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Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue | $ 1,018.6 | $ 1,018.7 | $ 1,080.4 | $ 1,004.8 | $ 1,037.9 | $ 1,020.2 | $ 1,009.5 | $ 979.0 | $ 4,122.5 | $ 4,046.6 | $ 3,525.1
Percent of total revenue |  |  |  |  |  |  |  |  | 100.00% | 100.00% | 100.00%
Total High-Value Products |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 87.00% | 86.00% | 84.00%
Nickel-based alloys and specialty alloys |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 32.00% | 30.00% | 28.00%
Precision forgings, castings and components |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 18.00% | 20.00% | 19.00%
Titanium and titanium-based alloys |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 18.00% | 17.00% | 17.00%
Precision and engineered strip |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 13.00% | 14.00% | 14.00%
Zirconium and related alloys |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 6.00% | 5.00% | 6.00%
Standard stainless products |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 13.00% | 14.00% | 16.00%
United States |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | $ 2,454.6 | $ 2,348.1 | $ 2,070.6
China |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 355.6 | 320.0 | 265.6
Germany |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 219.3 | 247.2 | 217.1
United Kingdom |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 173.8 | 242.1 | 231.6
France |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 155.5 | 183.6 | 165.6
Japan |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 147.7 | 214.9 | 131.7
Rest of World |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 616.0 | 490.7 | 442.9
Aerospace & Defense |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 2,130.4 | 1,965.5 | 1,718.1
Oil & Gas |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 510.6 | 546.2 | 418.2
Automotive |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 296.6 | 323.4 | 273.7
Energy |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 286.3 | 234.5 | 192.2
Food Equipment & Appliances |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 205.8 | 244.9 | 226.0
Construction/Mining |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 195.0 | 226.0 | 192.9
Medical |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 172.4 | 183.1 | 183.0
Electronics/Computers/Communications |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 163.2 | 156.9 | 151.6
Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 162.2 | 166.1 | 169.4
Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 4,322.8 | 4,212.6 | 3,654.5
Operating Segments | High Performance Materials & Components |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | $ 2,501.9 | $ 2,413.6 | $ 2,127.0
Percent of total revenue |  |  |  |  |  |  |  |  | 100.00% | 100.00% | 100.00%
Operating Segments | High Performance Materials & Components | Total High-Value Products |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 100.00% | 100.00% | 100.00%
Operating Segments | High Performance Materials & Components | Nickel-based alloys and specialty alloys |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 32.00% | 31.00% | 31.00%
Operating Segments | High Performance Materials & Components | Precision forgings, castings and components |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 30.00% | 34.00% | 32.00%
Operating Segments | High Performance Materials & Components | Titanium and titanium-based alloys |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 28.00% | 25.00% | 26.00%
Operating Segments | High Performance Materials & Components | Precision and engineered strip |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 0.00% | 0.00% | 0.00%
Operating Segments | High Performance Materials & Components | Zirconium and related alloys |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 10.00% | 10.00% | 11.00%
Operating Segments | High Performance Materials & Components | Standard stainless products |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 0.00% | 0.00% | 0.00%
Operating Segments | High Performance Materials & Components | United States |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | $ 1,319.7 | $ 1,214.1 | $ 1,096.5
Operating Segments | High Performance Materials & Components | China |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 103.0 | 83.1 | 51.1
Operating Segments | High Performance Materials & Components | Germany |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 178.2 | 192.7 | 170.5
Operating Segments | High Performance Materials & Components | United Kingdom |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 164.9 | 232.4 | 220.9
Operating Segments | High Performance Materials & Components | France |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 145.8 | 172.7 | 157.8
Operating Segments | High Performance Materials & Components | Japan |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 104.4 | 136.5 | 95.2
Operating Segments | High Performance Materials & Components | Rest of World |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 382.1 | 302.7 | 275.4
Operating Segments | High Performance Materials & Components | Aerospace & Defense |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 1,879.1 | 1,771.3 | 1,568.9
