|
SEGMENT REPORTING (Narrative) (Details) (USD $)
In Millions, unless otherwise specified |
3 Months Ended | 12 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
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Dec. 31, 2013
|
Sep. 30, 2013
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Jun. 30, 2013
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Mar. 31, 2013
|
Dec. 31, 2012
|
Sep. 30, 2012
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Jun. 30, 2012
|
Mar. 31, 2012
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Dec. 31, 2013
|
Dec. 31, 2012
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Dec. 31, 2011
|
|
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Revenues | $ 1,515.8 | $ 1,546.6 | $ 1,488.5 | $ 1,140.5 | $ 1,535.9 | $ 1,544.9 | $ 1,579.5 | $ 1,212.4 | $ 5,691.4 | $ 5,872.7 | $ 6,563.9 |
|
U.S. Iron Ore [Member]
|
Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Number Of Mines | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 5 | Ìý | Ìý |
| Revenues | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 2,667.9 | 2,723.3 | 3,509.9 |
|
Eastern Canadian Iron Ore [Member]
|
Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Number Of Mines | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 2 | Ìý | Ìý |
| Revenues | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 978.7 | 1,008.9 | 1,178.1 |
|
Asia Pacific Iron Ore [Member]
|
Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Number Of Mines | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 1 | Ìý | Ìý |
| Revenues | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 1,224.3 | 1,259.3 | 1,363.5 |
|
North American Coal [Member]
|
Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Revenues | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 821.9 | 881.1 | 512.1 |
|
North American Coal [Member] | Metallurgical Coal Mines [Member]
|
Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Number Of Mines | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 4 | Ìý | Ìý |
|
North American Coal [Member] | Thermal Coal Mines [Member]
|
Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Number Of Mines | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 1 | Ìý | Ìý |
|
Sales Revenue, Net [Member] | Customer Concentration Risk [Member]
|
Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Number of Customers | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 1 | 1 | 1,000,000 |
| Concentration Risk, Percentage | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 10.00% | Ìý | Ìý |
| Revenues | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | $ 1,000.0 | $ 923.7 | $ 1,400.0 |