Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2018	Apr. 20, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	CLEVELAND-CLIFFS INC.
Entity Central Index Key	0000764065
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		297,733,061
Trading Symbol	clf
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes

Statements Of Condensed Consolidated Financial Position - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
CURRENT ASSETS
Cash and cash equivalents	$ 786.6	$ 1,007.7
Accounts receivable, net	47.2	140.6
Inventories	324.4	183.4
Supplies and other inventories	81.7	93.9
Derivative assets	93.6	39.4
Loans to and accounts receivable from the Canadian Entities	50.4	51.6
Other current assets	28.5	28.0
TOTAL CURRENT ASSETS	1,412.4	1,544.6
PROPERTY, PLANT AND EQUIPMENT, NET	1,047.3	1,051.0
OTHER ASSETS
Deposits for property, plant and equipment	74.1	17.8
Income tax receivable	219.9	235.3
Other non-current assets	109.2	104.7
TOTAL OTHER ASSETS	403.2	357.8
TOTAL ASSETS	2,862.9	2,953.4
CURRENT LIABILITIES
Accounts payable	99.5	127.7
Accrued expenses	94.4	107.1
Accrued interest	28.2	31.4
Contingent claims	54.3	55.6
Partnership distribution payable	44.2	44.2
Other current liabilities	104.3	86.2
TOTAL CURRENT LIABILITIES	424.9	452.2
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES	251.4	257.7
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	181.2	196.5
LONG-TERM DEBT	2,308.2	2,304.2
OTHER LIABILITIES	182.0	186.9
TOTAL LIABILITIES	3,347.7	3,397.5
COMMITMENTS AND CONTINGENCIES (REFER TO NOTE 19)
CLIFFS SHAREHOLDERS' DEFICIT
Common Shares - par value $0.125 per share, Authorized - 600,000,000 shares (2017 - 600,000,000 shares); Issued - 301,886,794 shares (2017 - 301,886,794 shares); Outstanding - 297,733,061 shares (2017 - 297,400,968 shares)	37.7	37.7
Capital in excess of par value of shares	3,918.0	3,933.9
Retained deficit	(4,257.6)	(4,207.3)
Cost of 4,153,733 common shares in treasury (2017 - 4,485,826 shares)	(151.8)	(169.6)
Accumulated other comprehensive loss	(31.3)	(39.0)
TOTAL CLIFFS SHAREHOLDERS' DEFICIT	(485.0)	(444.3)
NONCONTROLLING INTEREST	0.2	0.2
TOTAL DEFICIT	(484.8)	(444.1)
TOTAL LIABILITIES AND DEFICIT	$ 2,862.9	$ 2,953.4

Statements Of Condensed Consolidated Financial Position (Parenthetical) - $ / shares	Mar. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Preferred stock, par value	$ 0	$ 0
Common Stock, Par or Stated Value Per Share	$ 0.125	$ 0.125
Common shares, authorized (in shares)	600,000,000	600,000,000
Common shares, issued (in shares)	301,886,794	301,886,794
Common shares, outstanding	297,733,061	297,400,968
Common shares in treasury	4,153,733	4,485,826
Preferred Class A [Member]
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)	3,000,000	3,000,000
Preferred Class B [Member]
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)	4,000,000	4,000,000

Statements Of Condensed Consolidated Operations - USD ($) shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
REVENUES FROM PRODUCT SALES AND SERVICES
Product	$ 220.7	$ 412.8
Freight and venture partners' cost reimbursements	18.3	48.8
TOTAL REVENUES	239.0	461.6
COST OF GOODS SOLD AND OPERATING EXPENSES	(242.6)	(365.3)
SALES MARGIN	(3.6)	96.3
OTHER OPERATING INCOME (EXPENSE)
Selling, general and administrative expenses	(27.7)	(27.7)
Miscellaneous - net	(8.7)	11.5
Other operating expense	(36.4)	(16.2)
OPERATING INCOME (LOSS)	(40.0)	80.1
OTHER INCOME (EXPENSE)
Interest expense, net	(33.5)	(42.8)
Loss on extinguishment of debt	0.0	(71.9)
Other non-operating income	4.4	2.5
TOTAL OTHER INCOME (EXPENSE)	(29.1)	(112.2)
LOSS FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	(69.1)	(32.1)
INCOME TAX BENEFIT (EXPENSE)	(15.7)	1.8
LOSS FROM CONTINUING OPERATIONS	(84.8)	(30.3)
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX	0.5	0.5
NET LOSS	(84.3)	(29.8)
LOSS ATTRIBUTABLE TO NONCONTROLLING INTEREST	0.0	1.7
NET LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$ (84.3)	$ (28.1)
LOSS PER COMMON SHARE ATTRIBUTABLE TO CLIFFS SHAREHOLDERS – BASIC
Continuing operations (in dollars per share)	$ (0.29)	$ (0.11)
Discontinued operations (in dollars per share)	0.00	0.00
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Basic (in dollars per share)	(0.29)	(0.11)
LOSS PER COMMON SHARE ATTRIBUTABLE TO CLIFFS SHAREHOLDERS – DILUTED
Continuing operations (in dollars per share)	(0.29)	(0.11)
Discontinued operations (in dollars per share)	0.00	0.00
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Diluted (in dollars per share)	$ (0.29)	$ (0.11)
AVERAGE NUMBER OF SHARES (IN THOUSANDS)
Basic	297,266	265,164
Diluted	297,266	265,164

Statements Of Condensed Consolidated Comprehensive Income (Loss) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
NET LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$ (84.3)	$ (28.1)
OTHER COMPREHENSIVE INCOME (LOSS)
Changes in pension and other post-retirement benefits, net of tax	6.7	4.7
Unrealized net gain (loss) on foreign currency translation	0.7	(12.7)
Unrealized net gain on derivative financial instruments, net of tax	0.3	0.0
OTHER COMPREHENSIVE INCOME (LOSS)	7.7	(8.0)
OTHER COMPREHENSIVE LOSS ATTRIBUTABLE TO THE NONCONTROLLING INTEREST	0.0	(5.0)
TOTAL COMPREHENSIVE LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$ (76.6)	$ (31.1)

Statements Of Condensed Consolidated Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
OPERATING ACTIVITIES
NET INCOME (LOSS)	$ (84.3)	$ (29.8)
Adjustments to reconcile net loss to net cash used by operating activities:
Depreciation, depletion and amortization	23.9	23.2
Loss on extinguishment/restructuring of debt	0.0	71.9
Gain on derivatives	(40.8)	(17.7)
Other	25.9	0.8
Changes in operating assets and liabilities:
Receivables and other assets	196.3	86.5
Inventories	(193.0)	(70.0)
Payables, accrued expenses and other liabilities	(70.9)	(90.0)
Net cash used by operating activities	(142.9)	(25.1)
INVESTING ACTIVITIES
Property, Plant and Equipment, Cash Additions	(12.4)	(25.9)
Purchase of property, plant and equipment	(59.0)	(2.0)
Other investing activities	0.0	0.5
Net cash used by investing activities	(71.4)	(27.4)
FINANCING ACTIVITIES
Proceeds from issuance of debt	0.0	500.0
Debt issuance costs	(1.5)	(8.5)
Net proceeds from issuance of common shares	0.0	661.3
Repurchase of debt	0.0	(1,115.5)
Distributions of partnership equity	0.0	(8.7)
Other financing activities	(5.5)	(5.6)
Net cash provided (used) by financing activities	(7.0)	23.0
EFFECT OF EXCHANGE RATE CHANGES ON CASH	0.2	1.4
DECREASE IN CASH AND CASH EQUIVALENTS	(221.1)	(28.1)
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	1,007.7	323.4
CASH AND CASH EQUIVALENTS AT END OF PERIOD	$ 786.6	$ 295.3

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES

3 Months Ended

Mar. 31, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES

NOTE 1 - BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with SEC rules and regulations and, in the opinion of management, include all adjustments (consisting of normal recurring adjustments) necessary to present fairly the financial position, results of operations, comprehensive income (loss) and cash flows for the periods presented. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Management bases its estimates on various assumptions and historical experience, which are believed to be reasonable; however, due to the inherent nature of estimates, actual results may differ significantly due to changed conditions or assumptions. The results of operations for the three months ended March 31, 2018 are not necessarily indicative of results to be expected for the year ending December 31, 2018 or any other future period. These unaudited condensed consolidated financial statements should be read in conjunction with the financial statements and notes included in our Annual Report on Form 10-K for the year ended December 31, 2017.

On January 25, 2018, we announced that we would accelerate the projected time frame for the planned closure of our Asia Pacific Iron Ore mining operations in Australia. On April 6, 2018, we committed to a course of action expected to lead to the permanent closure of the Asia Pacific Iron Ore mining operations and expect our final Asia Pacific Iron Ore shipment to occur by June 30, 2018. Factors considered in this decision include increasingly discounted prices for lower-iron-content ore, the quality of the remaining iron ore reserves and the lack of a legitimate offer from a qualified buyer. As a result, we recorded various adjustments to Inventories, Property, Plant and Equipment, Environmental and mine closure obligations and Supplies and other inventories consistent with our current mine plan. Refer to NOTE 5 - INVENTORIES, NOTE 6 - PROPERTY, PLANT AND EQUIPMENT and NOTE 13 - ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS for further information.

We report our results from continuing operations in two reportable segments: U.S. Iron Ore and Asia Pacific Iron Ore.

Basis of Consolidation

The unaudited condensed consolidated financial statements include our accounts and the accounts of our wholly-owned subsidiaries, including the following operations as of March 31, 2018:



Name	Location	Status of Operations
Northshore	Minnesota	Active
United Taconite	Minnesota	Active
Tilden	Michigan	Active
Empire	Michigan	Indefinitely Idled
Koolyanobbing¹	Western Australia	Active

¹ On April 6, 2018, we committed to a course of action expected to lead to the permanent closure of the Asia Pacific Iron Ore mining operations and expect our final Asia Pacific Iron Ore shipment to occur by June 30, 2018.

Intercompany transactions and balances are eliminated upon consolidation.

Equity Method Investments

Our 23% ownership interest in Hibbing is recorded as an equity method investment. As of March 31, 2018 and December 31, 2017, our investment in Hibbing was $7.3 million and $11.0 million, respectively, classified as Other liabilities in the Statements of Unaudited Condensed Consolidated Financial Position.

Foreign Currency

Our financial statements are prepared with the U.S. dollar as the reporting currency. The functional currency of our Australian subsidiaries is the Australian dollar. The functional currency of all other international subsidiaries is the U.S. dollar. The financial statements of our Australian subsidiaries are translated into U.S. dollars using the exchange rate at each balance sheet date for assets and liabilities and a weighted average exchange rate for each period for revenues, expenses, gains and losses. Translation adjustments are recorded as Accumulated other comprehensive loss. Income taxes generally are not provided for foreign currency translation adjustments. To the extent that monetary assets and liabilities, including short-term intercompany loans, are recorded in a currency other than the functional currency, these amounts are remeasured each reporting period, with the resulting gain or loss being recorded in the Statements of Unaudited Condensed Consolidated Operations. Transaction gains and losses resulting from remeasurement of short-term intercompany loans are included in Miscellaneous – net in the Statements of Unaudited Condensed Consolidated Operations.

The following represents the transaction gains and losses resulting from remeasurement:



	(In Millions)
	Three Months Ended March 31,
	2018			2017
Short-term intercompany loans	$	(0.2	)	$	15.1
Cash and cash equivalents	0.1			(1.2		)
Other	(0.2		)	(0.3		)
Net impact of transaction gains (losses) resulting from remeasurement	$	(0.3	)	$	13.6

Significant Accounting Policies

A detailed description of our significant accounting policies can be found in the audited financial statements for the fiscal year ended December 31, 2017 included in our Annual Report on Form 10-K filed with the SEC. There have been no material changes in our significant accounting policies and estimates from those disclosed therein other than those related to the adoption of Topic 606. Refer to NOTE 2 - NEW ACCOUNTING STANDARDS for further information.

NEW ACCOUNTING STANDARDS

3 Months Ended

Mar. 31, 2018

New Accounting Pronouncements and Changes in Accounting Principles [Abstract]

NEW ACCOUNTING STANDARDS

NOTE 2 - NEW ACCOUNTING STANDARDS

Adoption of New Accounting Standards

ASC Topic 606, Revenue from Contracts with Customers (Topic 606). On January 1, 2018, we adopted Topic 606 and applied it to all contracts that were not completed using the modified retrospective method. We recognized the cumulative effect of initially applying Topic 606 as an adjustment to the opening balance of Retained deficit of $34.0 million. The comparative period information has not been restated and continues to be reported under the accounting standards in effect for those periods. We do not expect that the adoption of Topic 606 will have a material impact to our annual net income on an ongoing basis.

Under Topic 606, revenue will generally be recognized upon delivery for our U.S. Iron Ore customers, which is earlier than under the previous guidance. As an example, for certain iron ore shipments where revenue was previously recognized upon title transfer when payment was received, we will now recognize revenue when control transfers, which is generally upon delivery. While we continue to retain title until we receive payment, we determined upon review of our customer contracts that the preponderance of control indicators pass to our customers' favor when we deliver our products; thus, we generally concluded control transfers at that point. As a result of the adoption of Topic 606 and vessel deliveries not occurring during the winter months because of the closure of the Soo Locks and the Welland Canal, our revenues and net income will be relatively lower than historical levels during the first quarter of each year and relatively higher than historical levels during the remaining three quarters in future years. However, the total amount of revenue recognized during the year should remain substantially the same as under previous accounting standards, assuming revenue rates and volumes are consistent between years.

The adoption of Topic 606 will not change the pattern or timing of revenue recognition for Asia Pacific Iron Ore, as control transfers when vessels are loaded, which is the same time title and the risk of loss transfers to our customers.

The cumulative effect of the changes made to our consolidated January 1, 2018 balance sheet for the adoption of Topic 606 were as follows:



	($ in Millions)
	Balance at December 31, 2017			Adjustments due to Topic 606			Balance at January 1, 2018
ASSETS
CURRENT ASSETS
Cash and cash equivalents	$	1,007.7		$	—		$	1,007.7
Accounts receivable, net	140.6			76.6			217.2
Inventories	183.4			(51.4		)	132.0
Supplies and other inventories	93.9			—			93.9
Derivative assets	39.4			11.6			51.0
Loans to and accounts receivable from the Canadian Entities	51.6			—			51.6
Other current assets	28.0			—			28.0
TOTAL CURRENT ASSETS	1,544.6			36.8			1,581.4
PROPERTY, PLANT AND EQUIPMENT, NET	1,051.0			—			1,051.0
OTHER ASSETS
Deposits for property, plant and equipment	17.8			—			17.8
Income tax receivable	235.3			—			235.3
Other non-current assets	104.7			—			104.7
TOTAL OTHER ASSETS	357.8			—			357.8
TOTAL ASSETS	$	2,953.4		$	36.8		$	2,990.2

LIABILITIES
CURRENT LIABILITIES
Accounts payable	$	127.7		$	1.4		$	129.1
Accrued expenses	107.1			—			107.1
Accrued interest	31.4			—			31.4
Contingent claims	55.6			—			55.6
Partnership distribution payable	44.2			—			44.2
Other current liabilities	86.2			1.4			87.6
TOTAL CURRENT LIABILITIES	452.2			2.8			455.0
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES	257.7			—			257.7
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	196.5			—			196.5
LONG-TERM DEBT	2,304.2			—			2,304.2
OTHER LIABILITIES	186.9			—			186.9
TOTAL LIABILITIES	3,397.5			2.8			3,400.3
EQUITY
CLIFFS SHAREHOLDERS' DEFICIT	(444.3		)	34.0			(410.3		)
NONCONTROLLING INTEREST	0.2			—			0.2
TOTAL DEFICIT	(444.1		)	34.0			(410.1		)
TOTAL LIABILITIES AND DEFICIT	$	2,953.4		$	36.8		$	2,990.2

The impact of adoption on our Statements of Unaudited Condensed Consolidated Operations and Statements of Unaudited Condensed Consolidated Financial Position is as follows:



	($ in Millions)
	Three Months Ended March 31, 2018
	As Reported			Balances without Adoption of Topic 606			Effect of Change
REVENUES FROM PRODUCT SALES AND SERVICES
Product	$	220.7		$	279.1		$	(58.4	)
Freight and venture partners' cost reimbursements	18.3			22.4			(4.1		)
	239.0			301.5			(62.5		)
COST OF GOODS SOLD AND OPERATING EXPENSES	(242.6		)	(286.2		)	43.6
SALES MARGIN	(3.6		)	15.3			(18.9		)
OTHER OPERATING EXPENSE
Selling, general and administrative expenses	(27.7		)	(27.7		)	—
Miscellaneous – net	(8.7		)	(8.7		)	—
	(36.4		)	(36.4		)	—
OPERATING LOSS	(40.0		)	(21.1		)	(18.9		)
OTHER INCOME (EXPENSE)
Interest expense, net	(33.5		)	(33.5		)	—
Other non-operating income	4.4			4.4			—
	(29.1		)	(29.1		)	—
LOSS FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	(69.1		)	(50.2		)	(18.9		)
INCOME TAX EXPENSE	(15.7		)	(15.7		)	—
LOSS FROM CONTINUING OPERATIONS	(84.8		)	(65.9		)	(18.9		)
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX	0.5			0.5			—
NET LOSS	(84.3		)	(65.4		)	(18.9		)
LOSS ATTRIBUTABLE TO NONCONTROLLING INTEREST	—			—			—
NET LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$	(84.3	)	$	(65.4	)	$	(18.9	)
LOSS PER COMMON SHARE ATTRIBUTABLE TO CLIFFS SHAREHOLDERS – BASIC
Continuing operations	$	(0.29	)	$	(0.23	)	$	(0.06	)
Discontinued operations	—			—			—
	$	(0.29	)	$	(0.23	)	$	(0.06	)
LOSS PER COMMON SHARE ATTRIBUTABLE TO CLIFFS SHAREHOLDERS – DILUTED
Continuing operations	$	(0.29	)	$	(0.23	)	$	(0.06	)
Discontinued operations	—			—			—
	$	(0.29	)	$	(0.23	)	$	(0.06	)
AVERAGE NUMBER OF SHARES (IN THOUSANDS)
Basic	297,266			297,266
Diluted	297,266			297,266



	($ in Millions)
	March 31, 2018
	As Reported			Balances without Adoption of Topic 606			Effect of Change
ASSETS
CURRENT ASSETS
Cash and cash equivalents	$	786.6		$	786.6		$	—
Accounts receivable, net	47.2			24.9			22.3
Inventories	324.4			332.0			(7.6		)
Supplies and other inventories	81.7			81.7			—
Derivative assets	93.6			91.3			2.3
Loans to and accounts receivable from the Canadian Entities	50.4			50.4			—
Other current assets	28.5			28.5			—
TOTAL CURRENT ASSETS	1,412.4			1,395.4			17.0
PROPERTY, PLANT AND EQUIPMENT, NET	1,047.3			1,047.3			—
OTHER ASSETS
Deposits for property, plant and equipment	74.1			74.1			—
Income tax receivable	219.9			219.9			—
Other non-current assets	109.2			109.2			—
TOTAL OTHER ASSETS	403.2			403.2			—
TOTAL ASSETS	2,862.9			2,845.9			17.0

LIABILITIES
CURRENT LIABILITIES
Accounts payable	$	99.5		$	99.2		$	0.3
Accrued expenses	94.4			94.4			—
Accrued interest	28.2			28.2			—
Contingent claims	54.3			54.3			—
Partnership distribution payable	44.2			44.2			—
Other current liabilities	104.3			104.0			0.3
TOTAL CURRENT LIABILITIES	424.9			424.3			0.6
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES	251.4			251.4			—
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	181.2			181.2			—
LONG-TERM DEBT	2,308.2			2,308.2			—
OTHER LIABILITIES	182.0			182.0			—
TOTAL LIABILITIES	3,347.7			3,347.1			0.6
EQUITY
CLIFFS SHAREHOLDERS' DEFICIT	(485.0		)	(501.4		)	16.4
NONCONTROLLING INTEREST	0.2			0.2			—
TOTAL DEFICIT	(484.8		)	(501.2		)	16.4
TOTAL LIABILITIES AND DEFICIT	$	2,862.9		$	2,845.9		$	17.0

The adoption of Topic 606 did not have an impact on net cash flows in our Statements of Unaudited Condensed Consolidated Cash Flows.

ASU 2017-07, Retirement Benefits - Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. On January 1, 2018, we adopted the amendments to ASC 715 regarding the presentation of net periodic pension and postretirement benefit costs. We retrospectively adopted the presentation of service cost separate from the other components of net periodic costs. The interest cost, expected return on assets, amortization of prior service costs, net remeasurement, and other costs have been reclassified from Cost of goods sold and operating expenses, Selling, general and administrative expenses and Miscellaneous – net to Other non-operating income. We elected to apply the practical expedient, which allows us to reclassify amounts disclosed previously in our Pension and other postretirement benefits footnote as the basis for applying retrospective presentation for comparative periods. On a prospective basis, only service costs will be included in amounts capitalized in inventory or property, plant, and equipment.

The effect of the retrospective presentation change related to the net periodic cost of our defined benefit pension and other postretirement employee benefits plans on our Statements of Unaudited Condensed Consolidated Operations was as follows:



	($ in Millions)
	Three Months Ended March 31, 2017
	As Revised			Previously Reported			Effect of Change
Cost of goods sold and operating expenses	$	(365.3	)	$	(365.9	)	$	0.6
Selling, general and administrative expenses	$	(27.7	)	$	(25.7	)	$	(2.0	)
Miscellaneous – net	$	11.5		$	11.9		$	(0.4	)
Operating income	$	80.1		$	81.9		$	(1.8	)
Other non-operating income	$	2.5		$	0.7		$	1.8
Net Loss	$	(29.8	)	$	(29.8	)	$	—

Recent Accounting Pronouncements

Issued and Not Effective

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). The new standard requires lessees to recognize a right-of-use asset and a lease liability on the balance sheet for all leases except for short-term leases. For lessees, leases will continue to be classified as either operating or finance leases in the Statements of Unaudited Condensed Consolidated Operations. We plan to adopt the standard on its effective date of January 1, 2019. The new standard may be adopted using either the modified retrospective approach, which requires application of the new guidance at the beginning of the earliest comparative period presented or the optional alternative approach, which requires application of the new guidance at the beginning of the standards effective date. We are currently finalizing our implementation plan, compiling an inventory of existing leases and evaluating the effect the updated standard will have on our consolidated financial statements and related disclosures.

SEGMENT REPORTING

3 Months Ended

Mar. 31, 2018

Segment Reporting [Abstract]

SEGMENT REPORTING

NOTE 3 - SEGMENT REPORTING

Our continuing operations are organized and managed according to geographic location: U.S. Iron Ore and Asia Pacific Iron Ore. Our U.S. Iron Ore segment is a major supplier of iron ore pellets to the North American steel industry from our mines and pellet plants located in Michigan and Minnesota. The Asia Pacific Iron Ore segment is located in Western Australia and provides iron ore to the seaborne market for Asian steel producers. There were no intersegment revenues in the first quarter of 2018 or 2017.

We evaluate segment performance based on sales margin, defined as revenues less cost of goods sold and operating expenses identifiable to each segment. Additionally, we evaluate performance on a segment basis, as well as a consolidated basis, based on EBITDA and Adjusted EBITDA. These measures allow management and investors to focus on our ability to service our debt as well as illustrate how the business and each operating segment are performing. Additionally, EBITDA and Adjusted EBITDA assist management and investors in their analysis and forecasting as these measures approximate the cash flows associated with operational earnings.

The following tables present a summary of our reportable segments including a reconciliation of segment sales margin to Loss from Continuing Operations Before Income Taxes and a reconciliation of Net Loss to EBITDA and Adjusted EBITDA:



	(In Millions)
	Three Months Ended March 31,
	2018					2017
Revenues from product sales and services:
U.S. Iron Ore	$	180.0		75	%	$	286.2		62	%
Asia Pacific Iron Ore	59.0			25	%	175.4			38	%
Total revenues from product sales and services	$	239.0		100	%	$	461.6		100	%

Sales margin:
U.S. Iron Ore	$	61.5				$	49.0
Asia Pacific Iron Ore	(65.1		)			47.3
Sales margin	(3.6		)			96.3
Other operating expense	(36.4		)			(16.2		)
Other expense	(29.1		)			(112.2		)
Loss from continuing operations before income taxes	$	(69.1	)			$	(32.1	)



	(In Millions)
	Three Months Ended March 31,
	2018			2017
Net Loss	$	(84.3	)	$	(29.8	)
Less:
Interest expense, net	(33.5		)	(42.8		)
Income tax benefit (expense)	(15.7		)	1.8
Depreciation, depletion and amortization	(23.9		)	(23.2		)
EBITDA	$	(11.2	)	$	34.4
Less:
Inventory impairments	$	(18.9	)	$	—
Impairment of long-lived assets	(2.6		)	—
Severance and retention costs	(1.5		)	—
Impact of discontinued operations	0.5			0.5
Foreign exchange remeasurement	(0.3		)	13.6
Loss on extinguishment of debt	—			(71.9		)
Adjusted EBITDA	$	11.6		$	92.2

EBITDA
U.S. Iron Ore	$	72.5		$	57.9
Asia Pacific Iron Ore	(63.7		)	51.4
Other	(20.0		)	(74.9		)
Total EBITDA	$	(11.2	)	$	34.4

Adjusted EBITDA:
U.S. Iron Ore	$	77.1		$	64.1
Asia Pacific Iron Ore	(39.6		)	53.8
Other	(25.9		)	(25.7		)
Total Adjusted EBITDA	$	11.6		$	92.2



	(In Millions)
	Three Months Ended March 31,
	2018		2017
Depreciation, depletion and amortization:
U.S. Iron Ore	$	15.8	$	16.4
Asia Pacific Iron Ore	6.7		4.7
Other	1.4		2.1
Total depreciation, depletion and amortization	$	23.9	$	23.2

Capital additions¹:
U.S. Iron Ore	$	18.7	$	27.1
Asia Pacific Iron Ore	—		0.2
Other²	60.2		—
Total capital additions	$	78.9	$	27.3

¹ Includes cash paid for capital additions of $71.4 million, including deposits of $59.0 million, and an increase in non-cash accruals of $7.5 million for the three months ended March 31, 2018 compared to cash paid for capital additions of $27.9 million, including deposits of $2.0 million, and a decrease in non-cash accruals of $0.6 million for the three months ended March 31, 2017.
² Includes capital additions related to our HBI project.

A summary of assets by segment is as follows:



	(In Millions)
	March 31, 2018		December 31, 2017
Assets:
U.S. Iron Ore	$	1,646.8	$	1,500.6
Asia Pacific Iron Ore	78.4		138.8
Total segment assets	1,725.2		1,639.4
Corporate and Other	1,137.7		1,314.0
Total assets	$	2,862.9	$	2,953.4

REVENUE

3 Months Ended

Mar. 31, 2018

Revenue from Contract with Customer [Abstract]

Revenue from Contract with Customer [Text Block]

NOTE 4 - REVENUE

Revenue is recognized generally when iron ore is delivered to our customers. Revenue is measured at the point control transfers and represents the amount of consideration we expect to receive in exchange for transferring goods. We offer standard payment terms to our customers, generally requiring settlement within 30 days.

