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ACQUISITION OF AK STEEL - Transaction Overview (Details) $ in Millions |  | 3 Months Ended | 4 Months Ended | 6 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Mar. 13, 2020 USD ($) | Jun. 30, 2020 USD ($) | Jun. 30, 2019 USD ($) | Jun. 30, 2020 USD ($) | Jun. 30, 2020 USD ($) | Jun. 30, 2019 USD ($) | Dec. 31, 2019 USD ($) | Jul. 01, 2020 USD ($)
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Revenues |  | $ 1,092.7 | $ 743.2 |  | $ 1,451.8 | [1] | $ 900.2 |  |
Net income (loss) |  | (123.9) | 160.8 |  | (176.0) |  | 138.7 |  |
Amortization of inventory step-up |  |  |  |  | 59.4 |  | 0.0 |  |
Acquisition-related costs |  | 18.4 | $ 0.0 |  | 60.9 |  | $ 0.0 |  |
AK Steel Holding Corporation [Member] |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Business Acquisition, Shares Exchange Ratio | 0.400 |  |  |  |  |  |  |  |
Business Acquisition, Revenue Reported by Acquired Entity for Last Annual Period |  |  |  |  |  |  |  | $ 6,359.4 |
Revenues |  | 715.1 |  | $ 932.6 |  |  |  |  |
Net income (loss) |  | (206.5) |  | (261.6) |  |  |  |  |
Amortization of inventory step-up |  | 36.2 |  | 59.4 |  |  |  |  |
Severance costs |  | 15.1 |  | $ 32.7 |  |  |  |  |
Acquisition-related costs |  | $ 1.8 |  |  | $ 25.0 |  |  |  |
Business Combination, Consideration Transferred | $ 1,535.1 |  |  |  |  |  |  |  |
Forecast [Member] | AK Steel Holding Corporation [Member] |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Cost synergies |  |  |  |  |  |  |  |  | $ 150.0
[1] | Includes Realization of deferred revenue of $34.6 million for the six months ended June 30, 2020.

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