Quarterly report pursuant to Section 13 or 15(d)

SUPPLEMENTARY GUARANTOR INFORMATION (Supplementary Statements of Condensed Consolidating Financial Position) (Details)

v3.10.0.1
SUPPLEMENTARY GUARANTOR INFORMATION (Supplementary Statements of Condensed Consolidating Financial Position) (Details) - USD ($)
$ in Millions
Jun. 30, 2018
Jan. 01, 2018
Dec. 31, 2017
Jun. 30, 2017
Dec. 31, 2016
Cash and cash equivalents $ 802.5 $ 978.3 $ 978.3 $ 270.4  
Accounts receivable, net 152.6 183.3 106.7    
Inventories 256.4 87.0 138.4    
Supplies and other inventories 88.6 88.8 88.8    
Derivative assets 174.7 49.5 37.9    
Current assets of discontinued operations 45.3 118.5 118.5    
Loans to and accounts receivable from the Canadian Entities 0.0 51.6 51.6    
Other current assets 26.8 24.4 24.4    
TOTAL CURRENT ASSETS 1,546.9 1,581.4 1,544.6    
PROPERTY, PLANT AND EQUIPMENT, NET 1,081.3 1,033.8 1,033.8    
Deposits for property, plant and equipment 85.7 17.8 17.8    
Income tax receivable 219.9   235.3    
Non-current assets of discontinued operations 0.0 20.3 20.3    
Investment in subsidiaries 0.0   0.0    
Long-term intercompany notes 0.0   0.0    
Other non-current assets 117.7 101.6 101.6    
TOTAL OTHER ASSETS 423.3 375.0 375.0    
Assets 3,051.5 2,990.2 2,953.4    
Accounts payable 119.0 100.9 99.5    
Accrued expenses 85.1 79.1 79.1    
Accrued interest 43.1 31.4 31.4    
Contingent claims 0.0 55.6 55.6    
Partnership distribution payable 44.2 44.2 44.2    
Current liabilities of discontinued operations 117.3 75.0 75.0    
Other current liabilities 66.2 68.8 67.4    
TOTAL CURRENT LIABILITIES 474.9 455.0 452.2    
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES 245.0 257.7 257.7    
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS 172.3 167.7 167.7    
LONG-TERM DEBT 2,297.0 2,304.2 2,304.2    
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS 10.3 52.2 52.2    
LONG-TERM INTERCOMPANY NOTES 0.0   0.0    
OTHER LIABILITIES 158.3 163.5 163.5    
Liabilities 3,357.8 3,400.3 3,397.5    
TOTAL CLIFFS SHAREHOLDERS' DEFICIT (306.3) (410.3) (444.3)    
NONCONTROLLING INTEREST 0.0 0.2 0.2    
TOTAL DEFICIT (306.3) (410.1) (444.1) $ (666.7) $ (1,330.5)
TOTAL LIABILITIES AND DEFICIT 3,051.5 $ 2,990.2 2,953.4    
Consolidation, Eliminations [Member]          
Cash and cash equivalents 0.0   0.0    
Accounts receivable, net (3.7)   (0.7)    
Inventories 0.0   0.0    
Supplies and other inventories 0.0   0.0    
Derivative assets 0.0   0.0    
Current assets of discontinued operations 0.0   0.0    
Loans to and accounts receivable from the Canadian Entities     0.0    
Other current assets 0.0   0.0    
TOTAL CURRENT ASSETS (3.7)   (0.7)    
PROPERTY, PLANT AND EQUIPMENT, NET 0.0   0.0    
Deposits for property, plant and equipment 0.0   0.0    
Income tax receivable 0.0   0.0    
Non-current assets of discontinued operations     0.0    
Investment in subsidiaries (1,332.7)   (1,054.2)    
Long-term intercompany notes (227.4)   (242.0)    
Other non-current assets 0.0   0.0    
TOTAL OTHER ASSETS (1,560.1)   (1,296.2)    
Assets (1,563.8)   (1,296.9)    
Accounts payable (3.7)   (0.7)    
Accrued expenses 0.0   0.0    
Accrued interest 0.0   0.0    
Contingent claims     0.0    
Partnership distribution payable 0.0   0.0    
Current liabilities of discontinued operations 0.0   0.0    
Other current liabilities 0.0   0.0    
TOTAL CURRENT LIABILITIES (3.7)   (0.7)    
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES 0.0   0.0    
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS 0.0   0.0    
LONG-TERM DEBT 0.0   0.0    
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS 0.0   0.0    
LONG-TERM INTERCOMPANY NOTES (227.4)   (242.0)    
OTHER LIABILITIES 0.0   0.0    
Liabilities (231.1)   (242.7)    
TOTAL CLIFFS SHAREHOLDERS' DEFICIT (1,332.7)   (1,054.2)    
NONCONTROLLING INTEREST     0.0    
TOTAL DEFICIT (1,332.7)   (1,054.2)    
TOTAL LIABILITIES AND DEFICIT (1,563.8)   (1,296.9)    
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]          
Cash and cash equivalents 2.5   27.3    
Accounts receivable, net 0.1   0.0    
Inventories 0.0   0.0    
Supplies and other inventories 0.0   0.0    
Derivative assets 0.0   0.0    
Current assets of discontinued operations 45.3   118.5    
Loans to and accounts receivable from the Canadian Entities     0.0    
Other current assets 3.2   0.5    
TOTAL CURRENT ASSETS 51.1   146.3    
PROPERTY, PLANT AND EQUIPMENT, NET 99.6   57.3    
Deposits for property, plant and equipment 81.9   16.5    