We enter into supply contracts of varying lengths to provide customers iron ore to use in their blast furnaces. Blast furnaces run continuously with a constant feed of iron ore and once shut down, cannot easily be restarted. As a result, we ship iron ore in large quantities for storage and use by customers at a later date. Customers do not simultaneously receive and consume the benefits of the iron ore. Based on our assessment of the factors that indicate the pattern of satisfaction, we transfer control of the iron ore at a point in time upon shipment or delivery of the product. The customer is able to direct the use of, and obtain substantially all of the benefits from, the product at the time the product is delivered.

We disaggregate Revenues from product sales and services based on geographical location. We sell a single product, iron ore, in the North American and Asian markets. Refer to NOTE 3 - SEGMENT REPORTING for further information on disaggregated revenue.

Certain of our U.S. Iron Ore and Asia Pacific Iron Ore customer supply agreements specify a provisional price, which is used for initial billing and cash collection. Revenue recorded in accordance with Topic 606 is calculated using the expected revenue rate at the point when control transfers. The final settlement includes market inputs for a specified period of time, which may vary by customer, but typically include one or more of the following: Platts 62% Price, pellet premiums, Platts international indexed freight rates and changes in specified Producer Price Indices, including industrial commodities, energy and steel. Changes in the expected revenue rate from the date control transfers through final settlement of contract terms is recorded in accordance with ASC Topic 815. Refer to NOTE 15 - DERIVATIVE INSTRUMENTS for further information on how our estimated expected and final revenue rates are determined.

A supply agreement with one U.S. Iron Ore customer provides for supplemental revenue or refunds based on the average annual daily market price for hot-rolled coil steel at the time the iron ore is consumed in the customer’s blast furnaces. As control transfers prior to consumption, the supplemental revenue is recorded in accordance with ASC Topic 815. Refer to NOTE 15 - DERIVATIVE INSTRUMENTS for further information on supplemental revenue or refunds.

Included within Revenues from product sales and services is derivative revenue related to ASC Topic 815 of $43.8 million and $1.3 million, for three months ended March 31, 2018 at our U.S. Iron Ore and Asia Pacific Iron Ore segments, respectively.

Practical expedients and exemptions

We have elected to treat all shipping and handling costs as fulfillment costs as a significant portion of these costs are incurred prior to control transfer.

We have various long-term sales contracts with minimum purchase and supply requirement provisions that extend beyond the current reporting period. The portion of our transaction price for these contracts that is allocated entirely to wholly unsatisfied performance obligations is based on market prices that have not yet been determined and therefore is variable in nature. As such, we have not disclosed the value of unsatisfied performance obligations pursuant to the practical expedient.

Deferred Revenue

The table below summarizes our deferred revenue balances:



	Deferred Revenue (Current)¹		Deferred Revenue (Long-Term)
Opening balance as of January 1, 2018	$	23.8	$	51.4
Closing balance as of March 31, 2018	31.0		51.4
Increase	$	7.2	$	—

¹ The opening balance includes a $1.4 million adjustment from the December 31, 2017 balance due to the adoption of Topic 606.

The terms of one of our U.S. Iron Ore pellet supply agreements required supplemental payments to be paid by the customer during the period 2009 through 2012, with the option to defer a portion of the 2009 monthly amount in exchange for interest payments until the deferred amount was repaid in 2013. Installment amounts received under this arrangement in excess of sales were classified as Other current liabilities and Other liabilities in the Statements of Unaudited Condensed Consolidated Financial Position upon receipt of payment. Revenue is recognized over the life of the supply agreement, which extends until 2022, in equal annual installments. As of March 31, 2018 and December 31, 2017, installment amounts received in excess of sales totaled $64.2 million related to this agreement. As of March 31, 2018 and December 31, 2017, deferred revenue of $12.8 million was recorded in Other current liabilities and $51.4 million was recorded as long-term in Other liabilities in the Statements of Unaudited Condensed Consolidated Financial Position, related to this agreement.

Due to the payment terms and the timing of cash receipts near a period end, cash receipts can exceed shipments for certain customers. Revenue recognized on these transactions totaling $18.2 million and $9.6 million was deferred and included in Other current liabilities in the Statements of Unaudited Condensed Consolidated Financial Position as of March 31, 2018 and December 31, 2017, respectively.

INVENTORIES

3 Months Ended

Mar. 31, 2018

Inventory Disclosure [Abstract]

Inventories

NOTE 5 - INVENTORIES

The following table presents the detail of our Inventories in the Statements of Unaudited Condensed Consolidated Financial Position:



	(In Millions)
	March 31, 2018						December 31, 2017
Segment	Finished Goods		Work-in Process		Total Inventory		Finished Goods		Work-in Process		Total Inventory
U.S. Iron Ore	$	267.2	$	36.0	$	303.2	$	127.1	$	11.3	$	138.4
Asia Pacific Iron Ore	20.2		1.0		21.2		33.3		11.7		45.0
Total	$	287.4	$	37.0	$	324.4	$	160.4	$	23.0	$	183.4

We recorded lower of cost or net realizable value inventory charges of $13.0 million and $9.1 million related to finished goods inventory and work-in process inventory, respectively, at Asia Pacific Iron Ore in Cost of goods sold and operating expenses in the Statements of Unaudited Condensed Consolidated Operations for the three months ended March 31, 2018. The charges were a result of the decline in our expected realized revenue rates for future sales of these tons. There were no lower of cost or net realizable value inventory adjustments recorded for the three months ended March 31, 2017.

We recorded an impairment charge of $1.4 million and $13.2 million related to finished goods inventory and work-in process inventory, respectively, at Asia Pacific Iron Ore in Cost of goods sold and operating expenses in the Statements of Consolidated Operations for the three months ended March 31, 2018. Inventory not expected to be sold prior to the closure of operations was impaired. There were no inventory impairment adjustments recorded for the three months ended March 31, 2017.

PROPERTY, PLANT AND EQUIPMENT

3 Months Ended

Mar. 31, 2018

Property, Plant and Equipment [Abstract]

PROPERTY, PLANT AND EQUIPMENT

NOTE 6 - PROPERTY, PLANT AND EQUIPMENT

The following table indicates the value of each of the major classes of our consolidated depreciable assets:



	(In Millions)
	March 31, 2018			December 31, 2017
Land rights and mineral rights	$	549.6		$	549.6
Office and information technology	66.3			66.3
Buildings	85.5			86.8
Mining equipment	594.0			594.4
Processing equipment	619.8			617.0
Electric power facilities	57.0			57.0
Land improvements	23.6			23.7
Asset retirement obligation	16.9			19.2
Other	30.3			30.3
Construction in-progress	48.1			35.1
	2,091.1			2,079.4
Allowance for depreciation and depletion	(1,043.8		)	(1,028.4		)
	$	1,047.3		$	1,051.0

We recorded depreciation and depletion expense of $21.3 million and $22.6 million in the Statements of Unaudited Condensed Consolidated Operations for the three months ended March 31, 2018 and March 31, 2017, respectively.

As of March 31, 2018, based on the anticipated closure of the Asia Pacific Iron Ore operations we determined that we would not recover the value of certain long-lived assets at our Asia Pacific Iron Ore operations. As a result, we recorded an impairment of $2.6 million in Miscellaneous – net in the Statements of Unaudited Condensed Consolidated Operations.

DEBT AND CREDIT FACILITIES

3 Months Ended

Mar. 31, 2018

Debt Disclosure [Abstract]

DEBT AND CREDIT FACILITIES

NOTE 7 - DEBT AND CREDIT FACILITIES

The following represents a summary of our long-term debt:



(In Millions)
March 31, 2018
Debt Instrument	Annual Effective Interest Rate	Total Principal Amount		Debt Issuance Costs			Unamortized Discounts			Total Debt
Secured Notes
$400 Million 4.875% 2024 Senior Notes	5.00%	$	400.0	$	(6.7	)	$	(2.5	)	$	390.8
Unsecured Notes
$400 Million 5.90% 2020 Senior Notes	5.98%	88.9		(0.2		)	(0.1		)	88.6
$500 Million 4.80% 2020 Senior Notes	4.83%	122.4		(0.2		)	(0.1		)	122.1
$700 Million 4.875% 2021 Senior Notes	4.89%	138.4		(0.3		)	(0.1		)	138.0
$316.25 Million 1.50% 2025 Convertible Senior Notes	6.26%	316.3		(6.3		)	(83.2		)	226.8
$1.075 Billion 5.75% 2025 Senior Notes	6.01%	1,075.0		(11.1		)	(16.0		)	1,047.9
$800 Million 6.25% 2040 Senior Notes	6.34%	298.4		(2.3		)	(3.4		)	292.7
ABL Facility	N/A	450.0		N/A			N/A			—
Fair Value Adjustment to Interest Rate Hedge										1.3
Long-term debt										$	2,308.2



(In Millions)
December 31, 2017
Debt Instrument	Annual Effective Interest Rate	Total Principal Amount		Debt Issuance Costs			Unamortized Discounts			Total Debt
Secured Notes
$400 Million 4.875% 2024 Senior Notes	5.00%	$	400.0	$	(7.1	)	$	(2.6	)	$	390.3
Unsecured Notes
$400 Million 5.90% 2020 Senior Notes	5.98%	88.9		(0.2		)	(0.1		)	88.6
$500 Million 4.80% 2020 Senior Notes	4.83%	122.4		(0.3		)	(0.1		)	122.0
$700 Million 4.875% 2021 Senior Notes	4.89%	138.4		(0.3		)	(0.1		)	138.0
$316.25 Million 1.50% 2025 Convertible Senior Notes	6.26%	316.3		(6.6		)	(85.6		)	224.1
$1.075 Billion 5.75% 2025 Senior Notes	6.01%	1,075.0		(11.3		)	(16.5		)	1,047.2
$800 Million 6.25% 2040 Senior Notes	6.34%	298.4		(2.4		)	(3.4		)	292.6
ABL Facility	N/A	550.0		N/A			N/A			—
Fair Value Adjustment to Interest Rate Hedge										1.4
Long-term debt										$	2,304.2

$1.075 Billion 5.75% 2025 Senior Notes

On February 27, 2017, we entered into an indenture among the Company, the guarantors party thereto and U.S. Bank National Association, as trustee, relating to the issuance of $500 million aggregate principal amount of 5.75% 2025 Senior Notes. On August 7, 2017, we issued an additional $575 million aggregate principal amount of our 5.75% 2025 Senior Notes. The second tranche was issued at 97.0% of face value. The 5.75% 2025 Senior Notes were issued in private transactions exempt from the registration requirements of the Securities Act. Pursuant to the registration rights agreement executed as part of these issuances, we filed on February 14, 2018 a registration statement with the SEC with respect to a registered offer to exchange the 5.75% 2025 Senior Notes for publicly registered notes, with all significant terms and conditions remaining the same.

Debt Maturities

The following represents a summary of our maturities of debt instruments based on the principal amounts outstanding at March 31, 2018:



	(In Millions)
	Maturities of Debt
2018	$	—
2019	—
2020	211.3
2021	138.4
2022	—
2023	—
2024 and thereafter	2,089.7
Total maturities of debt	$	2,439.4

ABL Facility

On February 28, 2018, we entered into an amended and restated senior secured asset-based revolving credit facility with various financial institutions. The ABL Facility amends and restates our prior $550.0 million Syndicated Facility Agreement, dated as of March 30, 2015. The ABL Facility will mature upon the earlier of February 28, 2023 or 60 days prior to the maturity of certain other material debt, and provides for up to $450.0 million in borrowings, comprised of (i) a $400.0 million U.S. tranche, including a $248.8 million sublimit for the issuance of letters of credit and a $100.0 million sublimit for U.S. swingline loans, and (ii) a $50.0 million Australian tranche, including a $24.4 million sublimit for the issuance of letters of credit and a $20.0 million sublimit for Australian swingline loans. Availability under both the U.S. tranche and Australian tranche of the ABL Facility is limited to an eligible U.S. borrowing base and Australian borrowing base, as applicable, determined by applying customary advance rates to eligible accounts receivable, inventory and certain mobile equipment.

The ABL Facility and certain bank products and hedge obligations are guaranteed by us and certain of our existing wholly-owned U.S. and Australian subsidiaries and are required to be guaranteed by certain of our future U.S. and Australian subsidiaries; provided, however, that the obligations of any U.S. entity will not be guaranteed by any Australian entity. Amounts outstanding under the ABL Facility are secured by (i) a first-priority security interest in the accounts receivable and other rights to payment, inventory, as-extracted collateral, certain investment property, deposit accounts, securities accounts, certain general intangibles and commercial tort claims, certain mobile equipment, commodities accounts, deposit accounts, securities accounts and other related assets of ours, the other borrowers and the guarantors, and proceeds and products of each of the foregoing (collectively, the “ABL Collateral”); provided, however, that the ABL Collateral owned by a borrower or guarantor that is organized under the laws of Australia (the “Australian Loan Parties”) shall only secure the Australian tranche and obligations of the borrowers and guarantors organized under the laws of Australia, (ii) a second-priority security interest in substantially all of our assets and the assets of the other borrowers and the guarantors (other than the Australian Loan Parties) other than the ABL Collateral (collectively, the “Notes Collateral” and, together with the ABL Collateral, the “Collateral”) and (iii) solely in the case of the obligations of the Australian Loan Parties under the ABL Facility, a featherweight floating security interest over substantially all assets of the Australian Loan Parties other than ABL Collateral, in each case, subject to certain customary exceptions.

Borrowings under the ABL Facility bear interest, at our option, at a base rate, an Australian base rate or, if certain conditions are met, a LIBOR rate, in each case plus an applicable margin. The base rate is equal to the greatest of the federal funds rate plus ½ of 1%, the LIBOR rate based on a one-month interest period plus 1% and the floating rate announced by Bank of America Merrill Lynch as its “prime rate" and 1%. The Australian base rate is equal to the LIBOR rate as of 11:00 a.m. on the first business day of each month for a one-month period. The LIBOR rate is a per annum fixed rate equal to LIBOR with respect to the applicable interest period and amount of LIBOR rate loan requested.

The ABL Facility contains customary representations and warranties and affirmative and negative covenants including, among others, covenants regarding the maintenance of certain financial ratios if certain conditions are triggered, covenants relating to financial reporting, covenants relating to the payment of dividends on, or purchase or redemption of, our capital stock, covenants relating to the incurrence or prepayment of certain debt, covenants relating to the incurrence of liens or encumbrances, covenants relating to compliance with laws, covenants relating to transactions with affiliates, covenants relating to mergers and sales of all or substantially all of our assets and limitations on changes in the nature of our business.

The ABL Facility provides for customary events of default, including, among other things, the event of nonpayment of principal, interest, fees, or other amounts, a representation or warranty proving to have been materially incorrect when made, failure to perform or observe certain covenants within a specified period of time, a cross-default to certain material indebtedness, the bankruptcy or insolvency of the Company and certain of its subsidiaries, monetary judgment defaults of a specified amount, invalidity of any loan documentation, a change of control of the Company, and ERISA defaults resulting in liability of a specified amount. If an event of a default exists (beyond any applicable grace or cure period, if any), the administrative agent may and, at the direction of the requisite number of lenders, shall declare all amounts owing under the ABL Facility immediately due and payable, terminate such lenders’ commitments to make loans under the ABL Facility and/or exercise any and all remedies and other rights under the ABL Facility. For certain events of default related to insolvency and receivership, the commitments of the lenders will be automatically terminated and all outstanding loans and other amounts will become immediately due and payable.

As of March 31, 2018 and December 31, 2017, we were in compliance with the ABL Facility liquidity requirements and, therefore, the springing financial covenant requiring a minimum fixed charge coverage ratio of 1.0 to 1.0 was not applicable.

As of March 31, 2018 and December 31, 2017, no loans were drawn under the ABL Facility and we had total availability of $314.1 million and $273.2 million, respectively, as a result of borrowing base limitations. As of March 31, 2018 and December 31, 2017, the principal amount of letter of credit obligations totaled $46.6 million and $46.5 million, respectively, to support business obligations primarily related to workers compensation and environmental obligations, thereby further reducing available borrowing capacity on our ABL Facility to $267.5 million and $226.7 million, respectively.

FAIR VALUE OF FINANCIAL INSTRUMENTS

3 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

FAIR VALUE MEASUREMENTS

NOTE 8 - FAIR VALUE MEASUREMENTS

The following represents the assets and liabilities of the Company measured at fair value:



	(In Millions)
	March 31, 2018
Description	Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Assets:
Cash equivalents	$	36.0	$	490.6	$	—	$	526.6
Derivative assets	—		—		93.6		93.6
Total	$	36.0	$	490.6	$	93.6	$	620.2
Liabilities:
Derivative liabilities	$	—	$	0.2	$	4.2	$	4.4
Total	$	—	$	0.2	$	4.2	$	4.4



	(In Millions)
	December 31, 2017
Description	Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Assets:
Cash equivalents	$	66.3	$	550.6	$	—	$	616.9
Derivative assets	—		—		39.4		39.4
Total	$	66.3	$	550.6	$	39.4	$	656.3
Liabilities:
Derivative liabilities	$	—	$	0.3	$	2.4	$	2.7
Total	$	—	$	0.3	$	2.4	$	2.7

Financial assets classified in Level 1 include money market funds and treasury bonds. The valuation of these instruments is based upon unadjusted quoted prices for identical assets in active markets.

The valuation of financial assets and liabilities classified in Level 2 is determined using a market approach based upon quoted prices for similar assets and liabilities in active markets or other inputs that are observable. Level 2 assets include commercial paper and certificates of deposit. Level 2 liabilities include commodity hedge contracts.

The Level 3 assets and liabilities include derivative assets that consist of freestanding derivative instruments related to certain supply agreements with one of our U.S. Iron Ore customers and derivative assets and liabilities related to certain provisional pricing arrangements with our U.S. Iron Ore and Asia Pacific Iron Ore customers.

The supply agreement included in our Level 3 assets includes provisions for supplemental revenue or refunds based on the average annual daily market price for hot-rolled coil steel at the time the iron ore product is consumed in the customer’s blast furnaces. We account for these provisions as derivative instruments at the time of sale and adjust the corresponding asset or liability to fair value as an adjustment to Product revenues each reporting period until the product is consumed and the amounts are settled. The fair value of the instruments are determined using a market approach based on the estimate of the average annual daily market price for hot-rolled coil steel. This estimate takes into consideration current market conditions and nonperformance risk. We had assets of $91.2 million and $37.9 million at March 31, 2018 and December 31, 2017, respectively, related to the supply agreement.

The provisional pricing arrangements included in our Level 3 assets/liabilities specify provisional price calculations, where the pricing mechanisms generally are based on market pricing, with the final revenue rate to be based on market inputs at a specified point in time in the future, per the terms of the supply agreements. The difference between the estimated final revenue rate at the date of sale and the estimated final revenue rate at the measurement date is characterized as a derivative and is required to be accounted for separately once the revenue has been recognized. The derivative instrument is adjusted to fair value through Product revenues each reporting period based upon current market data and forward-looking estimates provided by management until the final revenue rate is determined. We had assets of $2.4 million and $1.5 million at March 31, 2018 and December 31, 2017, respectively, related to provisional pricing arrangements. In addition, we had liabilities of $4.2 million and $2.4 million related to provisional pricing arrangements at March 31, 2018 and December 31, 2017, respectively.

The following table illustrates information about quantitative inputs and assumptions for the assets and liabilities categorized in Level 3 of the fair value hierarchy:

Qualitative/Quantitative Information About Level 3 Fair Value Measurements

(In Millions)

Fair Value at March 31, 2018

Balance Sheet

Location

Valuation Technique

Unobservable Input

Range or Point Estimate

(Weighted Average)

Customer supply agreements

$

91.2

Derivative assets

Market Approach

Management's Estimate of Market Hot-Rolled Coil Steel per net ton

$752

Provisional pricing arrangements

$

2.4

Derivative assets

Market Approach

Management's

Estimate of Platts 62% Price

per dry metric ton

$63 - $71
($66)

Provisional pricing arrangements

$

4.2

Other Current Liabilities

Market Approach

Management's

Estimate of Platts 62% Price

per dry metric ton

$63 - $71
($66)

The significant unobservable input used in the fair value measurement of our customer supply agreement is an estimate determined by management including the forward-looking estimate for the average annual daily market price for hot-rolled coil steel.

The significant unobservable inputs used in the fair value measurement of our provisional pricing arrangements are management’s estimates of Platts 62% Price based upon current market data and index pricing, of which includes forward-looking estimates determined by management.

We recognize any transfers between levels as of the beginning of the reporting period, including both transfers into and out of levels. There were no transfers between Level 1 and Level 2 and no transfers into or out of Level 3 of the fair value hierarchy during the three months ended March 31, 2018 and 2017. The following tables represent a reconciliation of the changes in fair value of financial instruments measured at fair value on a recurring basis using significant unobservable inputs (Level 3):



	(In Millions)
	Level 3 Assets
	Three Months Ended March 31,
	2018			2017
Beginning balance¹	$	51.0		$	31.6
Total gains (losses)
Included in earnings	49.1			42.1
Settlements	(6.5		)	(14.3		)
Ending balance - March 31	$	93.6		$	59.4
Total gains for the period included in earnings attributable to the change in unrealized gains on assets still held at the reporting date	$	44.5		$	33.2

¹ Beginning balance as of January 1, 2018 includes an $11.6 million adjustment for adoption of Topic 606.



	(In Millions)
	Level 3 Liabilities
	Three Months Ended March 31,
	2018			2017
Beginning balance	$	(2.4	)	$	(0.5	)
Total gains (losses)
Included in earnings	(4.0		)	(8.6		)
Settlements	2.2			—
Ending balance - March 31	$	(4.2	)	$	(9.1	)
Total losses for the period included in earnings attributable to the change in unrealized losses on liabilities still held at the reporting date	$	(4.2	)	$	(9.1	)

The carrying amount of certain financial instruments (e.g., Accounts receivable, net, Accounts payable and Accrued expenses) approximates fair value and, therefore, has been excluded from the table below. A summary of the carrying amount and fair value of other financial instruments were as follows:



		(In Millions)
		March 31, 2018				December 31, 2017
	Classification	Carrying Value		Fair Value		Carrying Value		Fair Value
Long-term debt:
Secured Notes
$400 Million 4.875% 2024 Senior Notes	Level 1	$	390.8	$	389.0	$	390.3	$	398.0
Unsecured Notes
$400 Million 5.90% 2020 Senior Notes	Level 1	88.6		89.1		88.6		88.0
$500 Million 4.80% 2020 Senior Notes	Level 1	122.1		120.3		122.0		118.8
$700 Million 4.875% 2021 Senior Notes	Level 1	138.0		135.4		138.0		130.8
$316.25 Million 1.50% 2025 Convertible Senior Notes	Level 1	226.8		340.0		224.1		352.9
$1.075 Billion 5.75% 2025 Senior Notes	Level 1	1,047.9		1,026.6		1,047.2		1,029.3
$800 Million 6.25% 2040 Senior Notes	Level 1	292.7		251.1		292.6		227.1
ABL Facility	Level 2	—		—		—		—
Fair value adjustment to interest rate hedge	Level 2	1.3		1.3		1.4		1.4
Total long-term debt		$	2,308.2	$	2,352.8	$	2,304.2	$	2,346.3

The fair value of long-term debt was determined using quoted market prices based upon current borrowing rates.

Items Measured at Fair Value on a Non-Recurring Basis

The following tables present information about the financial assets and liabilities that were measured on a fair value basis. The tables also indicate the fair value hierarchy of the valuation techniques used to determine such fair value.



	(In Millions)
	March 31, 2018
Description	Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total		Total Year-to-Date Loss
Assets:
Loans to and accounts receivables from the Canadian Entities	$	—	$	—	$	50.4	$	50.4	$	(1.2	)
Long-lived assets - Asia Pacific Iron Ore	$	—	$	—	$	—	$	—	$	(2.6	)



	(In Millions)
	December 31, 2017
Description	Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total		Total Year-to-Date Gains
Assets:
Loans to and accounts receivables from the Canadian Entities	$	—	$	—	$	51.6	$	51.6	$	3.0
Liabilities:
Guarantees	$	—	$	—	$	—	$	—	$	31.4

To assess the fair value and recoverability of the accounts receivable from the Canadian Entities, we estimated the fair value of the underlying net assets of the Canadian Entities available for distribution to their creditors in relation to the estimated creditor claims and the priority of those claims. These underlying amounts are denominated primarily in Canadian dollars and are remeasured on a quarterly basis.

We determined the fair value and recoverability of our Canadian investments by comparing the estimated fair value of the remaining underlying assets of the Canadian Entities to remaining estimated liabilities. We recorded the Canadian denominated guarantees at book value, which best approximated fair value.

Our estimates involve significant judgment and are based on currently available information, an assessment of the validity of certain claims and estimated payments made by the Canadian Entities. Our ultimate recovery is subject to the final liquidation value of the Canadian Entities.

During the three months ended March 31, 2018, we recorded an impairment of $2.6 million for our Asia Pacific Iron Ore reporting segment. Based on the anticipated closure of the Asia Pacific Iron Ore operations, we stated the value of these assets within Property, plant and equipment at their estimated fair value.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

PENSIONS AND OTHER POSTRETIREMENT BENEFITS

3 Months Ended

Mar. 31, 2018

Postemployment Benefits [Abstract]

PENSIONS AND OTHER POSTRETIREMENT BENEFITS

NOTE 9 - PENSIONS AND OTHER POSTRETIREMENT BENEFITS

We offer defined benefit pension plans, defined contribution pension plans and OPEB plans, primarily consisting of retiree healthcare benefits, to most employees in the U.S. as part of a total compensation and benefits program. We do not have employee retirement benefit obligations at our Asia Pacific Iron Ore operations. The defined benefit pension plans largely are noncontributory and benefits generally are based on a minimum formula or employees’ years of service and average earnings for a defined period prior to retirement.

On January 1, 2018, we adopted the amendments to ASC 715 regarding the presentation of net periodic pension and postretirement benefit costs. We retrospectively adopted the presentation of service cost separate from the other components of net periodic costs. Service costs are classified within Cost of goods sold and operating expenses, Selling, general and administrative expenses and Miscellaneous – net while the interest cost, expected return on assets, amortization of prior service costs, net remeasurement, and other costs are classified within Other non-operating income in our Statements of Unaudited Condensed Consolidated Operations.

The following are the components of defined benefit pension and OPEB costs and credits:

Defined Benefit Pension Costs



	(In Millions)
	Three Months Ended March 31,
	2018			2017
Service cost	$	4.7		$	4.8
Interest cost	7.6			7.5
Expected return on plan assets	(15.0		)	(13.5		)
Amortization:
Prior service costs	0.5			0.6
Net actuarial loss	5.3			5.3
Net periodic benefit cost	$	3.1		$	4.7

Other Postretirement Benefits Credits



	(In Millions)
	Three Months Ended March 31,
	2018			2017
Service cost	$	0.5		$	0.5
Interest cost	2.1			2.1
Expected return on plan assets	(4.6		)	(4.4		)
Amortization:
Prior service credits	(0.8		)	(0.7		)
Net actuarial loss	1.2			1.2
Net periodic benefit credit	$	(1.6	)	$	(1.3	)

Based on funding requirements, we made pension contributions of $2.3 million for the three months ended March 31, 2018, compared to no pension contributions for the three months ended March 31, 2017. OPEB contributions are typically made on an annual basis in the first quarter of each year, but due to plan funding requirements being met, no OPEB contributions were required or made for the three months ended March 31, 2018 and March 31, 2017.

