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Business Segments (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2015 | Sep. 30, 2015 | Jun. 30, 2015 | Mar. 31, 2015 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales | $ 796.1 | $ 770.5 | $ 810.5 | $ 757.5 | $ 738.9 | $ 832.7 | $ 1,022.5 | $ 1,125.5 | $ 3,134.6 | $ 3,719.6 | $ 4,223.4
External Sales [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales |  |  |  |  |  |  |  |  | 3,134.6 | 3,719.6 | 4,223.4
Operating Segments [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales |  |  |  |  |  |  |  |  | 3,240.3 | 3,870.6 | 4,404.8
Operating Segments [Member] | Intersegment Sales [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales |  |  |  |  |  |  |  |  | 105.7 | 151.0 | 181.4
Operating Segments [Member] | External Sales [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales |  |  |  |  |  |  |  |  | 3,134.6 | 3,719.6 | 4,223.4
Operating Segments [Member] | High Performance Materials & Components [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales |  |  |  |  |  |  |  |  | 1,979.5 | 2,062.7 | 2,084.6
Operating Segments [Member] | High Performance Materials & Components [Member] | Intersegment Sales [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales |  |  |  |  |  |  |  |  | 49.1 | 76.8 | 77.8
Operating Segments [Member] | High Performance Materials & Components [Member] | External Sales [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales |  |  |  |  |  |  |  |  | 1,930.4 | 1,985.9 | 2,006.8
Operating Segments [Member] | Flat Rolled Products [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales |  |  |  |  |  |  |  |  | 1,260.8 | 1,807.9 | 2,320.2
Operating Segments [Member] | Flat Rolled Products [Member] | Intersegment Sales [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales |  |  |  |  |  |  |  |  | 56.6 | 74.2 | 103.6
Operating Segments [Member] | Flat Rolled Products [Member] | External Sales [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales |  |  |  |  |  |  |  |  | $ 1,204.2 | $ 1,733.7 | $ 2,216.6

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