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Business Segments (Details2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Other Significant Reconciling Item [Line Items]
Depreciation and amortization	$ 160.8	$ 170.3	$ 189.9
Capital expenditures	122.7	202.2	144.5
Operating Segments [Member]
Segment Reporting Other Significant Reconciling Item [Line Items]
Depreciation and amortization	160.8	170.3	189.9
Capital expenditures	122.7	202.2	144.5
Operating Segments [Member] | High Performance Materials & Components [Member]
Segment Reporting Other Significant Reconciling Item [Line Items]
Depreciation and amortization	109.3	118.4	131.8
Capital expenditures	62.7	89.9	75.8
Operating Segments [Member] | Flat Rolled Products [Member]
Segment Reporting Other Significant Reconciling Item [Line Items]
Depreciation and amortization	45.6	48.8	55.6
Capital expenditures	59.1	111.8	68.0
Operating Segments [Member] | Corporate [Member]
Segment Reporting Other Significant Reconciling Item [Line Items]
Depreciation and amortization	5.9	3.1	2.5
Capital expenditures	$ 0.9	$ 0.5	$ 0.7

X

- Definition

The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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X

- Definition

The cash outflow for purchases of and capital improvements on property, plant and equipment (capital expenditures), software, and other intangible assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3213-108585

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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