Business Segments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting Information [Line Items]
Sales	$ 1,119.0	$ 1,056.8	$ 2,106.3	$ 2,155.8
Operating profit (loss):	65.2	70.2	108.7	147.7
Corporate expenses	(11.7)	(11.8)	(23.2)	(24.2)
Interest expense, net	(28.5)	(13.9)	(57.6)	(28.3)
Closed company and other expenses	(4.3)	(5.5)	(9.3)	(8.9)
Retirement benefit expense	(24.1)	(32.5)	(48.0)	(65.0)
Income (loss) from continuing operations before income tax provision (benefit)	(3.4)	6.5	(29.4)	21.3
Interest Costs Capitalized	1.4	10.6
High Performance Materials & Components
Segment Reporting Information [Line Items]
Total sales:	514.1	504.1	998.5	1,044.2
Operating profit (loss):	85.1	69.0	154.2	144.0
Flat Rolled Products
Segment Reporting Information [Line Items]
Total sales:	604.9	552.7	1,107.8	1,111.6
Operating profit (loss):	(19.9)	1.2	(45.5)	3.7
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales:	1,161.9	1,081.1	2,195.6	2,208.9
Operating Segments [Member] \| High Performance Materials & Components
Segment Reporting Information [Line Items]
Total sales:	531.4	520.5	1,035.5	1,080.5
Operating Segments [Member] \| Flat Rolled Products
Segment Reporting Information [Line Items]
Total sales:	630.5	560.6	1,160.1	1,128.4
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Total sales:	42.9	24.3	89.3	53.1
Intersegment Eliminations [Member] \| High Performance Materials & Components
Segment Reporting Information [Line Items]
Total sales:	17.3	16.4	37.0	36.3
Intersegment Eliminations [Member] \| Flat Rolled Products
Segment Reporting Information [Line Items]
Total sales:	$ 25.6	$ 7.9	$ 52.3	$ 16.8

corporate office expenses not allocable to business segments

No definition available.

Name:	ati_CorporateExpenses
Namespace Prefix:	ati_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Net interest expense - the cost of borrowed funds as interest charged against earnings during the period net of interest income derived from investments in debt securities and on cash and cash equivalents.

+ References

No definition available.

+ Details

Name:	ati_InterestExpenseNet
Namespace Prefix:	ati_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Other expense, net of gains on asset sales primarily includes charges incurred in connection with closed operations and other non-operating income or expense

+ References

No definition available.

+ Details

Name:	ati_OtherExpense
Namespace Prefix:	ati_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents defined benefit plan pension expense, and other postretirement benefit expense for both defined benefit and defined contribution plans

+ References

No definition available.

+ Details

Name:	ati_RetirementBenefitExpense
Namespace Prefix:	ati_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Business segment operating profit, which excludes costs for restructuring charges, retirement benefit income or expense, corproate expenses, interest expense, debt extinguishment costs and costs associated with closed operations. These costs are excluded for segment reporting to provide a profit measure based on what management considers to be controllable costs at the business segment level

+ References

No definition available.

+ Details

Name:	ati_SegmentOperatingProfitLoss
Namespace Prefix:	ati_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Sum of operating profit and nonoperating income or expense before Income or Loss from equity method investments, income taxes, extraordinary items, and noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(h)(1)(i))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

Name:	us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of interest capitalized during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Allowance for Funds Used during Construction

-URI http://asc.fasb.org/extlink&oid=6504829

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391

+ Details

Name:	us-gaap_InterestCostsCapitalized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

+ Details

Name:	us-gaap_Revenues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Aggregate revenue during the period from the sale of goods in the normal course of business, after deducting returns, allowances and discounts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1(a))

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

+ Details

Name:	us-gaap_SalesRevenueGoodsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_SegmentReportingInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration