Quarterly report pursuant to Section 13 or 15(d)

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

v3.5.0.2
SEGMENT REPORTING Segment Reporting (Summary of Assets by Segment) (Details) - USD ($)
$ in Millions
Jun. 30, 2016
Dec. 31, 2015
Segment Reporting Information [Line Items]    
Assets $ 1,851.0 $ 2,135.5
U.S. Iron Ore [Member]    
Segment Reporting Information [Line Items]    
Assets 1,510.3 1,476.4
Asia Pacific Iron Ore [Member]    
Segment Reporting Information [Line Items]    
Assets 166.4 202.5
Total Segment Assets [Member]    
Segment Reporting Information [Line Items]    
Assets 1,676.7 1,678.9
Corporate [Member]    
Segment Reporting Information [Line Items]    
Assets 174.3 441.7
Discontinued Operations [Member]    
Segment Reporting Information [Line Items]    
Assets of Discontinued Operations $ 0.0 $ 14.9