STOCK COMPENSATION PLANS

3 Months Ended

Mar. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock Compensation Plans

NOTE 10 - STOCK COMPENSATION PLANS

Employees’ Plans

On February 21, 2018, the Compensation and Organization Committee of the Board of Directors approved grants under the A&R 2015 Equity Plan to certain officers and employees for the 2018 to 2020 performance period. Shares granted under the awards consisted of 0.7 million restricted stock units and 0.7 million performance shares.

Restricted stock units granted during 2018 are subject to continued employment, are retention based and are payable in common shares or cash at a time determined by the Compensation Committee at its discretion. The outstanding restricted stock units that were granted in 2018 cliff vest on December 31, 2020.

Performance shares are subject to continued employment, and each performance share, if earned, entitles the holder to be paid out in common shares or cash in certain circumstances. Performance is measured on the basis of relative TSR for the period of January 1, 2018 to December 31, 2020 and measured against the constituents of the S&P Metals and Mining ETF Index at the beginning of the relevant performance period. The final payouts for the outstanding performance period grants will vary from zero to 200% of the original grant depending on whether and to what extent the Company achieves certain objectives and performance goals as established by the Compensation Committee.

Determination of Fair Value

The fair value of each performance share grant is estimated on the date of grant using a Monte Carlo simulation to forecast relative TSR performance. A correlation matrix of historic and projected stock prices was developed for both the Company and our predetermined peer group of mining and metals companies. The fair value assumes that performance goals will be achieved.

The expected term of the grant represents the time from the grant date to the end of the service period. We estimate the volatility of our common shares and that of the peer group of mining and metals companies using daily price intervals for all companies. The risk-free interest rate is the rate at the grant date on zero-coupon government bonds with a term commensurate with the remaining life of the performance period.

The following assumptions were utilized to estimate the fair value for the 2018 performance share grant:



Grant Date	Grant Date Market Price		Average Expected Term (Years)	Expected Volatility	Risk-Free Interest Rate	Dividend Yield	Fair Value		Fair Value (Percent of Grant Date Market Price)
February 21, 2018	$	7.53	2.86	86.8%	2.42%	—%	$	11.93	158.43%

INCOME TAXES	3 Months Ended
INCOME TAXES	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	NOTE 11 - INCOME TAXES Our 2018 estimated annual effective tax rate before discrete items is approximately 0.1%. The annual effective tax rate differs from the U.S. statutory rate of 21% primarily due to the deductions for percentage depletion in excess of cost depletion related to U.S. operations and the reversal of valuation allowance from operations in the current year. The 2017 estimated annual effective tax rate before discrete items at March 31, 2017 was 5.4%. For the three months ended March 31, 2018 and 2017, we recorded discrete items that resulted in an income tax expense of $15.7 million and a benefit of $0.1 million, respectively. The current year items relate primarily to a $14.5 million reduction of the refundable AMT credit recorded in Income tax receivable in our Statements of Unaudited Condensed Consolidated Financial Position based on the sequestration guidance issued by the Internal Revenue Service during the period ended March 31, 2018. This $14.5 million current year expense is a reduction of an asset and will not result in a cash tax outlay.

LEASE OBLIGATIONS

3 Months Ended

Mar. 31, 2018

Leases [Abstract]

LEASE OBLIGATIONS

NOTE 12 - LEASE OBLIGATIONS

We lease certain mining, production and other equipment under operating and capital leases. The capital leases are for varying lengths, generally at market interest rates and contain purchase and/or renewal options at the end of the terms. Some capital lease payments could be accelerated upon cancellation of certain contracts at Asia Pacific Iron Ore. Our operating lease expense was $1.6 million for the three months ended March 31, 2018, compared with $1.7 million for the comparable period in 2017.

Future minimum payments under capital leases and non-cancellable operating leases as of March 31, 2018 are as follows:



	(In Millions)
	Capital Leases		Operating Leases
2018 (April 1 - December 31)	$	14.7	$	3.3
2019	12.0		1.9
2020	11.0		1.8
2021	10.3		1.8
2022	2.1		1.8
2023 and thereafter	—		7.5
Total minimum lease payments	$	50.1	$	18.1
Amounts representing interest	7.6
Present value of net minimum lease payments¹	$	42.5

¹ The total is comprised of $14.6 million and $27.9 million classified as Other current liabilities and Other liabilities, respectively, in the Statements of Unaudited Condensed Consolidated Financial Position as of March 31, 2018.

ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS

3 Months Ended

Mar. 31, 2018

Environmental Remediation Obligations [Abstract]

ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS

NOTE 13 - ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS

We had environmental and mine closure liabilities of $202.5 million and $200.1 million at March 31, 2018 and December 31, 2017, respectively. The following is a summary of the obligations:



	(In Millions)
	March 31, 2018		December 31, 2017
Environmental	$	3.1	$	2.9
Mine closure
U.S. Iron Ore¹	170.7		168.4
Asia Pacific Iron Ore	28.7		28.8
Total mine closure	199.4		197.2
Total environmental and mine closure obligations	202.5		200.1
Less current portion	21.3		3.6
Long-term environmental and mine closure obligations	$	181.2	$	196.5

¹U.S. Iron Ore includes our active operating mines, our indefinitely idled Empire mine and a closed mine formerly operating as LTVSMC.

As of March 31, 2018, we reclassified $17.7 million of our mine closure liability from long-term Environmental and mine closure obligations to Other current liabilities based on our plan to begin reclamation activities at Asia Pacific Iron Ore later this year.

Mine Closure

The accrued mine closure obligation for our active mining operations provides for contractual and legal obligations associated with the eventual closure of the mining operations. The accretion of the liability and amortization of the related asset is recognized over the estimated mine lives for each location.

The following represents a roll forward of our mine closure obligation liability for the three months ended March 31, 2018 and for the year ended December 31, 2017:



	(In Millions)
	March 31, 2018			December 31, 2017
Mine closure obligation at beginning of period	$	197.2		$	204.0
Accretion expense	2.7			14.9
Remediation payments	(0.1		)	(5.6		)
Exchange rate changes	(0.5		)	1.5
Revision in estimated cash flows	0.1			(17.6		)
Mine closure obligation at end of period	$	199.4		$	197.2

For the year ended December 31, 2017, the revision in estimated cash flows relates primarily to updates to our estimates resulting from our three-year in-depth review of our mine closure obligations for each of our U.S. mines. The primary driver of the decrease in estimated cash flows was the Empire mine, as the mine closure obligation was reduced $26.2 million as a result of the refinement of the cash flows required for reclamation, remediation and structural removal. Prior estimates were based on RS Means (a common costing methodology used in the construction and demolition industry) costing data while the current estimate was compiled using a more detailed cost build-up approach. The overall decrease in estimated cash flows for our U.S. Iron Ore mines was offset partially by an increase in costs of $10.1 million relating to the refinement of expected costs to be incurred at the end of life of mine at our Asia Pacific Iron Ore operations.

GOODWILL AND OTHER INTANGIBLE ASSETS AND LIABILITIES

3 Months Ended

Mar. 31, 2018

Goodwill and Intangible Assets Disclosure [Abstract]

GOODWILL AND OTHER INTANGIBLE ASSETS AND LIABILITIES

NOTE 14 - GOODWILL AND OTHER INTANGIBLE ASSETS

Goodwill

The carrying amount of goodwill as of March 31, 2018 and December 31, 2017 was $2.0 million and related to our U.S. Iron Ore operating segment.

Other Intangible Assets

The following table is a summary of definite-lived intangible assets:



		(In Millions)
		March 31, 2018							December 31, 2017
	Classification	Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount		Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount
Permits	Other non-current assets	$	78.8	$	(28.9	)	$	49.9	$	78.8	$	(26.5	)	$	52.3

Amortization expense relating to other intangible assets was $2.6 million and $0.6 million for the three months ended March 31, 2018 and 2017, respectively, and is recognized in Cost of goods sold and operating expenses in the Statements of Unaudited Condensed Consolidated Operations. Amortization expense of other intangible assets is expected to continue to be immaterial going forward.

- Definition

The entire disclosure for the aggregate amount of goodwill and a description of intangible assets, which may include (a) for amortizable intangible assets (also referred to as finite-lived intangible assets), the carrying amount, the amount of any significant residual value, and the weighted-average amortization period, (b) for intangible assets not subject to amortization (also referred to as indefinite-lived intangible assets), the carrying amount, and (c) the amount of research and development assets acquired and written off in the period, including the line item in the income statement in which the amounts written off are aggregated, if not readily apparent from the income statement. Also discloses (a) for amortizable intangibles assets in total and by major class, the gross carrying amount and accumulated amortization, the total amortization expense for the period, and the estimated aggregate amortization expense for each of the five succeeding fiscal years, (b) for intangible assets not subject to amortization the carrying amount in total and by major class, and (c) for goodwill, in total and for each reportable segment, the changes in the carrying amount of goodwill during the period (including the aggregate amount of goodwill acquired, the aggregate amount of impairment losses recognized, and the amount of goodwill included in the gain (loss) on disposal of a reporting unit). If any part of goodwill has not been allocated to a reportable segment, discloses the unallocated amount and the reasons for not allocating. For each impairment loss recognized related to an intangible asset (excluding goodwill), discloses: (a) a description of the impaired intangible asset and the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method for determining fair value, (c) the caption in the income statement or the statement of activities in which the impairment loss is aggregated, and (d) the segment in which the impaired intangible asset is reported. For each goodwill impairment loss recognized, discloses: (a) a description of the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method of determining the fair value of the associated reporting unit, and (c) if a recognized impairment loss is an estimate not finalized and the reasons why the estimate is not final. May also disclose the nature and amount of any significant adjustments made to a previous estimate of an impairment loss.

+ References + Details

DERIVATIVE INSTRUMENTS

3 Months Ended

Mar. 31, 2018

Derivative Instruments and Hedging Activities Disclosure [Abstract]

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES

NOTE 15 - DERIVATIVE INSTRUMENTS

The following table presents the fair value of our derivative instruments and the classification of each in the Statements of Unaudited Condensed Consolidated Financial Position:



	(In Millions)
	Derivative Assets						Derivative Liabilities
	March 31, 2018			December 31, 2017			March 31, 2018			December 31, 2017
Derivative Instrument	Balance Sheet Location	Fair Value		Balance Sheet Location	Fair Value		Balance Sheet Location	Fair Value		Balance Sheet Location	Fair Value
Derivatives designated as hedging instruments under ASC 815:
Commodity Contracts		$	—		$	—	Other current liabilities	$	0.2	Other current liabilities	$	0.3
Derivatives not designated as hedging instruments under ASC 815:
Customer supply agreements	Derivative assets	$	91.2	Derivative assets	$	37.9		$	—		$	—
Provisional pricing arrangements	Derivative assets	2.4		Derivative assets	1.5		Other current liabilities	4.2		Other current liabilities	2.4
Total derivatives not designated as hedging instruments under ASC 815		$	93.6		$	39.4		$	4.2		$	2.4
Total derivatives		$	93.6		$	39.4		$	4.4		$	2.7

Cash Flow Hedges

Commodity Contracts

As of March 31, 2018, we had outstanding natural gas hedge contracts for a notional amount of 3.5 million MMBtu in the form of forward contracts with varying maturity dates ranging from April 2018 to February 2019. As of December 31, 2017, we had outstanding natural gas hedge contracts for a notional amount of 3.5 million MMBtu in the form of forward contracts with varying maturity dates ranging from January 2018 to November 2018. Changes in fair value of highly effective hedges are recorded as a component of Accumulated other comprehensive loss in the Statements of Unaudited Condensed Consolidated Financial Position.

During the three months ended March 31, 2018, we recorded an unrealized gain of $0.4 million in Other comprehensive income (loss) for changes in the fair value of these instruments and $0.1 million has been reclassified from Accumulated other comprehensive loss into earnings. We had no commodity contracts designated as hedge instruments for the three months ended March 31, 2017.

Derivatives Not Designated as Hedging Instruments

Customer Supply Agreements

Most of our U.S. Iron Ore long-term supply agreements are comprised of a base price with annual price adjustment factors. The base price is the primary component of the purchase price for each contract. The indexed price adjustment factors are integral to the iron ore supply contracts and vary based on the agreement, but typically include adjustments based upon changes in the Platts 62% Price, along with pellet premiums, published Platts international indexed freight rates and changes in specified Producer Price Indices, including those for industrial commodities, fuel and steel. The pricing adjustments generally operate in the same manner, with each factor typically comprising a portion of the price adjustment, although the weighting of each factor varies based upon the specific terms of each agreement. In most cases, these adjustment factors have not been finalized at the time our product is sold. In these cases, we historically have estimated the adjustment factors at each reporting period based upon the best third-party information available. The estimates are then adjusted to actual when the information has been finalized. The price adjustment factors have been evaluated to determine if they contain embedded derivatives. The price adjustment factors share the same economic characteristics and risks as the host contract and are integral to the host contract as inflation adjustments; accordingly, they have not been separately valued as derivative instruments.

A supply agreement with one U.S. Iron Ore customer provides for supplemental revenue or refunds to the customer based on the average annual daily steel market price for hot-rolled coil steel at the time the iron ore product is consumed in the customer’s blast furnace. The supplemental pricing is characterized as a freestanding derivative and is required to be accounted for separately once the product is delivered. The derivative instrument, which is finalized based on a future price, is adjusted to fair value as a revenue adjustment each reporting period until the pellets are consumed and the amounts are settled.

We recognized net derivative revenue of $41.9 million and $17.8 million in Product revenues in the Statements of Unaudited Condensed Consolidated Operations for the three months ended March 31, 2018 and 2017, respectively, related to the supplemental payments. Derivative assets, representing the fair value of the supplemental revenue, were $91.2 million and $37.9 million as of March 31, 2018 and December 31, 2017 in the Statements of Unaudited Condensed Consolidated Financial Position, respectively.

Provisional Pricing Arrangements

Certain of our U.S. Iron Ore and Asia Pacific Iron Ore customer supply agreements specify provisional price calculations, where the pricing mechanisms generally are based on market pricing, with the final revenue rate based on certain market inputs at a specified period in time in the future, per the terms of the supply agreements. Market inputs are tied to indexed price adjustment factors that are integral to the iron ore supply contracts and vary based on the agreement. The pricing mechanisms typically include adjustments based upon changes in the Platts 62% Price, along with pellet premiums, published Platts international indexed freight rates and changes in specified Producer Price Indices, including those for industrial commodities, fuel and steel. The pricing adjustments generally operate in the same manner, with each factor typically comprising a portion of the price adjustment, although the weighting of each factor varies based upon the specific terms of each agreement.

Revenue is recognized generally when iron ore is delivered to our customers. Revenue is measured at the point control transfers and represents the amount of consideration we expect to receive in exchange for transferring goods. Changes in the expected revenue rate from the date control transfers through final settlement of contract terms is recorded in accordance with ASC Topic 815 and is characterized as a freestanding derivative and accounted for separately. Subsequently, the derivative instruments for both U.S. Iron Ore and Asia Pacific Iron Ore are adjusted to fair value through Product revenues each reporting period based upon current market data and forward-looking estimates provided by management until the final revenue rate is determined.

At March 31, 2018, we recorded $2.4 million as Derivative assets and $4.2 million as derivative liabilities classified as Other current liabilities related to our estimate of the final revenue rate with our U.S. Iron Ore and Asia Pacific Iron Ore customers in the Statements of Unaudited Condensed Consolidated Financial Position. At December 31, 2017, we recorded $1.5 million as Derivative assets and $2.4 million as derivative liabilities classified as Other current liabilities related to our estimate of the final revenue rate with our U.S. Iron Ore and Asia Pacific Iron Ore customers in the Statements of Unaudited Condensed Consolidated Financial Position. These amounts represent the difference between the amount we expect to receive when revenue is initially measured at the point control transfers and our subsequent estimate of the final revenue rate based on the price calculations established in the supply agreements. We recognized net increases of $3.2 million and $15.7 million in Product revenues in the Statements of Unaudited Condensed Consolidated Operations for the three months ended March 31, 2018 and 2017, respectively, related to these arrangements.

The following summarizes the effect of our derivatives that are not designated as hedging instruments in the Statements of Unaudited Condensed Consolidated Operations:



(In Millions)
Derivatives Not Designated as Hedging Instruments	Location of Income (Loss) Recognized on Derivatives	Amount of Income (Loss) Recognized on Derivatives
		Three Months Ended March 31,
		2018		2017
Customer Supply Agreements	Product revenues	$	41.9	$	17.8
Provisional Pricing Arrangements	Product revenues	3.2		15.7
Commodity Contracts	Cost of goods sold and operating expenses	—		(1.3		)
Total		$	45.1	$	32.2

Refer to NOTE 8 - FAIR VALUE MEASUREMENTS for additional information.

SHAREHOLDERS' EQUITY

3 Months Ended

Mar. 31, 2018

Equity [Abstract]

SHAREHOLDERS' EQUITY

NOTE 16 - SHAREHOLDERS' DEFICIT

The following table reflects the changes in shareholders' deficit attributable to both us and the noncontrolling interests, primarily related to Tilden and Empire. We own 100% of both mines as of March 31, 2018 and 85% and 79% of each mine, respectively, as of March 31, 2017:



	(In Millions)
	Cliffs Shareholders’ Equity (Deficit)			Noncontrolling Interest		Total Equity (Deficit)
December 31, 2017	$	(444.3	)	$	0.2	$	(444.1	)
Adoption of accounting standard (Note 2)	34.0			—		34.0
Comprehensive loss
Net loss	(84.3		)	—		(84.3		)
Other comprehensive income	7.7			—		7.7
Total comprehensive loss	(76.6		)	—		(76.6		)
Stock and other incentive plans	1.9			—		1.9
March 31, 2018	$	(485.0	)	$	0.2	$	(484.8	)



	(In Millions)
	Cliffs Shareholders’ Equity (Deficit)			Noncontrolling Interest			Total Equity (Deficit)
December 31, 2016	$	(1,464.3	)	$	133.8		$	(1,330.5	)
Comprehensive loss
Net loss	(28.1		)	(1.7		)	(29.8		)
Other comprehensive loss	(3.0		)	(5.0		)	(8.0		)
Total comprehensive loss	(31.1		)	(6.7		)	(37.8		)
Issuance of common shares	661.3			—			661.3
Stock and other incentive plans	4.0			—			4.0
March 31, 2017	$	(830.1	)	$	127.1		$	(703.0	)

The following table reflects the changes in Accumulated other comprehensive loss related to Cliffs shareholders’ deficit:



	(In Millions)
	Changes in Pension and Other Post-Retirement Benefits, net of tax			Unrealized Net Gain on Foreign Currency Translation		Net Unrealized Gain (Loss) on Derivative Financial Instruments, net of tax			Accumulated Other Comprehensive Loss
December 31, 2017	$	(263.9	)	$	225.4	$	(0.5	)	$	(39.0	)
Other comprehensive income before reclassifications	0.5			0.7		0.4			1.6
Net loss (gain) reclassified from accumulated other comprehensive loss	6.2			—		(0.1		)	6.1
March 31, 2018	$	(257.2	)	$	226.1	$	(0.2	)	$	(31.3	)



	(In Millions)
	Changes in Pension and Other Post-Retirement Benefits, net of tax			Unrealized Net Gain (Loss) on Foreign Currency Translation			Accumulated Other Comprehensive Loss
December 31, 2016	$	(260.6	)	$	239.3		$	(21.3	)
Other comprehensive income (loss) before reclassifications	3.3			(12.7		)	(9.4		)
Net loss reclassified from accumulated other comprehensive loss	6.4			—			6.4
March 31, 2017	$	(250.9	)	$	226.6		$	(24.3	)

The following table reflects the details about Accumulated other comprehensive loss components related to Cliffs shareholders’ deficit:



	(In Millions)
Details about Accumulated Other Comprehensive Loss Components	Amount of (Gain)/Loss Reclassified into Income						Affected Line Item in the Statement of Unaudited Condensed Consolidated Operations
	Three Months Ended March 31,
	2018			2017
Amortization of pension and OPEB liability:
Prior service credits	$	(0.3	)	$	(0.1	)	Other non-operating income
Net actuarial loss	6.5			6.5			Other non-operating income
	$	6.2		$	6.4		Net of taxes

Unrealized loss on derivative financial instruments:
Commodity contracts	$	(0.1	)	$	—		Cost of goods sold and operating expenses
	$	(0.1	)	$	—		Net of taxes

Total reclassifications for the period, net of tax	$	6.1		$	6.4

RELATED PARTIES

3 Months Ended

Mar. 31, 2018

RELATED PARTIES

NOTE 17 - RELATED PARTIES

One of our four operating U.S. iron ore mines is a co-owned joint venture with companies that are integrated steel producers or their subsidiaries. We are the manager of such co-owned mine and rely on our joint venture partners to make their required capital contributions and to pay for their share of the iron ore pellets that we produce. Our joint venture partners are also our customers. The following is a summary of the mine ownership of the co-owned iron ore mine at March 31, 2018:



Mine	Cleveland-Cliffs Inc.		ArcelorMittal		U.S. Steel
Hibbing	23.0	%	62.3	%	14.7	%

Product revenues from related parties were as follows:



	(In Millions)
	Three Months Ended March 31,
	2018			2017
Product revenues from related parties	$	62.1		$	118.5
Total product revenues	$	220.7		$	412.8
Related party product revenue as a percent of total product revenue	28.1		%	28.7		%

The following table presents the classification of related party assets and liabilities in the Statements of Unaudited Condensed Consolidated Financial Position:



	(In Millions)
	Balance Sheet Location	March 31, 2018			December 31, 2017
Amounts due from related parties	Accounts receivable, net	$	7.9		$	68.1
Customer supply agreements and provisional pricing agreements	Derivative assets	91.3			37.9
Amounts due to related parties	Accounts payable	(1.2		)	—
Amounts due to related parties	Partnership distribution payable	(44.2		)	(44.2		)
Amounts due to related parties	Other current liabilities	(0.4		)	(12.3		)
Amounts due to related parties	Other liabilities	(42.0		)	(41.4		)
Net amounts due from related parties		$	11.4		$	8.1

During 2017, our ownership interest in Empire increased to 100% as we reached an agreement to distribute the noncontrolling interest net assets of $132.7 million to ArcelorMittal, in exchange for its interest in Empire. The net assets were agreed to be distributed in three installments of $44.2 million each, the first of which was paid upon the execution of the agreement and the remaining distributions are due in August 2018 and August 2019. The remaining two outstanding installments are reflected in Partnership distribution payable and Other liabilities in the Statements of Unaudited Condensed Consolidated Financial Position as of March 31, 2018.

A supply agreement with one U.S. Iron Ore customer provides for supplemental revenue or refunds to the customer based on the average annual daily market price for hot-rolled coil steel at the time the product is consumed in the customer’s blast furnace. The supplemental pricing is characterized as a freestanding derivative. Refer to NOTE 15 - DERIVATIVE INSTRUMENTS for further information.

EARNINGS PER SHARE

3 Months Ended

Mar. 31, 2018

Earnings Per Share [Abstract]

EARNINGS PER SHARE

NOTE 18 - EARNINGS PER SHARE

The following table summarizes the computation of basic and diluted earnings (loss) per share:



	(In Millions, Except Per Share Amounts)
	Three Months Ended March 31,
	2018			2017
Loss from Continuing Operations	$	(84.8	)	$	(30.3	)
Loss from Continuing Operations Attributable to Noncontrolling Interest	—			1.7
Net Loss from Continuing Operations Attributable to Cliffs Shareholders	$	(84.8	)	$	(28.6	)
Income from Discontinued Operations, net of tax	0.5			0.5
Net Loss Attributable to Cliffs Shareholders	$	(84.3	)	$	(28.1	)
Weighted Average Number of Shares:
Basic	297.3			265.2
Employee Stock Plans	—			—
Diluted	297.3			265.2
Loss per Common Share Attributable to Cliffs Common Shareholders - Basic:
Continuing operations	$	(0.29	)	$	(0.11	)
Discontinued operations	—			—
	$	(0.29	)	$	(0.11	)
Loss per Common Share Attributable to Cliffs Common Shareholders - Diluted:
Continuing operations	$	(0.29	)	$	(0.11	)
Discontinued operations	—			—
	$	(0.29	)	$	(0.11	)

The diluted earnings per share calculation excludes 3.8 million and 4.6 million shares for the three months ended March 31, 2018 and 2017, respectively, related to equity plan awards that would have been anti-dilutive.

