Accumulated Other Comprehensive Income (Loss) (Details 2) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization to net loss of net prior service cost (credits)		$ 1.5	$ (0.1)	$ 3.0	$ (0.3)
Amount reclassified from AOCI, Postretirement benefit plans, Actuarial losses		18.7	22.0	37.4	44.0
Income (loss) from continuing operations before income tax provision (benefit)		(21.6)	(3.4)	(1.0)	(29.4)
Income tax provision (benefit)		(7.7)	(2.9)	0.3	(12.9)
Loss from continuing operations		(13.9)	(0.5)	(1.3)	(16.5)
Amount reclassified from AOCI, Gain (loss) on derivatives		(945.5)	(1,029.5)	(1,961.5)	(1,946.6)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Post- retirement benefit plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization to net loss of net prior service cost (credits)	[1]	(1.5)	0.1	(3.0)	0.3
Amount reclassified from AOCI, Postretirement benefit plans, Actuarial losses	[1]	(18.7)	(22.0)	(37.4)	(44.0)
Income (loss) from continuing operations before income tax provision (benefit)	[2]	(20.2)	(21.9)	(40.4)	(43.7)
Income tax provision (benefit)		(7.7)	(8.4)	(15.4)	(16.8)
Loss from continuing operations		(12.5)	(13.5)	(25.0)	(26.9)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) from continuing operations before income tax provision (benefit)	[2]	2.1	0.5	4.8	(1.6)
Income tax provision (benefit)		0.8	0.2	1.8	(0.6)
Loss from continuing operations		1.3	0.3	3.0	(1.0)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member] | Nickel and other raw material contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amount reclassified from AOCI, Gain (loss) on derivatives	[3]	(3.9)	1.5	(7.5)	(1.3)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member] | Natural gas contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amount reclassified from AOCI, Gain (loss) on derivatives	[3]	(3.9)	1.6	(7.8)	3.9
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member] | Electricity contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amount reclassified from AOCI, Gain (loss) on derivatives	[3]	0.0	0.1	(0.2)	0.8
Reclassification out of Accumulated Other Comprehensive Income [Member] | Derivatives [Member] | Foreign exchange contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amount reclassified from AOCI, Gain (loss) on derivatives	[3]	$ 9.9	$ (2.7)	$ 20.3	$ (5.0)

[1] Amounts are included in the computation of pension and other postretirement benefit expense, which is reported in both cost of goods sold and selling and administrative expenses. For additional information, see Note 7.

[2] For pretax items, positive amounts are income and negative amounts are expense in terms of the impact to net income. Tax effects are presented in conformity with ATI’s presentation in the consolidated statements of operations.

[3] Amounts are included in cost of goods sold in the period or periods the hedged item affects earnings. For additional information, see Note 5.