Annual report pursuant to Section 13 and 15(d)

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

v3.8.0.1
SUPPLEMENTARY GUARANTOR INFORMATION (Supplementary Statements of Condensed Consolidating Financial Position) (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
CURRENT ASSETS        
Cash and cash equivalents $ 1,007.7 $ 323.4    
Accounts receivable, net 140.6 128.7    
Inventories 183.4 178.4    
Supplies and other inventories 93.9 91.4    
Derivative assets 39.4 33.1    
Loans to and accounts receivables from the Canadian Entities 51.6 48.6    
Other current assets 28.0 21.0    
TOTAL CURRENT ASSETS 1,544.6 824.6    
OTHER ASSETS        
PROPERTY, PLANT AND EQUIPMENT, NET 1,051.0 984.4 $ 1,059.0  
INCOME TAX RECEIVABLE 235.3 0.0    
INVESTMENT IN SUBSIDIARIES 0.0 0.0    
LONG-TERM INTERCOMPANY NOTES 0.0 0.0    
Other non-current assets 122.5 114.9    
TOTAL ASSETS 2,953.4 1,923.9 2,135.5  
CURRENT LIABILITIES        
Accounts payable 127.7 107.6    
Accrued employment costs 56.1 56.1    
State and local taxes payable 30.2 28.3    
Accrued expenses 33.7 41.1    
Accrued interest 31.4 40.2    
Accrued royalties 17.3 26.2    
Contingent claims 55.6 0.0    
Partnership distribution payable 44.2 8.7    
Other current liabilities 56.0 82.9    
TOTAL CURRENT LIABILITIES 452.2 391.1    
POSTEMPLOYMENT BENEFIT LIABILITIES        
Pensions 222.8 245.7    
Other postretirement benefits 34.9 34.8    
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES 257.7 280.5    
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS 196.5 193.9    
LONG-TERM DEBT 2,304.2 2,175.1    
LONG-TERM INTERCOMPANY NOTES 0.0 0.0    
OTHER LIABILITIES 186.9 213.8    
TOTAL LIABILITIES 3,397.5 3,254.4    
CLIFFS SHAREHOLDERS' DEFICIT        
TOTAL CLIFFS SHAREHOLDERS' DEFICIT (444.3) (1,464.3)    
NONCONTROLLING INTEREST 0.2 133.8    
TOTAL DEFICIT (444.1) (1,330.5) $ (1,811.6) $ (1,734.3)
TOTAL LIABILITIES AND DEFICIT 2,953.4 1,923.9    
Consolidation, Eliminations [Member]        
CURRENT ASSETS        
Cash and cash equivalents 0.0 0.0    
Accounts receivable, net (0.7) (0.8)    
Inventories 0.0 0.0    
Supplies and other inventories 0.0 0.0    
Derivative assets 0.0 0.0    
Loans to and accounts receivables from the Canadian Entities 0.0 0.0    
Other current assets 0.0 0.0    
TOTAL CURRENT ASSETS (0.7) (0.8)    
OTHER ASSETS        
PROPERTY, PLANT AND EQUIPMENT, NET 0.0 0.0    
INCOME TAX RECEIVABLE 0.0      
INVESTMENT IN SUBSIDIARIES (1,054.2) (907.0)    
LONG-TERM INTERCOMPANY NOTES (242.0) (197.0)    
Other non-current assets 0.0 0.0    
TOTAL ASSETS (1,296.9) (1,104.8)    
CURRENT LIABILITIES        
Accounts payable (0.7) (0.8)    
Accrued employment costs 0.0 0.0    
State and local taxes payable 0.0 0.0    
Accrued expenses 0.0 0.0    
Accrued interest 0.0 0.0    
Accrued royalties 0.0 0.0    
Contingent claims 0.0      
Partnership distribution payable 0.0 0.0    
Other current liabilities 0.0 0.0    
TOTAL CURRENT LIABILITIES (0.7) (0.8)    
POSTEMPLOYMENT BENEFIT LIABILITIES        
Pensions 0.0 0.0    
Other postretirement benefits 0.0 0.0    
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES 0.0 0.0    
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS 0.0 0.0    
LONG-TERM DEBT 0.0 0.0    
LONG-TERM INTERCOMPANY NOTES (242.0) (197.0)    
OTHER LIABILITIES 0.0 0.0    
TOTAL LIABILITIES (242.7) (197.8)    
CLIFFS SHAREHOLDERS' DEFICIT        
TOTAL CLIFFS SHAREHOLDERS' DEFICIT (1,054.2) (907.0)    
NONCONTROLLING INTEREST 0.0 0.0    
TOTAL DEFICIT (1,054.2) (907.0)    
TOTAL LIABILITIES AND DEFICIT (1,296.9) (1,104.8)    
Parent [Member] | Reportable Legal Entities [Member]        
CURRENT ASSETS        
Cash and cash equivalents 948.9 283.4    
Accounts receivable, net 4.5 4.5    
Inventories 0.0 0.0    
Supplies and other inventories 0.0 0.0    
Derivative assets 0.0 0.0    
Loans to and accounts receivables from the Canadian Entities 44.7 41.7    
Other current assets 16.4 8.6    
TOTAL CURRENT ASSETS 1,014.5 338.2    
OTHER ASSETS        
PROPERTY, PLANT AND EQUIPMENT, NET 17.5 21.4    
INCOME TAX RECEIVABLE 235.3      
INVESTMENT IN SUBSIDIARIES 1,024.3 882.4    
LONG-TERM INTERCOMPANY NOTES 0.0 0.0    
Other non-current assets 7.8 11.0    
TOTAL ASSETS 2,299.4 1,253.0    