COMMITMENTS AND CONTINGENCIES	3 Months Ended
COMMITMENTS AND CONTINGENCIES	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	NOTE 19 - COMMITMENTS AND CONTINGENCIES Contingencies We are currently the subject of, or party to, various claims and legal proceedings incidental to our operations. If management believes that a loss arising from these matters is probable and can reasonably be estimated, we record the amount of the loss or the minimum estimated liability when the loss is estimated using a range, and no point within the range is more probable than another. As additional information becomes available, any potential liability related to these matters is assessed and the estimates are revised, if necessary. Based on currently available information, management believes that the ultimate outcome of these matters, individually and in the aggregate, will not have a material effect on our financial position, results of operations or cash flows. However, these claims and legal proceedings are subject to inherent uncertainties and unfavorable rulings could occur. An unfavorable ruling could include monetary damages, additional funding requirements or an injunction. If an unfavorable ruling were to occur, there exists the possibility of a material impact on the financial position and results of operations for the period in which the ruling occurs or future periods. However, we do not believe that any pending claims or legal proceedings will result in a material liability in relation to our consolidated financial statements. Currently, we have recorded a liability in the Statements of Unaudited Condensed Consolidated Financial Position related to the following legal matters: Michigan Electricity Matters. On February 19, 2015, in connection with various proceedings before FERC with respect to certain cost allocations for continued operation of the Presque Isle Power Plant in Marquette, Michigan, FERC issued an order directing MISO to submit a revised methodology for allocating SSR costs that identified the load serving entities that require the operation of SSR units at the power plant for reliability purposes. On September 17, 2015, FERC issued an order conditionally approving MISO’s revised allocation methodology. On September 22, 2016, FERC denied requests for rehearing of the February 19 order, rejecting arguments that FERC did not have the authority to order refunds in a cost allocation case and to impose retroactive surcharges to effectuate such refunds. FERC, however, suspended any refunds and surcharges pending its review of a July 25, 2016 ALJ initial decision on the appropriate amount of SSR compensation. This suspension was ultimately lifted after FERC’s Order on Initial Decision of October 19, 2017, affirming in part and reversing in part certain aspects of the ALJ’s decision and FERC’s order on February 28, 2018, directing that refunds and surcharges be effectuated over a ten-month period beginning on the date of the order. Our current estimate of the potential liability to the Empire and Tilden mines is $13.0 million in the aggregate, based on a schedule of anticipated surcharges (including interest) for the Escanaba, White Pine and Presque Isle SSRs from Empire and Tilden's electricity supplier. Separate from these SSR compensation issues, Tilden and Empire, along with various Michigan-aligned parties, had filed petitions for review regarding allocation and non-cost SSR issues with the U.S. Court of Appeals for the D.C. Circuit. Oral arguments on those issues were completed on April 6, 2018. We will continue to vigorously challenge the imposition of any retroactive SSR costs before the U.S. Court of Appeals for the D.C. Circuit. As of March 31, 2018, $13.0 million is included in our Statements of Unaudited Condensed Consolidated Financial Position as part of Accrued expenses. CCAA Proceedings Effective January 27, 2015, following the commencement of CCAA proceedings for the Bloom Lake Group, we deconsolidated the Bloom Lake Group and certain other wholly-owned subsidiaries comprising substantially all of our Canadian operations. Additionally, on May 20, 2015, the Wabush Group commenced CCAA proceedings which resulted in the deconsolidation of the remaining Wabush Group entities that were not previously deconsolidated. As a result of this action, the CCAA protection granted to the Bloom Lake Group was extended to include the Wabush Group to facilitate the reorganization of each of their businesses and operations. Prior to the deconsolidations, certain of our wholly-owned subsidiaries made loans to the Canadian Entities for the purpose of funding their operations and had accounts receivable generated in the ordinary course of business. The loans, corresponding interest and the accounts receivable were considered intercompany transactions and eliminated in our consolidated financial statements. Since the deconsolidations, the loans, associated interest and accounts receivable are considered related party transactions and have been recognized in our consolidated financial statements at their estimated fair value of $50.4 million and $51.6 million classified as Loans to and accounts receivable from the Canadian Entities in the Statements of Unaudited Condensed Consolidated Financial Position as of March 31, 2018 and December 31, 2017, respectively. As of March 31, 2018, CCAA proceedings are ongoing and the majority of the assets of each of the Bloom Lake Group and the Wabush Group have been liquidated. The Monitor appointed by the court in the CCAA proceedings for the Bloom Lake Group and the Wabush Group has conducted a claims process pursuant to which creditors have filed claims against the Bloom Lake Group and the Wabush Group. The Monitor is reviewing all claims filed as part of this claims process. Currently, there is uncertainty as to the amount of the distribution that will be made to the creditors of the Bloom Lake Group and the Wabush Group, including, if any, to us, and whether we could be held liable for claims that may be asserted by or on behalf of the Bloom Lake Group or the Wabush Group or by their respective representatives against non-debtor affiliates of the Bloom Lake Group and the Wabush Group. The net proceeds of sale of the assets of the Bloom Lake Group and the Wabush Group are currently being held by the Monitor. Certain of these funds will be utilized to fund the accrued and ongoing costs of the CCAA proceedings and the remaining funds will be available for distribution to the creditors of the Bloom Lake Group and the Wabush Group. During 2017, we became aware that it was probable the Monitor will assert a preference claim against us and/or certain of our affiliates. We have an estimated liability of $54.3 million, which includes the value of our related-party claims against the Bloom Lake Group and the Wabush Group, classified as Contingent claims in the Statements of Unaudited Condensed Consolidated Financial Position as of March 31, 2018. During March 2018, we entered into a restructuring term sheet with the Bloom Lake Group and the Wabush Group, which documents the proposed terms of a plan of compromise or arrangement in the CCAA proceedings (the “Proposed Plan”) to be sponsored by us as negotiated between us and the Monitor. This Proposed Plan requires both creditor and court approval. Under the terms of this Proposed Plan, we and certain of our wholly owned subsidiaries have agreed to forego the benefit of any distributions or payments we may be entitled to receive as creditors of the Bloom Lake Group and the Wabush Group and to also make a C$5.0 million cash contribution to the Bloom Lake Group and the Wabush Group for distribution to other creditors. It is important to note that the Proposed Plan, as currently drafted, will not resolve certain employee claims which have been raised outside of the CCAA proceedings against us and certain of our affiliates and which will be addressed separately. If this Proposed Plan is approved by a majority of the creditors of both the Bloom Lake Group and the Wabush Group, and is also approved by the court in the CCAA proceedings, and is implemented in accordance with its terms, then the Proposed Plan will resolve all of our claims against the Bloom Lake Group and the Wabush Group and all claims by the Bloom Lake Group, the Wabush Group and their respective creditors against us, except as noted above. The net financial impact of the Proposed Plan is materially consistent with amounts previously recorded in our financial statements. However, if the creditors and the court do not approve the Proposed Plan, it is reasonably possible that future changes to our estimates and the ultimate amount paid on any claims could be material to our results of discontinued operations in future periods. We are not able to reasonably estimate such impact because there would be significant factual and legal issues to be resolved if the Proposed Plan is not approved. We will vigorously defend any claims if the Proposed Plan is not approved and implemented in accordance with its terms. The motion to authorize the Bloom Lake Group and the Wabush Group to file the Proposed Plan and to schedule meetings of the creditors of the Bloom Lake Group and the Wabush Group to consider and vote to approve or reject the Proposed Plan was approved by the court on April 20, 2018.

SUBSEQUENT EVENTS	3 Months Ended
SUBSEQUENT EVENTS	Mar. 31, 2018
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	NOTE 20 - SUBSEQUENT EVENTS We have evaluated subsequent events through the date of financial issuance.

SUPPLEMENTARY GUARANTOR INFORMATION

3 Months Ended

Mar. 31, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Supplemental Guarantor Information [Text Block]

NOTE 21 - SUPPLEMENTARY GUARANTOR INFORMATION

The accompanying unaudited condensed consolidating financial information has been prepared and presented pursuant to SEC Regulation S-X, Rule 3-10, “Financial Statements of Guarantors and Issuers of Guaranteed Securities Registered or Being Registered.” Certain of our subsidiaries (the "Guarantors") have guaranteed the obligations under the $1.075 billion 5.75% 2025 Senior Notes issued by Cleveland-Cliffs Inc. See NOTE 7 - DEBT AND CREDIT FACILITIES for further information.

The following presents the unaudited condensed consolidating financial information for: (i) the Parent Company and the Issuer of the guaranteed obligations (Cleveland-Cliffs Inc.); (ii) the Guarantor subsidiaries, on a combined basis; (iii) the non-guarantor subsidiaries, on a combined basis; (iv) consolidating eliminations; and (v) Cleveland-Cliffs Inc. and subsidiaries on a consolidated basis. Each Guarantor subsidiary is 100% owned by the Parent Company as of March 31, 2018 and December 31, 2017. The unaudited condensed consolidating financial information is presented as if the Guarantor structure at March 31, 2018 existed for all periods presented. As a result, the Guarantor subsidiaries within the unaudited condensed consolidating financial information as of March 31, 2018 and December 31, 2017 and for the three months ended March 31, 2018 and 2017 include results of subsidiaries that were previously less than wholly-owned and were historically non-guarantors until 100% ownership was obtained.

Each of the Guarantor subsidiaries fully and unconditionally guarantee, on a joint and several basis, the obligations of Cleveland-Cliffs Inc. under the $1.075 billion 5.75% 2025 Senior Notes. The guarantee of a Guarantor subsidiary will be automatically and unconditionally released and discharged, and such Guarantor subsidiary’s obligations under the guarantee and the related indenture governing the $1.075 billion 5.75% 2025 Senior Notes (the “Indenture”) will be automatically and unconditionally released and discharged, upon:

(a) any sale, exchange, transfer or disposition of such Guarantor subsidiary (by merger, consolidation, or the sale of) or the capital stock of such Guarantor subsidiary after which the applicable Guarantor subsidiary is no longer a subsidiary of the Company or the sale of all or substantially all of such Guarantor subsidiary’s assets (other than by lease);

(b) upon designation of any Guarantor subsidiary as an “excluded subsidiary” (as defined in the Indenture); and

(c) upon defeasance or satisfaction and discharge of the Indenture.

Each entity in the unaudited consolidating financial information follows the same accounting policies as described in the consolidated financial statements. The accompanying unaudited condensed consolidating financial information has been presented on the equity method of accounting for all periods presented. Under this method, investments in subsidiaries are recorded at cost and adjusted for the subsidiaries’ cumulative results of operations, capital contributions and distributions, and other changes in equity. Elimination entries include consolidating and eliminating entries for investments in subsidiaries, and intra-entity activity and balances.



Unaudited Condensed Consolidating Statement of Financial Position
As of March 31, 2018
(In Millions)
	Cleveland-Cliffs Inc.			Guarantor Subsidiaries		Non-Guarantor Subsidiaries			Eliminations			Consolidated
ASSETS
CURRENT ASSETS
Cash and cash equivalents	$	753.6		$	1.0	$	32.0		$	—		$	786.6
Accounts receivable, net	5.7			27.7		15.9			(2.1		)	47.2
Inventories	—			303.2		21.2			—			324.4
Supplies and other inventories	—			81.4		0.3			—			81.7
Derivative assets	—			93.6		—			—			93.6
Loans to and accounts receivable from the Canadian Entities	43.5			6.9		—			—			50.4
Other current assets	15.5			7.9		5.1			—			28.5
TOTAL CURRENT ASSETS	818.3			521.7		74.5			(2.1		)	1,412.4
PROPERTY, PLANT AND EQUIPMENT, NET	16.2			956.9		74.2			—			1,047.3
OTHER ASSETS
Deposits for property, plant and equipment	—			1.9		72.2			—			74.1
Income tax receivable	219.9			—		—			—			219.9
Investment in subsidiaries	1,185.7			27.4		—			(1,213.1		)	—
Long-term intercompany notes	—			—		242.0			(242.0		)	—
Other non-current assets	8.9			97.9		2.4			—			109.2
TOTAL OTHER ASSETS	1,414.5			127.2		316.6			(1,455.1		)	403.2
TOTAL ASSETS	$	2,249.0		$	1,605.8	$	465.3		$	(1,457.2	)	$	2,862.9
LIABILITIES
CURRENT LIABILITIES
Accounts payable	$	4.6		$	71.8	$	25.2		$	(2.1	)	$	99.5
Accrued expenses	11.1			60.0		23.3			—			94.4
Accrued interest	28.2			—		—			—			28.2
Contingent claims	54.3			—		—			—			54.3
Partnership distribution payable	—			44.2		—			—			44.2
Other current liabilities	1.8			63.3		39.2			—			104.3
TOTAL CURRENT LIABILITIES	100.0			239.3		87.7			(2.1		)	424.9
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES	66.1			429.6		(244.3		)	—			251.4
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	—			143.1		38.1			—			181.2
LONG-TERM DEBT	2,308.2			—		—			—			2,308.2
LONG-TERM INTERCOMPANY NOTES	242.0			—		—			(242.0		)	—
OTHER LIABILITIES	17.5			142.9		21.6			—			182.0
TOTAL LIABILITIES	2,733.8			954.9		(96.9		)	(244.1		)	3,347.7
EQUITY
TOTAL CLIFFS SHAREHOLDERS' DEFICIT	(484.8		)	650.9		562.0			(1,213.1		)	(485.0		)
NONCONTROLLING INTEREST	—			—		0.2			—			0.2
TOTAL DEFICIT	(484.8		)	650.9		562.2			(1,213.1		)	(484.8		)
TOTAL LIABILITIES AND DEFICIT	$	2,249.0		$	1,605.8	$	465.3		$	(1,457.2	)	$	2,862.9



Unaudited Condensed Consolidating Statement of Financial Position
As of December 31, 2017
(In Millions)
	Cleveland-Cliffs Inc.			Guarantor Subsidiaries		Non-Guarantor Subsidiaries			Eliminations			Consolidated
ASSETS
CURRENT ASSETS
Cash and cash equivalents	$	948.9		$	2.1	$	56.7		$	—		$	1,007.7
Accounts receivable, net	4.5			102.9		33.9			(0.7		)	140.6
Inventories	—			138.4		45.0			—			183.4
Supplies and other inventories	—			88.8		5.1			—			93.9
Derivative assets	—			37.9		1.5			—			39.4
Loans to and accounts receivable from the Canadian Entities	44.7			6.9		—			—			51.6
Other current assets	16.4			7.5		4.1			—			28.0
TOTAL CURRENT ASSETS	1,014.5			384.5		146.3			(0.7		)	1,544.6
PROPERTY, PLANT AND EQUIPMENT, NET	17.5			959.0		74.5			—			1,051.0
OTHER ASSETS
Deposits for property, plant and equipment	—			1.3		16.5			—			17.8
Income tax receivable	235.3			—		—			—			235.3
Investment in subsidiaries	1,024.3			29.9		—			(1,054.2		)	—
Long-term intercompany notes	—			—		242.0			(242.0		)	—
Other non-current assets	7.8			91.7		5.2			—			104.7
TOTAL OTHER ASSETS	1,267.4			122.9		263.7			(1,296.2		)	357.8
TOTAL ASSETS	$	2,299.4		$	1,466.4	$	484.5		$	(1,296.9	)	$	2,953.4
LIABILITIES
CURRENT LIABILITIES
Accounts payable	$	7.1		$	89.7	$	31.6		$	(0.7	)	$	127.7
Accrued expenses	19.0			59.9		28.2			—			107.1
Accrued interest	31.4			—		—			—			31.4
Contingent claims	55.6			—		—			—			55.6
Partnership distribution payable	—			44.2		—			—			44.2
Other current liabilities	2.1			63.5		20.6			—			86.2
TOTAL CURRENT LIABILITIES	115.2			257.3		80.4			(0.7		)	452.2
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES	66.4			430.6		(239.3		)	—			257.7
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	—			140.6		55.9			—			196.5
LONG-TERM DEBT	2,304.2			—		—			—			2,304.2
LONG-TERM INTERCOMPANY NOTES	242.0			—		—			(242.0		)	—
OTHER LIABILITIES	15.7			147.2		24.0			—			186.9
TOTAL LIABILITIES	2,743.5			975.7		(79.0		)	(242.7		)	3,397.5
EQUITY
TOTAL CLIFFS SHAREHOLDERS' DEFICIT	(444.1		)	490.7		563.3			(1,054.2		)	(444.3		)
NONCONTROLLING INTEREST	—			—		0.2			—			0.2
TOTAL DEFICIT	(444.1		)	490.7		563.5			(1,054.2		)	(444.1		)
TOTAL LIABILITIES AND DEFICIT	$	2,299.4		$	1,466.4	$	484.5		$	(1,296.9	)	$	2,953.4



Unaudited Condensed Consolidating Statement of Operations and Comprehensive Income (Loss)
For the Three Months Ended March 31, 2018
(In Millions)
	Cleveland-Cliffs Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Eliminations			Consolidated
REVENUES FROM PRODUCT SALES AND SERVICES
Product	$	—		$	169.2		$	51.5		$	—		$	220.7
Freight and venture partners' cost reimbursements	—			10.8			7.5			—			18.3
	—			180.0			59.0			—			239.0
COST OF GOODS SOLD AND OPERATING EXPENSES	—			(118.5		)	(124.1		)	—			(242.6		)
SALES MARGIN	—			61.5			(65.1		)	—			(3.6		)
OTHER OPERATING EXPENSE
Selling, general and administrative expenses	(20.1		)	(4.3		)	(3.3		)	—			(27.7		)
Miscellaneous – net	(0.2		)	(5.3		)	(3.2		)	—			(8.7		)
	(20.3		)	(9.6		)	(6.5		)	—			(36.4		)
OPERATING INCOME (LOSS)	(20.3		)	51.9			(71.6		)	—			(40.0		)
OTHER INCOME (EXPENSE)
Interest expense, net	(31.9		)	(0.8		)	(0.8		)	—			(33.5		)
Other non-operating income (expense)	(0.9		)	0.5			4.8			—			4.4
	(32.8		)	(0.3		)	4.0			—			(29.1		)
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	(53.1		)	51.6			(67.6		)	—			(69.1		)
INCOME TAX EXPENSE	(15.6		)	(0.1		)	—			—			(15.7		)
EQUITY IN INCOME (LOSS) OF SUBSIDIARIES	(15.7		)	4.5			—			11.2			—
INCOME (LOSS) FROM CONTINUING OPERATIONS	(84.4		)	56.0			(67.6		)	11.2			(84.8		)
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX	0.1			0.2			0.2			—			0.5
NET INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$	(84.3	)	$	56.2		$	(67.4	)	$	11.2		$	(84.3	)
OTHER COMPREHENSIVE INCOME	7.7			5.9			0.8			(6.7		)	7.7
TOTAL COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$	(76.6	)	$	62.1		$	(66.6	)	$	4.5		$	(76.6	)



Unaudited Condensed Consolidating Statement of Operations and Comprehensive Income (Loss)
For the Three Months Ended March 31, 2017
(In Millions)
	Cleveland-Cliffs Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Eliminations			Consolidated
REVENUES FROM PRODUCT SALES AND SERVICES
Product	$	—		$	247.3		$	165.5		$	—		$	412.8
Freight and venture partners' cost reimbursements	—			38.9			9.9			—			48.8
	—			286.2			175.4			—			461.6
COST OF GOODS SOLD AND OPERATING EXPENSES	—			(237.2		)	(128.1		)	—			(365.3		)
SALES MARGIN	—			49.0			47.3			—			96.3
OTHER OPERATING INCOME (EXPENSE)
Selling, general and administrative expenses	(19.5		)	(4.4		)	(3.8		)	—			(27.7		)
Miscellaneous – net	(0.1		)	(5.5		)	17.1			—			11.5
	(19.6		)	(9.9		)	13.3			—			(16.2		)
OPERATING INCOME (LOSS)	(19.6		)	39.1			60.6			—			80.1
OTHER INCOME (EXPENSE)
Interest expense, net	(41.6		)	—			(1.2		)	—			(42.8		)
Loss on extinguishment of debt	(71.9		)	—			—			—			(71.9		)
Other non-operating income (expense)	(1.0		)	(0.8		)	4.3			—			2.5
	(114.5		)	(0.8		)	3.1			—			(112.2		)
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	(134.1		)	38.3			63.7			—			(32.1		)
INCOME TAX BENEFIT (EXPENSE)	5.2			(0.8		)	(2.6		)	—			1.8
EQUITY IN INCOME OF SUBSIDIARIES	100.4			3.2			—			(103.6		)	—
INCOME (LOSS) FROM CONTINUING OPERATIONS	(28.5		)	40.7			61.1			(103.6		)	(30.3		)
INCOME (LOSS) FROM DISCONTINUED OPERATIONS, net of tax	0.4			0.2			(0.1		)	—			0.5
NET INCOME (LOSS)	(28.1		)	40.9			61.0			(103.6		)	(29.8		)
LOSS ATTRIBUTABLE TO NONCONTROLLING INTEREST	—			1.7			—			—			1.7
NET INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$	(28.1	)	$	42.6		$	61.0		$	(103.6	)	$	(28.1	)
OTHER COMPREHENSIVE INCOME (LOSS)	(3.0		)	10.8			(17.8		)	7.0			(3.0		)
TOTAL COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$	(31.1	)	$	53.4		$	43.2		$	(96.6	)	$	(31.1	)



Unaudited Condensed Consolidating Statement of Cash Flows
For the Three Months Ended March 31, 2018
(In Millions)
	Cleveland-Cliffs Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Eliminations			Consolidated
Net cash used by operating activities	$	(54.7	)	$	(62.8	)	$	(25.4	)	$	—		$	(142.9	)
INVESTING ACTIVITIES
Purchase of property, plant and equipment	—			(8.1		)	(4.3		)	—			(12.4		)
Deposits for property, plant and equipment	—			(0.8		)	(58.2		)	—			(59.0		)
Intercompany investing	(137.7		)	(4.8		)	—			142.5			—
Net cash used by investing activities	(137.7		)	(13.7		)	(62.5		)	142.5			(71.4		)
FINANCING ACTIVITIES
Debt issuance costs	(1.5		)	—			—			—			(1.5		)
Intercompany financing	—			75.9			66.6			(142.5		)	—
Other financing activities	(1.4		)	(0.5		)	(3.6		)	—			(5.5		)
Net cash provided (used) by financing activities	(2.9		)	75.4			63.0			(142.5		)	(7.0		)
EFFECT OF EXCHANGE RATE CHANGES ON CASH	—			—			0.2			—			0.2
DECREASE IN CASH AND CASH EQUIVALENTS	(195.3		)	(1.1		)	(24.7		)	—			(221.1		)
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	948.9			2.1			56.7			—			1,007.7
CASH AND CASH EQUIVALENTS AT END OF PERIOD	$	753.6		$	1.0		$	32.0		$	—		$	786.6



Unaudited Condensed Consolidating Statement of Cash Flows
For the Three Months Ended March 31, 2017
(In Millions)
	Cleveland-Cliffs Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Eliminations			Consolidated
Net cash provided (used) by operating activities	$	(99.5	)	$	(19.7	)	$	94.1		$	—		$	(25.1	)
INVESTING ACTIVITIES
Purchase of property, plant and equipment	(0.8		)	(24.9		)	(0.2		)	—			(25.9		)
Deposits for property, plant and equipment	—			(2.0		)	—			—			(2.0		)
Intercompany investing	(56.5		)	(0.5		)	(45.0		)	102.0			—
Other investing activities	—			0.5			—			—			0.5
Net cash used by investing activities	(57.3		)	(26.9		)	(45.2		)	102.0			(27.4		)
FINANCING ACTIVITIES
Net proceeds from issuance of common shares	661.3			—			—			—			661.3
Proceeds from issuance of debt	500.0			—			—			—			500.0
Debt issuance costs	(8.5		)	—			—			—			(8.5		)
Repurchase of debt	(1,115.5		)	—			—			—			(1,115.5		)
Distributions of partnership equity	—			(8.7		)	—			—			(8.7		)
Intercompany financing	45.1			55.8			1.1			(102.0		)	—
Other financing activities	(0.5		)	(0.7		)	(4.4		)	—			(5.6		)
Net cash provided (used) by financing activities	81.9			46.4			(3.3		)	(102.0		)	23.0
EFFECT OF EXCHANGE RATE CHANGES ON CASH	—			—			1.4			—			1.4
INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(74.9		)	(0.2		)	47.0			—			(28.1		)
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	283.4			2.5			37.5			—			323.4
CASH AND CASH EQUIVALENTS AT END OF PERIOD	$	208.5		$	2.3		$	84.5		$	—		$	295.3

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Policies)

3 Months Ended

Mar. 31, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule Of Subsidiaries

Basis of Consolidation

The unaudited condensed consolidated financial statements include our accounts and the accounts of our wholly-owned subsidiaries, including the following operations as of March 31, 2018:



Name	Location	Status of Operations
Northshore	Minnesota	Active
United Taconite	Minnesota	Active
Tilden	Michigan	Active
Empire	Michigan	Indefinitely Idled
Koolyanobbing¹	Western Australia	Active

¹ On April 6, 2018, we committed to a course of action expected to lead to the permanent closure of the Asia Pacific Iron Ore mining operations and expect our final Asia Pacific Iron Ore shipment to occur by June 30, 2018.

Intercompany transactions and balances are eliminated upon consolidation.

Equity Method Investments

Our 23% ownership interest in Hibbing is recorded as an equity method investment. As of March 31, 2018 and December 31, 2017, our investment in Hibbing was $7.3 million and $11.0 million, respectively, classified as Other liabilities in the Statements of Unaudited Condensed Consolidated Financial Position.

Foreign Currency

Our financial statements are prepared with the U.S. dollar as the reporting currency. The functional currency of our Australian subsidiaries is the Australian dollar. The functional currency of all other international subsidiaries is the U.S. dollar. The financial statements of our Australian subsidiaries are translated into U.S. dollars using the exchange rate at each balance sheet date for assets and liabilities and a weighted average exchange rate for each period for revenues, expenses, gains and losses. Translation adjustments are recorded as Accumulated other comprehensive loss. Income taxes generally are not provided for foreign currency translation adjustments. To the extent that monetary assets and liabilities, including short-term intercompany loans, are recorded in a currency other than the functional currency, these amounts are remeasured each reporting period, with the resulting gain or loss being recorded in the Statements of Unaudited Condensed Consolidated Operations. Transaction gains and losses resulting from remeasurement of short-term intercompany loans are included in Miscellaneous – net in the Statements of Unaudited Condensed Consolidated Operations.

The following represents the transaction gains and losses resulting from remeasurement:



	(In Millions)
	Three Months Ended March 31,
	2018			2017
Short-term intercompany loans	$	(0.2	)	$	15.1
Cash and cash equivalents	0.1			(1.2		)
Other	(0.2		)	(0.3		)
Net impact of transaction gains (losses) resulting from remeasurement	$	(0.3	)	$	13.6

Significant Accounting Policies

A detailed description of our significant accounting policies can be found in the audited financial statements for the fiscal year ended December 31, 2017 included in our Annual Report on Form 10-K filed with the SEC. There have been no material changes in our significant accounting policies and estimates from those disclosed therein other than those related to the adoption of Topic 606. Refer to NOTE 2 - NEW ACCOUNTING STANDARDS for further information.

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Tables)

3 Months Ended

Mar. 31, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule Of Subsidiaries

Basis of Consolidation

The unaudited condensed consolidated financial statements include our accounts and the accounts of our wholly-owned subsidiaries, including the following operations as of March 31, 2018:



Name	Location	Status of Operations
Northshore	Minnesota	Active
United Taconite	Minnesota	Active
Tilden	Michigan	Active
Empire	Michigan	Indefinitely Idled
Koolyanobbing¹	Western Australia	Active

¹ On April 6, 2018, we committed to a course of action expected to lead to the permanent closure of the Asia Pacific Iron Ore mining operations and expect our final Asia Pacific Iron Ore shipment to occur by June 30, 2018.

Intercompany transactions and balances are eliminated upon consolidation.

