY2019	ati	Contractwith Customer Liability Current Revenue Recognized ContractwithCustomerLiabilityCurrentRevenueRecognized	-76000000.0	USD
CY2018	ati	Contractwith Customer Liability Current Revenue Recognized ContractwithCustomerLiabilityCurrentRevenueRecognized	-42700000	USD
CY2019	ati	Contractwith Customer Liability Current Other ContractwithCustomerLiabilityCurrentOther	1900000	USD
CY2018	ati	Contractwith Customer Liability Current Other ContractwithCustomerLiabilityCurrentOther	2700000	USD
CY2019	ati	Contractwith Customer Liability Current Reclassification ContractwithCustomerLiabilityCurrentReclassification	-4500000	USD
CY2018	ati	Contractwith Customer Liability Current Reclassification ContractwithCustomerLiabilityCurrentReclassification	-14600000	USD
CY2018Q4	us-gaap	Contract With Customer Liability Noncurrent ContractWithCustomerLiabilityNoncurrent	7300000	USD
CY2018Q1	us-gaap	Contract With Customer Liability Noncurrent ContractWithCustomerLiabilityNoncurrent	22200000	USD
CY2019	ati	Contractwith Customer Liability Noncurrent Period Increase ContractwithCustomerLiabilityNoncurrentPeriodIncrease	24200000	USD
CY2018	ati	Contractwith Customer Liability Noncurrent Period Increase ContractwithCustomerLiabilityNoncurrentPeriodIncrease	700000	USD
CY2019	ati	Contractwith Customer Liability Noncurrent Reclassifiedto Revenue ContractwithCustomerLiabilityNoncurrentReclassifiedtoRevenue	-1100000	USD
CY2018	ati	Contractwith Customer Liability Noncurrent Reclassifiedto Revenue ContractwithCustomerLiabilityNoncurrentReclassifiedtoRevenue	-1000000.0	USD
CY2019	ati	Contractwith Customer Liability Noncurrent Revenue Recognized ContractwithCustomerLiabilityNoncurrentRevenueRecognized	0	USD
CY2018	ati	Contractwith Customer Liability Noncurrent Revenue Recognized ContractwithCustomerLiabilityNoncurrentRevenueRecognized	0	USD
CY2019	ati	Contractwith Customer Liability Noncurrent Other ContractwithCustomerLiabilityNoncurrentOther	0	USD
CY2018	ati	Contractwith Customer Liability Noncurrent Other ContractwithCustomerLiabilityNoncurrentOther	0	USD
CY2019	ati	Contractwith Customer Liability Noncurrent Reclassification ContractwithCustomerLiabilityNoncurrentReclassification	4500000	USD
CY2018	ati	Contractwith Customer Liability Noncurrent Reclassification ContractwithCustomerLiabilityNoncurrentReclassification	14600000	USD
CY2019Q4	us-gaap	Contract With Customer Liability Noncurrent ContractWithCustomerLiabilityNoncurrent	25900000	USD
CY2018Q4	us-gaap	Contract With Customer Liability Noncurrent ContractWithCustomerLiabilityNoncurrent	7300000	USD
CY2019Q4	us-gaap	Capitalized Contract Cost Net CapitalizedContractCostNet	6500000	USD
CY2018Q4	us-gaap	Capitalized Contract Cost Net CapitalizedContractCostNet	5200000	USD
CY2019	us-gaap	Capitalized Contract Cost Amortization CapitalizedContractCostAmortization	1400000	USD
CY2018	us-gaap	Capitalized Contract Cost Amortization CapitalizedContractCostAmortization	1200000	USD
CY2019Q4	us-gaap	Inventory Raw Materials And Supplies InventoryRawMaterialsAndSupplies	164900000	USD
CY2018Q4	us-gaap	Inventory Raw Materials And Supplies InventoryRawMaterialsAndSupplies	191500000	USD
CY2019Q4	us-gaap	Inventory Work In Process InventoryWorkInProcess	899600000	USD
CY2018Q4	us-gaap	Inventory Work In Process InventoryWorkInProcess	914100000	USD
CY2019Q4	us-gaap	Inventory Finished Goods InventoryFinishedGoods	161300000	USD
CY2018Q4	us-gaap	Inventory Finished Goods InventoryFinishedGoods	191100000	USD
CY2019Q4	us-gaap	Inventory Gross InventoryGross	1225800000	USD
CY2018Q4	us-gaap	Inventory Gross InventoryGross	1296700000	USD
CY2019Q4	us-gaap	Inventory Lifo Reserve InventoryLIFOReserve	-33600000	USD
CY2018Q4	us-gaap	Inventory Lifo Reserve InventoryLIFOReserve	-2900000	USD
CY2019Q4	us-gaap	Inventory Valuation Reserves InventoryValuationReserves	104100000	USD
CY2018Q4	us-gaap	Inventory Valuation Reserves InventoryValuationReserves	88500000	USD
CY2019Q4	us-gaap	Inventory Net InventoryNet	1155300000	USD
CY2018Q4	us-gaap	Inventory Net InventoryNet	1211100000	USD
CY2019Q4	us-gaap	Lifo Inventory Amount LIFOInventoryAmount	776100000	USD
CY2018Q4	us-gaap	Lifo Inventory Amount LIFOInventoryAmount	794300000	USD
CY2019	us-gaap	Inventory Lifo Reserve Period Charge InventoryLIFOReservePeriodCharge	-25500000	USD
CY2018	us-gaap	Inventory Lifo Reserve Period Charge InventoryLIFOReservePeriodCharge	28600000	USD
CY2017	us-gaap	Inventory Lifo Reserve Period Charge InventoryLIFOReservePeriodCharge	54200000	USD
CY2019	ati	Inventory Net Realizable Value Reserve Period Charge InventoryNetRealizableValueReservePeriodCharge	25600000	USD
CY2018	ati	Inventory Net Realizable Value Reserve Period Charge InventoryNetRealizableValueReservePeriodCharge	-27900000	USD
CY2017	ati	Inventory Net Realizable Value Reserve Period Charge InventoryNetRealizableValueReservePeriodCharge	-54000000.0	USD
CY2019	ati	Lifo Provision Benefitand Changein Debit Lifonr Vreservenet LifoProvisionBenefitandChangeinDebitLIFONRVreservenet	100000	USD
CY2018	ati	Lifo Provision Benefitand Changein Debit Lifonr Vreservenet LifoProvisionBenefitandChangeinDebitLIFONRVreservenet	700000	USD
CY2017	ati	Lifo Provision Benefitand Changein Debit Lifonr Vreservenet LifoProvisionBenefitandChangeinDebitLIFONRVreservenet	200000	USD
CY2019	us-gaap	Effect Of Lifo Inventory Liquidation On Income EffectOfLIFOInventoryLiquidationOnIncome	-1800000	USD
CY2017	us-gaap	Effect Of Lifo Inventory Liquidation On Income EffectOfLIFOInventoryLiquidationOnIncome	-4600000	USD
CY2017	ati	Inventory Market Based Valuation Period Charge InventoryMarketBasedValuationPeriodCharge	17700000	USD
CY2018	us-gaap	Effect Of Lifo Inventory Liquidation On Income EffectOfLIFOInventoryLiquidationOnIncome	800000	USD
CY2019Q4	us-gaap	Land Land	34600000	USD
CY2018Q4	us-gaap	Land Land	31500000	USD
CY2019Q4	us-gaap	Buildings And Improvements Gross BuildingsAndImprovementsGross	832700000	USD
CY2018Q4	us-gaap	Buildings And Improvements Gross BuildingsAndImprovementsGross	851700000	USD
CY2019Q4	us-gaap	Machinery And Equipment Gross MachineryAndEquipmentGross	3671300000	USD
CY2018Q4	us-gaap	Machinery And Equipment Gross MachineryAndEquipmentGross	3622700000	USD
CY2019Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	4538600000	USD
CY2018Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	4505900000	USD
CY2019Q4	us-gaap	Accumulated Depreciation Depletion And Amortization Property Plant And Equipment AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	2088500000	USD
CY2018Q4	us-gaap	Accumulated Depreciation Depletion And Amortization Property Plant And Equipment AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	2030900000	USD
CY2019Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	2450100000	USD
CY2018Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	2475000000.0	USD
CY2019Q4	us-gaap	Construction In Progress Gross ConstructionInProgressGross	177300000	USD
CY2018Q4	us-gaap	Construction In Progress Gross ConstructionInProgressGross	83700000	USD
CY2019	us-gaap	Goodwill Period Increase Decrease GoodwillPeriodIncreaseDecrease	-8900000	USD
CY2019Q4	us-gaap	Goodwill Impaired Accumulated Impairment Loss GoodwillImpairedAccumulatedImpairmentLoss	241000000.0	USD
CY2019Q4	us-gaap	Finite Lived Intangible Assets Gross FiniteLivedIntangibleAssetsGross	156200000	USD
CY2019Q4	us-gaap	Finite Lived Intangible Assets Accumulated Amortization FiniteLivedIntangibleAssetsAccumulatedAmortization	59900000	USD
CY2018Q4	us-gaap	Finite Lived Intangible Assets Gross FiniteLivedIntangibleAssetsGross	193700000	USD
CY2018Q4	us-gaap	Finite Lived Intangible Assets Accumulated Amortization FiniteLivedIntangibleAssetsAccumulatedAmortization	64000000.0	USD
CY2019	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	9500000	USD
CY2018	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	10000000	USD
