Annual report pursuant to Section 13 and 15(d)

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

v3.6.0.2
SEGMENT REPORTING SEGMENT REPORTING (Summary of Assets by Segment) (Details) - USD ($)
$ in Millions
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Segment Reporting Information [Line Items]      
Assets $ 1,923.9 $ 2,135.5 $ 3,147.2
U.S. Iron Ore [Member]      
Segment Reporting Information [Line Items]      
Assets 1,372.5 1,476.4 1,464.9
Asia Pacific Iron Ore [Member]      
Segment Reporting Information [Line Items]      
Assets 155.1 202.5 306.2
Total Segment Assets [Member]      
Segment Reporting Information [Line Items]      
Assets 1,527.6 1,678.9 1,771.1
Corporate [Member]      
Segment Reporting Information [Line Items]      
Assets 396.3 441.7 666.2
Discontinued Operations [Member]      
Segment Reporting Information [Line Items]      
Disposal Group, Including Discontinued Operation, Assets $ 0.0 $ 14.9 $ 709.9