Annual report pursuant to Section 13 and 15(d)

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) Accumulated Other Comprehensive Income (Loss) (Details)

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ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) Accumulated Other Comprehensive Income (Loss) (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2010
Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Member]
Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Member]
Mar. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Member]
Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Member]
Sep. 30, 2013
Accumulated Defined Benefit Plans Adjustment [Member]
Jun. 30, 2013
Accumulated Defined Benefit Plans Adjustment [Member]
Mar. 31, 2013
Accumulated Defined Benefit Plans Adjustment [Member]
Dec. 31, 2013
Accumulated Defined Benefit Plans Adjustment [Member]
Sep. 30, 2013
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Jun. 30, 2013
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Mar. 31, 2013
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Dec. 31, 2013
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Sep. 30, 2013
Accumulated Translation Adjustment [Member]
Jun. 30, 2013
Accumulated Translation Adjustment [Member]
Mar. 31, 2013
Accumulated Translation Adjustment [Member]
Dec. 31, 2013
Accumulated Translation Adjustment [Member]
Sep. 30, 2013
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Jun. 30, 2013
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Mar. 31, 2013
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Dec. 31, 2013
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Sep. 30, 2013
Accumulated Defined Benefit Plans Adjustment [Member]
Jun. 30, 2013
Accumulated Defined Benefit Plans Adjustment [Member]
Mar. 31, 2013
Accumulated Defined Benefit Plans Adjustment [Member]
Dec. 31, 2013
Accumulated Defined Benefit Plans Adjustment [Member]
Sep. 30, 2013
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Jun. 30, 2013
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Mar. 31, 2013
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Dec. 31, 2013
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Sep. 30, 2013
Accumulated Translation Adjustment [Member]
Jun. 30, 2013
Accumulated Translation Adjustment [Member]
Mar. 31, 2013
Accumulated Translation Adjustment [Member]
Dec. 31, 2013
Accumulated Translation Adjustment [Member]
Sep. 30, 2013
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Jun. 30, 2013
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Mar. 31, 2013
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Dec. 31, 2013
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Dec. 31, 2012
Cliffs Shareholders Equity [Member]
Dec. 31, 2011
Cliffs Shareholders Equity [Member]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax $ (204.9) $ (382.7) $ (408.9) $ (365.1) $ (370.8) $ (377.4) $ (305.1)                                                                            
Accumulated other comprehensive loss (112.9) (55.6) (92.6) (178.4) (239.6) (51.4) 45.9                                                                            
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax 6.2 2.1 2.6 10.7 6.3 4.7 33.6                                                                            
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax 106.7 316.3 312.5 190.4 167.6 319.6 314.7                                                                            
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax (20.9) 8.7 1.2 (14.4) (42.7) 1.7 2.7                                                                            
Other Comprehensive Income (Loss), before Reclassifications, before Tax               37.8 (197.7) (0.3) 49.3 (0.6) (1.5) (1.1) 154.5 3.5 (2.0) 2.5 (4.9) 22.8 (152.0) 3.3 (83.7) 12.1 (42.2) (5.0) (16.6)                                    
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)               23.4 9.5 4.5 16.2                                 6.3 8.1 6.4 5.7 0.9 3.6 0.1 0.4 0 0 0 0 16.2 (2.2) (2.0) 10.1    
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax (208.3) (33.8) 121.4                                                                                 26.2 (103.8)
Unrealized net gain (loss) on marketable securities, net of tax 3.1 (0.5) (31.0)                                                                                 (0.5) (31.0)
Unrealized net gain (loss) on foreign currency translation (208.6) 3.8 (2.2)                                                                                 3.8 (2.2)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax (51.7) 25.6 1.8                                                                                 7.5 (1.5)
Other Comprehensive Income (Loss), Net of Tax $ (26.8) $ 44.6 $ (156.1)                                                                                 $ 37.0 $ (138.5)