Business Segments (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) segment	Sep. 30, 2015 USD ($)
Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Abstract]
Number of business segments \| segment			2
Segment Reporting Information [Line Items]
Sales	$ 770.5	$ 832.7	$ 2,338.5	$ 2,980.7
Operating profit (loss):	26.2	(73.0)	(47.3)	14.3
LIFO and net realizable value reserves	0.0	(0.2)	0.4	0.0
Corporate expenses	(9.8)	(10.7)	(32.6)	(33.6)
Closed operations and other expenses	(15.4)	(6.5)	(24.6)	(18.6)
Restructuring and other charges	(499.9)	0.0	(509.9)	0.0
Interest expense, net	(32.6)	(27.5)	(91.2)	(81.0)
Income (loss) before income tax provision (benefit)	(531.5)	(117.9)	(705.2)	(118.9)
High Performance Materials & Components
Segment Reporting Information [Line Items]
Operating profit (loss):	47.0	18.8	114.9	136.1
Flat Rolled Products
Segment Reporting Information [Line Items]
Operating profit (loss):	(20.8)	(91.8)	(162.2)	(121.8)
Operating Segments
Segment Reporting Information [Line Items]
Sales	796.4	867.9	2,420.9	3,104.5
Operating Segments \| High Performance Materials & Components
Segment Reporting Information [Line Items]
Sales	474.7	490.1	1,493.7	1,588.5
Operating Segments \| Flat Rolled Products
Segment Reporting Information [Line Items]
Sales	321.7	377.8	927.2	1,516.0
Internal Customers \| Operating Segments
Segment Reporting Information [Line Items]
Sales	25.9	35.2	82.4	123.8
Internal Customers \| Operating Segments \| High Performance Materials & Components
Segment Reporting Information [Line Items]
Sales	12.9	15.4	40.5	59.9
Internal Customers \| Operating Segments \| Flat Rolled Products
Segment Reporting Information [Line Items]
Sales	13.0	19.8	41.9	63.9
External Customers \| Operating Segments
Segment Reporting Information [Line Items]
Sales	770.5	832.7	2,338.5	2,980.7
External Customers \| Operating Segments \| High Performance Materials & Components
Segment Reporting Information [Line Items]
Sales	461.8	474.7	1,453.2	1,528.6
External Customers \| Operating Segments \| Flat Rolled Products
Segment Reporting Information [Line Items]
Sales	$ 308.7	$ 358.0	$ 885.3	$ 1,452.1

corporate office expenses not allocable to business segments

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
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Aggregate revenue during the period from the sale of goods in the normal course of business, after deducting returns, allowances and discounts.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
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