CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement of Other Comprehensive Income [Abstract]
Net income (loss)	$ (32.2)	$ 37.3	$ (14.0)	$ 154.3
Currency translation adjustment
Unrealized net change arising during the period	12.4	15.3	3.9	10.1
Unrealized holding gain on securities
Net gain arising during the period	0.1	0	0.1	0.1
Derivatives
Net derivatives gain (loss) on hedge transactions	(18.1)	7.8	(21.0)	5.5
Reclassification to net income of net realized gain	4.3	0.6	5.5	3.5
Income taxes on derivative transactions	(5.3)	3.3	(6.0)	3.5
Total	(8.5)	5.1	(9.5)	5.5
Postretirement benefit plans
Amortization of net actuarial loss	33.5	29.9	100.5	89.8
Amortization to net income of net prior service credits	(3.8)	(2.9)	(11.4)	(8.8)
Income taxes on postretirement benefit plans	11.4	10.3	34.3	31.0
Total	18.3	16.7	54.8	50.0
Other comprehensive income, net of tax	22.3	37.1	49.3	65.7
Comprehensive income (loss)	(9.9)	74.4	35.3	220.0
Less: Comprehensive income attributable to noncontrolling interests	1.7	2.6	7.9	6.4
Comprehensive income (loss) attributable to ATI	$ (11.6)	$ 71.8	$ 27.4	$ 213.6