Quarterly report pursuant to Section 13 or 15(d)

NEW ACCOUNTING STANDARDS (Schedule of New Accounting Pronouncements and Changes in Accounting Principles) (Details)

v3.10.0.1
NEW ACCOUNTING STANDARDS (Schedule of New Accounting Pronouncements and Changes in Accounting Principles) (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Sep. 30, 2018
Sep. 30, 2017
Jan. 01, 2018
Dec. 31, 2017
Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                      
Revenue from Contract with Customer, Including Assessed Tax $ 684.7     $ 530.7     $ 1,525.9 $ 1,195.0      
Cash and cash equivalents 897.1     227.1     897.1 227.1 $ 978.3 $ 978.3  
Accounts receivable, net 141.4           141.4   183.3 106.7  
Inventories (187.9)           (187.9)   (87.0) (138.4)  
Supplies and other inventories 88.2           88.2   88.8 88.8  
Derivative assets 190.8           190.8   49.5 37.9  
Income tax receivable 110.3           110.3   13.3 13.3  
Current assets of discontinued operations 16.1           16.1   118.5 118.5  
Loans to and accounts receivable from the Canadian Entities 0.0           0.0   51.6 51.6  
Other current assets 18.8           18.8   11.1 11.1  
TOTAL CURRENT ASSETS 1,650.6           1,650.6   1,581.4 1,544.6  
PROPERTY, PLANT AND EQUIPMENT, NET 1,144.8           1,144.8   1,033.8 1,033.8  
Deposits for property, plant and equipment 94.6           94.6   17.8 17.8  
Income tax receivable 113.6           113.6   235.3 235.3  
Non-current assets of discontinued operations 0.0           0.0   20.3 20.3  
Other non-current assets 121.4           121.4   101.6 101.6  
TOTAL OTHER ASSETS 329.6           329.6   375.0 375.0  
Assets 3,125.0           3,125.0   2,990.2 2,953.4  
Accounts payable 140.8           140.8   100.9 99.5  
Accrued expenses 95.1           95.1   79.1 79.1  
Accrued interest 26.2           26.2   31.4 31.4  
Contingent claims 0.0           0.0   55.6 55.6  
Partnership distribution payable 43.1           43.1   44.2 44.2  
Current liabilities of discontinued operations 14.2           14.2   75.0 75.0  
Other current liabilities (61.3)           (61.3)   (68.8) (67.4)  
TOTAL CURRENT LIABILITIES 380.7           380.7   455.0 452.2  
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES 225.0           225.0   257.7 257.7  
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS 174.4           174.4   167.7 167.7  
LONG-TERM DEBT 2,300.0           2,300.0   2,304.2 2,304.2  
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS 9.3           9.3   52.2 52.2  
OTHER LIABILITIES 121.8           121.8   163.5 163.5  
Liabilities 3,211.2           3,211.2   3,400.3 3,397.5  
TOTAL CLIFFS SHAREHOLDERS' DEFICIT (86.2)           (86.2)   (410.3) (444.3)  
NONCONTROLLING INTEREST 0.0           0.0   0.2 0.2  
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest (86.2) $ (306.3) $ (484.8) (833.1) $ (666.7) $ (703.0) (86.2) (833.1) (410.1) (444.1) $ (1,330.5)
TOTAL LIABILITIES AND DEFICIT 3,125.0           3,125.0   2,990.2 $ 2,953.4  
Freight and venture partners' cost reimbursements 57.1     66.0     110.2 159.2      
Revenues 741.8     596.7     1,636.1 1,354.2      
COST OF GOODS SOLD AND OPERATING EXPENSES (480.2)     (438.9)     (1,028.5) (1,002.7)      
SALES MARGIN 261.6     157.8     607.6 351.5      
Selling, general and administrative expenses (30.1)     (23.8)     (81.4) (75.5)      
Miscellaneous - net (6.0)     (5.3)     (16.2) 1.3      
Other operating expense (36.1)     (29.1)     (97.6) (74.2)      
OPERATING INCOME 225.5     128.7     510.0 277.3      
Interest expense, net (29.5)     (27.6)     (93.1) (99.1)      
Gain (loss) on extinguishment of debt 0.0     (88.6)     0.2 (165.4)      
Other non-operating income 4.3     2.6     13.1 7.6      
TOTAL OTHER INCOME (EXPENSE) (25.2)     (113.6)     (79.8) (256.9)      
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES 200.3     15.1     430.2 20.4      
INCOME TAX BENEFIT (EXPENSE) (0.5)     7.2     (14.4) 7.2      
INCOME FROM CONTINUING OPERATIONS 199.8     22.3     415.8 27.6      
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX 238.0     30.6     102.8 25.6      
NET INCOME 437.8 $ 165.1 $ (84.3) 52.9 $ 30.1 $ (29.8) 518.6 53.2      
LOSS ATTRIBUTABLE TO NONCONTROLLING INTEREST 0.0     0.5     0.0 3.9      
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 437.8     $ 53.4     $ 518.6 $ 57.1      
Continuing operations (in dollars per share) $ 0.67     $ 0.08     $ 1.40 $ 0.11      
