Acquisition of Business (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Business Acquisition [Line Items]
Business Acquisition, Name of Acquired Entity	Ladish Co., Inc.
Business Acquisition, Description of Acquired Entity	Based in Wisconsin, ATI Ladish engineers, produces and markets high-strength, high technology forged and cast metal components for a wide variety of load-bearing and fatigue-resisting applications in the jet engine, aerospace and industrial markets, for both domestic and international customers.
Business Acquisition, Effective Date of Acquisition	5/9/2011
Business Acquisition, Cost of Acquired Entity, Cash Paid	$ 384.0
Purchases of businesses and investments in ventures	349.2	0	38.9
Business Acquisition, Cost of Acquired Entity, Purchase Price	897.6
Cost in excess of net assets acquired	737.7	206.8
Business Acquisition, Purchase Price Allocation, Status	final
Ladish [Member]
Business Acquisition [Line Items]
Business Acquisition, Name of Acquired Entity	Ladish
Business Acquisition, Revenue Reported by Acquired Entity for Last Annual Period		403.1
Business Acquisition, Effective Date of Acquisition	May 9, 2011
Purchases of businesses and investments in ventures	349.2
Stock Issued During Period, Shares, Acquisitions	7.3
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangibles	166.0
Cost in excess of net assets acquired	$ 530.0