SEGMENT REPORTING (Schedule Of Segment Reporting Information, By Segment) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Revenues from producet sales and services, percent	100.00%	100.00%	100.00%	100.00%
Revenues from product sales and services	$ 698.4	$ 553.3	$ 1,729.3	$ 1,355.0
Sales margin	160.2	85.4	401.0	207.8
Other operating expense	(30.5)	(50.7)	(74.8)	(98.7)
Other income (expense)	(116.7)	(66.9)	(266.2)	8.3
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest	13.0	(32.2)	60.0	117.4
Net Income (Loss)	52.9	(27.8)	53.2	118.5
Interest expense, net	(28.9)	(48.7)	(103.1)	(156.2)
Income Tax Expense (Benefit)	(7.6)	(7.1)	(6.8)	(1.7)
Depreciation, depletion and amortization	21.5	26.8	66.3	88.9
EBITDA	95.7	40.6	215.8	361.9
Gain (loss) on extinguishment/restructuring of debt	(88.6)	(18.3)	(165.4)	164.1
Adjusted EBITDA	154.4	61.9	383.6	199.7
Property, Plant and Equipment, Additions	27.1	26.4	79.6	44.5
Payments To Acquire Property Plant And Equipment Net			78.9	45.8
Capital Expenditures Incurred but Not yet Paid			0.7	(1.3)
Foreign Currency Transaction Gain (Loss), before Tax	(2.4)	(0.3)	11.2	(1.2)
INCOME (LOSS) FROM DISCONTINUED OPERATIONS, NET OF TAX	$ 32.3	$ (2.7)	$ (13.6)	$ (0.6)
U.S. Iron Ore [Member]
Segment Reporting Information [Line Items]
Revenues from producet sales and services, percent	85.00%	77.00%	78.00%	72.00%
Revenues from product sales and services	$ 596.7	$ 428.3	$ 1,354.2	$ 975.5
Sales margin	157.2	66.5	349.8	149.7
Depreciation, depletion and amortization	16.5	18.8	49.6	65.1
EBITDA	168.9	61.1	381.8	196.6
Adjusted EBITDA	174.2	65.3	399.8	208.6
Property, Plant and Equipment, Additions	$ 19.2	$ 25.8	$ 70.9	$ 39.5
Asia Pacific Iron Ore [Member]
Segment Reporting Information [Line Items]
Revenues from producet sales and services, percent	15.00%	23.00%	22.00%	28.00%
Revenues from product sales and services	$ 101.7	$ 125.0	$ 375.1	$ 379.5
Sales margin	3.0	18.9	51.2	58.1
Depreciation, depletion and amortization	3.3	6.3	11.3	19.2
EBITDA	2.3	21.2	54.9	69.6
Adjusted EBITDA	4.9	23.7	61.7	73.2
Property, Plant and Equipment, Additions	0.8	0.2	1.6	0.2
All Other Segments [Member]
Segment Reporting Information [Line Items]
Depreciation, depletion and amortization	1.7	1.7	5.4	4.6
EBITDA	(75.5)	(41.7)	(220.9)	95.7
Adjusted EBITDA	(24.7)	(27.1)	(77.9)	(82.1)
Property, Plant and Equipment, Additions	7.1	0.4	7.1	4.8
EBITDA Calculation [Member]
Segment Reporting Information [Line Items]
Depreciation, depletion and amortization	21.5	26.8	66.3	88.9
Adjusted EBITDA Calculation [Member]
Segment Reporting Information [Line Items]
Severance and contractor termination costs	$ 0.0	$ 0.0	$ 0.0	$ (0.1)