Financial Information for Subsidiary and Guarantor Parent (I.S.) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Statement [Abstract]
Sales	$ 972.4	$ 1,131.5	$ 3,128.2	$ 3,645.5
Cost of sales	919.3	988.8	2,886.9	3,139.6
Selling and administrative expenses	70.6	77.6	210.1	243.3
Income (loss) before interest, other income and income taxes	(17.5)	65.1	31.2	262.6
Interest expense, net	(18.2)	(17.2)	(46.5)	(55.7)
Other income (loss) including equity in income of unconsolidated subsidiaries	0.4	0.2	1.3	0.6
Income (loss) before income taxes	(35.3)	48.1	(14.0)	207.5
Income tax provision (benefit)	(8.5)	14.8	(4.4)	66.6
Income (loss) from continuing operations	(26.8)	33.3	(9.6)	140.9
Income (loss)from discontinued operations, net of tax	(5.4)	4.0	(4.4)	13.4
Net income (loss)	(32.2)	37.3	(14.0)	154.3
Less: Net income (loss) attributable to noncontrolling interests	1.6	2.0	5.4	6.4
Net income (loss) attributable to ATI	(33.8)	35.3	(19.4)	147.9
Comprehensive income (loss) attributable to ATI	(11.6)	71.8	27.4	213.6
Parent Company
Income Statement [Abstract]
Sales	0	0	0	0
Cost of sales	19.4	15.1	55.5	41.8
Selling and administrative expenses	35.4	33.7	88.9	109.1
Income (loss) before interest, other income and income taxes	(54.8)	(48.8)	(144.4)	(150.9)
Interest expense, net	(17.3)	(14.7)	(45.5)	(47.3)
Other income (loss) including equity in income of unconsolidated subsidiaries	36.8	111.6	175.9	405.7
Income (loss) before income taxes	(35.3)	48.1	(14.0)	207.5
Income tax provision (benefit)	(8.5)	14.8	(4.4)	66.6
Income (loss) from continuing operations	(26.8)	33.3	(9.6)	140.9
Income (loss)from discontinued operations, net of tax	(5.4)	4.0	(4.4)	13.4
Net income (loss)	(32.2)	37.3	(14.0)	154.3
Less: Net income (loss) attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to ATI	(32.2)	37.3	(14.0)	154.3
Comprehensive income (loss) attributable to ATI	(9.9)	74.4	35.3	220.0
Subsidiaries
Income Statement [Abstract]
Sales	422.3	483.6	1,375.2	1,614.2
Cost of sales	424.3	453.8	1,359.5	1,488.7
Selling and administrative expenses	7.4	10.8	27.3	33.2
Income (loss) before interest, other income and income taxes	(9.4)	19.0	(11.6)	92.3
Interest expense, net	(9.7)	(2.7)	(27.0)	(7.9)
Other income (loss) including equity in income of unconsolidated subsidiaries	0.1	(5.2)	0.6	(16.1)
Income (loss) before income taxes	(19.0)	11.1	(38.0)	68.3
Income tax provision (benefit)	(6.6)	4.6	(9.8)	26.9
Income (loss) from continuing operations	(12.4)	6.5	(28.2)	41.4
Income (loss)from discontinued operations, net of tax	0	0	0	0
Net income (loss)	(12.4)	6.5	(28.2)	41.4
Less: Net income (loss) attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to ATI	(12.4)	6.5	(28.2)	41.4
Comprehensive income (loss) attributable to ATI	(12.2)	6.3	(27.8)	40.6
NonGuarantor Subsidiaries
Income Statement [Abstract]
Sales	550.1	647.9	1,753.0	2,031.3
Cost of sales	475.6	519.9	1,471.9	1,609.1
Selling and administrative expenses	27.8	33.1	93.9	101.0
Income (loss) before interest, other income and income taxes	46.7	94.9	187.2	321.2
Interest expense, net	8.8	0.2	26.0	(0.5)
Other income (loss) including equity in income of unconsolidated subsidiaries	0.3	7.8	0.8	24.2
Income (loss) before income taxes	55.8	102.9	214.0	344.9
Income tax provision (benefit)	22.4	33.3	76.6	116.9
Income (loss) from continuing operations	33.4	69.6	137.4	228.0
Income (loss)from discontinued operations, net of tax	(2.5)	4.6	(0.2)	16.1
Net income (loss)	30.9	74.2	137.2	244.1
Less: Net income (loss) attributable to noncontrolling interests	1.6	2.0	5.4	6.4
Net income (loss) attributable to ATI	29.3	72.2	131.8	237.7
Comprehensive income (loss) attributable to ATI	42.0	87.3	134.8	249.2
Consolidation Eliminations
Income Statement [Abstract]
Sales	0	0	0	0
Cost of sales	0	0	0	0
Selling and administrative expenses	0	0	0	0
Income (loss) before interest, other income and income taxes	0	0	0	0
Interest expense, net	0	0	0	0
Other income (loss) including equity in income of unconsolidated subsidiaries	(36.8)	(114.0)	(176.0)	(413.2)
Income (loss) before income taxes	(36.8)	(114.0)	(176.0)	(413.2)
Income tax provision (benefit)	(15.8)	(37.9)	(66.8)	(143.8)
Income (loss) from continuing operations	(21.0)	(76.1)	(109.2)	(269.4)
Income (loss)from discontinued operations, net of tax	2.5	(4.6)	0.2	(16.1)
Net income (loss)	(18.5)	(80.7)	(109.0)	(285.5)
Less: Net income (loss) attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to ATI	(18.5)	(80.7)	(109.0)	(285.5)
Comprehensive income (loss) attributable to ATI	$ (31.5)	$ (96.2)	$ (114.9)	$ (296.2)