Annual report pursuant to Section 13 and 15(d)

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

v3.10.0.1
SEGMENT REPORTING (Summary of Assets by Segment) (Details) - USD ($)
$ in Millions
Dec. 31, 2018
Jan. 01, 2018
Dec. 31, 2017
Dec. 31, 2016
Segment Reporting Information [Line Items]        
TOTAL ASSETS $ 3,529.6 $ 2,990.2 $ 2,953.4 $ 1,923.9
Mining and Pelletizing [Member]        
Segment Reporting Information [Line Items]        
TOTAL ASSETS 1,694.1   1,500.6 1,372.5
Metallics [Member]        
Segment Reporting Information [Line Items]        
TOTAL ASSETS 265.9   13.4 0.0
Total Segment Assets [Member]        
Segment Reporting Information [Line Items]        
TOTAL ASSETS 1,960.0   1,514.0 1,372.5
Corporate [Member]        
Segment Reporting Information [Line Items]        
TOTAL ASSETS 1,557.2   1,300.6 396.3
Discontinued Operations [Member]        
Segment Reporting Information [Line Items]        
Disposal Group, Including Discontinued Operation, Assets $ 12.4   $ 138.8 $ 155.1