EARNINGS PER SHARE (Earnings Per Share Computation) (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income from Continuing Operations Attributable to Parent	$ 115.2	$ 87.8	$ 368.2	$ 713.9
Income from Discontinued Operations, net of tax	2.0	(2.7)	2.0	5.1
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	117.2	85.1	370.2	719.0
PREFERRED STOCK DIVIDENDS	(12.9)	0	(35.9)	0
NET INCOME ATTRIBUTABLE TO CLIFFS COMMON SHAREHOLDERS	104.3	85.1	334.3	719.0
Weighted Average Number of Shares:
Basic	153,029	142,396	151,288	142,332
Depositary Shares	25,216	0	21,114	0
Employee Stock Plans	214	499	222	448
Diluted	178,459	142,895	172,624	142,780
Earnings per Common Share Attributable to Cliffs Common Shareholders - Basic:
Continuing operations	$ 0.67	$ 0.62	$ 2.20	$ 5.02
Discontinued operations	$ 0.01	$ (0.02)	$ 0.01	$ 0.04
Earnings per Common Share Attributable to Cliffs Common Shareholders - Basic:	$ 0.68	$ 0.60	$ 2.21	$ 5.06
Earnings per Common Share Attributable to Cliffs Common Shareholders - Diluted:
Continuing operations	$ 0.65	$ 0.61	$ 2.13	$ 5.00
Discontinued operations	$ 0.01	$ (0.02)	$ 0.01	$ 0.04
Earnings per Common Share Attributable to Cliffs Common Shareholders - Diluted:	$ 0.66	$ 0.59	$ 2.14	$ 5.04
Preferred Class A [Member]
PREFERRED STOCK DIVIDENDS	$ (12.9)		$ (35.9)