CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Statement [Abstract]
Sales	$ 1,022.5	$ 1,119.0	$ 2,148.0	$ 2,106.3
Costs and expenses:
Cost of sales	945.5	1,029.5	1,961.5	1,946.6
Selling and administrative expenses	72.4	65.7	135.5	133.4
Income before interest, other income and income taxes	4.6	23.8	51.0	26.3
Interest expense, net	(26.8)	(28.5)	(53.5)	(57.6)
Other income, net	0.6	1.3	1.5	1.9
Loss from continuing operations before income taxes	(21.6)	(3.4)	(1.0)	(29.4)
Income tax provision (benefit)	(7.7)	(2.9)	0.3	(12.9)
Loss from continuing operations	(13.9)	(0.5)	(1.3)	(16.5)
Income (loss) from discontinued operations, net of tax	0.0	(0.2)	0.0	(2.1)
Net income (loss)	(13.9)	(0.7)	(1.3)	(18.6)
Less: Net income attributable to noncontrolling interests	2.5	3.3	5.1	5.4
Net income (loss) attributable to ATI	$ (16.4)	$ (4.0)	$ (6.4)	$ (24.0)
Continuing operations attributable to ATI per common share (in dollars per share)	$ (0.15)	$ (0.03)	$ (0.06)	$ (0.20)
Discontinued operations attributable to ATI per common share (in dollars per share)	0.00	0.00	0.00	(0.02)
Basic net income (loss) attributable to ATI per common share (in dollars per share)	(0.15)	(0.03)	(0.06)	(0.22)
Continuing operations attributable to ATI per common share (in dollars per share)	(0.15)	(0.03)	(0.06)	(0.20)
Discontinued operations attributable to ATI per common share (in dollars per share)	0.00	0.00	0.00	(0.02)
Diluted net income (loss) attributable to ATI per common share (in dollars per share)	(0.15)	(0.03)	(0.06)	(0.22)
Dividends declared per common share (in dollars per share)	$ 0.18	$ 0.18	$ 0.36	$ 0.36
Loss from continuing operations, net of tax	$ (16.4)	$ (3.8)	$ (6.4)	$ (21.9)
Loss from discontinued operations, net of tax	$ 0.0	$ (0.2)	$ 0.0	$ (2.1)