Quarterly report pursuant to Section 13 or 15(d)

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

v2.4.0.8
SEGMENT REPORTING Segment Reporting (Summary of Assets by Segment) (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2014
Dec. 31, 2013
Segment Reporting Information [Line Items]    
Assets $ 13,202.8 $ 13,121.9
U.S. Iron Ore [Member]
   
Segment Reporting Information [Line Items]    
Assets 1,742.9 1,671.6
Eastern Canadian Iron Ore [Member]
   
Segment Reporting Information [Line Items]    
Assets 7,854.2 7,915.5
Asia Pacific Iron Ore [Member]
   
Segment Reporting Information [Line Items]    
Assets 1,074.9 1,078.4
North American Coal [Member]
   
Segment Reporting Information [Line Items]    
Assets 1,784.4 1,841.8
All Other Segments [Member]
   
Segment Reporting Information [Line Items]    
Assets 467.5 455.6
Total Segment Assets [Member]
   
Segment Reporting Information [Line Items]    
Assets 12,923.9 12,962.9
Corporate [Member]
   
Segment Reporting Information [Line Items]    
Assets $ 278.9 $ 159.0