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SHAREHOLDERS' EQUITY Accumulate Other Comprehensive Income (Loss) (Details) (USD $)
In Millions, unless otherwise specified |
3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | ||||||||||||||||||||||||||||||||
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Sep. 30, 2013
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Sep. 30, 2012
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Sep. 30, 2013
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Sep. 30, 2012
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Jun. 30, 2013
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Mar. 31, 2013
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Dec. 31, 2012
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Dec. 31, 2011
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Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Member]
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Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Member]
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Mar. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Member]
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Sep. 30, 2013
Accumulated Defined Benefit Plans Adjustment [Member]
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Jun. 30, 2013
Accumulated Defined Benefit Plans Adjustment [Member]
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Mar. 31, 2013
Accumulated Defined Benefit Plans Adjustment [Member]
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Sep. 30, 2013
Accumulated Net Unrealized Investment Gain (Loss) [Member]
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Jun. 30, 2013
Accumulated Net Unrealized Investment Gain (Loss) [Member]
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Mar. 31, 2013
Accumulated Net Unrealized Investment Gain (Loss) [Member]
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Sep. 30, 2013
Accumulated Translation Adjustment [Member]
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Jun. 30, 2013
Accumulated Translation Adjustment [Member]
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Mar. 31, 2013
Accumulated Translation Adjustment [Member]
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Sep. 30, 2013
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
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Jun. 30, 2013
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
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Mar. 31, 2013
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
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Sep. 30, 2013
Accumulated Defined Benefit Plans Adjustment [Member]
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Jun. 30, 2013
Accumulated Defined Benefit Plans Adjustment [Member]
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Mar. 31, 2013
Accumulated Defined Benefit Plans Adjustment [Member]
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Sep. 30, 2013
Accumulated Net Unrealized Investment Gain (Loss) [Member]
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Jun. 30, 2013
Accumulated Net Unrealized Investment Gain (Loss) [Member]
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Mar. 31, 2013
Accumulated Net Unrealized Investment Gain (Loss) [Member]
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Sep. 30, 2013
Accumulated Translation Adjustment [Member]
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Jun. 30, 2013
Accumulated Translation Adjustment [Member]
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Mar. 31, 2013
Accumulated Translation Adjustment [Member]
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Sep. 30, 2013
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
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Jun. 30, 2013
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
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Mar. 31, 2013
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
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Sep. 30, 2012
Cliffs Shareholders Equity [Member]
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| Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax | $ (365.1) | $ (392.5) | $ (365.1) | $ (392.5) | $ (370.8) | $ (377.4) | $ (382.7) | $ (408.9) | ||||||||||||||||||||||||||||
| Accumulated other comprehensive loss | (178.4) | (51.0) | (178.4) | (51.0) | (239.6) | (51.4) | (55.6) | (92.6) | ||||||||||||||||||||||||||||
| Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax | 10.7 | 2.0 | 10.7 | 2.0 | 6.3 | 4.7 | 2.1 | 2.6 | ||||||||||||||||||||||||||||
| Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax | 190.4 | 324.7 | 190.4 | 324.7 | 167.6 | 319.6 | 316.3 | 312.5 | ||||||||||||||||||||||||||||
| Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax | (14.4) | 14.8 | (14.4) | 14.8 | (42.7) | 1.7 | 8.7 | 1.2 | ||||||||||||||||||||||||||||
| Other Comprehensive Income (Loss), before Reclassifications, before Tax | 37.8 | (197.7) | (0.3) | (0.6) | (1.5) | (1.1) | 3.5 | (2.0) | 2.5 | 22.8 | (152.0) | 3.3 | 12.1 | (42.2) | (5.0) | |||||||||||||||||||||
| Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) | 23.4 | 9.5 | 4.5 | 6.3 | 8.1 | 6.4 | 0.9 | 3.6 | 0.1 | 0 | 0 | 0 | 16.2 | (2.2) | (2.0) | |||||||||||||||||||||
| Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax | (6.6) | (7.6) | (20.8) | (20.9) | 16.4 | |||||||||||||||||||||||||||||||
| Unrealized net gain (loss) on marketable securities, net of tax | 4.4 | (0.1) | 7.6 | (0.6) | (0.6) | |||||||||||||||||||||||||||||||
| Unrealized net gain (loss) on foreign currency translation | 22.8 | 18.6 | (124.9) | 12.2 | 12.2 | |||||||||||||||||||||||||||||||
| Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax | 28.3 | 14.2 | (23.1) | 13.6 | 13.6 | |||||||||||||||||||||||||||||||
| Other Comprehensive Income (Loss), Net of Tax | $ 62.1 | $ 40.3 | $ (119.6) | $ 46.1 | $ 41.6 | |||||||||||||||||||||||||||||||