Discontinued operations (in dollars per share) 0.80     0.10     0.35 0.09      
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Basic (in dollars per share) 1.47     0.18     1.75 0.20      
Continuing operations (in dollars per share) 0.64     0.08     1.37 0.11      
Discontinued operations (in dollars per share) 0.77     0.10     0.34 0.08      
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Diluted (in dollars per share) $ 1.41     $ 0.18     $ 1.71 $ 0.19      
Basic 297,878     296,100     297,587 285,771      
Diluted 310,203     301,100     303,518 290,512      
Accounting Standards Update 2017-07 [Member]                      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                      
COST OF GOODS SOLD AND OPERATING EXPENSES       $ (0.6)       $ (1.7)      
Selling, general and administrative expenses       2.0       5.9      
Miscellaneous - net       (0.4)       (1.1)      
OPERATING INCOME       (1.8)       (5.3)      
Other non-operating income       1.8       5.3      
NET INCOME       0.0       0.0      
Calculated under Revenue Guidance in Effect before Topic 606 [Member]                      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                      
Revenue from Contract with Customer, Including Assessed Tax $ 675.6           $ 1,471.2        
Cash and cash equivalents 897.1           897.1        
Accounts receivable, net 34.8           34.8        
Inventories (257.5)           (257.5)        
Supplies and other inventories 88.2           88.2        
Derivative assets 156.6           156.6        
Income tax receivable 110.3           110.3        
Current assets of discontinued operations 16.1           16.1        
Other current assets 18.8           18.8        
TOTAL CURRENT ASSETS 1,579.4           1,579.4        
PROPERTY, PLANT AND EQUIPMENT, NET 1,144.8           1,144.8        
Deposits for property, plant and equipment 94.6           94.6        
Income tax receivable 113.6           113.6        
Other non-current assets 121.4           121.4        
TOTAL OTHER ASSETS 329.6           329.6        
Assets 3,053.8           3,053.8        
Accounts payable 140.1           140.1        
Accrued expenses 95.1           95.1        
Accrued interest 26.2           26.2        
Partnership distribution payable 43.1           43.1        
Current liabilities of discontinued operations 14.2           14.2        
Other current liabilities (61.5)           (61.5)        
TOTAL CURRENT LIABILITIES 380.2           380.2        
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES 225.0           225.0        
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS 174.4           174.4        
LONG-TERM DEBT 2,300.0           2,300.0        
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS 9.3           9.3        
OTHER LIABILITIES 121.8           121.8        
Liabilities 3,210.7           3,210.7        
TOTAL CLIFFS SHAREHOLDERS' DEFICIT (156.9)           (156.9)        
TOTAL LIABILITIES AND DEFICIT 3,053.8           3,053.8        
Freight and venture partners' cost reimbursements 56.5           107.7        
Revenues 732.1           1,578.9        
COST OF GOODS SOLD AND OPERATING EXPENSES (475.9)           (1,006.6)        
SALES MARGIN 256.2           572.3        
Selling, general and administrative expenses (30.1)           (81.4)        
Miscellaneous - net             (16.2)        
Other operating expense (36.1)           (97.6)        
OPERATING INCOME 220.1           474.7        
Interest expense, net (29.5)           (93.1)        
Gain (loss) on extinguishment of debt 0.0           0.2        
Other non-operating income 4.3           13.1        
TOTAL OTHER INCOME (EXPENSE) (25.2)           (79.8)        
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES 194.9           394.9        
INCOME TAX BENEFIT (EXPENSE) (0.5)           (14.4)        
INCOME FROM CONTINUING OPERATIONS 194.4           380.5        
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX 238.0           102.8        
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 432.4           $ 483.3        
Continuing operations (in dollars per share) $ 0.65           $ 1.28        
Discontinued operations (in dollars per share) 0.80           0.35        
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Basic (in dollars per share) 1.45           1.63        