CY2019Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Next Twelve Months FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths	8000000	USD
CY2019Q2	ati	Number Of Facilities Sold NumberOfFacilitiesSold	2	facility
CY2019Q2	ati	Number Of Facilities Sold NumberOfFacilitiesSold	2	facility
CY2019Q4	ati	Retained Earnings Equity Method Undistributed Earnings RetainedEarningsEquityMethodUndistributedEarnings	14500000	USD
CY2018	us-gaap	Deconsolidation Gain Or Loss Amount DeconsolidationGainOrLossAmount	15900000	USD
CY2019Q4	us-gaap	Asset Retirement Obligation AssetRetirementObligation	23700000	USD
CY2018Q4	us-gaap	Asset Retirement Obligation AssetRetirementObligation	23100000	USD
CY2017Q4	us-gaap	Asset Retirement Obligation AssetRetirementObligation	23500000	USD
CY2019	us-gaap	Asset Retirement Obligation Accretion Expense AssetRetirementObligationAccretionExpense	900000	USD
CY2018	us-gaap	Asset Retirement Obligation Accretion Expense AssetRetirementObligationAccretionExpense	800000	USD
CY2019	us-gaap	Asset Retirement Obligation Liabilities Settled AssetRetirementObligationLiabilitiesSettled	300000	USD
CY2018	us-gaap	Asset Retirement Obligation Liabilities Settled AssetRetirementObligationLiabilitiesSettled	1200000	USD
CY2019Q4	us-gaap	Asset Retirement Obligation AssetRetirementObligation	23700000	USD
CY2018Q4	us-gaap	Asset Retirement Obligation AssetRetirementObligation	23100000	USD
CY2019Q4	us-gaap	Cash Cash	190800000	USD
CY2018Q4	us-gaap	Cash Cash	264400000	USD
CY2019Q4	us-gaap	Money Market Funds At Carrying Value MoneyMarketFundsAtCarryingValue	300000000.0	USD
CY2018Q4	us-gaap	Money Market Funds At Carrying Value MoneyMarketFundsAtCarryingValue	117600000	USD
CY2019Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	490800000	USD
CY2018Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	382000000.0	USD
CY2019Q4	us-gaap	Employee Related Liabilities Current EmployeeRelatedLiabilitiesCurrent	94500000	USD
CY2018Q4	us-gaap	Employee Related Liabilities Current EmployeeRelatedLiabilitiesCurrent	95800000	USD
CY2019Q4	us-gaap	Interest Payable Current InterestPayableCurrent	25000000.0	USD
CY2018Q4	us-gaap	Interest Payable Current InterestPayableCurrent	36600000	USD
CY2019	ati	Rent Royalty And Other Income RentRoyaltyAndOtherIncome	2900000	USD
CY2018	ati	Rent Royalty And Other Income RentRoyaltyAndOtherIncome	3100000	USD
CY2017	ati	Rent Royalty And Other Income RentRoyaltyAndOtherIncome	3500000	USD
CY2019	us-gaap	Gain Loss On Disposition Of Assets1 GainLossOnDispositionOfAssets1	90700000	USD
CY2018	us-gaap	Gain Loss On Disposition Of Assets1 GainLossOnDispositionOfAssets1	1300000	USD
CY2017	us-gaap	Gain Loss On Disposition Of Assets1 GainLossOnDispositionOfAssets1	500000	USD
CY2019	us-gaap	Income Loss From Equity Method Investments IncomeLossFromEquityMethodInvestments	-10700000	USD
CY2018	us-gaap	Income Loss From Equity Method Investments IncomeLossFromEquityMethodInvestments	-1000000.0	USD
CY2017	us-gaap	Income Loss From Equity Method Investments IncomeLossFromEquityMethodInvestments	0	USD
CY2019	us-gaap	Gain Loss On Sale Of Business GainLossOnSaleOfBusiness	-1900000	USD
CY2018	us-gaap	Gain Loss On Sale Of Business GainLossOnSaleOfBusiness	0	USD
CY2017	us-gaap	Gain Loss On Sale Of Business GainLossOnSaleOfBusiness	0	USD
CY2019	us-gaap	Deconsolidation Gain Or Loss Amount DeconsolidationGainOrLossAmount	0	USD
CY2018	us-gaap	Deconsolidation Gain Or Loss Amount DeconsolidationGainOrLossAmount	15900000	USD
CY2017	us-gaap	Deconsolidation Gain Or Loss Amount DeconsolidationGainOrLossAmount	0	USD
CY2019	ati	Other Asset Impairment Charges And Due From Affiliates Allowance For Credit Loss OtherAssetImpairmentChargesAndDueFromAffiliatesAllowanceForCreditLoss	11400000	USD
CY2018	ati	Other Asset Impairment Charges And Due From Affiliates Allowance For Credit Loss OtherAssetImpairmentChargesAndDueFromAffiliatesAllowanceForCreditLoss	0	USD
CY2017	ati	Other Asset Impairment Charges And Due From Affiliates Allowance For Credit Loss OtherAssetImpairmentChargesAndDueFromAffiliatesAllowanceForCreditLoss	0	USD
CY2019	ati	Other Other Nonoperating Income Expense OtherOtherNonoperatingIncomeExpense	100000	USD
CY2018	ati	Other Other Nonoperating Income Expense OtherOtherNonoperatingIncomeExpense	1200000	USD
CY2017	ati	Other Other Nonoperating Income Expense OtherOtherNonoperatingIncomeExpense	0	USD
CY2019	us-gaap	Other Nonoperating Income Expense OtherNonoperatingIncomeExpense	69700000	USD
CY2018	us-gaap	Other Nonoperating Income Expense OtherNonoperatingIncomeExpense	20500000	USD
CY2017	us-gaap	Other Nonoperating Income Expense OtherNonoperatingIncomeExpense	4000000.0	USD
CY2019	us-gaap	Gain Loss On Sale Of Property GainLossOnSaleOfProperty	91700000	USD
CY2019Q4	us-gaap	Deferred Finance Costs Net DeferredFinanceCostsNet	12300000	USD
CY2018Q4	us-gaap	Deferred Finance Costs Net DeferredFinanceCostsNet	10400000	USD
CY2019Q4	ati	Total Debt TotalDebt	1398900000	USD
CY2018Q4	ati	Total Debt TotalDebt	1542100000	USD
CY2019Q4	us-gaap	Debt Current DebtCurrent	11500000	USD
CY2018Q4	us-gaap	Debt Current DebtCurrent	6600000	USD
CY2019Q4	us-gaap	Long Term Debt And Capital Lease Obligations LongTermDebtAndCapitalLeaseObligations	1387400000	USD
CY2018Q4	us-gaap	Long Term Debt And Capital Lease Obligations LongTermDebtAndCapitalLeaseObligations	1535500000	USD
CY2019	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	-21600000	USD
CY2019	us-gaap	Payments Of Debt Extinguishment Costs PaymentsOfDebtExtinguishmentCosts	20900000	USD
CY2019	us-gaap	Write Off Of Deferred Debt Issuance Cost WriteOffOfDeferredDebtIssuanceCost	700000	USD
CY2017	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	-37000000.0	USD
CY2017	us-gaap	Payments Of Debt Extinguishment Costs PaymentsOfDebtExtinguishmentCosts	35800000	USD
CY2017	us-gaap	Write Off Of Deferred Debt Issuance Cost WriteOffOfDeferredDebtIssuanceCost	1200000	USD
CY2019	us-gaap	Interest Expense Debt InterestExpenseDebt	104900000	USD
CY2018	us-gaap	Interest Expense Debt InterestExpenseDebt	102100000	USD
CY2017	us-gaap	Interest Expense Debt InterestExpenseDebt	134900000	USD
CY2019	us-gaap	Interest Costs Capitalized InterestCostsCapitalized	4700000	USD
CY2018	us-gaap	Interest Costs Capitalized InterestCostsCapitalized	4100000	USD
CY2017	us-gaap	Interest Costs Capitalized InterestCostsCapitalized	2600000	USD
CY2019	us-gaap	Interest Paid InterestPaid	105700000	USD
CY2018	us-gaap	Interest Paid InterestPaid	102600000	USD
CY2017	us-gaap	Interest Paid InterestPaid	133800000	USD
CY2019	us-gaap	Investment Income Interest InvestmentIncomeInterest	5900000	USD
CY2018	us-gaap	Investment Income Interest InvestmentIncomeInterest	1100000	USD
CY2017	us-gaap	Investment Income Interest InvestmentIncomeInterest	1100000	USD
CY2019Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Next Twelve Months LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths	11500000	USD
CY2019Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Two LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo	4800000	USD
CY2019Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Three LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree	291500000	USD
CY2019Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Four LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour	502700000	USD
CY2019Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Five LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive	100700000	USD
CY2019	us-gaap	Payments Of Debt Issuance Costs PaymentsOfDebtIssuanceCosts	5500000	USD
CY2019Q4	ati	Progress Payments Made On Behalf Of Company Paid ProgressPaymentsMadeOnBehalfOfCompanyPaid	5300000	USD
CY2020Q1	ati	Progress Payments Made On Behalf Of Company Scheduled To Be Paid ProgressPaymentsMadeOnBehalfOfCompanyScheduledToBePaid	8200000	USD
CY2019	us-gaap	Finance Lease Right Of Use Asset Amortization FinanceLeaseRightOfUseAssetAmortization	1700000	USD