Foreign Currency

The following represents the transaction gains and losses resulting from remeasurement:



	(In Millions)
	Three Months Ended March 31,
	2018			2017
Short-term intercompany loans	$	(0.2	)	$	15.1
Cash and cash equivalents	0.1			(1.2		)
Other	(0.2		)	(0.3		)
Net impact of transaction gains (losses) resulting from remeasurement	$	(0.3	)	$	13.6

NEW ACCOUNTING STANDARDS (Tables)

3 Months Ended

Mar. 31, 2018

New Accounting Pronouncements and Changes in Accounting Principles [Abstract]

Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block]

The cumulative effect of the changes made to our consolidated January 1, 2018 balance sheet for the adoption of Topic 606 were as follows:



	($ in Millions)
	Balance at December 31, 2017			Adjustments due to Topic 606			Balance at January 1, 2018
ASSETS
CURRENT ASSETS
Cash and cash equivalents	$	1,007.7		$	—		$	1,007.7
Accounts receivable, net	140.6			76.6			217.2
Inventories	183.4			(51.4		)	132.0
Supplies and other inventories	93.9			—			93.9
Derivative assets	39.4			11.6			51.0
Loans to and accounts receivable from the Canadian Entities	51.6			—			51.6
Other current assets	28.0			—			28.0
TOTAL CURRENT ASSETS	1,544.6			36.8			1,581.4
PROPERTY, PLANT AND EQUIPMENT, NET	1,051.0			—			1,051.0
OTHER ASSETS
Deposits for property, plant and equipment	17.8			—			17.8
Income tax receivable	235.3			—			235.3
Other non-current assets	104.7			—			104.7
TOTAL OTHER ASSETS	357.8			—			357.8
TOTAL ASSETS	$	2,953.4		$	36.8		$	2,990.2

LIABILITIES
CURRENT LIABILITIES
Accounts payable	$	127.7		$	1.4		$	129.1
Accrued expenses	107.1			—			107.1
Accrued interest	31.4			—			31.4
Contingent claims	55.6			—			55.6
Partnership distribution payable	44.2			—			44.2
Other current liabilities	86.2			1.4			87.6
TOTAL CURRENT LIABILITIES	452.2			2.8			455.0
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES	257.7			—			257.7
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	196.5			—			196.5
LONG-TERM DEBT	2,304.2			—			2,304.2
OTHER LIABILITIES	186.9			—			186.9
TOTAL LIABILITIES	3,397.5			2.8			3,400.3
EQUITY
CLIFFS SHAREHOLDERS' DEFICIT	(444.3		)	34.0			(410.3		)
NONCONTROLLING INTEREST	0.2			—			0.2
TOTAL DEFICIT	(444.1		)	34.0			(410.1		)
TOTAL LIABILITIES AND DEFICIT	$	2,953.4		$	36.8		$	2,990.2

The impact of adoption on our Statements of Unaudited Condensed Consolidated Operations and Statements of Unaudited Condensed Consolidated Financial Position is as follows:



	($ in Millions)
	Three Months Ended March 31, 2018
	As Reported			Balances without Adoption of Topic 606			Effect of Change
REVENUES FROM PRODUCT SALES AND SERVICES
Product	$	220.7		$	279.1		$	(58.4	)
Freight and venture partners' cost reimbursements	18.3			22.4			(4.1		)
	239.0			301.5			(62.5		)
COST OF GOODS SOLD AND OPERATING EXPENSES	(242.6		)	(286.2		)	43.6
SALES MARGIN	(3.6		)	15.3			(18.9		)
OTHER OPERATING EXPENSE
Selling, general and administrative expenses	(27.7		)	(27.7		)	—
Miscellaneous – net	(8.7		)	(8.7		)	—
	(36.4		)	(36.4		)	—
OPERATING LOSS	(40.0		)	(21.1		)	(18.9		)
OTHER INCOME (EXPENSE)
Interest expense, net	(33.5		)	(33.5		)	—
Other non-operating income	4.4			4.4			—
	(29.1		)	(29.1		)	—
LOSS FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	(69.1		)	(50.2		)	(18.9		)
INCOME TAX EXPENSE	(15.7		)	(15.7		)	—
LOSS FROM CONTINUING OPERATIONS	(84.8		)	(65.9		)	(18.9		)
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX	0.5			0.5			—
NET LOSS	(84.3		)	(65.4		)	(18.9		)
LOSS ATTRIBUTABLE TO NONCONTROLLING INTEREST	—			—			—
NET LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$	(84.3	)	$	(65.4	)	$	(18.9	)
LOSS PER COMMON SHARE ATTRIBUTABLE TO CLIFFS SHAREHOLDERS – BASIC
Continuing operations	$	(0.29	)	$	(0.23	)	$	(0.06	)
Discontinued operations	—			—			—
	$	(0.29	)	$	(0.23	)	$	(0.06	)
LOSS PER COMMON SHARE ATTRIBUTABLE TO CLIFFS SHAREHOLDERS – DILUTED
Continuing operations	$	(0.29	)	$	(0.23	)	$	(0.06	)
Discontinued operations	—			—			—
	$	(0.29	)	$	(0.23	)	$	(0.06	)
AVERAGE NUMBER OF SHARES (IN THOUSANDS)
Basic	297,266			297,266
Diluted	297,266			297,266



	($ in Millions)
	March 31, 2018
	As Reported			Balances without Adoption of Topic 606			Effect of Change
ASSETS
CURRENT ASSETS
Cash and cash equivalents	$	786.6		$	786.6		$	—
Accounts receivable, net	47.2			24.9			22.3
Inventories	324.4			332.0			(7.6		)
Supplies and other inventories	81.7			81.7			—
Derivative assets	93.6			91.3			2.3
Loans to and accounts receivable from the Canadian Entities	50.4			50.4			—
Other current assets	28.5			28.5			—
TOTAL CURRENT ASSETS	1,412.4			1,395.4			17.0
PROPERTY, PLANT AND EQUIPMENT, NET	1,047.3			1,047.3			—
OTHER ASSETS
Deposits for property, plant and equipment	74.1			74.1			—
Income tax receivable	219.9			219.9			—
Other non-current assets	109.2			109.2			—
TOTAL OTHER ASSETS	403.2			403.2			—
TOTAL ASSETS	2,862.9			2,845.9			17.0

LIABILITIES
CURRENT LIABILITIES
Accounts payable	$	99.5		$	99.2		$	0.3
Accrued expenses	94.4			94.4			—
Accrued interest	28.2			28.2			—
Contingent claims	54.3			54.3			—
Partnership distribution payable	44.2			44.2			—
Other current liabilities	104.3			104.0			0.3
TOTAL CURRENT LIABILITIES	424.9			424.3			0.6
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES	251.4			251.4			—
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	181.2			181.2			—
LONG-TERM DEBT	2,308.2			2,308.2			—
OTHER LIABILITIES	182.0			182.0			—
TOTAL LIABILITIES	3,347.7			3,347.1			0.6
EQUITY
CLIFFS SHAREHOLDERS' DEFICIT	(485.0		)	(501.4		)	16.4
NONCONTROLLING INTEREST	0.2			0.2			—
TOTAL DEFICIT	(484.8		)	(501.2		)	16.4
TOTAL LIABILITIES AND DEFICIT	$	2,862.9		$	2,845.9		$	17.0

The effect of the retrospective presentation change related to the net periodic cost of our defined benefit pension and other postretirement employee benefits plans on our Statements of Unaudited Condensed Consolidated Operations was as follows:



	($ in Millions)
	Three Months Ended March 31, 2017
	As Revised			Previously Reported			Effect of Change
Cost of goods sold and operating expenses	$	(365.3	)	$	(365.9	)	$	0.6
Selling, general and administrative expenses	$	(27.7	)	$	(25.7	)	$	(2.0	)
Miscellaneous – net	$	11.5		$	11.9		$	(0.4	)
Operating income	$	80.1		$	81.9		$	(1.8	)
Other non-operating income	$	2.5		$	0.7		$	1.8
Net Loss	$	(29.8	)	$	(29.8	)	$	—

SEGMENT REPORTING (Tables)

3 Months Ended

Mar. 31, 2018

Segment Reporting [Abstract]

Schedule Of Segment Reporting Information, By Segment

The following tables present a summary of our reportable segments including a reconciliation of segment sales margin to Loss from Continuing Operations Before Income Taxes and a reconciliation of Net Loss to EBITDA and Adjusted EBITDA:



	(In Millions)
	Three Months Ended March 31,
	2018					2017
Revenues from product sales and services:
U.S. Iron Ore	$	180.0		75	%	$	286.2		62	%
Asia Pacific Iron Ore	59.0			25	%	175.4			38	%
Total revenues from product sales and services	$	239.0		100	%	$	461.6		100	%

Sales margin:
U.S. Iron Ore	$	61.5				$	49.0
Asia Pacific Iron Ore	(65.1		)			47.3
Sales margin	(3.6		)			96.3
Other operating expense	(36.4		)			(16.2		)
Other expense	(29.1		)			(112.2		)
Loss from continuing operations before income taxes	$	(69.1	)			$	(32.1	)



	(In Millions)
	Three Months Ended March 31,
	2018			2017
Net Loss	$	(84.3	)	$	(29.8	)
Less:
Interest expense, net	(33.5		)	(42.8		)
Income tax benefit (expense)	(15.7		)	1.8
Depreciation, depletion and amortization	(23.9		)	(23.2		)
EBITDA	$	(11.2	)	$	34.4
Less:
Inventory impairments	$	(18.9	)	$	—
Impairment of long-lived assets	(2.6		)	—
Severance and retention costs	(1.5		)	—
Impact of discontinued operations	0.5			0.5
Foreign exchange remeasurement	(0.3		)	13.6
Loss on extinguishment of debt	—			(71.9		)
Adjusted EBITDA	$	11.6		$	92.2

EBITDA
U.S. Iron Ore	$	72.5		$	57.9
Asia Pacific Iron Ore	(63.7		)	51.4
Other	(20.0		)	(74.9		)
Total EBITDA	$	(11.2	)	$	34.4

Adjusted EBITDA:
U.S. Iron Ore	$	77.1		$	64.1
Asia Pacific Iron Ore	(39.6		)	53.8
Other	(25.9		)	(25.7		)
Total Adjusted EBITDA	$	11.6		$	92.2



	(In Millions)
	Three Months Ended March 31,
	2018		2017
Depreciation, depletion and amortization:
U.S. Iron Ore	$	15.8	$	16.4
Asia Pacific Iron Ore	6.7		4.7
Other	1.4		2.1
Total depreciation, depletion and amortization	$	23.9	$	23.2

Capital additions¹:
U.S. Iron Ore	$	18.7	$	27.1
Asia Pacific Iron Ore	—		0.2
Other²	60.2		—
Total capital additions	$	78.9	$	27.3

¹ Includes cash paid for capital additions of $71.4 million, including deposits of $59.0 million, and an increase in non-cash accruals of $7.5 million for the three months ended March 31, 2018 compared to cash paid for capital additions of $27.9 million, including deposits of $2.0 million, and a decrease in non-cash accruals of $0.6 million for the three months ended March 31, 2017.
² Includes capital additions related to our HBI project.

Summary of Assets by Segment

A summary of assets by segment is as follows:



	(In Millions)
	March 31, 2018		December 31, 2017
Assets:
U.S. Iron Ore	$	1,646.8	$	1,500.6
Asia Pacific Iron Ore	78.4		138.8
Total segment assets	1,725.2		1,639.4
Corporate and Other	1,137.7		1,314.0
Total assets	$	2,862.9	$	2,953.4

REVENUE (Tables)

3 Months Ended

Mar. 31, 2018

Revenue from Contract with Customer [Abstract]

Deferred Revenue Disclosure

The table below summarizes our deferred revenue balances:



	Deferred Revenue (Current)¹		Deferred Revenue (Long-Term)
Opening balance as of January 1, 2018	$	23.8	$	51.4
Closing balance as of March 31, 2018	31.0		51.4
Increase	$	7.2	$	—

¹ The opening balance includes a $1.4 million adjustment from the December 31, 2017 balance due to the adoption of Topic 606.

INVENTORIES (Tables)

3 Months Ended

Mar. 31, 2018

Inventory Disclosure [Abstract]

Schedule Of Inventories

The following table presents the detail of our Inventories in the Statements of Unaudited Condensed Consolidated Financial Position:



	(In Millions)
	March 31, 2018						December 31, 2017
Segment	Finished Goods		Work-in Process		Total Inventory		Finished Goods		Work-in Process		Total Inventory
U.S. Iron Ore	$	267.2	$	36.0	$	303.2	$	127.1	$	11.3	$	138.4
Asia Pacific Iron Ore	20.2		1.0		21.2		33.3		11.7		45.0
Total	$	287.4	$	37.0	$	324.4	$	160.4	$	23.0	$	183.4

PROPERTY, PLANT AND EQUIPMENT (Tables)

3 Months Ended

Mar. 31, 2018

Property, Plant and Equipment [Abstract]

Value Of Each Of The Major Classes Of Consolidated Depreciable Assets

The following table indicates the value of each of the major classes of our consolidated depreciable assets:



	(In Millions)
	March 31, 2018			December 31, 2017
Land rights and mineral rights	$	549.6		$	549.6
Office and information technology	66.3			66.3
Buildings	85.5			86.8
Mining equipment	594.0			594.4
Processing equipment	619.8			617.0
Electric power facilities	57.0			57.0
Land improvements	23.6			23.7
Asset retirement obligation	16.9			19.2
Other	30.3			30.3
Construction in-progress	48.1			35.1
	2,091.1			2,079.4
Allowance for depreciation and depletion	(1,043.8		)	(1,028.4		)
	$	1,047.3		$	1,051.0

DEBT AND CREDIT FACILITIES (Tables)

3 Months Ended

Mar. 31, 2018

Debt Disclosure [Abstract]

Schedule Of Long-Term Debt

The following represents a summary of our long-term debt:



(In Millions)
March 31, 2018
Debt Instrument	Annual Effective Interest Rate	Total Principal Amount		Debt Issuance Costs			Unamortized Discounts			Total Debt
Secured Notes
$400 Million 4.875% 2024 Senior Notes	5.00%	$	400.0	$	(6.7	)	$	(2.5	)	$	390.8
Unsecured Notes
$400 Million 5.90% 2020 Senior Notes	5.98%	88.9		(0.2		)	(0.1		)	88.6
$500 Million 4.80% 2020 Senior Notes	4.83%	122.4		(0.2		)	(0.1		)	122.1
$700 Million 4.875% 2021 Senior Notes	4.89%	138.4		(0.3		)	(0.1		)	138.0
$316.25 Million 1.50% 2025 Convertible Senior Notes	6.26%	316.3		(6.3		)	(83.2		)	226.8
$1.075 Billion 5.75% 2025 Senior Notes	6.01%	1,075.0		(11.1		)	(16.0		)	1,047.9
$800 Million 6.25% 2040 Senior Notes	6.34%	298.4		(2.3		)	(3.4		)	292.7
ABL Facility	N/A	450.0		N/A			N/A			—
Fair Value Adjustment to Interest Rate Hedge										1.3
Long-term debt										$	2,308.2



(In Millions)
December 31, 2017
Debt Instrument	Annual Effective Interest Rate	Total Principal Amount		Debt Issuance Costs			Unamortized Discounts			Total Debt
Secured Notes
$400 Million 4.875% 2024 Senior Notes	5.00%	$	400.0	$	(7.1	)	$	(2.6	)	$	390.3
Unsecured Notes
$400 Million 5.90% 2020 Senior Notes	5.98%	88.9		(0.2		)	(0.1		)	88.6
$500 Million 4.80% 2020 Senior Notes	4.83%	122.4		(0.3		)	(0.1		)	122.0
$700 Million 4.875% 2021 Senior Notes	4.89%	138.4		(0.3		)	(0.1		)	138.0
$316.25 Million 1.50% 2025 Convertible Senior Notes	6.26%	316.3		(6.6		)	(85.6		)	224.1
$1.075 Billion 5.75% 2025 Senior Notes	6.01%	1,075.0		(11.3		)	(16.5		)	1,047.2
$800 Million 6.25% 2040 Senior Notes	6.34%	298.4		(2.4		)	(3.4		)	292.6
ABL Facility	N/A	550.0		N/A			N/A			—
Fair Value Adjustment to Interest Rate Hedge										1.4
Long-term debt										$	2,304.2

Schedule of Maturities of Long-term Debt

Debt Maturities

The following represents a summary of our maturities of debt instruments based on the principal amounts outstanding at March 31, 2018:



	(In Millions)
	Maturities of Debt
2018	$	—
2019	—
2020	211.3
2021	138.4
2022	—
2023	—
2024 and thereafter	2,089.7
Total maturities of debt	$	2,439.4

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21475-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e),(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21538-112644

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21506-112644

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28541-108399

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21521-112644

+ Details

FAIR VALUE MEASUREMENTS (Tables)

3 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

Fair Value, by Balance Sheet Grouping [Table Text Block]

The following represents the assets and liabilities of the Company measured at fair value:



	(In Millions)
	March 31, 2018
Description	Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Assets:
Cash equivalents	$	36.0	$	490.6	$	—	$	526.6
Derivative assets	—		—		93.6		93.6
Total	$	36.0	$	490.6	$	93.6	$	620.2
Liabilities:
Derivative liabilities	$	—	$	0.2	$	4.2	$	4.4
Total	$	—	$	0.2	$	4.2	$	4.4



	(In Millions)
	December 31, 2017
Description	Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Assets:
Cash equivalents	$	66.3	$	550.6	$	—	$	616.9
Derivative assets	—		—		39.4		39.4
Total	$	66.3	$	550.6	$	39.4	$	656.3
Liabilities:
Derivative liabilities	$	—	$	0.3	$	2.4	$	2.7
Total	$	—	$	0.3	$	2.4	$	2.7

Fair Value, Recurring and Nonrecurring, Valuation Techniques

The following table illustrates information about quantitative inputs and assumptions for the assets and liabilities categorized in Level 3 of the fair value hierarchy:

Qualitative/Quantitative Information About Level 3 Fair Value Measurements

(In Millions)

Fair Value at March 31, 2018

Balance Sheet

Location

Valuation Technique

Unobservable Input

Range or Point Estimate

(Weighted Average)

Customer supply agreements

$

91.2

Derivative assets

Market Approach

Management's Estimate of Market Hot-Rolled Coil Steel per net ton

$752

Provisional pricing arrangements

$

2.4

Derivative assets

Market Approach

Management's

Estimate of Platts 62% Price

per dry metric ton

$63 - $71
($66)

Provisional pricing arrangements

$

4.2

Other Current Liabilities

Market Approach

Management's

Estimate of Platts 62% Price

per dry metric ton

$63 - $71
($66)

Fair Value, Assets Measured On Recurring Basis, Unobservable Input Reconciliation



	(In Millions)
	Level 3 Assets
	Three Months Ended March 31,
	2018			2017
Beginning balance¹	$	51.0		$	31.6
Total gains (losses)
Included in earnings	49.1			42.1
Settlements	(6.5		)	(14.3		)
Ending balance - March 31	$	93.6		$	59.4
Total gains for the period included in earnings attributable to the change in unrealized gains on assets still held at the reporting date	$	44.5		$	33.2

¹ Beginning balance as of January 1, 2018 includes an $11.6 million adjustment for adoption of Topic 606.

Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation



	(In Millions)
	Level 3 Liabilities
	Three Months Ended March 31,
	2018			2017
Beginning balance	$	(2.4	)	$	(0.5	)
Total gains (losses)
Included in earnings	(4.0		)	(8.6		)
Settlements	2.2			—
Ending balance - March 31	$	(4.2	)	$	(9.1	)
Total losses for the period included in earnings attributable to the change in unrealized losses on liabilities still held at the reporting date	$	(4.2	)	$	(9.1	)

Schedule Of Carrying Value And Fair Value Of Financial Instruments

A summary of the carrying amount and fair value of other financial instruments were as follows:



		(In Millions)
		March 31, 2018				December 31, 2017
	Classification	Carrying Value		Fair Value		Carrying Value		Fair Value
Long-term debt:
Secured Notes
$400 Million 4.875% 2024 Senior Notes	Level 1	$	390.8	$	389.0	$	390.3	$	398.0
Unsecured Notes
$400 Million 5.90% 2020 Senior Notes	Level 1	88.6		89.1		88.6		88.0
$500 Million 4.80% 2020 Senior Notes	Level 1	122.1		120.3		122.0		118.8
$700 Million 4.875% 2021 Senior Notes	Level 1	138.0		135.4		138.0		130.8
$316.25 Million 1.50% 2025 Convertible Senior Notes	Level 1	226.8		340.0		224.1		352.9
$1.075 Billion 5.75% 2025 Senior Notes	Level 1	1,047.9		1,026.6		1,047.2		1,029.3
$800 Million 6.25% 2040 Senior Notes	Level 1	292.7		251.1		292.6		227.1
ABL Facility	Level 2	—		—		—		—
Fair value adjustment to interest rate hedge	Level 2	1.3		1.3		1.4		1.4
Total long-term debt		$	2,308.2	$	2,352.8	$	2,304.2	$	2,346.3

Fair Value Measurements, Nonrecurring [Table Text Block]

Items Measured at Fair Value on a Non-Recurring Basis

The following tables present information about the financial assets and liabilities that were measured on a fair value basis. The tables also indicate the fair value hierarchy of the valuation techniques used to determine such fair value.



	(In Millions)
	March 31, 2018
Description	Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total		Total Year-to-Date Loss
Assets:
Loans to and accounts receivables from the Canadian Entities	$	—	$	—	$	50.4	$	50.4	$	(1.2	)
Long-lived assets - Asia Pacific Iron Ore	$	—	$	—	$	—	$	—	$	(2.6	)



	(In Millions)
	December 31, 2017
Description	Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total		Total Year-to-Date Gains
Assets:
Loans to and accounts receivables from the Canadian Entities	$	—	$	—	$	51.6	$	51.6	$	3.0
Liabilities:
Guarantees	$	—	$	—	$	—	$	—	$	31.4

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Tables)

3 Months Ended

Mar. 31, 2018

Postemployment Benefits [Abstract]

Schedule of Net Benefit Costs

The following are the components of defined benefit pension and OPEB costs and credits:

Defined Benefit Pension Costs



	(In Millions)
	Three Months Ended March 31,
	2018			2017
Service cost	$	4.7		$	4.8
Interest cost	7.6			7.5
Expected return on plan assets	(15.0		)	(13.5		)
Amortization:
Prior service costs	0.5			0.6
Net actuarial loss	5.3			5.3
Net periodic benefit cost	$	3.1		$	4.7

Other Postretirement Benefits Credits



	(In Millions)
	Three Months Ended March 31,
	2018			2017
Service cost	$	0.5		$	0.5
Interest cost	2.1			2.1
Expected return on plan assets	(4.6		)	(4.4		)
Amortization:
Prior service credits	(0.8		)	(0.7		)
Net actuarial loss	1.2			1.2
Net periodic benefit credit	$	(1.6	)	$	(1.3	)

STOCK COMPENSATION PLANS (Tables)

3 Months Ended

Mar. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions [Table Text Block]

The following assumptions were utilized to estimate the fair value for the 2018 performance share grant:



Grant Date	Grant Date Market Price		Average Expected Term (Years)	Expected Volatility	Risk-Free Interest Rate	Dividend Yield	Fair Value		Fair Value (Percent of Grant Date Market Price)
February 21, 2018	$	7.53	2.86	86.8%	2.42%	—%	$	11.93	158.43%

LEASE OBLIGATIONS (Tables)

3 Months Ended

Mar. 31, 2018

Leases [Abstract]

Schedule Of Future Minimum Lease Payments For Capital Leases And Operating Leases

Future minimum payments under capital leases and non-cancellable operating leases as of March 31, 2018 are as follows:



	(In Millions)
	Capital Leases		Operating Leases
2018 (April 1 - December 31)	$	14.7	$	3.3
2019	12.0		1.9
2020	11.0		1.8
2021	10.3		1.8
2022	2.1		1.8
2023 and thereafter	—		7.5
Total minimum lease payments	$	50.1	$	18.1
Amounts representing interest	7.6
Present value of net minimum lease payments¹	$	42.5

¹ The total is comprised of $14.6 million and $27.9 million classified as Other current liabilities and Other liabilities, respectively, in the Statements of Unaudited Condensed Consolidated Financial Position as of March 31, 2018.

ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Tables)

3 Months Ended

Mar. 31, 2018

Environmental Remediation Obligations [Abstract]

Summary Of Mine Closure Obligations

The following is a summary of the obligations:



	(In Millions)
	March 31, 2018		December 31, 2017
Environmental	$	3.1	$	2.9
Mine closure
U.S. Iron Ore¹	170.7		168.4
Asia Pacific Iron Ore	28.7		28.8
Total mine closure	199.4		197.2
Total environmental and mine closure obligations	202.5		200.1
Less current portion	21.3		3.6
Long-term environmental and mine closure obligations	$	181.2	$	196.5

¹U.S. Iron Ore includes our active operating mines, our indefinitely idled Empire mine and a closed mine formerly operating as LTVSMC.

