Discontinued Operations - Narrative (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2013	Sep. 30, 2014 Iron Castings Business	Jun. 30, 2014 Iron Castings Business	Sep. 30, 2014 Iron Castings Business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Severance Costs		$ 0.5	$ 1.2	$ 1.7
Restructuring Charge	9.5
Restructuring Charges, Net of Tax	$ 8.1

Amount charged against earnings in the period for incurred and estimated costs associated with exit from or disposal of business activities or restructurings pursuant to a duly authorized plan, including asset reitrement obligations.

No definition available.

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