Annual report pursuant to Section 13 and 15(d)

ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Narrative) (Details)

v3.6.0.2
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Narrative) (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2016
USD ($)
T
Dec. 31, 2015
USD ($)
Site Contingency [Line Items]    
Accrual for Environmental Loss Contingencies, Period Increase (Decrease) $ 9.2 $ (45.2)
Proved Developed and Undeveloped Reserves, Net, Period Increase (Decrease) | T 115,000,000  
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current And Noncurrent $ 206.8 234.0
Payments for Environmental Liabilities 2.4 2.6
Accrual for Environmental Loss Contingencies 2.8 3.6
Mine Reclamation and Closing Liability, current and noncurrent 204.0 230.4
Previously Owned Or Operating Facilities [Member] | LTV Steel Mining Company [Member]    
Site Contingency [Line Items]    
Mine Reclamation and Closing Liability, current and noncurrent 25.5 $ 24.1
Selenium [Domain]    
Site Contingency [Line Items]    
Accrual for Environmental Loss Contingencies, Period Increase (Decrease) $ 29.6