Asset Retirement Obligation Disclosure

The following represents a roll forward of our mine closure obligation liability for the three months ended March 31, 2018 and for the year ended December 31, 2017:



	(In Millions)
	March 31, 2018			December 31, 2017
Mine closure obligation at beginning of period	$	197.2		$	204.0
Accretion expense	2.7			14.9
Remediation payments	(0.1		)	(5.6		)
Exchange rate changes	(0.5		)	1.5
Revision in estimated cash flows	0.1			(17.6		)
Mine closure obligation at end of period	$	199.4		$	197.2

GOODWILL AND OTHER INTANGIBLE ASSETS AND LIABILITIES (Tables)

3 Months Ended

Mar. 31, 2018

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule Of Finite-Lived Intangible Assets By Major Class

The following table is a summary of definite-lived intangible assets:



		(In Millions)
		March 31, 2018							December 31, 2017
	Classification	Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount		Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount
Permits	Other non-current assets	$	78.8	$	(28.9	)	$	49.9	$	78.8	$	(26.5	)	$	52.3

DERIVATIVE INSTRUMENTS (Tables)

3 Months Ended

Mar. 31, 2018

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Schedule Of Derivative Instruments In Statement Of Financial Position, Fair Value

The following table presents the fair value of our derivative instruments and the classification of each in the Statements of Unaudited Condensed Consolidated Financial Position:



	(In Millions)
	Derivative Assets						Derivative Liabilities
	March 31, 2018			December 31, 2017			March 31, 2018			December 31, 2017
Derivative Instrument	Balance Sheet Location	Fair Value		Balance Sheet Location	Fair Value		Balance Sheet Location	Fair Value		Balance Sheet Location	Fair Value
Derivatives designated as hedging instruments under ASC 815:
Commodity Contracts		$	—		$	—	Other current liabilities	$	0.2	Other current liabilities	$	0.3
Derivatives not designated as hedging instruments under ASC 815:
Customer supply agreements	Derivative assets	$	91.2	Derivative assets	$	37.9		$	—		$	—
Provisional pricing arrangements	Derivative assets	2.4		Derivative assets	1.5		Other current liabilities	4.2		Other current liabilities	2.4
Total derivatives not designated as hedging instruments under ASC 815		$	93.6		$	39.4		$	4.2		$	2.4
Total derivatives		$	93.6		$	39.4		$	4.4		$	2.7

Schedule Of Derivatives Not Designated As Hedging Instruments Statements Of Financial Performance Location Table

The following summarizes the effect of our derivatives that are not designated as hedging instruments in the Statements of Unaudited Condensed Consolidated Operations:



(In Millions)
Derivatives Not Designated as Hedging Instruments	Location of Income (Loss) Recognized on Derivatives	Amount of Income (Loss) Recognized on Derivatives
		Three Months Ended March 31,
		2018		2017
Customer Supply Agreements	Product revenues	$	41.9	$	17.8
Provisional Pricing Arrangements	Product revenues	3.2		15.7
Commodity Contracts	Cost of goods sold and operating expenses	—		(1.3		)
Total		$	45.1	$	32.2

SHAREHOLDERS' EQUITY (Tables)

3 Months Ended

Mar. 31, 2018

Equity [Abstract]

Schedule of Stockholders Equity

The following table reflects the changes in shareholders' deficit attributable to both us and the noncontrolling interests, primarily related to Tilden and Empire. We own 100% of both mines as of March 31, 2018 and 85% and 79% of each mine, respectively, as of March 31, 2017:



	(In Millions)
	Cliffs Shareholders’ Equity (Deficit)			Noncontrolling Interest		Total Equity (Deficit)
December 31, 2017	$	(444.3	)	$	0.2	$	(444.1	)
Adoption of accounting standard (Note 2)	34.0			—		34.0
Comprehensive loss
Net loss	(84.3		)	—		(84.3		)
Other comprehensive income	7.7			—		7.7
Total comprehensive loss	(76.6		)	—		(76.6		)
Stock and other incentive plans	1.9			—		1.9
March 31, 2018	$	(485.0	)	$	0.2	$	(484.8	)



	(In Millions)
	Cliffs Shareholders’ Equity (Deficit)			Noncontrolling Interest			Total Equity (Deficit)
December 31, 2016	$	(1,464.3	)	$	133.8		$	(1,330.5	)
Comprehensive loss
Net loss	(28.1		)	(1.7		)	(29.8		)
Other comprehensive loss	(3.0		)	(5.0		)	(8.0		)
Total comprehensive loss	(31.1		)	(6.7		)	(37.8		)
Issuance of common shares	661.3			—			661.3
Stock and other incentive plans	4.0			—			4.0
March 31, 2017	$	(830.1	)	$	127.1		$	(703.0	)

Schedule of Accumulated Other Comprehensive Income (Loss)

The following table reflects the changes in Accumulated other comprehensive loss related to Cliffs shareholders’ deficit:



	(In Millions)
	Changes in Pension and Other Post-Retirement Benefits, net of tax			Unrealized Net Gain on Foreign Currency Translation		Net Unrealized Gain (Loss) on Derivative Financial Instruments, net of tax			Accumulated Other Comprehensive Loss
December 31, 2017	$	(263.9	)	$	225.4	$	(0.5	)	$	(39.0	)
Other comprehensive income before reclassifications	0.5			0.7		0.4			1.6
Net loss (gain) reclassified from accumulated other comprehensive loss	6.2			—		(0.1		)	6.1
March 31, 2018	$	(257.2	)	$	226.1	$	(0.2	)	$	(31.3	)



	(In Millions)
	Changes in Pension and Other Post-Retirement Benefits, net of tax			Unrealized Net Gain (Loss) on Foreign Currency Translation			Accumulated Other Comprehensive Loss
December 31, 2016	$	(260.6	)	$	239.3		$	(21.3	)
Other comprehensive income (loss) before reclassifications	3.3			(12.7		)	(9.4		)
Net loss reclassified from accumulated other comprehensive loss	6.4			—			6.4
March 31, 2017	$	(250.9	)	$	226.6		$	(24.3	)

Details of Accumulated Other Comprehensive Income (Loss) Components

The following table reflects the details about Accumulated other comprehensive loss components related to Cliffs shareholders’ deficit:



	(In Millions)
Details about Accumulated Other Comprehensive Loss Components	Amount of (Gain)/Loss Reclassified into Income						Affected Line Item in the Statement of Unaudited Condensed Consolidated Operations
	Three Months Ended March 31,
	2018			2017
Amortization of pension and OPEB liability:
Prior service credits	$	(0.3	)	$	(0.1	)	Other non-operating income
Net actuarial loss	6.5			6.5			Other non-operating income
	$	6.2		$	6.4		Net of taxes

Unrealized loss on derivative financial instruments:
Commodity contracts	$	(0.1	)	$	—		Cost of goods sold and operating expenses
	$	(0.1	)	$	—		Net of taxes

Total reclassifications for the period, net of tax	$	6.1		$	6.4

RELATED PARTIES (Tables)

3 Months Ended

Mar. 31, 2018

Summary Of Other Ownership Interests

The following is a summary of the mine ownership of the co-owned iron ore mine at March 31, 2018:



Mine	Cleveland-Cliffs Inc.		ArcelorMittal		U.S. Steel
Hibbing	23.0	%	62.3	%	14.7	%

Product revenues from related parties were as follows:



	(In Millions)
	Three Months Ended March 31,
	2018			2017
Product revenues from related parties	$	62.1		$	118.5
Total product revenues	$	220.7		$	412.8
Related party product revenue as a percent of total product revenue	28.1		%	28.7		%

Summary of Balance Sheet Presentation [Table Text Block]

The following table presents the classification of related party assets and liabilities in the Statements of Unaudited Condensed Consolidated Financial Position:



	(In Millions)
	Balance Sheet Location	March 31, 2018			December 31, 2017
Amounts due from related parties	Accounts receivable, net	$	7.9		$	68.1
Customer supply agreements and provisional pricing agreements	Derivative assets	91.3			37.9
Amounts due to related parties	Accounts payable	(1.2		)	—
Amounts due to related parties	Partnership distribution payable	(44.2		)	(44.2		)
Amounts due to related parties	Other current liabilities	(0.4		)	(12.3		)
Amounts due to related parties	Other liabilities	(42.0		)	(41.4		)
Net amounts due from related parties		$	11.4		$	8.1

EARNINGS PER SHARE (Tables)

3 Months Ended

Mar. 31, 2018

Earnings Per Share [Abstract]

Earnings Per Share Computation

The following table summarizes the computation of basic and diluted earnings (loss) per share:



	(In Millions, Except Per Share Amounts)
	Three Months Ended March 31,
	2018			2017
Loss from Continuing Operations	$	(84.8	)	$	(30.3	)
Loss from Continuing Operations Attributable to Noncontrolling Interest	—			1.7
Net Loss from Continuing Operations Attributable to Cliffs Shareholders	$	(84.8	)	$	(28.6	)
Income from Discontinued Operations, net of tax	0.5			0.5
Net Loss Attributable to Cliffs Shareholders	$	(84.3	)	$	(28.1	)
Weighted Average Number of Shares:
Basic	297.3			265.2
Employee Stock Plans	—			—
Diluted	297.3			265.2
Loss per Common Share Attributable to Cliffs Common Shareholders - Basic:
Continuing operations	$	(0.29	)	$	(0.11	)
Discontinued operations	—			—
	$	(0.29	)	$	(0.11	)
Loss per Common Share Attributable to Cliffs Common Shareholders - Diluted:
Continuing operations	$	(0.29	)	$	(0.11	)
Discontinued operations	—			—
	$	(0.29	)	$	(0.11	)

SUPPLEMENTARY GUARANTOR INFORMATION (Tables)

3 Months Ended

Mar. 31, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Supplemental Condensed Consolidating Financial Position



Unaudited Condensed Consolidating Statement of Financial Position
As of March 31, 2018
(In Millions)
	Cleveland-Cliffs Inc.			Guarantor Subsidiaries		Non-Guarantor Subsidiaries			Eliminations			Consolidated
ASSETS
CURRENT ASSETS
Cash and cash equivalents	$	753.6		$	1.0	$	32.0		$	—		$	786.6
Accounts receivable, net	5.7			27.7		15.9			(2.1		)	47.2
Inventories	—			303.2		21.2			—			324.4
Supplies and other inventories	—			81.4		0.3			—			81.7
Derivative assets	—			93.6		—			—			93.6
Loans to and accounts receivable from the Canadian Entities	43.5			6.9		—			—			50.4
Other current assets	15.5			7.9		5.1			—			28.5
TOTAL CURRENT ASSETS	818.3			521.7		74.5			(2.1		)	1,412.4
PROPERTY, PLANT AND EQUIPMENT, NET	16.2			956.9		74.2			—			1,047.3
OTHER ASSETS
Deposits for property, plant and equipment	—			1.9		72.2			—			74.1
Income tax receivable	219.9			—		—			—			219.9
Investment in subsidiaries	1,185.7			27.4		—			(1,213.1		)	—
Long-term intercompany notes	—			—		242.0			(242.0		)	—
Other non-current assets	8.9			97.9		2.4			—			109.2
TOTAL OTHER ASSETS	1,414.5			127.2		316.6			(1,455.1		)	403.2
TOTAL ASSETS	$	2,249.0		$	1,605.8	$	465.3		$	(1,457.2	)	$	2,862.9
LIABILITIES
CURRENT LIABILITIES
Accounts payable	$	4.6		$	71.8	$	25.2		$	(2.1	)	$	99.5
Accrued expenses	11.1			60.0		23.3			—			94.4
Accrued interest	28.2			—		—			—			28.2
Contingent claims	54.3			—		—			—			54.3
Partnership distribution payable	—			44.2		—			—			44.2
Other current liabilities	1.8			63.3		39.2			—			104.3
TOTAL CURRENT LIABILITIES	100.0			239.3		87.7			(2.1		)	424.9
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES	66.1			429.6		(244.3		)	—			251.4
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	—			143.1		38.1			—			181.2
LONG-TERM DEBT	2,308.2			—		—			—			2,308.2
LONG-TERM INTERCOMPANY NOTES	242.0			—		—			(242.0		)	—
OTHER LIABILITIES	17.5			142.9		21.6			—			182.0
TOTAL LIABILITIES	2,733.8			954.9		(96.9		)	(244.1		)	3,347.7
EQUITY
TOTAL CLIFFS SHAREHOLDERS' DEFICIT	(484.8		)	650.9		562.0			(1,213.1		)	(485.0		)
NONCONTROLLING INTEREST	—			—		0.2			—			0.2
TOTAL DEFICIT	(484.8		)	650.9		562.2			(1,213.1		)	(484.8		)
TOTAL LIABILITIES AND DEFICIT	$	2,249.0		$	1,605.8	$	465.3		$	(1,457.2	)	$	2,862.9



Unaudited Condensed Consolidating Statement of Financial Position
As of December 31, 2017
(In Millions)
	Cleveland-Cliffs Inc.			Guarantor Subsidiaries		Non-Guarantor Subsidiaries			Eliminations			Consolidated
ASSETS
CURRENT ASSETS
Cash and cash equivalents	$	948.9		$	2.1	$	56.7		$	—		$	1,007.7
Accounts receivable, net	4.5			102.9		33.9			(0.7		)	140.6
Inventories	—			138.4		45.0			—			183.4
Supplies and other inventories	—			88.8		5.1			—			93.9
Derivative assets	—			37.9		1.5			—			39.4
Loans to and accounts receivable from the Canadian Entities	44.7			6.9		—			—			51.6
Other current assets	16.4			7.5		4.1			—			28.0
TOTAL CURRENT ASSETS	1,014.5			384.5		146.3			(0.7		)	1,544.6
PROPERTY, PLANT AND EQUIPMENT, NET	17.5			959.0		74.5			—			1,051.0
OTHER ASSETS
Deposits for property, plant and equipment	—			1.3		16.5			—			17.8
Income tax receivable	235.3			—		—			—			235.3
Investment in subsidiaries	1,024.3			29.9		—			(1,054.2		)	—
Long-term intercompany notes	—			—		242.0			(242.0		)	—
Other non-current assets	7.8			91.7		5.2			—			104.7
TOTAL OTHER ASSETS	1,267.4			122.9		263.7			(1,296.2		)	357.8
TOTAL ASSETS	$	2,299.4		$	1,466.4	$	484.5		$	(1,296.9	)	$	2,953.4
LIABILITIES
CURRENT LIABILITIES
Accounts payable	$	7.1		$	89.7	$	31.6		$	(0.7	)	$	127.7
Accrued expenses	19.0			59.9		28.2			—			107.1
Accrued interest	31.4			—		—			—			31.4
Contingent claims	55.6			—		—			—			55.6
Partnership distribution payable	—			44.2		—			—			44.2
Other current liabilities	2.1			63.5		20.6			—			86.2
TOTAL CURRENT LIABILITIES	115.2			257.3		80.4			(0.7		)	452.2
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES	66.4			430.6		(239.3		)	—			257.7
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	—			140.6		55.9			—			196.5
LONG-TERM DEBT	2,304.2			—		—			—			2,304.2
LONG-TERM INTERCOMPANY NOTES	242.0			—		—			(242.0		)	—
OTHER LIABILITIES	15.7			147.2		24.0			—			186.9
TOTAL LIABILITIES	2,743.5			975.7		(79.0		)	(242.7		)	3,397.5
EQUITY
TOTAL CLIFFS SHAREHOLDERS' DEFICIT	(444.1		)	490.7		563.3			(1,054.2		)	(444.3		)
NONCONTROLLING INTEREST	—			—		0.2			—			0.2
TOTAL DEFICIT	(444.1		)	490.7		563.5			(1,054.2		)	(444.1		)
TOTAL LIABILITIES AND DEFICIT	$	2,299.4		$	1,466.4	$	484.5		$	(1,296.9	)	$	2,953.4

Schedule of Supplemental Statements of Condensed Consolidating Operations and Comprehensive Income (Loss)



Unaudited Condensed Consolidating Statement of Operations and Comprehensive Income (Loss)
For the Three Months Ended March 31, 2018
(In Millions)
	Cleveland-Cliffs Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Eliminations			Consolidated
REVENUES FROM PRODUCT SALES AND SERVICES
Product	$	—		$	169.2		$	51.5		$	—		$	220.7
Freight and venture partners' cost reimbursements	—			10.8			7.5			—			18.3
	—			180.0			59.0			—			239.0
COST OF GOODS SOLD AND OPERATING EXPENSES	—			(118.5		)	(124.1		)	—			(242.6		)
SALES MARGIN	—			61.5			(65.1		)	—			(3.6		)
OTHER OPERATING EXPENSE
Selling, general and administrative expenses	(20.1		)	(4.3		)	(3.3		)	—			(27.7		)
Miscellaneous – net	(0.2		)	(5.3		)	(3.2		)	—			(8.7		)
	(20.3		)	(9.6		)	(6.5		)	—			(36.4		)
OPERATING INCOME (LOSS)	(20.3		)	51.9			(71.6		)	—			(40.0		)
OTHER INCOME (EXPENSE)
Interest expense, net	(31.9		)	(0.8		)	(0.8		)	—			(33.5		)
Other non-operating income (expense)	(0.9		)	0.5			4.8			—			4.4
	(32.8		)	(0.3		)	4.0			—			(29.1		)
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	(53.1		)	51.6			(67.6		)	—			(69.1		)
INCOME TAX EXPENSE	(15.6		)	(0.1		)	—			—			(15.7		)
EQUITY IN INCOME (LOSS) OF SUBSIDIARIES	(15.7		)	4.5			—			11.2			—
INCOME (LOSS) FROM CONTINUING OPERATIONS	(84.4		)	56.0			(67.6		)	11.2			(84.8		)
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX	0.1			0.2			0.2			—			0.5
NET INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$	(84.3	)	$	56.2		$	(67.4	)	$	11.2		$	(84.3	)
OTHER COMPREHENSIVE INCOME	7.7			5.9			0.8			(6.7		)	7.7
TOTAL COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$	(76.6	)	$	62.1		$	(66.6	)	$	4.5		$	(76.6	)



Unaudited Condensed Consolidating Statement of Operations and Comprehensive Income (Loss)
For the Three Months Ended March 31, 2017
(In Millions)
	Cleveland-Cliffs Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Eliminations			Consolidated
REVENUES FROM PRODUCT SALES AND SERVICES
Product	$	—		$	247.3		$	165.5		$	—		$	412.8
Freight and venture partners' cost reimbursements	—			38.9			9.9			—			48.8
	—			286.2			175.4			—			461.6
COST OF GOODS SOLD AND OPERATING EXPENSES	—			(237.2		)	(128.1		)	—			(365.3		)
SALES MARGIN	—			49.0			47.3			—			96.3
OTHER OPERATING INCOME (EXPENSE)
Selling, general and administrative expenses	(19.5		)	(4.4		)	(3.8		)	—			(27.7		)
Miscellaneous – net	(0.1		)	(5.5		)	17.1			—			11.5
	(19.6		)	(9.9		)	13.3			—			(16.2		)
OPERATING INCOME (LOSS)	(19.6		)	39.1			60.6			—			80.1
OTHER INCOME (EXPENSE)
Interest expense, net	(41.6		)	—			(1.2		)	—			(42.8		)
Loss on extinguishment of debt	(71.9		)	—			—			—			(71.9		)
Other non-operating income (expense)	(1.0		)	(0.8		)	4.3			—			2.5
	(114.5		)	(0.8		)	3.1			—			(112.2		)
INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	(134.1		)	38.3			63.7			—			(32.1		)
INCOME TAX BENEFIT (EXPENSE)	5.2			(0.8		)	(2.6		)	—			1.8
EQUITY IN INCOME OF SUBSIDIARIES	100.4			3.2			—			(103.6		)	—
INCOME (LOSS) FROM CONTINUING OPERATIONS	(28.5		)	40.7			61.1			(103.6		)	(30.3		)
INCOME (LOSS) FROM DISCONTINUED OPERATIONS, net of tax	0.4			0.2			(0.1		)	—			0.5
NET INCOME (LOSS)	(28.1		)	40.9			61.0			(103.6		)	(29.8		)
LOSS ATTRIBUTABLE TO NONCONTROLLING INTEREST	—			1.7			—			—			1.7
NET INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$	(28.1	)	$	42.6		$	61.0		$	(103.6	)	$	(28.1	)
OTHER COMPREHENSIVE INCOME (LOSS)	(3.0		)	10.8			(17.8		)	7.0			(3.0		)
TOTAL COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$	(31.1	)	$	53.4		$	43.2		$	(96.6	)	$	(31.1	)

Schedule of Supplemental Statements of Condensed Consolidating Cash Flows



Unaudited Condensed Consolidating Statement of Cash Flows
For the Three Months Ended March 31, 2018
(In Millions)
	Cleveland-Cliffs Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Eliminations			Consolidated
Net cash used by operating activities	$	(54.7	)	$	(62.8	)	$	(25.4	)	$	—		$	(142.9	)
INVESTING ACTIVITIES
Purchase of property, plant and equipment	—			(8.1		)	(4.3		)	—			(12.4		)
Deposits for property, plant and equipment	—			(0.8		)	(58.2		)	—			(59.0		)
Intercompany investing	(137.7		)	(4.8		)	—			142.5			—
Net cash used by investing activities	(137.7		)	(13.7		)	(62.5		)	142.5			(71.4		)
FINANCING ACTIVITIES
Debt issuance costs	(1.5		)	—			—			—			(1.5		)
Intercompany financing	—			75.9			66.6			(142.5		)	—
Other financing activities	(1.4		)	(0.5		)	(3.6		)	—			(5.5		)
Net cash provided (used) by financing activities	(2.9		)	75.4			63.0			(142.5		)	(7.0		)
EFFECT OF EXCHANGE RATE CHANGES ON CASH	—			—			0.2			—			0.2
DECREASE IN CASH AND CASH EQUIVALENTS	(195.3		)	(1.1		)	(24.7		)	—			(221.1		)
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	948.9			2.1			56.7			—			1,007.7
CASH AND CASH EQUIVALENTS AT END OF PERIOD	$	753.6		$	1.0		$	32.0		$	—		$	786.6



Unaudited Condensed Consolidating Statement of Cash Flows
For the Three Months Ended March 31, 2017
(In Millions)
	Cleveland-Cliffs Inc.			Guarantor Subsidiaries			Non-Guarantor Subsidiaries			Eliminations			Consolidated
Net cash provided (used) by operating activities	$	(99.5	)	$	(19.7	)	$	94.1		$	—		$	(25.1	)
INVESTING ACTIVITIES
Purchase of property, plant and equipment	(0.8		)	(24.9		)	(0.2		)	—			(25.9		)
Deposits for property, plant and equipment	—			(2.0		)	—			—			(2.0		)
Intercompany investing	(56.5		)	(0.5		)	(45.0		)	102.0			—
Other investing activities	—			0.5			—			—			0.5
Net cash used by investing activities	(57.3		)	(26.9		)	(45.2		)	102.0			(27.4		)
FINANCING ACTIVITIES
Net proceeds from issuance of common shares	661.3			—			—			—			661.3
Proceeds from issuance of debt	500.0			—			—			—			500.0
Debt issuance costs	(8.5		)	—			—			—			(8.5		)
Repurchase of debt	(1,115.5		)	—			—			—			(1,115.5		)
Distributions of partnership equity	—			(8.7		)	—			—			(8.7		)
Intercompany financing	45.1			55.8			1.1			(102.0		)	—
Other financing activities	(0.5		)	(0.7		)	(4.4		)	—			(5.6		)
Net cash provided (used) by financing activities	81.9			46.4			(3.3		)	(102.0		)	23.0
EFFECT OF EXCHANGE RATE CHANGES ON CASH	—			—			1.4			—			1.4
INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(74.9		)	(0.2		)	47.0			—			(28.1		)
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	283.4			2.5			37.5			—			323.4
CASH AND CASH EQUIVALENTS AT END OF PERIOD	$	208.5		$	2.3		$	84.5		$	—		$	295.3

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule Of Subsidiaries) (Details)	3 Months Ended
	Mar. 31, 2018
Northshore [Member]
Related Party Transaction [Line Items]
Entity Address, State or Province	Minnesota
United Taconite [Member]
Related Party Transaction [Line Items]
Entity Address, State or Province	Minnesota
Tilden [Member]
Related Party Transaction [Line Items]
Entity Address, State or Province	Michigan
Empire [Member]
Related Party Transaction [Line Items]
Entity Address, State or Province	Michigan
Koolyanobbing [Member]
Related Party Transaction [Line Items]
Entity Address, State or Province	Western Australia

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Foreign Currency Translation) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Foreign Currency Transaction Gain (Loss), before Tax	$ (0.3)	$ 13.6
Short-term intercompany loan [Member]
Foreign Currency Transaction Gain (Loss), before Tax	(0.2)	15.1
Cash and Cash Equivalents [Member]
Foreign Currency Transaction Gain (Loss), before Tax	0.1	(1.2)
Other Remeasurement
Foreign Currency Transaction Gain (Loss), before Tax	$ (0.2)	$ (0.3)

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details) - Hibbing [Member] - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Other Noncurrent Assets [Member]
Related Party Transaction [Line Items]
Ownership interest, equity method investment	23.00%	23.00%
Other Noncurrent Liabilities [Member]
Related Party Transaction [Line Items]
Equity Method Investments	$ 7.3	$ 11.0

NEW ACCOUNTING STANDARDS (Schedule of New Accounting Pronouncements and Changes in Accounting Principles) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and cash equivalents	$ 786.6	$ 295.3	$ 1,007.7	$ 1,007.7
Accounts receivable, net	47.2		217.2	140.6
Inventories	(324.4)		(132.0)	(183.4)
Supplies and other inventories	81.7		93.9	93.9
Derivative assets	93.6		51.0	39.4
Loans to and accounts receivable from the Canadian Entities	50.4		51.6	51.6
Other current assets	28.5		28.0	28.0
Assets, Current	1,412.4		1,581.4	1,544.6
PROPERTY, PLANT AND EQUIPMENT, NET	1,047.3		1,051.0	1,051.0
Deposits for property, plant and equipment	74.1		17.8	17.8
Income tax receivable	219.9		235.3	235.3
Other non-current assets	109.2		104.7	104.7
Total Other Assets	403.2		357.8	357.8
Assets	2,862.9		2,990.2	2,953.4
Accounts payable	99.5		129.1	127.7
Accrued expenses	94.4		107.1	107.1
Accrued interest	28.2		31.4	31.4
Contingent claims	54.3		55.6	55.6
Partnership distribution payable	44.2		44.2	44.2
Other current liabilities	104.3		87.6	86.2
Liabilities, Current	424.9		455.0	452.2
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES	251.4		257.7	257.7
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	181.2		196.5	196.5
LONG-TERM DEBT	2,308.2		2,304.2	2,304.2
OTHER LIABILITIES	182.0		186.9	186.9
Liabilities	3,347.7		3,400.3	3,397.5
Stockholders' Equity Attributable to Parent	(485.0)		(410.3)	(444.3)
Stockholders' Equity Attributable to Noncontrolling Interest	0.2		0.2	0.2
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(484.8)	(703.0)	(410.1)	(444.1)	$ (1,330.5)
Liabilities and Equity	2,862.9		2,990.2	$ 2,953.4
Product	(220.7)	(412.8)
Freight and venture partners' cost reimbursements	(18.3)	(48.8)
Revenues	239.0	461.6
Cost of Goods and Services Sold	(242.6)	(365.3)
Sales margin	(3.6)	96.3
Selling, General and Administrative Expense	(27.7)	(27.7)
Miscellaneous - net	(8.7)	11.5
Other operating expense	(36.4)	(16.2)
Operating Income (Loss)	(40.0)	80.1
Interest expense, net	(33.5)	(42.8)
Other non-operating income	4.4	2.5
Other expense	(29.1)	(112.2)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(69.1)	(32.1)
Income Tax Expense (Benefit)	(15.7)	1.8
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(84.8)	(30.3)
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX	0.5	0.5
Net Loss	(84.3)	(29.8)
LOSS ATTRIBUTABLE TO NONCONTROLLING INTEREST	0.0	1.7
NET LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$ (84.3)	$ (28.1)
Income (Loss) from Continuing Operations, Per Basic Share	$ (0.29)	$ (0.11)
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share	0.00	0.00
Earnings Per Share, Basic	(0.29)	(0.11)
Income (Loss) from Continuing Operations, Per Diluted Share	(0.29)	(0.11)
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Diluted Share	0.00	0.00
Earnings Per Share, Diluted	$ (0.29)	$ (0.11)
Basic	297,266	265,164
Diluted	297,266	265,164
Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of Goods and Services Sold		$ (365.9)
Selling, General and Administrative Expense		(25.7)
Miscellaneous - net		11.9
Operating Income (Loss)		81.9
Other non-operating income		0.7
Net Loss		(29.8)
Accounting Standards Update 2017-07 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of Goods and Services Sold		0.6
Selling, General and Administrative Expense		(2.0)
Miscellaneous - net		(0.4)
Operating Income (Loss)		(1.8)
Other non-operating income		1.8
Net Loss		$ 0.0
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and cash equivalents	$ 786.6
Accounts receivable, net	24.9
Inventories	(332.0)
Supplies and other inventories	81.7
Derivative assets	91.3
Loans to and accounts receivable from the Canadian Entities	50.4
Other current assets	28.5
Assets, Current	1,395.4
PROPERTY, PLANT AND EQUIPMENT, NET	1,047.3
Deposits for property, plant and equipment	74.1
Income tax receivable	219.9
Other non-current assets	109.2
Total Other Assets	403.2
Assets	2,845.9
Accounts payable	99.2
Accrued expenses	94.4
Accrued interest	28.2
Contingent claims	54.3
Partnership distribution payable	44.2
Other current liabilities	104.0
Liabilities, Current	424.3
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES	251.4
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	181.2
LONG-TERM DEBT	2,308.2
OTHER LIABILITIES	182.0
Liabilities	3,347.1
Stockholders' Equity Attributable to Parent	(501.4)
Stockholders' Equity Attributable to Noncontrolling Interest	0.2
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(501.2)
Liabilities and Equity	2,845.9
Product	(279.1)
Freight and venture partners' cost reimbursements	(22.4)
Revenues	301.5
Cost of Goods and Services Sold	(286.2)
Sales margin	15.3
Selling, General and Administrative Expense	(27.7)
Miscellaneous - net	(8.7)
Other operating expense	(36.4)
Operating Income (Loss)	(21.1)
Interest expense, net	(33.5)
Other non-operating income	4.4
Other expense	(29.1)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(50.2)
Income Tax Expense (Benefit)	(15.7)
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(65.9)
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX	0.5
Net Loss	(65.4)
LOSS ATTRIBUTABLE TO NONCONTROLLING INTEREST	0.0
NET LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$ (65.4)
Income (Loss) from Continuing Operations, Per Basic Share	$ (0.23)
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share	0.00
Earnings Per Share, Basic	(0.23)
Income (Loss) from Continuing Operations, Per Diluted Share	(0.23)
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Diluted Share	0.00
Earnings Per Share, Diluted	$ (0.23)
Basic	297,266
Diluted	297,266
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and cash equivalents	$ 0.0		0.0
Accounts receivable, net	22.3		76.6
Inventories	(7.6)		(51.4)
Supplies and other inventories	0.0		0.0
Derivative assets	2.3		11.6
Loans to and accounts receivable from the Canadian Entities	0.0		0.0
Other current assets	0.0		0.0
Assets, Current	17.0		36.8
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
Other non-current assets	0.0		0.0
Total Other Assets	0.0		0.0
Assets	17.0		36.8
Accounts payable	0.3		1.4
Accrued expenses	0.0		0.0
Accrued interest	0.0		0.0
Contingent claims	0.0		0.0
Partnership distribution payable	0.0		0.0
Other current liabilities	0.3		1.4
Liabilities, Current	0.6		2.8
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
OTHER LIABILITIES	0.0		0.0
Liabilities	0.6		2.8
Stockholders' Equity Attributable to Parent	16.4		34.0
Stockholders' Equity Attributable to Noncontrolling Interest	0.0		0.0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	16.4
Liabilities and Equity	17.0		$ 36.8
Product	(58.4)
Freight and venture partners' cost reimbursements	(4.1)
Revenues	62.5
Cost of Goods and Services Sold	(43.6)
Sales margin	(18.9)
Selling, General and Administrative Expense	0.0
Miscellaneous - net	0.0
Other operating expense	0.0
Operating Income (Loss)	(18.9)
Interest expense, net	0.0
Other non-operating income	0.0
Other expense	0.0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(18.9)
Income Tax Expense (Benefit)	0.0
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(18.9)
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX	0.0
Net Loss	(18.9)
LOSS ATTRIBUTABLE TO NONCONTROLLING INTEREST	0.0
NET LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$ (18.9)
Income (Loss) from Continuing Operations, Per Basic Share	$ (0.06)
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share	0.00
Earnings Per Share, Basic	(0.06)
Income (Loss) from Continuing Operations, Per Diluted Share	(0.06)
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Diluted Share	0.00
Earnings Per Share, Diluted	$ (0.06)

