Quarterly report pursuant to Section 13 or 15(d)

EARNINGS PER SHARE (Earnings Per Share Computation) (Details)

v3.8.0.1
EARNINGS PER SHARE (Earnings Per Share Computation) (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Loss from Continuing Operations $ (84.8) $ (30.3)
Net Income (Loss) Attributable to Noncontrolling Interest 0.0 (1.7)
Net Loss from Continuing Operations Attributable to Cliffs Shareholders (84.8) (28.6)
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX 0.5 0.5
NET LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ (84.3) $ (28.1)
Weighted Average Number of Shares:    
Basic 297,266 265,164
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements 0 0
Diluted 297,266 265,164
Loss per Common Share Attributable to Cliffs Common Shareholders - Basic:    
Continuing operations (in dollars per share) $ (0.29) $ (0.11)
Discontinued operations (in dollars per share) 0.00 0.00
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Basic (in dollars per share) (0.29) (0.11)
Loss per Common Share Attributable to Cliffs Common Shareholders - Diluted:    
Continuing operations (in dollars per share) (0.29) (0.11)
Discontinued operations (in dollars per share) 0.00 0.00
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Diluted (in dollars per share) $ (0.29) $ (0.11)