CY2019	us-gaap	Finance Lease Interest Expense FinanceLeaseInterestExpense	500000	USD
CY2019	us-gaap	Operating Lease Cost OperatingLeaseCost	20500000	USD
CY2019	us-gaap	Short Term Lease Cost ShortTermLeaseCost	3100000	USD
CY2019	us-gaap	Variable Lease Cost VariableLeaseCost	800000	USD
CY2019	us-gaap	Sublease Income SubleaseIncome	0	USD
CY2019	us-gaap	Lease Cost LeaseCost	26600000	USD
CY2019	us-gaap	Finance Lease Interest Payment On Liability FinanceLeaseInterestPaymentOnLiability	500000	USD
CY2019	us-gaap	Operating Lease Payments OperatingLeasePayments	20800000	USD
CY2019	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	2400000	USD
CY2019	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	14100000	USD
CY2019	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	35900000	USD
CY2019Q4	us-gaap	Finance Lease Weighted Average Remaining Lease Term1 FinanceLeaseWeightedAverageRemainingLeaseTerm1	P4Y
CY2019Q4	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P6Y
CY2019Q4	us-gaap	Finance Lease Weighted Average Discount Rate Percent FinanceLeaseWeightedAverageDiscountRatePercent	0.053
CY2019Q4	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.070
CY2018	us-gaap	Lease And Rental Expense LeaseAndRentalExpense	24400000	USD
CY2017	us-gaap	Lease And Rental Expense LeaseAndRentalExpense	21100000	USD
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due Next Twelve Months LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths	20000000.0	USD
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Two LesseeOperatingLeaseLiabilityPaymentsDueYearTwo	18200000	USD
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Three LesseeOperatingLeaseLiabilityPaymentsDueYearThree	15300000	USD
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Four LesseeOperatingLeaseLiabilityPaymentsDueYearFour	11700000	USD
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Five LesseeOperatingLeaseLiabilityPaymentsDueYearFive	8000000.0	USD
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due After Year Five LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive	24600000	USD
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due LesseeOperatingLeaseLiabilityPaymentsDue	97800000	USD
CY2019Q4	us-gaap	Lessee Operating Lease Liability Undiscounted Excess Amount LesseeOperatingLeaseLiabilityUndiscountedExcessAmount	20100000	USD
CY2019Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	77700000	USD
CY2019Q4	us-gaap	Finance Lease Liability Payments Due Next Twelve Months FinanceLeaseLiabilityPaymentsDueNextTwelveMonths	4500000	USD
CY2019Q4	us-gaap	Finance Lease Liability Payments Due Year Two FinanceLeaseLiabilityPaymentsDueYearTwo	4200000	USD
CY2019Q4	us-gaap	Finance Lease Liability Payments Due Year Three FinanceLeaseLiabilityPaymentsDueYearThree	3900000	USD
CY2019Q4	us-gaap	Finance Lease Liability Payments Due Year Four FinanceLeaseLiabilityPaymentsDueYearFour	2700000	USD
CY2019Q4	us-gaap	Finance Lease Liability Payments Due Year Five FinanceLeaseLiabilityPaymentsDueYearFive	700000	USD
CY2019Q4	us-gaap	Finance Lease Liability Payments Due After Year Five FinanceLeaseLiabilityPaymentsDueAfterYearFive	0	USD
CY2019Q4	us-gaap	Finance Lease Liability Payments Due FinanceLeaseLiabilityPaymentsDue	16000000.0	USD
CY2019Q4	us-gaap	Finance Lease Liability Undiscounted Excess Amount FinanceLeaseLiabilityUndiscountedExcessAmount	1500000	USD
CY2019Q4	us-gaap	Finance Lease Liability FinanceLeaseLiability	14500000	USD
CY2019	ati	Percentage Of Raw Material Usage Hedged PercentageOfRawMaterialUsageHedged	0.07
CY2019Q4	us-gaap	Derivative Fair Value Of Derivative Asset DerivativeFairValueOfDerivativeAsset	5600000	USD
CY2018Q4	us-gaap	Derivative Fair Value Of Derivative Asset DerivativeFairValueOfDerivativeAsset	3400000	USD
CY2019Q4	us-gaap	Derivative Fair Value Of Derivative Liability DerivativeFairValueOfDerivativeLiability	7500000	USD
CY2018Q4	us-gaap	Derivative Fair Value Of Derivative Liability DerivativeFairValueOfDerivativeLiability	10400000	USD
CY2019	us-gaap	Cash Flow Hedge Gain Loss To Be Reclassified Within Twelve Months CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths	-900000	USD
CY2019Q4	us-gaap	Other Comprehensive Income Loss Cash Flow Hedge Gain Loss Reclassification Tax OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax	6000000.0	USD
CY2019	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	44800000	USD
CY2018	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	39900000	USD
CY2017	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	35500000	USD
CY2019	ati	Projected Retirement Benefit Expense In Next Year ProjectedRetirementBenefitExpenseInNextYear	60000000	USD
CY2019Q4	us-gaap	Defined Benefit Plan Expected Amortization Of Prior Service Cost Credit Next Fiscal Year DefinedBenefitPlanExpectedAmortizationOfPriorServiceCostCreditNextFiscalYear	-3200000	USD
CY2019Q4	us-gaap	Defined Benefit Plan Expected Amortization Of Gain Loss Next Fiscal Year DefinedBenefitPlanExpectedAmortizationOfGainLossNextFiscalYear	-85300000	USD
CY2019Q4	us-gaap	Defined Benefit Plan Expected Amortization Next Fiscal Year DefinedBenefitPlanExpectedAmortizationNextFiscalYear	82100000	USD
CY2016Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-1093700000	USD
CY2017	us-gaap	Other Comprehensive Income Loss Before Reclassifications Net Of Tax OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax	10100000	USD
CY2017	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	-55800000	USD
CY2017	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	65900000	USD
CY2017Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-1027800000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Before Reclassifications Net Of Tax OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax	-132500000	USD
CY2018	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	-26500000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	-106000000.0	USD
CY2018Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-1133800000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Before Reclassifications Net Of Tax OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax	-136900000	USD
CY2019	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	-69000000.0	USD
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	-67900000	USD
CY2019Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-1201700000	USD
CY2016Q4	ati	Accumulated Other Comprehensive Income Loss Netof Tax Attributableto Noncontrolling Interest AccumulatedOtherComprehensiveIncomeLossNetofTaxAttributabletoNoncontrollingInterest	9700000	USD
CY2017	ati	Other Comprehensive Income Lossbefore Reclassifications Netof Tax Attributableto Noncontrolling Interest OtherComprehensiveIncomeLossbeforeReclassificationsNetofTaxAttributabletoNoncontrollingInterest	7600000	USD
CY2017	ati	Reclassificationfrom Accumulated Other Comprehensive Income Current Period Netof Tax Attributableto Noncontrolling Interest ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetofTaxAttributabletoNoncontrollingInterest	0	USD
CY2017	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Noncontrolling Interest OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest	7600000	USD
CY2017Q4	ati	Accumulated Other Comprehensive Income Loss Netof Tax Attributableto Noncontrolling Interest AccumulatedOtherComprehensiveIncomeLossNetofTaxAttributabletoNoncontrollingInterest	17300000	USD
CY2018	ati	Other Comprehensive Income Lossbefore Reclassifications Netof Tax Attributableto Noncontrolling Interest OtherComprehensiveIncomeLossbeforeReclassificationsNetofTaxAttributabletoNoncontrollingInterest	-6200000	USD
CY2018	ati	Reclassificationfrom Accumulated Other Comprehensive Income Current Period Netof Tax Attributableto Noncontrolling Interest ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetofTaxAttributabletoNoncontrollingInterest	0	USD
