CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Statement [Abstract]
Sales	$ 832.7	$ 1,069.6	$ 2,980.7	$ 3,175.9
Costs and expenses:
Cost of sales	861.4	972.6	2,822.9	2,919.2
Selling and administrative expenses	62.5	68.7	198.0	202.1
Income (loss) before interest, other income and income taxes	(91.2)	28.3	(40.2)	54.6
Interest expense, net	(27.5)	(25.2)	(81.0)	(82.8)
Other income, net	0.8	1.0	2.3	2.9
Income (loss) from continuing operations before income taxes	(117.9)	4.1	(118.9)	(25.3)
Income tax provision (benefit)	23.4	0.5	23.7	(12.4)
Income (loss) from continuing operations	(141.3)	3.6	(142.6)	(12.9)
Income (loss) from discontinued operations, net of tax	0.0	(0.7)	0.0	(2.8)
Net income (loss)	(141.3)	2.9	(142.6)	(15.7)
Less: Net income attributable to noncontrolling interests	3.3	3.6	8.4	9.0
Net income (loss) attributable to ATI	$ (144.6)	$ (0.7)	$ (151.0)	$ (24.7)
Continuing operations attributable to ATI per common share (in dollars per share)	$ (1.35)	$ 0.00	$ (1.41)	$ (0.20)
Discontinued operations attributable to ATI per common share (in dollars per share)	0.00	(0.01)	0.00	(0.03)
Basic net loss attributable to ATI per common share (in dollars per share)	(1.35)	(0.01)	(1.41)	(0.23)
Continuing operations attributable to ATI per common share (in dollars per share)	(1.35)	0.00	(1.41)	(0.20)
Discontinued operations attributable to ATI per common share (in dollars per share)	0.00	(0.01)	0.00	(0.03)
Diluted net loss attributable to ATI per common share (in dollars per share)	(1.35)	(0.01)	(1.41)	(0.23)
Dividends declared per common share (in dollars per share)	$ 0.18	$ 0.18	$ 0.54	$ 0.54
Loss from continuing operations, net of tax	$ (144.6)	$ 0.0	$ (151.0)	$ (21.9)
Loss from discontinued operations, net of tax	$ 0.0	$ (0.7)	$ 0.0	$ (2.8)