Income tax receivable 0.0   0.0    
Non-current assets of discontinued operations     20.3    
Investment in subsidiaries 0.0   0.0    
Long-term intercompany notes 227.4   242.0    
Other non-current assets 1.7   2.1    
TOTAL OTHER ASSETS 311.0   280.9    
Assets 461.7   484.5    
Accounts payable 28.7   3.4    
Accrued expenses 0.5   0.2    
Accrued interest 0.0   0.0    
Contingent claims     0.0    
Partnership distribution payable 0.0   0.0    
Current liabilities of discontinued operations 117.3   75.0    
Other current liabilities 1.7   1.8    
TOTAL CURRENT LIABILITIES 148.2   80.4    
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES (249.3)   (239.3)    
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS 27.0   27.1    
LONG-TERM DEBT 0.0   0.0    
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS 10.3   52.2    
LONG-TERM INTERCOMPANY NOTES 0.0   0.0    
OTHER LIABILITIES 0.6   0.6    
Liabilities (63.2)   (79.0)    
TOTAL CLIFFS SHAREHOLDERS' DEFICIT 524.9   563.3    
NONCONTROLLING INTEREST     0.2    
TOTAL DEFICIT 524.9   563.5    
TOTAL LIABILITIES AND DEFICIT 461.7   484.5    
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]          
Cash and cash equivalents 1.6   2.1    
Accounts receivable, net 148.2   102.9    
Inventories 256.4   138.4    
Supplies and other inventories 88.6   88.8    
Derivative assets 174.6   37.9    
Current assets of discontinued operations 0.0   0.0    
Loans to and accounts receivable from the Canadian Entities     6.9    
Other current assets 7.7   7.5    
TOTAL CURRENT ASSETS 677.1   384.5    
PROPERTY, PLANT AND EQUIPMENT, NET 966.2   959.0    
Deposits for property, plant and equipment 3.8   1.3    
Income tax receivable 0.0   0.0    
Non-current assets of discontinued operations     0.0    
Investment in subsidiaries 32.8   29.9    
Long-term intercompany notes 0.0   0.0    
Other non-current assets 107.3   91.7    
TOTAL OTHER ASSETS 143.9   122.9    
Assets 1,787.2   1,466.4    
Accounts payable 88.8   89.7    
Accrued expenses 71.0   59.9    
Accrued interest 0.0   0.0    
Contingent claims     0.0    
Partnership distribution payable 44.2   44.2    
Current liabilities of discontinued operations 0.0   0.0    
Other current liabilities 62.7   63.5    
TOTAL CURRENT LIABILITIES 266.7   257.3    
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES 428.4   430.6    
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS 145.3   140.6    
LONG-TERM DEBT 0.0   0.0    
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS 0.0   0.0    
LONG-TERM INTERCOMPANY NOTES 0.0   0.0    
OTHER LIABILITIES 139.0   147.2    
Liabilities 979.4   975.7    
TOTAL CLIFFS SHAREHOLDERS' DEFICIT 807.8   490.7    
NONCONTROLLING INTEREST     0.0    
TOTAL DEFICIT 807.8   490.7    
TOTAL LIABILITIES AND DEFICIT 1,787.2   1,466.4    
Reportable Legal Entities [Member] | Cliffs Shareholders Equity [Member]          
Cash and cash equivalents 798.4   948.9    
Accounts receivable, net 8.0   4.5    
Inventories 0.0   0.0    
Supplies and other inventories 0.0   0.0    
Derivative assets 0.1   0.0    
Current assets of discontinued operations 0.0   0.0    
Loans to and accounts receivable from the Canadian Entities     44.7    
Other current assets 15.9   16.4    
TOTAL CURRENT ASSETS 822.4   1,014.5    
PROPERTY, PLANT AND EQUIPMENT, NET 15.5   17.5    
Deposits for property, plant and equipment 0.0   0.0    
Income tax receivable 219.9   235.3    
Non-current assets of discontinued operations     0.0    
Investment in subsidiaries 1,299.9   1,024.3    
Long-term intercompany notes 0.0   0.0    
Other non-current assets 8.7   7.8    
TOTAL OTHER ASSETS 1,528.5   1,267.4    
Assets 2,366.4   2,299.4    
Accounts payable 5.2   7.1    
Accrued expenses 13.6   19.0    
Accrued interest 43.1   31.4    
Contingent claims     55.6    
Partnership distribution payable 0.0   0.0    
Current liabilities of discontinued operations 0.0   0.0    
Other current liabilities 1.8   2.1    
TOTAL CURRENT LIABILITIES 63.7   115.2    
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES 65.9   66.4    
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS 0.0   0.0    
LONG-TERM DEBT 2,297.0   2,304.2    
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS 0.0   0.0    
LONG-TERM INTERCOMPANY NOTES 227.4   242.0    
OTHER LIABILITIES 18.7   15.7    
Liabilities 2,672.7   2,743.5    
TOTAL CLIFFS SHAREHOLDERS' DEFICIT (306.3)   (444.1)    
NONCONTROLLING INTEREST     0.0    
TOTAL DEFICIT (306.3)   (444.1)    
TOTAL LIABILITIES AND DEFICIT $ 2,366.4   $ 2,299.4