CY2018	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Noncontrolling Interest OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest	-6200000	USD
CY2018Q4	ati	Accumulated Other Comprehensive Income Loss Netof Tax Attributableto Noncontrolling Interest AccumulatedOtherComprehensiveIncomeLossNetofTaxAttributabletoNoncontrollingInterest	11100000	USD
CY2019	ati	Other Comprehensive Income Lossbefore Reclassifications Netof Tax Attributableto Noncontrolling Interest OtherComprehensiveIncomeLossbeforeReclassificationsNetofTaxAttributabletoNoncontrollingInterest	-1300000	USD
CY2019	ati	Reclassificationfrom Accumulated Other Comprehensive Income Current Period Netof Tax Attributableto Noncontrolling Interest ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetofTaxAttributabletoNoncontrollingInterest	0	USD
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Noncontrolling Interest OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest	-1300000	USD
CY2019Q4	ati	Accumulated Other Comprehensive Income Loss Netof Tax Attributableto Noncontrolling Interest AccumulatedOtherComprehensiveIncomeLossNetofTaxAttributabletoNoncontrollingInterest	9800000	USD
CY2019Q4	us-gaap	Other Comprehensive Income Loss Cash Flow Hedge Gain Loss Reclassification Tax OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax	6000000.0	USD
CY2019Q4	us-gaap	Preferred Stock Shares Issued PreferredStockSharesIssued	0	shares
CY2017Q4	us-gaap	Stock Issued During Period Shares New Issues StockIssuedDuringPeriodSharesNewIssues	17000000	shares
CY2017Q4	us-gaap	Shares Issued Price Per Share SharesIssuedPricePerShare	24.00
CY2017	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	397800000	USD
CY2019Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant	4100000	shares
CY2018Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	1055000	shares
CY2018Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	28300000
CY2017Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	1320000	shares
CY2017Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	32500000
CY2016Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	1852000	shares
CY2016Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	51500000
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod	396000	shares
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	10800000
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod	290000	shares
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	7800000
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod	378000	shares
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	7100000
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod	681000	shares
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue	14500000
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod	540000	shares
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue	11700000
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod	591000	shares
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue	16900000
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeited In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod	14000	shares
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeitures Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue	400000
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeited In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod	15000	shares
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeitures Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue	300000
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeited In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod	319000	shares
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeitures Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue	9200000
CY2019Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	756000	shares
CY2019Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	24200000
CY2018Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	1055000	shares
CY2018Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	28300000
CY2017Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	1320000	shares
CY2017Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	32500000
CY2019	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	190200000	USD
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	190800000	USD
CY2017	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	-119800000	USD
CY2019	us-gaap	Income Loss From Continuing Operations Before Income Taxes Foreign IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign	51400000	USD
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Foreign IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign	56900000	USD
CY2017	us-gaap	Income Loss From Continuing Operations Before Income Taxes Foreign IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign	33300000	USD
CY2019	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	241600000	USD
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	247700000	USD
CY2017	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	-86500000	USD
CY2019	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	2200000	USD
CY2018	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	1000000.0	USD
CY2017	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	-800000	USD
CY2019	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	200000	USD
CY2018	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	-800000	USD
CY2017	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	-1300000	USD
CY2019	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	8100000	USD
CY2018	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	10100000	USD
CY2017	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	6200000	USD
CY2019	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	10500000	USD
CY2018	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	10300000	USD
CY2017	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	4100000	USD
CY2019	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	-4600000	USD
CY2018	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	1300000	USD
CY2017	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	2400000	USD
CY2019	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	-40400000	USD
CY2018	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	-500000	USD
CY2017	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	-14400000	USD
CY2019	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	6000000.0	USD
CY2018	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	-100000	USD
CY2017	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	1100000	USD
CY2019	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	-39000000.0	USD
CY2018	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	700000	USD
CY2017	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	-10900000	USD
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	-28500000	USD
CY2018	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	11000000.0	USD
CY2017	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	-6800000	USD
CY2019	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	50700000	USD
CY2018	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	52000000.0	USD
CY2017	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	-30300000	USD
CY2019	us-gaap	Income Tax Reconciliation Nondeductible Expense Impairment Losses IncomeTaxReconciliationNondeductibleExpenseImpairmentLosses	0	USD
CY2018	ati	Tax Cuts And Jobs Act Foreign Earnings Inclusion Global Intangible Low Taxed Income Gilti TaxCutsAndJobsActForeignEarningsInclusionGlobalIntangibleLowTaxedIncomeGILTI	25700000	USD
CY2018	us-gaap	Income Tax Reconciliation Repatriation Of Foreign Earnings IncomeTaxReconciliationRepatriationOfForeignEarnings	5400000	USD
