Consolidated Statements of Income (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement [Abstract]
Sales	$ 4,223.4	$ 4,043.5	$ 4,666.9
Costs and expenses:
Cost of sales	3,844.8	3,790.9	4,041.4
Selling and administrative expenses	272.5	276.4	321.6
Restructuring costs	0	67.5	0
Income (loss) before interest, other income and income taxes	106.1	(91.3)	303.9
Interest expense, net	(108.7)	(65.2)	(71.6)
Other income, net	4.1	1.7	0
Income (loss) from continuing operations before income taxes	1.5	(154.8)	232.3
Income tax provision (benefit)	(8.7)	(63.6)	72.4
Income (loss) from continuing operations	10.2	(91.2)	159.9
Income (loss) from discontinued operations, net of tax	(0.6)	252.8	7.9
Net income	9.6	161.6	167.8
Less: Net income attributable to noncontrolling interests	12.2	7.6	9.4
Net income (loss) attributable to ATI	(2.6)	154.0	158.4
Basic net income (loss) per common share
Continuing operations attributable to ATI per common share (in dollars per share)	$ (0.02)	$ (0.93)	$ 1.42
Discontinued operations attributable to ATI per common share (in dollars per share)	$ (0.01)	$ 2.37	$ 0.07
Basic net income attributable to ATI per common share (in dollars per share)	$ (0.03)	$ 1.44	$ 1.49
Diluted net income (loss) per common share
Continuing operations attributable to ATI per common share (in dollars per share)	$ (0.02)	$ (0.93)	$ 1.36
Discontinued operations attributable to ATI per common share (in dollars per share)	$ (0.01)	$ 2.37	$ 0.07
Diluted net income attributable to ATI per common share (in dollars per share)	$ (0.03)	$ 1.44	$ 1.43
Income (loss) from continuing operations, net of tax	(2.0)	(98.8)	150.5
Income (loss) from discontinued operations, net of tax	$ (0.6)	$ 252.8	$ 7.9