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SEGMENT REPORTING Segment Reporting (Summary of Assets by Segment) (Details) - USD ($) $ in Millions | Sep. 30, 2016 | Dec. 31, 2015
--- | --- | ---
Segment Reporting Information [Line Items] |  |
Assets | $ 1,772.9 | $ 2,135.5
U.S. Iron Ore [Member] |  |
Segment Reporting Information [Line Items] |  |
Assets | 1,429.0 | 1,476.4
Asia Pacific Iron Ore [Member] |  |
Segment Reporting Information [Line Items] |  |
Assets | 137.7 | 202.5
Total Segment Assets [Member] |  |
Segment Reporting Information [Line Items] |  |
Assets | 1,566.7 | 1,678.9
Corporate [Member] |  |
Segment Reporting Information [Line Items] |  |
Assets | 206.2 | 441.7
Discontinued Operations [Member] |  |
Segment Reporting Information [Line Items] |  |
Assets of Discontinued Operations | $ 0.0 | $ 14.9

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