CY2018	us-gaap	Income Tax Reconciliation Nondeductible Expense Impairment Losses IncomeTaxReconciliationNondeductibleExpenseImpairmentLosses	0	USD
CY2017	us-gaap	Income Tax Reconciliation Nondeductible Expense Impairment Losses IncomeTaxReconciliationNondeductibleExpenseImpairmentLosses	36600000	USD
CY2019	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	300000	USD
CY2018	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	-500000	USD
CY2017	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	0	USD
CY2019	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	-90100000	USD
CY2018	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	-48000000.0	USD
CY2017	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	-14500000	USD
CY2019	us-gaap	Income Tax Reconciliation Repatriation Of Foreign Earnings IncomeTaxReconciliationRepatriationOfForeignEarnings	3500000	USD
CY2018	us-gaap	Income Tax Reconciliation Repatriation Of Foreign Earnings IncomeTaxReconciliationRepatriationOfForeignEarnings	5400000	USD
CY2017	us-gaap	Income Tax Reconciliation Repatriation Of Foreign Earnings IncomeTaxReconciliationRepatriationOfForeignEarnings	14200000	USD
CY2019	ati	Effective Income Tax Rate Reconciliation Restructuring EffectiveIncomeTaxRateReconciliationRestructuring	4200000	USD
CY2018	ati	Effective Income Tax Rate Reconciliation Restructuring EffectiveIncomeTaxRateReconciliationRestructuring	0	USD
CY2017	ati	Effective Income Tax Rate Reconciliation Restructuring EffectiveIncomeTaxRateReconciliationRestructuring	0	USD
CY2019	ati	Income Tax Reconciliation U.S.Taxreform IncomeTaxReconciliationU.S.taxreform	0	USD
CY2018	ati	Income Tax Reconciliation U.S.Taxreform IncomeTaxReconciliationU.S.taxreform	5900000	USD
CY2017	ati	Income Tax Reconciliation U.S.Taxreform IncomeTaxReconciliationU.S.taxreform	-4100000	USD
CY2019	us-gaap	Income Tax Reconciliation Foreign Income Tax Rate Differential IncomeTaxReconciliationForeignIncomeTaxRateDifferential	2700000	USD
CY2018	us-gaap	Income Tax Reconciliation Foreign Income Tax Rate Differential IncomeTaxReconciliationForeignIncomeTaxRateDifferential	3200000	USD
CY2017	us-gaap	Income Tax Reconciliation Foreign Income Tax Rate Differential IncomeTaxReconciliationForeignIncomeTaxRateDifferential	-3500000	USD
CY2019	us-gaap	Income Tax Reconciliation Prior Year Income Taxes IncomeTaxReconciliationPriorYearIncomeTaxes	0	USD
CY2018	us-gaap	Income Tax Reconciliation Prior Year Income Taxes IncomeTaxReconciliationPriorYearIncomeTaxes	-5800000	USD
CY2017	us-gaap	Income Tax Reconciliation Prior Year Income Taxes IncomeTaxReconciliationPriorYearIncomeTaxes	-5200000	USD
CY2019	ati	Effective Income Tax Rate Reconciliation Withholding Taxes EffectiveIncomeTaxRateReconciliationWithholdingTaxes	2700000	USD
CY2018	ati	Effective Income Tax Rate Reconciliation Withholding Taxes EffectiveIncomeTaxRateReconciliationWithholdingTaxes	2700000	USD
CY2017	ati	Effective Income Tax Rate Reconciliation Withholding Taxes EffectiveIncomeTaxRateReconciliationWithholdingTaxes	2200000	USD
CY2019	us-gaap	Income Tax Reconciliation Tax Holidays IncomeTaxReconciliationTaxHolidays	4100000	USD
CY2018	us-gaap	Income Tax Reconciliation Tax Holidays IncomeTaxReconciliationTaxHolidays	4800000	USD
CY2017	us-gaap	Income Tax Reconciliation Tax Holidays IncomeTaxReconciliationTaxHolidays	3700000	USD
CY2019	us-gaap	Income Tax Reconciliation Other Reconciling Items IncomeTaxReconciliationOtherReconcilingItems	1600000	USD
CY2018	us-gaap	Income Tax Reconciliation Other Reconciling Items IncomeTaxReconciliationOtherReconcilingItems	900000	USD
CY2017	us-gaap	Income Tax Reconciliation Other Reconciling Items IncomeTaxReconciliationOtherReconcilingItems	1500000	USD
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	-28500000	USD
CY2018	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	11000000.0	USD
CY2017	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	-6800000	USD
CY2017	ati	Tax Cutsand Jobs Actof2017 Changein Tax Rate Deferred Tax Liability Income Tax Expense Benefit TaxCutsandJobsActof2017ChangeinTaxRateDeferredTaxLiabilityIncomeTaxExpenseBenefit	2600000	USD
CY2017	ati	Tax Cutsand Jobs Actof2017 Changein Tax Rate Deferred Tax Asset Valuation Allowance Increase Decrease TaxCutsandJobsActof2017ChangeinTaxRateDeferredTaxAssetValuationAllowanceIncreaseDecrease	1500000	USD
CY2017	ati	Income Tax Reconciliation U.S.Taxreform IncomeTaxReconciliationU.S.taxreform	-4100000	USD
CY2018	ati	Tax Cutsand Jobs Act Transition Taxfor Accumulated Foreign Earnings Income Tax Expense TaxCutsandJobsActTransitionTaxforAccumulatedForeignEarningsIncomeTaxExpense	5900000	USD
CY2019	ati	Tax Cuts And Jobs Act Foreign Earnings Inclusion Global Intangible Low Taxed Income Gilti TaxCutsAndJobsActForeignEarningsInclusionGlobalIntangibleLowTaxedIncomeGILTI	16800000	USD
CY2019	us-gaap	Income Tax Reconciliation Repatriation Of Foreign Earnings IncomeTaxReconciliationRepatriationOfForeignEarnings	3500000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Pensions DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensions	155500000	USD
CY2018Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Pensions DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensions	159400000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Postretirement Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPostretirementBenefits	83800000	USD
CY2018Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Postretirement Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPostretirementBenefits	87300000	USD
CY2019	ati	Tax Cuts And Jobs Act Estimate Of Federal Limit On Deductible Interest Expense TaxCutsAndJobsActEstimateOfFederalLimitOnDeductibleInterestExpense	24000000	USD
CY2019	ati	Effective Income Tax Rate Reconciliation Restructuring EffectiveIncomeTaxRateReconciliationRestructuring	4200000	USD
CY2015	ati	Numberof Yearsin Cumulative Loss Profit Position NumberofYearsinCumulativeLossProfitPosition	3	year
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	247700000	USD
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	190800000	USD
CY2019	us-gaap	Valuation Allowance Deferred Tax Asset Change In Amount ValuationAllowanceDeferredTaxAssetChangeInAmount	-45100000	USD
CY2019Q4	us-gaap	Other Comprehensive Income Loss Cash Flow Hedge Gain Loss Reclassification Tax OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax	6000000.0	USD
CY2019Q4	us-gaap	Deferred Tax Assets Operating Loss Carryforwards DeferredTaxAssetsOperatingLossCarryforwards	264400000	USD
CY2018Q4	us-gaap	Deferred Tax Assets Operating Loss Carryforwards DeferredTaxAssetsOperatingLossCarryforwards	307500000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Credit Carryforwards DeferredTaxAssetsTaxCreditCarryforwards	42600000	USD
CY2018Q4	us-gaap	Deferred Tax Assets Tax Credit Carryforwards DeferredTaxAssetsTaxCreditCarryforwards	49700000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	86100000	USD
CY2018Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	69700000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	632400000	USD
CY2018Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	673600000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	94500000	USD
CY2018Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	194800000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Net DeferredTaxAssetsNet	537900000	USD
CY2018Q4	us-gaap	Deferred Tax Assets Net DeferredTaxAssetsNet	478800000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Property Plant And Equipment DeferredTaxLiabilitiesPropertyPlantAndEquipment	364200000	USD
CY2018Q4	us-gaap	Deferred Tax Liabilities Property Plant And Equipment DeferredTaxLiabilitiesPropertyPlantAndEquipment	371500000	USD
CY2019Q4	ati	Deferred Tax Liabilities Inventory DeferredTaxLiabilitiesInventory	65500000	USD
