Consolidated Statements of Operations - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Sales	$ 3,719.6	$ 4,223.4	$ 4,043.5
Costs and expenses:
Cost of sales	3,659.3	3,844.8	3,790.9
Selling and administrative expenses	238.8	272.5	276.4
Impairment of goodwill	126.6	0.0	0.0
Restructuring charges	64.3	0.0	67.5
Income (loss) before interest, other income and income taxes	(369.4)	106.1	(91.3)
Interest expense, net	(110.2)	(108.7)	(65.2)
Other income, net	1.6	4.1	1.7
Income (loss) from continuing operations before income taxes	(478.0)	1.5	(154.8)
Income tax benefit	(112.1)	(8.7)	(63.6)
Income (loss) from continuing operations	(365.9)	10.2	(91.2)
Income (loss) from discontinued operations, net of tax	0.0	(0.6)	252.8
Net income (loss)	(365.9)	9.6	161.6
Less: Net income attributable to noncontrolling interests	12.0	12.2	7.6
Net income (loss) attributable to ATI	$ (377.9)	$ (2.6)	$ 154.0
Basic net income (loss) per common share
Continuing operations attributable to ATI per common share (in dollars per share)	$ (3.53)	$ (0.02)	$ (0.93)
Discontinued operations attributable to ATI per common share (in dollars per share)	0.00	(0.01)	2.37
Basic net income attributable to ATI per common share (in dollars per share)	(3.53)	(0.03)	1.44
Diluted net income (loss) per common share
Continuing operations attributable to ATI per common share (in dollars per share)	(3.53)	(0.02)	(0.93)
Discontinued operations attributable to ATI per common share (in dollars per share)	0.00	(0.01)	2.37
Diluted net income attributable to ATI per common share (in dollars per share)	$ (3.53)	$ (0.03)	$ 1.44
Loss from continuing operations, net of tax	$ (377.9)	$ (2.0)	$ (98.8)
Income (loss) from discontinued operations, net of tax	$ 0.0	$ (0.6)	$ 252.8