Per Share Information (Details) - USD ($) $ / shares in Units, shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Earnings Per Share Reconciliation [Abstract]
Loss attributable to ATI	$ (18,800,000)	$ (16,400,000)	$ (120,000,000)	$ (6,400,000)
Redeemable noncontrolling interest	0	0	0	(100,000)
4.75% Convertible Senor Notes due 2022	0	0	0	0
Loss attributable to ATI after assumed conversions	$ (18,800,000)	$ (16,400,000)	$ (120,000,000)	$ (6,500,000)
Denominator for basic net loss per common share – weighted average shares	107.3	107.3	107.3	107.2
Share-based compensation	0.0	0.0	0.0	0.0
Effective of dilutive securities: 4.75% Convertible Senior Notes due 2022	0.0	0.0	0.0	0.0
Denominator for diluted net loss per common share – adjusted weighted average shares and assumed conversions	107.3	107.3	107.3	107.2
Basic income (loss) from continuing operations attributable to ATI per common share (in dollars per share)	$ (0.18)	$ (0.15)	$ (1.12)	$ (0.06)
Diluted income (loss) from continuing operations attributable to ATI per common share (in dollars per share)	$ (0.18)	$ (0.15)	$ (1.12)	$ (0.06)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount	9.3	1.2	5.0	1.0