Quarterly report pursuant to Section 13 or 15(d)

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

v3.4.0.3
SEGMENT REPORTING Segment Reporting (Summary of Assets by Segment) (Details) - USD ($)
$ in Millions
Mar. 31, 2016
Dec. 31, 2015
Segment Reporting Information [Line Items]    
Assets $ 1,886.3 $ 2,135.5
U.S. Iron Ore [Member]    
Segment Reporting Information [Line Items]    
Assets 1,475.1 1,476.4
Asia Pacific Iron Ore [Member]    
Segment Reporting Information [Line Items]    
Assets 180.6 202.5
Total Segment Assets [Member]    
Segment Reporting Information [Line Items]    
Assets 1,655.7 1,678.9
Corporate [Member]    
Segment Reporting Information [Line Items]    
Assets 230.1 441.7
Discontinued Operations [Member]    
Segment Reporting Information [Line Items]    
Assets of Discontinued Operations $ 0.5 $ 14.9