Continuing operations (in dollars per share) 0.62           1.25        
Discontinued operations (in dollars per share) 0.77           0.34        
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Diluted (in dollars per share) $ 1.39           $ 1.59        
Basic 297,878           297,587        
Diluted 310,203           303,518        
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]                      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                      
Revenue from Contract with Customer, Including Assessed Tax $ 9.1           $ 54.7        
Cash and cash equivalents 0.0           0.0   0.0    
Accounts receivable, net 106.6           106.6   76.6    
Inventories (69.6)           (69.6)   (51.4)    
Supplies and other inventories 0.0           0.0   0.0    
Derivative assets 34.2           34.2   11.6    
Income tax receivable 0.0           0.0   0.0    
Current assets of discontinued operations 0.0           0.0   0.0    
Loans to and accounts receivable from the Canadian Entities                 0.0    
Other current assets 0.0           0.0   0.0    
TOTAL CURRENT ASSETS 71.2           71.2   36.8    
PROPERTY, PLANT AND EQUIPMENT, NET 0.0           0.0   0.0    
Deposits for property, plant and equipment 0.0           0.0   0.0    
Income tax receivable 0.0           0.0   0.0    
Non-current assets of discontinued operations                 0.0    
Other non-current assets 0.0           0.0   0.0    
TOTAL OTHER ASSETS 0.0           0.0   0.0    
Assets 71.2           71.2   36.8    
Accounts payable 0.7           0.7   1.4    
Accrued expenses 0.0           0.0   0.0    
Accrued interest 0.0           0.0   0.0    
Contingent claims                 0.0    
Partnership distribution payable 0.0           0.0   0.0    
Current liabilities of discontinued operations 0.0           0.0   0.0    
Other current liabilities (0.2)           (0.2)   (1.4)    
TOTAL CURRENT LIABILITIES 0.5           0.5   2.8    
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES 0.0           0.0   0.0    
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS 0.0           0.0   0.0    
LONG-TERM DEBT 0.0           0.0   0.0    
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS 0.0           0.0   0.0    
OTHER LIABILITIES 0.0           0.0   0.0    
Liabilities 0.5           0.5   2.8    
TOTAL CLIFFS SHAREHOLDERS' DEFICIT 70.7           70.7   34.0    
NONCONTROLLING INTEREST                 0.0    
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest                 34.0    
TOTAL LIABILITIES AND DEFICIT 71.2           71.2   $ 36.8    
Freight and venture partners' cost reimbursements 0.6           2.5        
Revenues 9.7           57.2        
COST OF GOODS SOLD AND OPERATING EXPENSES (4.3)           (21.9)        
SALES MARGIN 5.4           35.3        
Selling, general and administrative expenses 0.0           0.0        
Miscellaneous - net 0.0           0.0        
Other operating expense 0.0           0.0        
OPERATING INCOME 5.4           35.3        
Interest expense, net 0.0           0.0        
Gain (loss) on extinguishment of debt 0.0           0.0        
Other non-operating income 0.0           0.0        
TOTAL OTHER INCOME (EXPENSE) 0.0           0.0        
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES 5.4           35.3        
INCOME TAX BENEFIT (EXPENSE) 0.0           0.0        
INCOME FROM CONTINUING OPERATIONS 5.4           35.3        
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX 0.0           0.0        
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 5.4           $ 35.3        
Continuing operations (in dollars per share) $ 0.02           $ 0.12        
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) 0.02           0.12        
Continuing operations (in dollars per share) 0.02           0.12        
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) $ 0.02           $ 0.12        
Previously Reported [Member]                      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                      
COST OF GOODS SOLD AND OPERATING EXPENSES       (439.5)       (1,004.4)      
Selling, general and administrative expenses       (21.8)       (69.6)      
Miscellaneous - net       (4.9)       2.4      
OPERATING INCOME       130.5       282.6      
Other non-operating income       0.8       2.3      
NET INCOME       $ 52.9       $ 53.2