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
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