Quarterly report pursuant to Section 13 or 15(d)

SEGMENT REPORTING Segment Reporting (Summary of Assets by Segment) (Details)

v3.3.0.814
SEGMENT REPORTING Segment Reporting (Summary of Assets by Segment) (Details) - USD ($)
$ in Millions
Sep. 30, 2015
Dec. 31, 2014
Segment Reporting Information [Line Items]    
Assets $ 2,271.5 $ 3,164.0
U.S. Iron Ore [Member]    
Segment Reporting Information [Line Items]    
Assets 1,498.3 1,464.9
Asia Pacific Iron Ore [Member]    
Segment Reporting Information [Line Items]    
Assets 210.5 274.6
All Other Segments [Member]    
Segment Reporting Information [Line Items]    
Assets 26.3 147.0
Total Segment Assets [Member]    
Segment Reporting Information [Line Items]    
Assets 1,735.1 1,886.5
Corporate [Member]    
Segment Reporting Information [Line Items]    
Assets 395.0 546.8
Discontinued Operations [Member]    
Segment Reporting Information [Line Items]    
Disposal Group, Including Discontinued Operation, Assets $ 141.4 $ 730.7