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Business Segments (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales | $ 1,037.9 | $ 1,020.2 | $ 1,009.5 | $ 979.0 | $ 909.9 | $ 869.1 | $ 880.2 | $ 865.9 | $ 4,046.6 | $ 3,525.1 | $ 3,134.6
Operating Segments |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales |  |  |  |  |  |  |  |  | 4,212.6 | 3,654.5 | 3,240.3
Operating Segments | Intersegment Sales [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales |  |  |  |  |  |  |  |  | 166.0 | 129.4 | 105.7
Operating Segments | External Sales [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales |  |  |  |  |  |  |  |  | 4,046.6 | 3,525.1 | 3,134.6
Operating Segments | High Performance Materials & Components |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales |  |  |  |  |  |  |  |  | 2,413.6 | 2,127.0 | 1,979.5
Operating Segments | High Performance Materials & Components | Intersegment Sales [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales |  |  |  |  |  |  |  |  | 79.4 | 59.6 | 49.1
Operating Segments | High Performance Materials & Components | External Sales [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales |  |  |  |  |  |  |  |  | 2,334.2 | 2,067.4 | 1,930.4
Operating Segments | Flat Rolled Products |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales |  |  |  |  |  |  |  |  | 1,799.0 | 1,527.5 | 1,260.8
Operating Segments | Flat Rolled Products | Intersegment Sales [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales |  |  |  |  |  |  |  |  | 86.6 | 69.8 | 56.6
Operating Segments | Flat Rolled Products | External Sales [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sales |  |  |  |  |  |  |  |  | $ 1,712.4 | $ 1,457.7 | $ 1,204.2

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- Definition Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130543-203045 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130539-203045 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130545-203045 + Details
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