CONSOLIDATED STATEMENTS OF OPERATIONS (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Income Statement [Abstract]
Sales	$ 1,125.5	$ 987.3
Costs and expenses:
Cost of sales	1,016.0	917.1
Selling and administrative expenses	63.1	67.7
Income before interest, other income and income taxes	46.4	2.5
Interest expense, net	(26.7)	(29.1)
Other income, net	0.9	0.6
Income (loss) from continuing operations before income taxes	20.6	(26.0)
Income tax provision (benefit)	8.0	(10.0)
Income (loss) from continuing operations	12.6	(16.0)
Income (loss) from discontinued operations, net of tax	0	(1.9)
Net income (loss)	12.6	(17.9)
Less: Net income attributable to noncontrolling interests	2.6	2.1
Net income (loss) attributable to ATI	10.0	(20.0)
Continuing operations attributable to ATI per common share (in dollars per share)	$ 0.09	$ (0.17)
Discontinued operations attributable to ATI per common share (in dollars per share)	$ 0.00	$ (0.02)
Basic net income (loss) attributable to ATI per common share (in dollars per share)	$ 0.09	$ (0.19)
Continuing operations attributable to ATI per common share (in dollars per share)	$ 0.09	$ (0.17)
Discontinued operations attributable to ATI per common share (in dollars per share)	$ 0.00	$ (0.02)
Diluted net income (loss) attributable to ATI per common share (in dollars per share)	$ 0.09	$ (0.19)
Dividends declared per common share (in dollars per share)	$ 0.18	$ 0.18
Income (loss) from continuing operations, net of tax	10.0	(18.1)
Loss from discontinued operations, net of tax	$ 0	$ (1.9)