Per Share Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share Reconciliation [Abstract]
Loss from continuing operations attributable to ATI	$ (16.4)	$ (3.8)	$ (6.4)	$ (21.9)
Redeemable noncontrolling interest	0.0	0.0	(0.1)	0.0
Loss from continuing operations available to ATI after assumed conversions	$ (16.4)	$ (3.8)	$ (6.5)	$ (21.9)
Denominator for basic net loss per common share-weighted average shares	107,300,000	107,100,000	107,200,000	107,000,000
Share-based compensation	0	0	0	0
4.25% Convertible Notes due 2014	0	0	0	0
Denominator for diluted net loss per common share – adjusted weighted average shares assuming conversions	107,300,000	107,100,000	107,200,000	107,000,000
Basic income (loss) from continuing operations attributable to ATI per common share (in dollars per share)	$ (0.15)	$ (0.03)	$ (0.06)	$ (0.20)
Diluted income (loss) from continuing operations attributable to ATI per common share (in dollars per share)	$ (0.15)	$ (0.03)	$ (0.06)	$ (0.20)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount	1,200,000	7,000,000	1,000,000	8,500,000.0