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Inventories Narrative (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Sep. 30, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Jan. 01, 2018
Inventory [Line Items] |  |  |  |  |
LIFO inventory amount |  | $ 794.3 | $ 821.2 |  |
Inventory valuation reserves |  | (88.5) | (121.5) |  |
Effect of LIFO liquidation on income |  | 0.8 | (4.6) | $ (61.5) |
Inventories, net |  | 1,211.1 | 1,176.1 |  |
Adjustment from current cost to LIFO cost basis |  | 2.9 | 43.1 |  |
ASU 2014-09 |  |  |  |  |
Inventory [Line Items] |  |  |  |  |
Inventory valuation reserves |  |  |  |  | $ 11.8
Inventories, net |  | 9.5 |  |  | 28.8
Adjustment from current cost to LIFO cost basis |  |  |  |  | (11.8)
ASU 2014-09 | Transferred over Time |  |  |  |  |
Inventory [Line Items] |  |  |  |  |
Inventories, net |  | 5.4 |  |  | $ (34.2)
Titanium sponge inventory | SEC Schedule, 12-09, Reserve, Inventory |  |  |  |  |
Inventory [Line Items] |  |  |  |  |
Inventory valuation charges | $ 11.3 |  |  |  |
Industrial titanium products | SEC Schedule, 12-09, Reserve, Inventory |  |  |  |  |
Inventory [Line Items] |  |  |  |  |
Inventory valuation charges |  |  |  | $ 17.7 |
Net Realizable Value Reserve |  |  |  |  |
Inventory [Line Items] |  |  |  |  |
Inventory valuation reserves |  | $ (8.0) | $ (47.5) |  |

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