CURRENT LIABILITIES        
Accounts payable 7.1 1.6    
Accrued employment costs 13.7 15.6    
State and local taxes payable 0.0 0.0    
Accrued expenses 5.3 7.6    
Accrued interest 31.4 40.2    
Accrued royalties 0.0 0.0    
Contingent claims 55.6      
Partnership distribution payable 0.0 0.0    
Other current liabilities 2.1 23.0    
TOTAL CURRENT LIABILITIES 115.2 88.0    
POSTEMPLOYMENT BENEFIT LIABILITIES        
Pensions 59.2 56.9    
Other postretirement benefits 7.2 7.6    
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES 66.4 64.5    
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS 0.0 0.0    
LONG-TERM DEBT 2,304.2 2,175.1    
LONG-TERM INTERCOMPANY NOTES 242.0 197.0    
OTHER LIABILITIES 15.7 58.9    
TOTAL LIABILITIES 2,743.5 2,583.5    
CLIFFS SHAREHOLDERS' DEFICIT        
TOTAL CLIFFS SHAREHOLDERS' DEFICIT (444.1) (1,330.5)    
NONCONTROLLING INTEREST 0.0 0.0    
TOTAL DEFICIT (444.1) (1,330.5)    
TOTAL LIABILITIES AND DEFICIT 2,299.4 1,253.0    
Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]        
CURRENT ASSETS        
Cash and cash equivalents 2.1 2.5    
Accounts receivable, net 102.9 59.3    
Inventories 138.4 137.0    
Supplies and other inventories 88.8 86.4    
Derivative assets 37.9 31.7    
Loans to and accounts receivables from the Canadian Entities 6.9 6.9    
Other current assets 7.5 8.2    
TOTAL CURRENT ASSETS 384.5 332.0    
OTHER ASSETS        
PROPERTY, PLANT AND EQUIPMENT, NET 959.0 937.7    
INCOME TAX RECEIVABLE 0.0      
INVESTMENT IN SUBSIDIARIES 29.9 24.6    
LONG-TERM INTERCOMPANY NOTES 0.0 0.0    
Other non-current assets 93.0 94.1    
TOTAL ASSETS 1,466.4 1,388.4    
CURRENT LIABILITIES        
Accounts payable 89.7 92.6    
Accrued employment costs 38.9 34.6    
State and local taxes payable 30.0 28.1    
Accrued expenses 13.2 14.4    
Accrued interest 0.0 0.0    
Accrued royalties 7.8 13.0    
Contingent claims 0.0      
Partnership distribution payable 44.2 8.7    
Other current liabilities 33.5 35.3    
TOTAL CURRENT LIABILITIES 257.3 226.7    
POSTEMPLOYMENT BENEFIT LIABILITIES        
Pensions 403.6 397.4    
Other postretirement benefits 27.0 26.5    
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES 430.6 423.9    
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS 140.6 153.9    
LONG-TERM DEBT 0.0 0.0    
LONG-TERM INTERCOMPANY NOTES 0.0 0.0    
OTHER LIABILITIES 147.2 118.8    
TOTAL LIABILITIES 975.7 923.3    
CLIFFS SHAREHOLDERS' DEFICIT        
TOTAL CLIFFS SHAREHOLDERS' DEFICIT 490.7 331.5    
NONCONTROLLING INTEREST 0.0 133.6    
TOTAL DEFICIT 490.7 465.1    
TOTAL LIABILITIES AND DEFICIT 1,466.4 1,388.4    
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]        
CURRENT ASSETS        
Cash and cash equivalents 56.7 37.5    
Accounts receivable, net 33.9 65.7    
Inventories 45.0 41.4    
Supplies and other inventories 5.1 5.0    
Derivative assets 1.5 1.4    
Loans to and accounts receivables from the Canadian Entities 0.0 0.0    
Other current assets 4.1 4.2    
TOTAL CURRENT ASSETS 146.3 155.2    
OTHER ASSETS        
PROPERTY, PLANT AND EQUIPMENT, NET 74.5 25.3    
INCOME TAX RECEIVABLE 0.0      
INVESTMENT IN SUBSIDIARIES 0.0 0.0    
LONG-TERM INTERCOMPANY NOTES 242.0 197.0    
Other non-current assets 21.7 9.8    
TOTAL ASSETS 484.5 387.3    
CURRENT LIABILITIES        
Accounts payable 31.6 14.2    
Accrued employment costs 3.5 5.9    
State and local taxes payable 0.2 0.2    
Accrued expenses 15.2 19.1    
Accrued interest 0.0 0.0    
Accrued royalties 9.5 13.2    
Contingent claims 0.0      
Partnership distribution payable 0.0 0.0    
Other current liabilities 20.4 24.6    
TOTAL CURRENT LIABILITIES 80.4 77.2    
POSTEMPLOYMENT BENEFIT LIABILITIES        
Pensions (240.0) (208.6)    
Other postretirement benefits 0.7 0.7    
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES (239.3) (207.9)    
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS 55.9 40.0    
LONG-TERM DEBT 0.0 0.0    
LONG-TERM INTERCOMPANY NOTES 0.0 0.0    
OTHER LIABILITIES 24.0 36.1    
TOTAL LIABILITIES (79.0) (54.6)    
CLIFFS SHAREHOLDERS' DEFICIT        
TOTAL CLIFFS SHAREHOLDERS' DEFICIT 563.3 441.7    
NONCONTROLLING INTEREST 0.2 0.2    
TOTAL DEFICIT 563.5 441.9    
TOTAL LIABILITIES AND DEFICIT $ 484.5 $ 387.3