CY2018Q4	ati	Deferred Tax Liabilities Inventory DeferredTaxLiabilitiesInventory	67100000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Goodwill And Intangible Assets DeferredTaxLiabilitiesGoodwillAndIntangibleAssets	23700000	USD
CY2018Q4	us-gaap	Deferred Tax Liabilities Goodwill And Intangible Assets DeferredTaxLiabilitiesGoodwillAndIntangibleAssets	29900000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	27000000.0	USD
CY2018Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	14500000	USD
CY2019Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	480400000	USD
CY2018Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	483000000.0	USD
CY2019Q4	us-gaap	Deferred Tax Assets Liabilities Net DeferredTaxAssetsLiabilitiesNet	57500000	USD
CY2018Q4	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	4200000	USD
CY2019	us-gaap	Income Taxes Paid IncomeTaxesPaid	15100000	USD
CY2018	us-gaap	Income Taxes Paid IncomeTaxesPaid	9700000	USD
CY2017	us-gaap	Income Taxes Paid IncomeTaxesPaid	10400000	USD
CY2019	us-gaap	Proceeds From Income Tax Refunds ProceedsFromIncomeTaxRefunds	9200000	USD
CY2018	us-gaap	Proceeds From Income Tax Refunds ProceedsFromIncomeTaxRefunds	1600000	USD
CY2017	us-gaap	Proceeds From Income Tax Refunds ProceedsFromIncomeTaxRefunds	7100000	USD
CY2019	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	5900000	USD
CY2018	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	8100000	USD
CY2017	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	3300000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Undistributed Foreign Earnings DeferredTaxLiabilitiesUndistributedForeignEarnings	3500000	USD
CY2018Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	14700000	USD
CY2017Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	14700000	USD
CY2016Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	22700000	USD
CY2019	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	0	USD
CY2018	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	0	USD
CY2017	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	0	USD
CY2019	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions	0	USD
CY2018	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions	100000	USD
CY2017	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions	700000	USD
CY2019	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	900000	USD
CY2018	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	700000	USD
CY2017	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	700000	USD
CY2019	us-gaap	Unrecognized Tax Benefits Reductions Resulting From Lapse Of Applicable Statute Of Limitations UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations	1200000	USD
CY2018	us-gaap	Unrecognized Tax Benefits Reductions Resulting From Lapse Of Applicable Statute Of Limitations UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations	600000	USD
CY2017	us-gaap	Unrecognized Tax Benefits Reductions Resulting From Lapse Of Applicable Statute Of Limitations UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations	400000	USD
CY2019	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Settlements With Taxing Authorities UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities	0	USD
CY2018	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Settlements With Taxing Authorities UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities	0	USD
CY2017	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Settlements With Taxing Authorities UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities	7600000	USD
CY2019Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	14400000	USD
CY2018Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	14700000	USD
CY2017Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	14700000	USD
CY2019Q4	ati	Unrecognized Tax Benefits Reductionof Operating Loss Carryforwards UnrecognizedTaxBenefitsReductionofOperatingLossCarryforwards	11500000	USD
CY2018Q4	ati	Unrecognized Tax Benefits Reductionof Operating Loss Carryforwards UnrecognizedTaxBenefitsReductionofOperatingLossCarryforwards	12100000	USD
CY2017Q4	ati	Unrecognized Tax Benefits Reductionof Operating Loss Carryforwards UnrecognizedTaxBenefitsReductionofOperatingLossCarryforwards	11700000	USD
CY2019Q4	us-gaap	Unrecognized Tax Benefits That Would Impact Effective Tax Rate UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate	3000000	USD
CY2019Q4	us-gaap	Significant Change In Unrecognized Tax Benefits Is Reasonably Possible Amount Of Unrecorded Benefit SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleAmountOfUnrecordedBenefit	2000000	USD
CY2019Q4	us-gaap	Unrecognized Tax Benefits Income Tax Penalties And Interest Accrued UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued	2700000	USD
CY2019	us-gaap	Number Of Reportable Segments NumberOfReportableSegments	2000000	segment
CY2019	ati	Revenue From International Sales RevenueFromInternationalSales	1667900000	USD
CY2018	ati	Revenue From International Sales RevenueFromInternationalSales	1698400000	USD
CY2017	ati	Revenue From International Sales RevenueFromInternationalSales	1454500000	USD
CY2019	ati	Entity Wide Disclosure On Geographic Areas Revenue From External Foreign Customers Attributed To Entitys Country Of Domicile EntityWideDisclosureOnGeographicAreasRevenueFromExternalForeignCustomersAttributedToEntitysCountryOfDomicile	1262600000	USD
CY2018	ati	Entity Wide Disclosure On Geographic Areas Revenue From External Foreign Customers Attributed To Entitys Country Of Domicile EntityWideDisclosureOnGeographicAreasRevenueFromExternalForeignCustomersAttributedToEntitysCountryOfDomicile	1303800000	USD
CY2017	ati	Entity Wide Disclosure On Geographic Areas Revenue From External Foreign Customers Attributed To Entitys Country Of Domicile EntityWideDisclosureOnGeographicAreasRevenueFromExternalForeignCustomersAttributedToEntitysCountryOfDomicile	1078600000	USD
CY2019	ati	Segment Operating Profit Loss SegmentOperatingProfitLoss	380700000	USD
CY2018	ati	Segment Operating Profit Loss SegmentOperatingProfitLoss	413200000	USD
CY2017	ati	Segment Operating Profit Loss SegmentOperatingProfitLoss	283400000	USD
CY2019	ati	Lifo Provision Benefitand Changein Debit Lifonr Vreservenet LifoProvisionBenefitandChangeinDebitLIFONRVreservenet	100000	USD
CY2018	ati	Lifo Provision Benefitand Changein Debit Lifonr Vreservenet LifoProvisionBenefitandChangeinDebitLIFONRVreservenet	700000	USD
CY2017	ati	Lifo Provision Benefitand Changein Debit Lifonr Vreservenet LifoProvisionBenefitandChangeinDebitLIFONRVreservenet	200000	USD
CY2019	ati	Corporate Expenses CorporateExpenses	66800000	USD
CY2018	ati	Corporate Expenses CorporateExpenses	58100000	USD
CY2017	ati	Corporate Expenses CorporateExpenses	50500000	USD
CY2019	ati	Other Expense OtherExpense	25500000	USD
CY2018	ati	Other Expense OtherExpense	21600000	USD
CY2017	ati	Other Expense OtherExpense	34000000.0	USD
CY2019	ati	Restructuringandothercharges Restructuringandothercharges	4500000	USD
CY2018	ati	Restructuringandothercharges Restructuringandothercharges	0	USD
CY2017	ati	Restructuringandothercharges Restructuringandothercharges	0	USD
CY2019	us-gaap	Goodwill Impairment Loss GoodwillImpairmentLoss	0	USD
CY2018	us-gaap	Goodwill Impairment Loss GoodwillImpairmentLoss	0	USD
CY2017	us-gaap	Goodwill Impairment Loss GoodwillImpairmentLoss	114400000	USD
CY2019	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	-21600000	USD
CY2018	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	0	USD
CY2017	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	-37000000.0	USD
CY2019	us-gaap	Deconsolidation Gain Or Loss Amount DeconsolidationGainOrLossAmount	0	USD
CY2018	us-gaap	Deconsolidation Gain Or Loss Amount DeconsolidationGainOrLossAmount	15900000	USD
CY2017	us-gaap	Deconsolidation Gain Or Loss Amount DeconsolidationGainOrLossAmount	0	USD
CY2019	ati	Other Asset Impairment Charges And Due From Affiliates Allowance For Credit Loss OtherAssetImpairmentChargesAndDueFromAffiliatesAllowanceForCreditLoss	11400000	USD
