Selected Quarterly Financial Data (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Selected Quarterly Financial Information Abstract
Sales Revenue Net	$ 1,251.4	$ 1,352.6	$ 1,351.6	$ 1,227.4	$ 1,037.6	$ 1,058.8	$ 1,052.0	$ 899.4
Gross Profit	169.0	215.8	223.0	205.4	127.3	89.8	151.8	121.4
Net income (loss) attributable to ATI	31.7	62.3	64.0	56.3	15.1	1.0	36.4	18.2	214.3	70.7	31.7
Basic net income (loss) attributable to ATI per common share	$ 0.30	$ 0.59	$ 0.63	$ 0.58	$ 0.16	$ 0.01	$ 0.37	$ 0.19	$ 2.09	$ 0.73	$ 0.33
Diluted net income (loss) attributable to ATI per common share	$ 0.29	$ 0.56	$ 0.59	$ 0.54	$ 0.15	$ 0.01	$ 0.36	$ 0.18	$ 1.97	$ 0.72	$ 0.32
Weighted Average Number Of Shares Outstanding Basic	106,358,868	106,341,817	103,405,003	98,767,947	98,593,745	98,576,117	98,563,774	98,317,319	102,500,000	97,400,000	97,200,000
Unusual Or Infrequent Item [Line Items]
Debt extinguishment costs									0	0	(9.2)
Income Tax Reconciliation Other Adjustments				2.7		3.9		3.7
Proceeds From Income Tax Refunds									41.0	20.9	124.3
Accelerated Share Based Compensation Expense Netof Tax				3.1
Business Combination, Separately Recognized Transactions, Expenses and Losses Recognized	1.1	8.3	12.7
Restructuring and Related Cost, Incurred Cost	1.7
Income Tax Reconciliation Deductions Medicare Prescription Drug Benefit Subsidy								$ (5.3)		$ (5.3)