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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income (Loss) from Continuing Operations Attributable to Parent	$ (5,879.6)	$ 115.2	$ (5,939.0)	$ 368.2
INCOME FROM DISCONTINUED OPERATIONS, net of tax	0	2.0	0	2.0
Net Income (Loss) Attributable to Cliffs Shareholders	(5,879.6)	117.2	(5,939.0)	370.2
PREFERRED STOCK DIVIDENDS	(12.8)	(12.9)	(38.4)	(35.9)
NET INCOME ATTRIBUTABLE TO CLIFFS COMMON SHAREHOLDERS	(5,892.4)	104.3	(5,977.4)	334.3
Earnings (Loss) Per Common Share Attributable to Cliffs Common Shareholders - Basic
Continuing operations	$ (38.49)	$ 0.67	$ (39.05)	$ 2.20
Discontinued operations	$ 0.00	$ 0.01	$ 0.00	$ 0.01
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Basic:	$ (38.49)	$ 0.68	$ (39.05)	$ 2.21
Earnings (Loss) Per Common Share Attributable to Cliffs Shareholders - Diluted
Continuing operations	$ (38.49)	$ 0.65	$ (39.05)	$ 2.13
Discontinued operations	$ 0.00	$ 0.01	$ 0.00	$ 0.01
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Diluted:	$ (38.49)	$ 0.66	$ (39.05)	$ 2.14
Weighted Average Number of Shares:
Basic	153,108	153,029	153,085	151,288
Depositary Shares	0	25,230	0	21,109
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	0	200	0	227
Diluted	153,108	178,459	153,085	172,624
Preferred Class A [Member]
PREFERRED STOCK DIVIDENDS	$ (12.8)	$ (12.9)	$ (38.4)	$ (35.9)