CY2018	ati	Other Asset Impairment Charges And Due From Affiliates Allowance For Credit Loss OtherAssetImpairmentChargesAndDueFromAffiliatesAllowanceForCreditLoss	0	USD
CY2017	ati	Other Asset Impairment Charges And Due From Affiliates Allowance For Credit Loss OtherAssetImpairmentChargesAndDueFromAffiliatesAllowanceForCreditLoss	0	USD
CY2019	us-gaap	Gain Loss On Sales Of Assets And Asset Impairment Charges GainLossOnSalesOfAssetsAndAssetImpairmentCharges	89800000	USD
CY2018	us-gaap	Gain Loss On Sales Of Assets And Asset Impairment Charges GainLossOnSalesOfAssetsAndAssetImpairmentCharges	0	USD
CY2017	us-gaap	Gain Loss On Sales Of Assets And Asset Impairment Charges GainLossOnSalesOfAssetsAndAssetImpairmentCharges	0	USD
CY2019	ati	Interest Expense Net InterestExpenseNet	99000000.0	USD
CY2018	ati	Interest Expense Net InterestExpenseNet	101000000.0	USD
CY2017	ati	Interest Expense Net InterestExpenseNet	133800000	USD
CY2019	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	241600000	USD
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	247700000	USD
CY2017	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	-86500000	USD
CY2019	ati	Restructuringandothercharges Restructuringandothercharges	4500000	USD
CY2019	us-gaap	Gain Loss On Sales Of Assets And Asset Impairment Charges GainLossOnSalesOfAssetsAndAssetImpairmentCharges	89800000	USD
CY2019	us-gaap	Gain Loss On Sale Of Property GainLossOnSaleOfProperty	91700000	USD
CY2019Q4	us-gaap	Assets Assets	5634600000	USD
CY2018Q4	us-gaap	Assets Assets	5501800000	USD
CY2017Q4	us-gaap	Assets Assets	5185400000	USD
CY2019Q4	us-gaap	Assets Assets	5634600000	USD
CY2019Q4	ati	Entity Wide Disclosure On Geographic Areas Total Assets Attributed To Individual Countries Percentage Amount EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount	1
CY2018Q4	us-gaap	Assets Assets	5501800000	USD
CY2018Q4	ati	Entity Wide Disclosure On Geographic Areas Total Assets Attributed To Individual Countries Percentage Amount EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount	1
CY2017Q4	us-gaap	Assets Assets	5185400000	USD
CY2017Q4	ati	Entity Wide Disclosure On Geographic Areas Total Assets Attributed To Individual Countries Percentage Amount EntityWideDisclosureOnGeographicAreasTotalAssetsAttributedToIndividualCountriesPercentageAmount	1
CY2019	us-gaap	Income Loss From Continuing Operations IncomeLossFromContinuingOperations	257600000	USD
CY2018	us-gaap	Income Loss From Continuing Operations IncomeLossFromContinuingOperations	222400000	USD
CY2017	us-gaap	Income Loss From Continuing Operations IncomeLossFromContinuingOperations	-91900000	USD
CY2019	us-gaap	Interest On Convertible Debt Net Of Tax InterestOnConvertibleDebtNetOfTax	12800000	USD
CY2018	us-gaap	Interest On Convertible Debt Net Of Tax InterestOnConvertibleDebtNetOfTax	12900000	USD
CY2017	us-gaap	Interest On Convertible Debt Net Of Tax InterestOnConvertibleDebtNetOfTax	0	USD
CY2019	us-gaap	Net Income Loss Available To Common Stockholders Diluted NetIncomeLossAvailableToCommonStockholdersDiluted	270400000	USD
CY2018	us-gaap	Net Income Loss Available To Common Stockholders Diluted NetIncomeLossAvailableToCommonStockholdersDiluted	235300000	USD
CY2017	us-gaap	Net Income Loss Available To Common Stockholders Diluted NetIncomeLossAvailableToCommonStockholdersDiluted	-91900000	USD
CY2019	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	125800000	shares
CY2018	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	125200000	shares
CY2017	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	110100000	shares
CY2019	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	800000	shares
CY2018	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	800000	shares
CY2017	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	0	shares
CY2019	us-gaap	Incremental Common Shares Attributable To Conversion Of Debt Securities IncrementalCommonSharesAttributableToConversionOfDebtSecurities	19900000	shares
CY2018	us-gaap	Incremental Common Shares Attributable To Conversion Of Debt Securities IncrementalCommonSharesAttributableToConversionOfDebtSecurities	19900000	shares
CY2017	us-gaap	Incremental Common Shares Attributable To Conversion Of Debt Securities IncrementalCommonSharesAttributableToConversionOfDebtSecurities	0	shares
CY2019	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	146500000	shares
CY2018	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	145900000	shares
CY2017	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	110100000	shares
CY2019	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	2.05
CY2018	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	1.78
CY2017	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	-0.83
CY2019	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	1.85
CY2018	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	1.61
CY2017	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	-0.83
CY2019	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	0	shares
CY2017	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	20800000	shares
CY2019Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	490800000	USD
CY2019Q4	us-gaap	Accounts Receivable Net Current AccountsReceivableNetCurrent	554100000	USD
CY2019Q4	us-gaap	Notes Receivable Related Parties Current NotesReceivableRelatedPartiesCurrent	0	USD
CY2019Q4	us-gaap	Contract With Customer Asset Net Current ContractWithCustomerAssetNetCurrent	38500000	USD
CY2019Q4	us-gaap	Inventory Net InventoryNet	1155300000	USD
CY2019Q4	us-gaap	Other Assets Current OtherAssetsCurrent	64300000	USD
CY2019Q4	us-gaap	Assets Current AssetsCurrent	2303000000.0	USD
CY2019Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	2450100000	USD
CY2019Q4	us-gaap	Goodwill Goodwill	525800000	USD
CY2019Q4	us-gaap	Notes Receivable Related Parties Noncurrent NotesReceivableRelatedPartiesNoncurrent	0	USD
CY2019Q4	us-gaap	Equity Method Investments EquityMethodInvestments	0	USD
CY2019Q4	us-gaap	Other Assets Noncurrent OtherAssetsNoncurrent	355700000	USD
CY2019Q4	us-gaap	Assets Assets	5634600000	USD
CY2019Q4	us-gaap	Accounts Payable Current AccountsPayableCurrent	521200000	USD
CY2019Q4	us-gaap	Notes Payable Related Parties Classified Current NotesPayableRelatedPartiesClassifiedCurrent	0	USD
CY2019Q4	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	78700000	USD
CY2019Q4	us-gaap	Debt Current DebtCurrent	11500000	USD
CY2019Q4	us-gaap	Accrued Liabilities Current AccruedLiabilitiesCurrent	237800000	USD
CY2019Q4	us-gaap	Liabilities Current LiabilitiesCurrent	849200000	USD
CY2019Q4	us-gaap	Long Term Debt And Capital Lease Obligations LongTermDebtAndCapitalLeaseObligations	1387400000	USD
CY2019Q4	us-gaap	Notes Payable Related Parties Noncurrent NotesPayableRelatedPartiesNoncurrent	0	USD
CY2019Q4	us-gaap	Other Postretirement Defined Benefit Plan Liabilities Noncurrent OtherPostretirementDefinedBenefitPlanLiabilitiesNoncurrent	312500000	USD
CY2019Q4	us-gaap	Defined Benefit Pension Plan Liabilities Noncurrent DefinedBenefitPensionPlanLiabilitiesNoncurrent	731500000	USD
CY2019Q4	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	160800000	USD
CY2019Q4	us-gaap	Liabilities Liabilities	3441400000	USD
CY2019Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	2193200000	USD
CY2019Q4	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	5634600000	USD
CY2019	us-gaap	Selling General And Administrative Expense SellingGeneralAndAdministrativeExpense	267200000	USD
CY2019	us-gaap	Restructuring Settlement And Impairment Provisions RestructuringSettlementAndImpairmentProvisions	4500000	USD
CY2019	us-gaap	Operating Income Loss OperatingIncomeLoss	366100000	USD
CY2019	ati	Nonoperatingretirementbenefitexpense Nonoperatingretirementbenefitexpense	73600000	USD
CY2019	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	4122500000	USD
