Business Segments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue	$ 1,396.3	$ 1,398.3	$ 2,791.2	$ 2,679.6
Segment Reporting Information Intersegment Sales	38.9	46.7	81.3	100.6
Segment Reporting Information Sales To External Customers	1,357.4	1,351.6	2,709.9	2,579.0
Segment Operating Profit (Loss)	159.9	173.4	323.1	335.8
Depreciation and amortization			96.2	80.6
Segment Operating Profit (Loss)	159.9	173.4	323.1	335.8
Corporate Expenses	(15.8)	(25.8)	(37.5)	(51.6)
Interest expense, net	18.6	23.7	38.5	46.7
Other Expense	(5.2)	(4.2)	(12.1)	(4.7)
Retirement Benefit Expense	(30.6)	(19.4)	(61.2)	(38.7)
Income Before Income Taxes	89.7	100.3	173.8	194.1
High Performance Metals [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue	587.6	524.6	1,195.4	957.7
Segment Reporting Information Intersegment Sales	21.4	27.4	47.9	61.1
Segment Reporting Information Sales To External Customers	566.2	497.2	1,147.5	896.6
Segment Operating Profit (Loss)	102.2	92.9	206.3	178.5
Segment Operating Profit (Loss)	102.2	92.9	206.3	178.5
Flat-Rolled Products [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue	665.5	735.8	1,308.8	1,454.8
Segment Reporting Information Intersegment Sales	8.1	8.5	15.4	16.9
Segment Reporting Information Sales To External Customers	657.4	727.3	1,293.4	1,437.9
Segment Operating Profit (Loss)	44.5	73.7	91.3	137.1
Segment Operating Profit (Loss)	44.5	73.7	91.3	137.1
Engineered Products [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information Revenue	143.2	137.9	287.0	267.1
Segment Reporting Information Intersegment Sales	9.4	10.8	18.0	22.6
Segment Reporting Information Sales To External Customers	133.8	127.1	269.0	244.5
Segment Operating Profit (Loss)	13.2	6.8	25.5	20.2
Segment Operating Profit (Loss)	$ 13.2	$ 6.8	$ 25.5	$ 20.2

corporate office expenses not allocable to business segments

No definition available.

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

- Definition

Sum of segment operating profit, corporate expenses, net interest income or expense, retirement benefit income or expenses, and other expenses including closed company operations, nonoperating income (expense) before income (loss) from equity method investments, income taxes, extraordinary items, cumulative effects of changes in accounting principles, and noncontrolling interest.

+ References

No definition available.

+ Details

Name:	ati_IncomeBeforeIncomeTaxes
Namespace Prefix:	ati_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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:	credit
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:	credit
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

The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585

+ Details

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

- Definition

Aggregate revenue recognized during the period (derived from goods sold, services rendered, insurance premiums, or other activities that constitute an entity's earning process). For financial services companies, also includes investment and interest income, and sales and trading gains.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 5

-Section 03

-Paragraph 1

Reference 2: 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=6880815&loc=d3e20235-122688

+ Details

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

- Definition

Amount of revenue from transactions with other operating segments of the same entity.

+ References

+ Details

Name:	us-gaap_RevenuesFromTransactionsWithOtherOperatingSegmentsOfSameEntity
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

- Definition

Amount of total revenue for the reportable segments, including revenue from external customers, transactions with other operating segments of the same entity, and (gross) interest revenue. All considered to be "operating revenue" for purposes of the taxonomy.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 131

-Paragraph 27

-Subparagraph a, b, c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 280

-SubTopic 10

-Section 50

-Paragraph 22

-Subparagraph (a),(b),(c)

-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8736-108599

+ Details

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