DISCONTINUED OPERATIONS Schedule of Disposal Groups, including Discontinued Operations, Income Statement, Balance Sheet and Cash Flows (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
LOSS FROM DISCONTINUED OPERATIONS, net of tax	$ (928.5)	$ (140.4)
Short-term assets of discontinued operations	197.2		330.6
Long-term assets of discontinued operations	0		400.1
Short-term liabilities of discontinued operations	265.0		400.6
LONG-TERM LIABILITIES OF DISCONTINUED OPERATIONS	125.2		436.1
Depreciation, depletion and amortization	33.0	141.1
Payments to Acquire Property, Plant, and Equipment	15.9	103.3
Asset Impairment Charges, Cash Flows	76.6	0
North American Coal [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
LOSS FROM DISCONTINUED OPERATIONS, net of tax	(75.7)	(46.3)
Short-term assets of discontinued operations	188.6		143.8
Long-term assets of discontinued operations	0		130.4
Short-term liabilities of discontinued operations	197.7		81.3
LONG-TERM LIABILITIES OF DISCONTINUED OPERATIONS	0		125.9
Depreciation, depletion and amortization	3.2	29.9
Payments to Acquire Property, Plant, and Equipment	2.5	10.0
Asset Impairment Charges, Cash Flows	73.4	0
Eastern Canadian Iron Ore [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
LOSS FROM DISCONTINUED OPERATIONS, net of tax	(852.7)	(91.2)
Short-term assets of discontinued operations	8.6		183.5
Long-term assets of discontinued operations	0		256.0
Short-term liabilities of discontinued operations	67.3		316.3
LONG-TERM LIABILITIES OF DISCONTINUED OPERATIONS	125.2		304.6
Depreciation, depletion and amortization	0	41.2
Payments to Acquire Property, Plant, and Equipment	0	75.6
Asset Impairment Charges, Cash Flows	0	0
Other Canadian Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
LOSS FROM DISCONTINUED OPERATIONS, net of tax	(0.1)	(2.9)
Short-term assets of discontinued operations	0		3.3
Long-term assets of discontinued operations	0		13.7
Short-term liabilities of discontinued operations	0		3.0
LONG-TERM LIABILITIES OF DISCONTINUED OPERATIONS	0		5.6
Depreciation, depletion and amortization	0	0.1
Payments to Acquire Property, Plant, and Equipment	0	0
Asset Impairment Charges, Cash Flows	0	0
Canadian Entities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
LOSS FROM DISCONTINUED OPERATIONS, net of tax	(852.8)	(94.1)
Short-term assets of discontinued operations	8.6		186.8
Long-term assets of discontinued operations	0		269.7
Short-term liabilities of discontinued operations	67.3		319.3
LONG-TERM LIABILITIES OF DISCONTINUED OPERATIONS	125.2		310.2
Depreciation, depletion and amortization	0	41.3
Payments to Acquire Property, Plant, and Equipment	0	75.6
Asset Impairment Charges, Cash Flows	0	0
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Depreciation, depletion and amortization	3.2	71.2
Payments to Acquire Property, Plant, and Equipment	2.5	85.6
Asset Impairment Charges, Cash Flows	$ 73.4	$ 0