CY2019	us-gaap	Cost Of Goods And Services Sold CostOfGoodsAndServicesSold	3484700000	USD
CY2019	us-gaap	Gross Profit GrossProfit	637800000	USD
CY2019	ati	Interest Expense Net InterestExpenseNet	99000000.0	USD
CY2019	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	-21600000	USD
CY2019	us-gaap	Other Nonoperating Income Expense OtherNonoperatingIncomeExpense	69700000	USD
CY2019	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	241600000	USD
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	-28500000	USD
CY2019	us-gaap	Profit Loss ProfitLoss	270100000	USD
CY2019	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	12500000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	257600000	USD
CY2019	us-gaap	Profit Loss ProfitLoss	270100000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Net Of Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax	-4000000.0	USD
CY2019	us-gaap	Other Comprehensive Income Loss Derivatives Qualifying As Hedges Net Of Tax OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax	10300000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	75500000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-69200000	USD
CY2019	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	200900000	USD
CY2019	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	11200000	USD
CY2019	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	189700000	USD
CY2019	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	230100000	USD
CY2019	us-gaap	Payments To Acquire Productive Assets PaymentsToAcquireProductiveAssets	168200000	USD
CY2019	ati	Proceeds Paymentsfrom Intercompany Activites Investing Activities ProceedsPaymentsfromIntercompanyActivitesInvestingActivities	0	USD
CY2019	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	92000000.0	USD
CY2019	us-gaap	Payments For Proceeds From Businesses And Interest In Affiliates PaymentsForProceedsFromBusinessesAndInterestInAffiliates	-158100000	USD
CY2019	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	200000	USD
CY2019	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	81700000	USD
CY2019	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	350000000.0	USD
CY2019	us-gaap	Repayments Of Long Term Debt And Capital Securities RepaymentsOfLongTermDebtAndCapitalSecurities	507600000	USD
CY2019	us-gaap	Proceeds From Repayments Of Other Debt ProceedsFromRepaymentsOfOtherDebt	4900000	USD
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CY2019Q4	ati	Environmental Remediation Obligation For Formerly Owned Sites EnvironmentalRemediationObligationForFormerlyOwnedSites	13000000	USD
CY2019Q4	ati	Environmental Remediation Obligation For Owned Or Controlled Sites With Closed Operations EnvironmentalRemediationObligationForOwnedOrControlledSitesWithClosedOperations	1000000	USD
CY2019Q4	ati	Environmental Remediation Obligation For Ongoing Operations EnvironmentalRemediationObligationForOngoingOperations	1000000	USD
CY2019Q4	us-gaap	Loss Contingency Range Of Possible Loss Portion Not Accrued LossContingencyRangeOfPossibleLossPortionNotAccrued	16000000	USD
CY2019Q1	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	1004800000	USD
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CY2019Q3	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	1018700000	USD
CY2019Q4	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	1018600000	USD
CY2019Q3	us-gaap	Net Income Loss NetIncomeLoss	111000000.0	USD
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CY2019Q1	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.12
CY2019Q1	us-gaap	Gross Profit GrossProfit	131100000	USD
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CY2019Q1	us-gaap	Profit Loss ProfitLoss	16300000	USD
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CY2019Q1	us-gaap	Net Income Loss NetIncomeLoss	15000000.0	USD
CY2019Q2	us-gaap	Net Income Loss NetIncomeLoss	75100000	USD
CY2019Q2	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.60
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CY2019Q4	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.41
CY2019Q1	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	125800000	shares
CY2019Q2	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	126100000	shares
CY2019Q3	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	126100000	shares
CY2019Q4	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	126100000	shares
CY2018Q1	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	979000000.0	USD
CY2018Q2	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	1009500000	USD
CY2018Q3	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	1020200000	USD
CY2018Q4	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	1037900000	USD
CY2018Q1	us-gaap	Gross Profit GrossProfit	148600000	USD
CY2018Q2	us-gaap	Gross Profit GrossProfit	173700000	USD
CY2018Q3	us-gaap	Gross Profit GrossProfit	160400000	USD
CY2018Q4	us-gaap	Gross Profit GrossProfit	147600000	USD
CY2018Q1	us-gaap	Profit Loss ProfitLoss	60500000	USD
CY2018Q2	us-gaap	Profit Loss ProfitLoss	75600000	USD
CY2018Q3	us-gaap	Profit Loss ProfitLoss	55600000	USD
CY2018Q4	us-gaap	Profit Loss ProfitLoss	45000000.0	USD
CY2018Q1	us-gaap	Net Income Loss NetIncomeLoss	58000000.0	USD
CY2018Q2	us-gaap	Net Income Loss NetIncomeLoss	72800000	USD
CY2018Q3	us-gaap	Net Income Loss NetIncomeLoss	50500000	USD
CY2018Q4	us-gaap	Net Income Loss NetIncomeLoss	41100000	USD
CY2018Q1	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.46
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CY2018Q3	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.40
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CY2018Q2	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	125700000	shares
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CY2018Q4	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	125700000	shares
CY2019Q2	us-gaap	Gain Loss On Sale Of Property GainLossOnSaleOfProperty	29300000	USD
CY2019Q2	ati	Gain Loss On Disposition Of Oil And Gas And Timber Property Net Of Tax GainLossOnDispositionOfOilAndGasAndTimberPropertyNetOfTax	27300000	USD
CY2019Q3	us-gaap	Gain Loss On Sale Of Property GainLossOnSaleOfProperty	62400000	USD
CY2019Q3	ati	Gain Loss On Disposition Of Oil And Gas And Timber Property Net Of Tax GainLossOnDispositionOfOilAndGasAndTimberPropertyNetOfTax	60500000	USD
CY2019Q4	ati	Restructuringandothercharges Restructuringandothercharges	4500000	USD
CY2019Q4	ati	Restructuring And Other Charges Net Of Tax RestructuringAndOtherChargesNetOfTax	4300000	USD
CY2019Q4	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	-21600000	USD
CY2019Q4	us-gaap	Extinguishment Of Debt Gain Loss Net Of Tax ExtinguishmentOfDebtGainLossNetOfTax	-20500000	USD
CY2019Q4	ati	Other Asset Impairment Charges And Due From Affiliates Allowance For Credit Loss OtherAssetImpairmentChargesAndDueFromAffiliatesAllowanceForCreditLoss	11400000	USD
CY2019Q4	ati	Other Asset Impairment Charges And Due From Affiliates Allowance For Credit Loss Net Of Tax OtherAssetImpairmentChargesAndDueFromAffiliatesAllowanceForCreditLossNetOfTax	10800000	USD
CY2019Q4	us-gaap	Valuation Allowance Deferred Tax Asset Change In Amount ValuationAllowanceDeferredTaxAssetChangeInAmount	-41900000	USD
CY2018Q1	us-gaap	Deconsolidation Gain Or Loss Amount DeconsolidationGainOrLossAmount	15900000	USD
CY2018Q1	ati	Deconsolidation Gain Loss Amount Netoftax DeconsolidationGainLossAmountNetoftax	14700000	USD

Files In Submission

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$ATI
ATI INC Stock $ati

2019 Q4 Form 8-K Financial Statement

#000162828020008258 Filed on May 22, 2020

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$ATI ATI INC Stock $ati

2019 Q4 Form 8-K Financial Statement

#000162828020008258 Filed on May 22, 2020

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$ATI
ATI INC Stock $ati