Difference between amount at which an investment accounted for under the equity method of accounting is carried (reported) on the balance sheet and amount of underlying equity in net assets the reporting Entity has in the investee.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Gain (loss) related to the termination of a contract between the parties. The termination may be due to many causes including early termination of a lease by a lessee, a breach of contract by one party, or a failure to perform.

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Losses recognized in the current period on contracts which are expected to generate losses, which are probable and can be reasonably estimated, in a future period.

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The amount of cash paid for the settlement of litigation or for other legal issues during the period.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Investments in Affiliates (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Investments in Affiliates (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Gain on termination of pellet agreement and related transportation costs		$ 0.0	$ 19.3	$ (69.5)
Combined Metals of Chicago, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage (in hundredths)		40.00%
Delaco Processing, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage (in hundredths)		49.00%
Rockport Roll Shop LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage (in hundredths)		50.00%
Spartan Steel Coating, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage (in hundredths)		48.00%
Difference between carrying amount and underlying equity		$ 9.2
Cost of Products Sold [Member]
Schedule of Equity Method Investments [Line Items]
Share of income (loss) from equity method investments		$ 6.6	$ 7.0	12.3
Global Settlement Agreement [Member] \| Magnetation LLC [Member]
Schedule of Equity Method Investments [Line Items]
Payments for Legal Settlements				36.6
Iron Ore Pellets Agreements [Member]
Schedule of Equity Method Investments [Line Items]
Gain on termination of pellet agreement and related transportation costs	$ 19.3
Iron Ore Pellets Agreements [Member] \| Magnetation LLC [Member]
Schedule of Equity Method Investments [Line Items]
Loss on Contracts				$ 32.9
Gain on termination of pellet agreement and related transportation costs	$ 19.3