Operating Segments | High Performance Materials & Components | Oil & Gas |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 64.3 | 74.9 | 63.9
Operating Segments | High Performance Materials & Components | Automotive |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 10.5 | 9.5 | 8.8
Operating Segments | High Performance Materials & Components | Energy |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 156.9 | 131.4 | 113.1
Operating Segments | High Performance Materials & Components | Food Equipment & Appliances |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 0.3 | 0.4 | 1.1
Operating Segments | High Performance Materials & Components | Construction/Mining |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 42.5 | 72.8 | 51.1
Operating Segments | High Performance Materials & Components | Medical |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 159.2 | 168.5 | 170.4
Operating Segments | High Performance Materials & Components | Electronics/Computers/Communications |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 5.8 | 7.9 | 4.4
Operating Segments | High Performance Materials & Components | Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 79.5 | 97.5 | 85.7
Operating Segments | Flat Rolled Products |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | $ 1,820.9 | $ 1,799.0 | $ 1,527.5
Percent of total revenue |  |  |  |  |  |  |  |  | 100.00% | 100.00% | 100.00%
Operating Segments | Flat Rolled Products | Total High-Value Products |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 70.00% | 66.00% | 63.00%
Operating Segments | Flat Rolled Products | Nickel-based alloys and specialty alloys |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 32.00% | 28.00% | 24.00%
Operating Segments | Flat Rolled Products | Precision forgings, castings and components |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 0.00% | 0.00% | 0.00%
Operating Segments | Flat Rolled Products | Titanium and titanium-based alloys |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 6.00% | 5.00% | 5.00%
Operating Segments | Flat Rolled Products | Precision and engineered strip |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 32.00% | 33.00% | 34.00%
Operating Segments | Flat Rolled Products | Zirconium and related alloys |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 0.00% | 0.00% | 0.00%
Operating Segments | Flat Rolled Products | Standard stainless products |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percent of total revenue |  |  |  |  |  |  |  |  | 30.00% | 34.00% | 37.00%
Operating Segments | Flat Rolled Products | United States |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | $ 1,134.9 | $ 1,134.0 | $ 974.1
Operating Segments | Flat Rolled Products | China |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 252.6 | 236.9 | 214.5
Operating Segments | Flat Rolled Products | Germany |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 41.1 | 54.5 | 46.6
Operating Segments | Flat Rolled Products | United Kingdom |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 8.9 | 9.7 | 10.7
Operating Segments | Flat Rolled Products | France |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 9.7 | 10.9 | 7.8
Operating Segments | Flat Rolled Products | Japan |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 43.3 | 78.4 | 36.5
Operating Segments | Flat Rolled Products | Rest of World |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 233.9 | 188.0 | 167.5
Operating Segments | Flat Rolled Products | Aerospace & Defense |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 251.3 | 194.2 | 149.2
Operating Segments | Flat Rolled Products | Oil & Gas |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 446.3 | 471.3 | 354.3
Operating Segments | Flat Rolled Products | Automotive |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 286.1 | 313.9 | 264.9
Operating Segments | Flat Rolled Products | Energy |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 129.4 | 103.1 | 79.1
Operating Segments | Flat Rolled Products | Food Equipment & Appliances |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 205.5 | 244.5 | 224.9
Operating Segments | Flat Rolled Products | Construction/Mining |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 152.5 | 153.2 | 141.8
Operating Segments | Flat Rolled Products | Medical |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 13.2 | 14.6 | 12.6
Operating Segments | Flat Rolled Products | Electronics/Computers/Communications |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 157.4 | 149.0 | 147.2
Operating Segments | Flat Rolled Products | Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 82.7 | 68.6 | 83.7
External Customers | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 4,122.5 | 4,046.6 | 3,525.1
External Customers | Operating Segments | High Performance Materials & Components |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 2,398.1 | 2,334.2 | 2,067.4
External Customers | Operating Segments | Flat Rolled Products |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | $ 1,724.4 | $ 1,712.4 | $ 1,457.7

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Namespace Prefix: | us-gaap_
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