NEW ACCOUNTING STANDARDS (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Stockholders' Equity Attributable to Parent	$ (485.0)	$ (410.3)	$ (444.3)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Stockholders' Equity Attributable to Parent	$ 16.4	$ 34.0

SEGMENT REPORTING (Schedule Of Segment Reporting Information, By Segment) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Impairment Charges	$ (18,900,000)	$ 0
Impairment of Long-Lived Assets Held-for-use	$ (2,600,000)	$ 0
Revenues from producet sales and services, percent	100.00%	100.00%
Revenues	$ 239,000,000	$ 461,600,000
Sales margin	(3,600,000)	96,300,000
Other operating expense	(36,400,000)	(16,200,000)
Other expense	(29,100,000)	(112,200,000)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(69,100,000)	(32,100,000)
Net Loss	(84,300,000)	(29,800,000)
Interest expense, net	(33,500,000)	(42,800,000)
Income Tax Expense (Benefit)	15,700,000	(1,800,000)
Depreciation, depletion and amortization	23,900,000	23,200,000
EBITDA	(11,200,000)	34,400,000
Severance Costs	1,500,000	0
Loss on extinguishment of debt	0	(71,900,000)
Adjusted EBITDA	11,600,000	92,200,000
Property, Plant and Equipment, Additions	78,900,000	27,300,000
Payments To Acquire Property Plant And Equipment Net	71,400,000	27,900,000
Capital Expenditures Incurred but Not yet Paid	7,500,000	600,000
Foreign Currency Transaction Gain (Loss), before Tax	(300,000)	13,600,000
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX	$ 500,000	$ 500,000
U.S. Iron Ore [Member]
Segment Reporting Information [Line Items]
Revenues from producet sales and services, percent	75.00%	62.00%
Revenues	$ 180,000,000	$ 286,200,000
Sales margin	61,500,000	49,000,000
Depreciation, depletion and amortization	15,800,000	16,400,000
EBITDA	72,500,000	57,900,000
Adjusted EBITDA	77,100,000	64,100,000
Property, Plant and Equipment, Additions	$ 18,700,000	$ 27,100,000
Asia Pacific Iron Ore [Member]
Segment Reporting Information [Line Items]
Revenues from producet sales and services, percent	25.00%	38.00%
Revenues	$ 59,000,000	$ 175,400,000
Sales margin	(65,100,000)	47,300,000
Depreciation, depletion and amortization	6,700,000	4,700,000
EBITDA	(63,700,000)	51,400,000
Adjusted EBITDA	(39,600,000)	53,800,000
Property, Plant and Equipment, Additions	0	200,000
All Other Segments [Member]
Segment Reporting Information [Line Items]
Depreciation, depletion and amortization	1,400,000	2,100,000
EBITDA	(20,000,000)	(74,900,000)
Adjusted EBITDA	(25,900,000)	(25,700,000)
Property, Plant and Equipment, Additions	60,200,000	0
EBITDA Calculation [Member]
Segment Reporting Information [Line Items]
Depreciation, depletion and amortization	$ 23,900,000	$ 23,200,000

SEGMENT REPORTING (Summary of Assets by Segment) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Assets	$ 2,862.9	$ 2,990.2	$ 2,953.4
U.S. Iron Ore [Member]
Segment Reporting Information [Line Items]
Assets	1,646.8		1,500.6
Asia Pacific Iron Ore [Member]
Segment Reporting Information [Line Items]
Assets	78.4		138.8
Total Segment Assets [Member]
Segment Reporting Information [Line Items]
Assets	1,725.2		1,639.4
Corporate [Member]
Segment Reporting Information [Line Items]
Assets	$ 1,137.7		$ 1,314.0

REVENUE (Deferred Revenue) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Deferred Revenue Arrangement [Line Items]
Deferred Revenue, Noncurrent	$ 51.4	$ 51.4
Deferred Revenue, Current	31.0	$ 23.8
Other Current Liabilities [Member]
Deferred Revenue Arrangement [Line Items]
Deferred Revenue, Period Increase (Decrease)	7.2
Other Noncurrent Liabilities [Member]
Deferred Revenue Arrangement [Line Items]
Deferred Revenue, Period Increase (Decrease)	$ 0.0

- Definition

The carrying amount of consideration received or receivable as of the balance sheet date on potential earnings that were not recognized as revenue in conformity with GAAP, and which are expected to be recognized as such within one year or the normal operating cycle, if longer, including sales, license fees, and royalties, but excluding interest income.

+ References + Details

- Definition

The noncurrent portion of deferred revenue amount as of balance sheet date. Deferred revenue is a liability related to a revenue producing activity for which revenue has not yet been recognized, and is not expected to be recognized in the next twelve months. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

+ References + Details

REVENUE (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
REVENUE (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Revenues	$ 239.0	$ 461.6
Deferred Revenue, Current	31.0			$ 23.8
Deferred Revenue, Noncurrent	51.4			51.4
Other current liabilities	104.3		$ 87.6	86.2
Customer Supplemental Payments [Member]
Deferred Revenue	64.2			64.2
Deferred Revenue, Current	12.8			12.8
Deferred Revenue, Noncurrent				51.4
Take or Pay Contracts [Member]
Deferred Revenue	18.2			$ 9.6
U.S. Iron Ore [Member]
Revenues	180.0	286.2
U.S. Iron Ore [Member] \| Derivative Adjustment [Member]
Revenues	43.8
Asia Pacific Iron Ore [Member]
Revenues	59.0	$ 175.4
Asia Pacific Iron Ore [Member] \| Derivative Adjustment [Member]
Revenues	1.3
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenues	62.5
Other current liabilities	$ 0.3		$ 1.4

INVENTORIES (Schedule Of Inventories) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Inventory, Net [Abstract]
Finished Goods	$ 287.4		$ 160.4
Work-in Process	37.0		23.0
Total Inventory	324.4	$ 132.0	183.4
U.S. Iron Ore [Member]
Inventory, Net [Abstract]
Finished Goods	267.2		127.1
Work-in Process	36.0		11.3
Total Inventory	303.2		138.4
Asia Pacific Iron Ore [Member]
Inventory, Net [Abstract]
Finished Goods	20.2		33.3
Work-in Process	1.0		11.7
Total Inventory	$ 21.2		$ 45.0

INVENTORIES (Narrative) (Details) - USD ($)	3 Months Ended
INVENTORIES (Narrative) (Details) - USD ($)	Mar. 31, 2018	Mar. 31, 2017
Inventory [Line Items]
Impairment Charges	$ (18,900,000)	$ 0
LCM inventory adjustment		$ 0
Finished Goods [Domain]
Inventory [Line Items]
Impairment Charges	1,400,000
LCM inventory adjustment	13,000,000
Work in Process [Domain]
Inventory [Line Items]
Impairment Charges	13,200,000
LCM inventory adjustment	$ 9,100,000

PROPERTY, PLANT AND EQUIPMENT (Value Of Each Of The Major Classes Of Consolidated Depreciable Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 2,091.1		$ 2,079.4
Allowance for depreciation and depletion	(1,043.8)		(1,028.4)
Property, plant and equipment, net	1,047.3	$ 1,051.0	1,051.0
Land Rights And Mineral Rights [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	549.6		549.6
Office And Information Technology [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	66.3		66.3
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	85.5		86.8
Mining Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	594.0		594.4
Processing Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	619.8		617.0
Electric Power Facilities [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	57.0		57.0
Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	23.6		23.7
Asset Retirement Obligation [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	16.9		19.2
Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	30.3		30.3
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 48.1		$ 35.1

PROPERTY, PLANT AND EQUIPMENT (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Property, Plant and Equipment [Abstract]
Depreciation and depletion	$ 21.3	$ 22.6
Impairment Charges, CIP	$ (2.6)

DEBT AND CREDIT FACILITIES (Schedule Of Long-Term Debt) (Details) - USD ($)	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
LONG-TERM DEBT	$ 2,308,200,000	$ 2,304,200,000	$ 2,304,200,000
$400 Million 4.875% 2024 Senior Notes [Domain]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	5.00%		5.00%
Debt Instrument, Par Value	$ 400,000,000		$ 400,000,000
Unamortized Debt Issuance Expense	(6,700,000)		(7,100,000)
Debt Instrument, Unamortized Discount	(2,500,000)		(2,600,000)
Long-term Debt	$ 390,800,000		$ 390,300,000
$400 Million 5.90% 2020 Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	5.98%		5.98%
Debt Instrument, Par Value	$ 88,900,000		$ 88,900,000
Unamortized Debt Issuance Expense	(200,000)		(200,000)
Debt Instrument, Unamortized Discount	(100,000)		(100,000)
Long-term Debt	$ 88,600,000		$ 88,600,000
$500 million 4.80% 2020 Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	4.83%		4.83%
Debt Instrument, Par Value	$ 122,400,000		$ 122,400,000
Unamortized Debt Issuance Expense	(200,000)		(300,000)
Debt Instrument, Unamortized Discount	(100,000)		(100,000)
Long-term Debt	$ 122,100,000		$ 122,000,000
$700 Million 4.875% 2021 Senior Note [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	4.89%		4.89%
Debt Instrument, Par Value	$ 138,400,000		$ 138,400,000
Unamortized Debt Issuance Expense	(300,000)		(300,000)
Debt Instrument, Unamortized Discount	(100,000)		(100,000)
Long-term Debt	$ 138,000,000		$ 138,000,000
$316 Million 1.5% 2025 Senior Notes [Domain]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	6.26%		6.26%
Debt Instrument, Par Value	$ 316,300,000		$ 316,300,000
Unamortized Debt Issuance Expense	(6,300,000)		(6,600,000)
Debt Instrument, Unamortized Discount	(83,200,000)		(85,600,000)
Long-term Debt	$ 226,800,000		$ 224,100,000
$1,075 Million 5.75% 2025 Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	6.01%		6.01%
Debt Instrument, Par Value	$ 1,075,000,000		$ 1,075,000,000
Unamortized Debt Issuance Expense	(11,100,000)		(11,300,000)
Debt Instrument, Unamortized Discount	(16,000,000)		(16,500,000)
Long-term Debt	$ 1,047,900,000		$ 1,047,200,000
$800 Million 6.25% 2040 Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	6.34%		6.34%
Debt Instrument, Par Value	$ 298,400,000		$ 298,400,000
Unamortized Debt Issuance Expense	(2,300,000)		(2,400,000)
Debt Instrument, Unamortized Discount	(3,400,000)		(3,400,000)
Long-term Debt	292,700,000		292,600,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Par Value	450,000,000		550,000,000
Credit facility, amount outstanding	0		0
Interest Rate Swap [Member]
Debt Instrument [Line Items]
Fair Value Adjustment to Interest Rate Hedge	$ 1,300,000		$ 1,400,000

DEBT AND CREDIT FACILITIES (Schedule of Debt Maturities) (Details) $ in Millions	Mar. 31, 2018 USD ($)
Debt Disclosure [Abstract]
Debt Maturities 2018	$ 0.0
Debt Maturities 2019	0.0
Debt Maturities 2020	211.3
Debt Maturities 2021	138.4
Debt Maturities 2022	0.0
Debt Maturities 2023	0.0
2024 and thereafter	2,089.7
Total maturities of debt	$ 2,439.4

DEBT AND CREDIT FACILITIES (Narrative) (Details) - USD ($)	3 Months Ended
	Sep. 30, 2017	Mar. 31, 2017	Mar. 31, 2018	Dec. 31, 2017
$1,075 Million 5.75% 2025 Senior Notes [Member]
Line of Credit Facility [Line Items]
Proceeds from Issuance of Debt	$ 575,000,000	$ 500,000,000
Debt Instrument, Interest Rate, Stated Percentage			5.75%
Debt issuance, discount rate			97.00%
Debt Instrument, Par Value			$ 1,075,000,000	$ 1,075,000,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Par Value			450,000,000	550,000,000
U.S. Tranche			400,000,000
Sublimit for Issuers of Letters of Credit for U.S. Tranche			248,800,000
Sublimit for U.S. Swingline Loans			100,000,000
Australian Tranche			50,000,000
Sublimit for Issuance of Letters of Credit for Australian Tranche			24,400,000
Sublimit for Australian Swingline Loans			20,000,000
Credit facility, amount outstanding			0	0
Line of Credit Facility, Maximum Borrowing Capacity			314,100,000	273,200,000
Letters of credit outstanding			46,600,000	46,500,000
Credit facility remaining capacity			$ 267,500,000	$ 226,700,000

FAIR VALUE MEASUREMENTS (Fair Value of Assets and Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	$ 526.6		$ 616.9
Derivative assets	93.6	$ 51.0	39.4
Total Asset	620.2		656.3
Derivative Liability	4.4		2.7
Total Liability	4.4		2.7
Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	36.0		66.3
Derivative assets	0.0		0.0
Total Asset	36.0		66.3
Derivative Liability	0.0		0.0
Total Liability	0.0		0.0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	490.6		550.6
Derivative assets	0.0		0.0
Total Asset	490.6		550.6
Derivative Liability	0.2		0.3
Total Liability	0.2		0.3
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	0.0		0.0
Derivative assets	93.6		39.4
Total Asset	93.6		39.4
Derivative Liability	4.2		2.4
Total Liability	$ 4.2		$ 2.4

FAIR VALUE MEASUREMENTS (Schedule Of Quantitative Inputs And Assumptions For Level 3 Assets And Liabilities) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	$ 93,600,000	$ 51,000,000	$ 39,400,000
Management Estimate of 62% Fe	62.00%
Derivative Liability	$ 4,400,000		2,700,000
Not Designated as Hedging Instrument [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	93,600,000		39,400,000
Derivative Liability	4,200,000		2,400,000
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	93,600,000		39,400,000
Derivative Liability	$ 4,200,000		2,400,000
Fair Value, Inputs, Level 3 [Member] \| Not Designated as Hedging Instrument [Member] \| Managements Estimate Of 62% Fee [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Management Estimate of 62% Fe	62.00%
Fair Value, Inputs, Level 3 [Member] \| Not Designated as Hedging Instrument [Member] \| Market Approach Valuation Technique [Member] \| Provisional Pricing Arrangements [Member] \| Managements Estimate Of 62% Fee [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement with unobservable inputs derivative asset range	$ 66
Fair Value, Inputs, Level 3 [Member] \| Not Designated as Hedging Instrument [Member] \| Market Approach Valuation Technique [Member] \| Provisional Pricing Arrangements [Member] \| Managements Estimate Of 62% Fee [Member] \| Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement with unobservable inputs derivative asset range	63
Fair Value, Inputs, Level 3 [Member] \| Not Designated as Hedging Instrument [Member] \| Market Approach Valuation Technique [Member] \| Provisional Pricing Arrangements [Member] \| Managements Estimate Of 62% Fee [Member] \| Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement with unobservable inputs derivative asset range	71
Fair Value, Inputs, Level 3 [Member] \| Not Designated as Hedging Instrument [Member] \| Market Approach Valuation Technique [Member] \| Customer Supply Agreement [Member] \| Customer's Hot-Rolled Steel Estimate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement with unobservable inputs derivative asset range	752
Derivative Financial Instruments, Assets [Member] \| Not Designated as Hedging Instrument [Member] \| Provisional Pricing Arrangements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	2,400,000		1,500,000
Derivative Financial Instruments, Assets [Member] \| Not Designated as Hedging Instrument [Member] \| Customer Supply Agreement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	91,200,000		37,900,000
Other Current Liabilities [Member] \| Not Designated as Hedging Instrument [Member] \| Provisional Pricing Arrangements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability	4,200,000		2,400,000
Other Current Liabilities [Member] \| Fair Value, Inputs, Level 3 [Member] \| Not Designated as Hedging Instrument [Member] \| Customer Supply Agreement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability	0		$ 0
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	$ 2,300,000	$ 11,600,000

FAIR VALUE MEASUREMENTS (Fair Value, Assets and Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Assets Measured On Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance1	$ 51.0	$ 31.6
Total gains (losses)
Included in earnings	49.1	42.1
Settlements	(6.5)	(14.3)
Ending balance - March 31	93.6	59.4
Total gains for the period included in earnings attributable to the change in unrealized gains on assets still held at the reporting date	44.5	33.2
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	(2.4)	(0.5)
Total gains (losses)
Included in earnings	(4.0)	(8.6)
Settlements	2.2	0.0
Ending balance - March 31	(4.2)	(9.1)
Total losses for the period included in earnings attributable to the change in unrealized losses on liabilities still held at the reporting date	$ (4.2)	$ (9.1)

FAIR VALUE MEASUREMENTS (Carrying Value And Fair Value Of Financial Instruments Disclosure) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Fair Value [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	$ 2,352.8	$ 2,346.3
Fair Value [Member] \| Fair Value, Inputs, Level 2 [Member] \| Interest Rate Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Adjustment to Interest Rate Hedge	1.3	1.4
Carrying Value [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	2,308.2	2,304.2
Carrying Value [Member] \| Fair Value, Inputs, Level 2 [Member] \| Interest Rate Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Adjustment to Interest Rate Hedge	1.3	1.4
Senior Notes [Member] \| Fair Value [Member] \| Fair Value, Inputs, Level 1 [Member] \| $400 Million 4.875% 2024 Senior Notes [Domain]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	389.0	398.0
Senior Notes [Member] \| Fair Value [Member] \| Fair Value, Inputs, Level 1 [Member] \| $400 Million 5.90% 2020 Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	89.1	88.0
Senior Notes [Member] \| Fair Value [Member] \| Fair Value, Inputs, Level 1 [Member] \| $500 million 4.80% 2020 Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	120.3	118.8
Senior Notes [Member] \| Fair Value [Member] \| Fair Value, Inputs, Level 1 [Member] \| $700 Million 4.875% 2021 Senior Note [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	135.4	130.8
Senior Notes [Member] \| Fair Value [Member] \| Fair Value, Inputs, Level 1 [Member] \| $316 Million 1.5% 2025 Senior Notes [Domain]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	340.0	352.9
Senior Notes [Member] \| Fair Value [Member] \| Fair Value, Inputs, Level 1 [Member] \| $1,075 Million 5.75% 2025 Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	1,026.6	1,029.3
Senior Notes [Member] \| Fair Value [Member] \| Fair Value, Inputs, Level 1 [Member] \| $800 Million 6.25% 2040 Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	251.1	227.1
Senior Notes [Member] \| Carrying Value [Member] \| Fair Value, Inputs, Level 1 [Member] \| $400 Million 4.875% 2024 Senior Notes [Domain]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	390.8	390.3
Senior Notes [Member] \| Carrying Value [Member] \| Fair Value, Inputs, Level 1 [Member] \| $400 Million 5.90% 2020 Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	88.6	88.6
Senior Notes [Member] \| Carrying Value [Member] \| Fair Value, Inputs, Level 1 [Member] \| $500 million 4.80% 2020 Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	122.1	122.0
Senior Notes [Member] \| Carrying Value [Member] \| Fair Value, Inputs, Level 1 [Member] \| $700 Million 4.875% 2021 Senior Note [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	138.0	138.0
Senior Notes [Member] \| Carrying Value [Member] \| Fair Value, Inputs, Level 1 [Member] \| $316 Million 1.5% 2025 Senior Notes [Domain]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	226.8	224.1
Senior Notes [Member] \| Carrying Value [Member] \| Fair Value, Inputs, Level 1 [Member] \| $1,075 Million 5.75% 2025 Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	1,047.9	1,047.2
Senior Notes [Member] \| Carrying Value [Member] \| Fair Value, Inputs, Level 1 [Member] \| $800 Million 6.25% 2040 Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	292.7	292.6
Line of Credit [Member] \| Fair Value [Member] \| Fair Value, Inputs, Level 2 [Member] \| Revolving Credit Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	0.0	0.0
Line of Credit [Member] \| Carrying Value [Member] \| Fair Value, Inputs, Level 2 [Member] \| Revolving Credit Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	$ 0.0	$ 0.0

FAIR VALUE MEASUREMENTS (Fair Value Measurements, Nonrecurring) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Jan. 01, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans to and accounts receivable from the Canadian Entities	$ 50.4		$ 51.6	$ 51.6
Fair Value, Asset, Measured on a Nonrecurring Basis, Gain (Loss) Included in Earnings	(1.2)		3.0
Impairment Charges, CIP	(2.6)
Contingent Liabilities recognized in Consolidated Financials			0.0
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX	$ 0.5	$ 0.5
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent Liabilities recognized in Consolidated Financials			0.0
Wabush Scully Mine Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX			$ 31.4

- Definition

Amount after tax of income (loss) from a discontinued operation including the portion attributable to the noncontrolling interest. Includes, but is not limited to, the income (loss) from operations during the phase-out period, gain (loss) on disposal, gain (loss) for reversal of write-down (write-down) to fair value, less cost to sell, and adjustments to a prior period gain (loss) on disposal.

+ References + Details

FAIR VALUE MEASUREMENTS (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Fair Value, Assets And Liabilities Components [Line Items]
Derivative assets	$ 93.6	$ 51.0	$ 39.4
Derivative Liability	$ 4.4		2.7
Management Estimate of 62% Fe	62.00%
Impairment Charges, CIP	$ 2.6
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets And Liabilities Components [Line Items]
Derivative assets	0.0		0.0
Derivative Liability	0.0		0.0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets And Liabilities Components [Line Items]
Derivative assets	0.0		0.0
Derivative Liability	0.2		0.3
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets And Liabilities Components [Line Items]
Derivative assets	93.6		39.4
Derivative Liability	4.2		2.4
Not Designated as Hedging Instrument [Member]
Fair Value, Assets And Liabilities Components [Line Items]
Derivative assets	93.6		39.4
Derivative Liability	4.2		2.4
Derivative Financial Instruments, Assets [Member] \| Not Designated as Hedging Instrument [Member] \| Customer Supply Agreement [Member]
Fair Value, Assets And Liabilities Components [Line Items]
Derivative assets	91.2		37.9
Derivative Financial Instruments, Assets [Member] \| Not Designated as Hedging Instrument [Member] \| Provisional Pricing Arrangements [Member]
Fair Value, Assets And Liabilities Components [Line Items]
Derivative assets	2.4		1.5
Other Current Liabilities [Member] \| Not Designated as Hedging Instrument [Member] \| Customer Supply Agreement [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets And Liabilities Components [Line Items]
Derivative Liability	0.0		0.0
Other Current Liabilities [Member] \| Not Designated as Hedging Instrument [Member] \| Provisional Pricing Arrangements [Member]
Fair Value, Assets And Liabilities Components [Line Items]
Derivative Liability	$ 4.2		$ 2.4

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Estimated Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 4.7	$ 4.8
Interest cost	7.6	7.5
Expected return on plan assets	(15.0)	(13.5)
Prior service credits	0.5	0.6
Net actuarial loss	5.3	5.3
Net periodic benefit credit	3.1	4.7
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0.5	0.5
Interest cost	2.1	2.1
Expected return on plan assets	(4.6)	(4.4)
Prior service credits	(0.8)	(0.7)
Net actuarial loss	1.2	1.2
Net periodic benefit credit	$ (1.6)	$ (1.3)

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension Plans, Defined Benefit [Member]
Definted Benefit Plan Disclosure [Line Items]
Payment for Pension Benefits	$ 2.3	$ 0.0
Other Postretirement Benefit Plans, Defined Benefit [Member]
Definted Benefit Plan Disclosure [Line Items]
OPEB Contributions	$ 0.0	$ 0.0

STOCK COMPENSATION PLANS (Assumptions Utilized to Estimate Fair Value for Performance Share Grants) (Details)	3 Months Ended
	Mar. 31, 2018 $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant Date Market Price	$ 7.53
Average Expected Term	2 years 10 months 9 days
Expected Volatility	86.80%
Risk-Free Interest Rate	2.42%
Dividend Yield	0.00%
Fair Value	$ 11.93
Fair Value (Percent of Grant Date Market Price)	158.43%

STOCK COMPENSATION PLANS (Narrative) (Details) - 2015 Equity Plan [Member] shares in Millions	3 Months Ended
	Mar. 31, 2018 shares
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted shares granted	0.7
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted shares granted	0.7
2017 to 2019 Performance Period [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Goods And Nonemployee Services Transaction Valuation Method Payout Rate	0.00%
2017 to 2019 Performance Period [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Goods And Nonemployee Services Transaction Valuation Method Payout Rate	200.00%

INCOME TAXES (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
INCOME TAXES (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, Percent	0.10%	5.40%
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%
Income Tax Expense (Benefit)	$ 15.7	$ (1.8)
Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount		$ (0.1)
Change in refundable AMT, amount	$ 14.5

LEASE OBLIGATIONS (Future Minimum Lease Payments) (Details) $ in Millions	Mar. 31, 2018 USD ($)
Capital Leases
2018 (April 1 - December 31)	$ 14.7
2019	12.0
2020	11.0
2021	10.3
2022	2.1
2023 and thereafter	0.0
Total minimum lease payments	50.1
Amounts representing interest	7.6
Present value of net minimum lease payments	42.5
Operating Leases
2018 (April 1 - December 31)	3.3
2019	1.9
2020	1.8
2021	1.8
2022	1.8
2023 and thereafter	7.5
Total minimum lease payments	18.1
Other Current Liabilities [Member]
Capital Leases
Present value of net minimum lease payments	14.6
Other Noncurrent Liabilities [Member]
Capital Leases
Present value of net minimum lease payments	$ 27.9

LEASE OBLIGATIONS (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Leases [Abstract]
Operating lease expense	$ 1.6	$ 1.7

ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Summary Of Mine Closure Obligations) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Environmental	$ 3.1	$ 2.9
Mine Reclamation and Closing Liability, current and noncurrent	199.4	197.2
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current And Noncurrent	202.5	200.1
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current	21.3	3.6
Environmental Loss Contingency And Mine Reclamation And Closing Liability Noncurrent	181.2	196.5
U.S. Iron Ore [Member] \| Owned Or Operating Facilities [Member]
Loss Contingencies [Line Items]
Mine Reclamation and Closing Liability, current and noncurrent	170.7	168.4
Asia Pacific Iron Ore [Member]
Loss Contingencies [Line Items]
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current	17.7
Asia Pacific Iron Ore [Member] \| Owned Or Operating Facilities [Member]
Loss Contingencies [Line Items]
Mine Reclamation and Closing Liability, current and noncurrent	$ 28.7	$ 28.8

ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Asset Retirement Obligation Disclosure) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Asset Retirement Obligation [Roll Forward]
Asset retirement obligation at beginning of period	$ 197.2	$ 204.0
Accretion expense	2.7	14.9
Asset Retirement Obligation, Liabilities Settled	(0.1)	(5.6)
Exchange rate changes	(0.5)	1.5
Revision in estimated cash flows	0.1	(17.6)
Asset retirement obligation at end of period	$ 199.4	$ 197.2

ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Mar. 31, 2018
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current	$ 3.6	$ 21.3
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current And Noncurrent	200.1	202.5
U.S. Iron Ore [Member]
Accrual for Environmental Loss Contingencies, Period Increase (Decrease)	(26.2)
Asia Pacific Iron Ore [Member]
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current		$ 17.7
Accrual for Environmental Loss Contingencies, Period Increase (Decrease)	$ (10.1)

GOODWILL AND OTHER INTANGIBLE ASSETS AND LIABILITIES (Schedule Of Finite-Lived Intangible Assets By Major Class) (Details) - Permits [Member] - Other Assets [Member] - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Definite lived intangible assets - Gross Carrying Amount	$ 78.8	$ 78.8
Definite lived intangible assets - Accumulated Amortization	(28.9)	(26.5)
Definite lived intangible assets - Net Carrying Amount	$ 49.9	$ 52.3

GOODWILL AND OTHER INTANGIBLE ASSETS AND LIABILITIES (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Cost of Sales [Member]
Goodwill [Line Items]
Amortization expense relating to intangible assets	$ 2.6	$ 0.6
U.S. Iron Ore [Member]
Goodwill [Line Items]
Goodwill	$ 2.0		$ 2.0

DERIVATIVE INSTRUMENTS (Schedule Of Derivative Instruments In Statement Of Financial Position, Fair Value) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative assets	$ 93.6	$ 51.0	$ 39.4
Derivative Liability	4.4		2.7
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	93.6		39.4
Derivative Liability	4.2		2.4
Not Designated as Hedging Instrument [Member] \| Customer Supply Agreement [Member] \| Derivative Financial Instruments, Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	91.2		37.9
Not Designated as Hedging Instrument [Member] \| Provisional Pricing Arrangements [Member] \| Derivative Financial Instruments, Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	2.4		1.5
Not Designated as Hedging Instrument [Member] \| Provisional Pricing Arrangements [Member] \| Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	4.2		2.4
Fair Value, Inputs, Level 3 [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	93.6		39.4
Derivative Liability	4.2		2.4
Fair Value, Inputs, Level 3 [Member] \| Designated as Hedging Instrument [Member] \| Commodity Contract [Member] \| Derivative Financial Instruments, Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	0.0		0.0
Fair Value, Inputs, Level 3 [Member] \| Designated as Hedging Instrument [Member] \| Commodity Contract [Member] \| Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	0.2		0.3
Fair Value, Inputs, Level 3 [Member] \| Not Designated as Hedging Instrument [Member] \| Customer Supply Agreement [Member] \| Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	$ 0.0		$ 0.0

DERIVATIVE INSTRUMENTS (Schedule Of Derivatives Not Designated As Hedging Instruments) (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 45.1	$ 32.2
Customer Supply Agreement [Member] \| Product Revenues [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain/(loss) recognized in income on derivative	41.9	17.8
Provisional Pricing Arrangements [Member] \| Product Revenues [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain/(loss) recognized in income on derivative	3.2	15.7
Commodity Contract [Member] \| Other Nonoperating Income (Expense) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 0.0	$ (1.3)

DERIVATIVE INSTRUMENTS (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Derivative [Line Items]
Natural Gas Hedges	$ 3.5			$ 3.5
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	(0.4)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0.1
Derivative assets	93.6		$ 51.0	39.4
Derivative Liability	4.4			2.7
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative assets	93.6			39.4
Derivative Liability	4.2			2.4
Customer Supply Agreement [Member] \| Not Designated as Hedging Instrument [Member] \| Product Revenues [Member]
Derivative [Line Items]
Amount of gain/(loss) recognized in income on derivative	41.9	$ 17.8
Customer Supply Agreement [Member] \| Not Designated as Hedging Instrument [Member] \| Derivative Financial Instruments, Assets [Member]
Derivative [Line Items]
Derivative assets	91.2			37.9
Provisional Pricing Arrangements [Member] \| Not Designated as Hedging Instrument [Member] \| Product Revenues [Member]
Derivative [Line Items]
Amount of gain/(loss) recognized in income on derivative	3.2	$ 15.7
Provisional Pricing Arrangements [Member] \| Not Designated as Hedging Instrument [Member] \| Derivative Financial Instruments, Assets [Member]
Derivative [Line Items]
Derivative assets	$ 2.4			$ 1.5

SHAREHOLDERS' EQUITY (Schedule of Shareholders' Equity) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Stockholders' Equity Attributable to Parent	$ (485.0)		$ (410.3)	$ (444.3)
Stockholders' Equity Attributable to Noncontrolling Interest	0.2		0.2	0.2
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(484.8)	$ (703.0)	$ (410.1)	(444.1)	$ (1,330.5)
Cumulative Effect of New Accounting Principle in Period of Adoption	34.0
NET LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	(84.3)	(28.1)
Net Income (Loss) Attributable to Noncontrolling Interest	0.0	(1.7)
Net Loss	(84.3)	(29.8)
Other comprehensive income (loss)	7.7	(3.0)
OTHER COMPREHENSIVE LOSS ATTRIBUTABLE TO THE NONCONTROLLING INTEREST	0.0	(5.0)
Other Comprehensive Income (Loss), Net of Tax	7.7	(8.0)
TOTAL COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	(76.6)	(31.1)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(76.6)	(37.8)
Stock and Other Incentive Plans	1.9	4.0
Cliffs Shareholders Equity [Member]
Stockholders' Equity Attributable to Parent	(485.0)	(830.1)		(444.3)	(1,464.3)
Cumulative Effect of New Accounting Principle in Period of Adoption	34.0
Net Income (Loss) Available to Common Stockholders, Basic	(84.3)	(28.1)
Other comprehensive income (loss)	7.7	(3.0)
TOTAL COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	(76.6)	(31.1)
Stock and Other Incentive Plans	1.9	4.0
Noncontrolling Interest [Member]
Stockholders' Equity Attributable to Noncontrolling Interest	0.2	127.1		$ 0.2	$ 133.8
Cumulative Effect of New Accounting Principle in Period of Adoption	0.0
Net Income (Loss) Attributable to Noncontrolling Interest	0.0	(1.7)
OTHER COMPREHENSIVE LOSS ATTRIBUTABLE TO THE NONCONTROLLING INTEREST	0.0	(5.0)
OTHER COMPREHENSIVE LOSS (INCOME) ATTRIBUTABLE TO THE NONCONTROLLING INTEREST	0.0	(6.7)
Stock and Other Incentive Plans	$ 0.0	0.0
Common Stock [Member]
Stock Issued During Period, Value, New Issues		661.3
Common Stock [Member] \| Cliffs Shareholders Equity [Member]
Stock Issued During Period, Value, New Issues		661.3
Common Stock [Member] \| Noncontrolling Interest [Member]
Stock Issued During Period, Value, New Issues		$ 0.0

SHAREHOLDERS' EQUITY (Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	$ (444.1)	$ (1,330.5)
Ending Balance	(484.8)	(703.0)
Changes in Pension and Other Post-Retirement Benefits, net of tax [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(263.9)	(260.6)
Other comprehensive income (loss) before reclassifications	0.5	3.3
Net loss reclassified from accumulated other comprehensive income (loss)	6.2	6.4
Ending Balance	(257.2)	(250.9)
Unrealized Net Gain (Loss) on Foreign Currency Translation [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	225.4	239.3
Other comprehensive income (loss) before reclassifications	0.7	(12.7)
Net loss reclassified from accumulated other comprehensive income (loss)	0.0	0.0
Ending Balance	226.1	226.6
Net Unrealized Gain (Loss) on Derivative Financial Instruments, net of tax [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(0.5)
Other comprehensive income (loss) before reclassifications	0.4
Net loss reclassified from accumulated other comprehensive income (loss)	(0.1)
Ending Balance	(0.2)
Accumulated Other Comprehensive Income (Loss) [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(39.0)	(21.3)
Other comprehensive income (loss) before reclassifications	1.6	(9.4)
Net loss reclassified from accumulated other comprehensive income (loss)	6.1	6.4
Ending Balance	$ (31.3)	$ (24.3)

SHAREHOLDERS' EQUITY (Details of Accumulated Other Comprehensive Income (Loss) Components) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ 0.1
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(0.1)	$ 0.0
Net loss reclassified from accumulated other comprehensive income (loss)	6.1	6.4
Realized Gain Loss On Derivatives [Member] \| Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amount of gain/(loss) recognized in income on derivative	(0.1)	0.0
Accumulated Defined Benefit Plans Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net loss reclassified from accumulated other comprehensive income (loss)	6.2	6.4
Accumulated Defined Benefit Plans Adjustment [Member] \| Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Prior service credits	(0.3)	(0.1)
Defined Benefit Plan, Amortization of Gain (Loss)	6.5	6.5
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Gain (Loss) Recognized in Net Periodic Benefit Cost, before Tax	$ 6.2	$ 6.4

SHAREHOLDERS' EQUITY (Narrative (Details)	Mar. 31, 2018	Mar. 31, 2017
Noncontrolling Interest, Ownership Percentage by Parent	100.00%
Empire [Member]
Noncontrolling Interest, Ownership Percentage by Parent	100.00%	79.00%
Tilden [Member]
Noncontrolling Interest, Ownership Percentage by Parent	100.00%	85.00%

RELATED PARTIES (Summary Of Other Ownership Interests) (Details) - Hibbing [Member]	Mar. 31, 2018	Dec. 31, 2017
Arcelor Mittal [Member]
Related Party Transaction [Line Items]
Ownership interest, equity method investment	62.30%
U. S. Steel Canada [Member]
Related Party Transaction [Line Items]
Ownership interest, equity method investment	14.70%
Other Noncurrent Assets [Member]
Related Party Transaction [Line Items]
Ownership interest, equity method investment	23.00%	23.00%

RELATED PARTIES (Summary Of Related Party Transactions Table Disclosure) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Related Party Transactions [Abstract]
Product revenues from related parties	$ 62.1	$ 118.5
Product	$ 220.7	$ 412.8
Related party product revenue as a percent of total product revenue	28.10%	28.70%

RELATED PARTIES (Summary of Balance Sheet Presentation) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Partnership distribution payable	$ 44.2	$ 44.2	$ 44.2
Related Party Transaction, Due from (to) Related Party	11.4		8.1
Trade Accounts Receivable [Member]
Related Party Transaction [Line Items]
Due from Related Parties, Current	7.9		68.1
Derivative [Member]
Related Party Transaction [Line Items]
Due from Related Parties, Current	91.3		37.9
Due to Related Parties, Current	(42.0)		(41.4)
Accounts Payable [Member]
Related Party Transaction [Line Items]
Due to Related Parties, Current	(1.2)		0.0
Other Current Liabilities [Member]
Related Party Transaction [Line Items]
Due to Related Parties, Current	$ (0.4)		$ (12.3)

RELATED PARTIES (Narrative) (Details) $ in Millions	3 Months Ended
RELATED PARTIES (Narrative) (Details) $ in Millions	Mar. 31, 2018 USD ($) Facility	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2017
Segment Reporting Information [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent	100.00%
Partnership distribution payable	$ 44.2	$ 44.2	$ 44.2
U.S. Iron Ore [Member]
Segment Reporting Information [Line Items]
Number of mines (in number of facilities) \| Facility	4
Joint Venture Partners [Member] \| U.S. Iron Ore [Member]
Segment Reporting Information [Line Items]
Number of mines (in number of facilities) \| Facility	1
Tilden [Member]
Segment Reporting Information [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent	100.00%			85.00%
Empire [Member]
Segment Reporting Information [Line Items]
Purchase of Noncontrolling Interest	$ 132.7
Noncontrolling Interest, Ownership Percentage by Parent	100.00%			79.00%
Empire [Member] \| Other Noncurrent Liabilities [Member]
Segment Reporting Information [Line Items]
Noncontrolling Interest Purchase, Installment Amount	$ 44.2

EARNINGS PER SHARE (Earnings Per Share Computation) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Loss from Continuing Operations	$ (84.8)	$ (30.3)
Net Income (Loss) Attributable to Noncontrolling Interest	0.0	(1.7)
Net Loss from Continuing Operations Attributable to Cliffs Shareholders	(84.8)	(28.6)
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX	0.5	0.5
NET LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$ (84.3)	$ (28.1)
Weighted Average Number of Shares:
Basic	297,266	265,164
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	0	0
Diluted	297,266	265,164
Loss per Common Share Attributable to Cliffs Common Shareholders - Basic:
Continuing operations (in dollars per share)	$ (0.29)	$ (0.11)
Discontinued operations (in dollars per share)	0.00	0.00
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Basic (in dollars per share)	(0.29)	(0.11)
Loss per Common Share Attributable to Cliffs Common Shareholders - Diluted:
Continuing operations (in dollars per share)	(0.29)	(0.11)
Discontinued operations (in dollars per share)	0.00	0.00
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Diluted (in dollars per share)	$ (0.29)	$ (0.11)

EARNINGS PER SHARE (Narrative) (Details) - shares shares in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	3.8	4.6

COMMITMENTS AND CONTINGENCIES (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Loss Contingency Accrual	$ 5.0
Loans to and accounts receivable from the Canadian Entities	50.4	$ 51.6	$ 51.6
Contingent claims	54.3	$ 55.6	$ 55.6
Michigan Electricity Matters [Member]
Loss Contingencies [Line Items]
Loss Contingency Accrual	$ 13.0

SUPPLEMENTARY GUARANTOR INFORMATION (Supplementary Statements of Condensed Consolidating Financial Position) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Cash and cash equivalents	$ 786.6	$ 1,007.7	$ 1,007.7	$ 295.3
Accounts receivable, net	47.2	217.2	140.6
Inventories	324.4	132.0	183.4
Supplies and other inventories	81.7	93.9	93.9
Derivative assets	93.6	51.0	39.4
Loans to and accounts receivable from the Canadian Entities	50.4	51.6	51.6
Other current assets	28.5	28.0	28.0
Assets, Current	1,412.4	1,581.4	1,544.6
PROPERTY, PLANT AND EQUIPMENT, NET	1,047.3	1,051.0	1,051.0
Deposits for property, plant and equipment	74.1	17.8	17.8
Income Taxes Receivable	219.9		235.3
Investment in subsidiaries	0.0		0.0
Long term intercompany notes	0.0		0.0
Other non-current assets	109.2	104.7	104.7
Total Other Assets	403.2	357.8	357.8
Assets	2,862.9	2,990.2	2,953.4
Accounts payable	99.5	129.1	127.7
Accrued expenses	94.4	107.1	107.1
Accrued interest	28.2	31.4	31.4
Contingent claims	54.3	55.6	55.6
Partnership distribution payable	44.2	44.2	44.2
Other current liabilities	104.3	87.6	86.2
Liabilities, Current	424.9	455.0	452.2
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES	251.4	257.7	257.7
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	181.2	196.5	196.5
LONG-TERM DEBT	2,308.2	2,304.2	2,304.2
Long term intercompany notes payable	0.0		0.0
OTHER LIABILITIES	182.0	186.9	186.9
Liabilities	3,347.7	3,400.3	3,397.5
Stockholders' Equity Attributable to Parent	(485.0)	(410.3)	(444.3)
Stockholders' Equity Attributable to Noncontrolling Interest	0.2	0.2	0.2
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(484.8)	(410.1)	(444.1)	$ (703.0)	$ (1,330.5)
Liabilities and Equity	2,862.9	$ 2,990.2	2,953.4
Consolidation, Eliminations [Member]
Cash and cash equivalents	0.0		0.0
Accounts receivable, net	(2.1)		(0.7)
Inventories	0.0		0.0
Supplies and other inventories	0.0		0.0
Derivative assets	0.0		0.0
Loans to and accounts receivable from the Canadian Entities	0.0		0.0
Other current assets	0.0		0.0
Assets, Current	(2.1)		(0.7)
PROPERTY, PLANT AND EQUIPMENT, NET	0.0		0.0
Deposits for property, plant and equipment	0.0		0.0
Income Taxes Receivable	0.0		0.0
Investment in subsidiaries	(1,213.1)		(1,054.2)
Long term intercompany notes	(242.0)		(242.0)
Other non-current assets	0.0		0.0
Total Other Assets	(1,455.1)		(1,296.2)
Assets	(1,457.2)		(1,296.9)
Accounts payable	(2.1)		(0.7)
Accrued expenses	0.0		0.0
Accrued interest	0.0		0.0
Contingent claims	0.0		0.0
Partnership distribution payable	0.0		0.0
Other current liabilities	0.0		0.0
Liabilities, Current	(2.1)		(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
Long term intercompany notes payable	(242.0)		(242.0)
OTHER LIABILITIES	0.0		0.0
Liabilities	(244.1)		(242.7)
Stockholders' Equity Attributable to Parent	(1,213.1)		(1,054.2)
Stockholders' Equity Attributable to Noncontrolling Interest	0.0		0.0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(1,213.1)		(1,054.2)
Liabilities and Equity	(1,457.2)		(1,296.9)
Reportable Legal Entities [Member] \| Non-Guarantor Subsidiaries [Member]
Cash and cash equivalents	32.0		56.7
Accounts receivable, net	15.9		33.9
Inventories	21.2		45.0
Supplies and other inventories	0.3		5.1
Derivative assets	0.0		1.5
Loans to and accounts receivable from the Canadian Entities	0.0		0.0
Other current assets	5.1		4.1
Assets, Current	74.5		146.3
PROPERTY, PLANT AND EQUIPMENT, NET	74.2		74.5
Deposits for property, plant and equipment	72.2		16.5
Income Taxes Receivable	0.0		0.0
Investment in subsidiaries	0.0		0.0
Long term intercompany notes	242.0		242.0
Other non-current assets	2.4		5.2
Total Other Assets	316.6		263.7
Assets	465.3		484.5
Accounts payable	25.2		31.6
Accrued expenses	23.3		28.2
Accrued interest	0.0		0.0
Contingent claims	0.0		0.0
Partnership distribution payable	0.0		0.0
Other current liabilities	39.2		20.6
Liabilities, Current	87.7		80.4
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES	(244.3)		(239.3)
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	38.1		55.9
LONG-TERM DEBT	0.0		0.0
Long term intercompany notes payable	0.0		0.0
OTHER LIABILITIES	21.6		24.0
Liabilities	(96.9)		(79.0)
Stockholders' Equity Attributable to Parent	562.0		563.3
Stockholders' Equity Attributable to Noncontrolling Interest	0.2		0.2
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	562.2		563.5
Liabilities and Equity	465.3		484.5
Reportable Legal Entities [Member] \| Guarantor Subsidiaries [Member]
Cash and cash equivalents	1.0		2.1
Accounts receivable, net	27.7		102.9
Inventories	303.2		138.4
Supplies and other inventories	81.4		88.8
Derivative assets	93.6		37.9
Loans to and accounts receivable from the Canadian Entities	6.9		6.9
Other current assets	7.9		7.5
Assets, Current	521.7		384.5
PROPERTY, PLANT AND EQUIPMENT, NET	956.9		959.0
Deposits for property, plant and equipment	1.9		1.3
Income Taxes Receivable	0.0		0.0
Investment in subsidiaries	27.4		29.9
Long term intercompany notes	0.0		0.0
Other non-current assets	97.9		91.7
Total Other Assets	127.2		122.9
Assets	1,605.8		1,466.4
Accounts payable	71.8		89.7
Accrued expenses	60.0		59.9
Accrued interest	0.0		0.0
Contingent claims	0.0		0.0
Partnership distribution payable	44.2		44.2
Other current liabilities	63.3		63.5
Liabilities, Current	239.3		257.3
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES	429.6		430.6
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	143.1		140.6
LONG-TERM DEBT	0.0		0.0
Long term intercompany notes payable	0.0		0.0
OTHER LIABILITIES	142.9		147.2
Liabilities	954.9		975.7
Stockholders' Equity Attributable to Parent	650.9		490.7
Stockholders' Equity Attributable to Noncontrolling Interest	0.0		0.0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	650.9		490.7
Liabilities and Equity	1,605.8		1,466.4
Reportable Legal Entities [Member] \| Cliffs Shareholders Equity [Member]
Cash and cash equivalents	753.6		948.9
Accounts receivable, net	5.7		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 receivable from the Canadian Entities	43.5		44.7
Other current assets	15.5		16.4
Assets, Current	818.3		1,014.5
PROPERTY, PLANT AND EQUIPMENT, NET	16.2		17.5
Deposits for property, plant and equipment	0.0		0.0
Income Taxes Receivable	219.9		235.3
Investment in subsidiaries	1,185.7		1,024.3
Long term intercompany notes	0.0		0.0
Other non-current assets	8.9		7.8
Total Other Assets	1,414.5		1,267.4
Assets	2,249.0		2,299.4
Accounts payable	4.6		7.1
Accrued expenses	11.1		19.0
Accrued interest	28.2		31.4
Contingent claims	54.3		55.6
Partnership distribution payable	0.0		0.0
Other current liabilities	1.8		2.1
Liabilities, Current	100.0		115.2
PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES	66.1		66.4
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	0.0		0.0
LONG-TERM DEBT	2,308.2		2,304.2
Long term intercompany notes payable	242.0		242.0
OTHER LIABILITIES	17.5		15.7
Liabilities	2,733.8		2,743.5
Stockholders' Equity Attributable to Parent	(484.8)		(444.1)
Stockholders' Equity Attributable to Noncontrolling Interest	0.0		0.0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(484.8)		(444.1)
Liabilities and Equity	$ 2,249.0		$ 2,299.4

SUPPLEMENTARY GUARANTOR INFORMATION (Supplementary Statements of Condensed Consolidating Operations and Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Product	$ 220.7	$ 412.8
Freight and venture partners' cost reimbursements	18.3	48.8
Revenues	239.0	461.6
Cost of Goods and Services Sold	(242.6)	(365.3)
Sales margin	(3.6)	96.3
Selling, General and Administrative Expense	(27.7)	(27.7)
Miscellaneous - net	(8.7)	11.5
Other operating expense	(36.4)	(16.2)
Operating Income (Loss)	(40.0)	80.1
Interest expense, net	(33.5)	(42.8)
Loss on extinguishment of debt	0.0	(71.9)
Other non-operating income	4.4	2.5
Other expense	(29.1)	(112.2)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(69.1)	(32.1)
Income Tax Expense (Benefit)	(15.7)	1.8
Equity in income (loss) of subsidiaries	0.0	0.0
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(84.8)	(30.3)
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX	0.5	0.5
Net Loss	(84.3)	(29.8)
LOSS ATTRIBUTABLE TO NONCONTROLLING INTEREST	0.0	1.7
NET LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	(84.3)	(28.1)
Other comprehensive income (loss)	7.7	(3.0)
TOTAL COMPREHENSIVE LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	(76.6)	(31.1)
Reportable Legal Entities [Member] \| Cliffs Shareholders Equity [Member]
Product	0.0	0.0
Freight and venture partners' cost reimbursements	0.0	0.0
Revenues	0.0	0.0
Cost of Goods and Services Sold	0.0	0.0
Sales margin	0.0	0.0
Selling, General and Administrative Expense	(20.1)	(19.5)
Miscellaneous - net	(0.2)	(0.1)
Other operating expense	(20.3)	(19.6)
Operating Income (Loss)	(20.3)	(19.6)
Interest expense, net	(31.9)	(41.6)
Loss on extinguishment of debt		(71.9)
Other non-operating income	(0.9)	(1.0)
Other expense	(32.8)	(114.5)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(53.1)	(134.1)
Income Tax Expense (Benefit)	(15.6)	5.2
Equity in income (loss) of subsidiaries	(15.7)	100.4
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(84.4)	(28.5)
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX	0.1	0.4
Net Loss		(28.1)
LOSS ATTRIBUTABLE TO NONCONTROLLING INTEREST		0.0
NET LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	(84.3)	(28.1)
Other comprehensive income (loss)	7.7	(3.0)
TOTAL COMPREHENSIVE LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	(76.6)	(31.1)
Reportable Legal Entities [Member] \| Guarantor Subsidiaries [Member]
Product	169.2	247.3
Freight and venture partners' cost reimbursements	10.8	38.9
Revenues	180.0	286.2
Cost of Goods and Services Sold	(118.5)	(237.2)
Sales margin	61.5	49.0
Selling, General and Administrative Expense	(4.3)	(4.4)
Miscellaneous - net	(5.3)	(5.5)
Other operating expense	(9.6)	(9.9)
Operating Income (Loss)	51.9	39.1
Interest expense, net	(0.8)	0.0
Loss on extinguishment of debt		0.0
Other non-operating income	0.5	(0.8)
Other expense	(0.3)	(0.8)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	51.6	38.3
Income Tax Expense (Benefit)	(0.1)	(0.8)
Equity in income (loss) of subsidiaries	4.5	3.2
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	56.0	40.7
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX	0.2	0.2
Net Loss		40.9
LOSS ATTRIBUTABLE TO NONCONTROLLING INTEREST		1.7
NET LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	56.2	42.6
Other comprehensive income (loss)	5.9	10.8
TOTAL COMPREHENSIVE LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	62.1	53.4
Reportable Legal Entities [Member] \| Non-Guarantor Subsidiaries [Member]
Product	51.5	165.5
Freight and venture partners' cost reimbursements	7.5	9.9
Revenues	59.0	175.4
Cost of Goods and Services Sold	(124.1)	(128.1)
Sales margin	(65.1)	47.3
Selling, General and Administrative Expense	(3.3)	(3.8)
Miscellaneous - net	(3.2)	17.1
Other operating expense	(6.5)	13.3
Operating Income (Loss)	(71.6)	60.6
Interest expense, net	(0.8)	(1.2)
Loss on extinguishment of debt		0.0
Other non-operating income	4.8	4.3
Other expense	4.0	3.1
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(67.6)	63.7
Income Tax Expense (Benefit)	0.0	(2.6)
Equity in income (loss) of subsidiaries	0.0	0.0
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(67.6)	61.1
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX	0.2	(0.1)
Net Loss		61.0
LOSS ATTRIBUTABLE TO NONCONTROLLING INTEREST		0.0
NET LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	(67.4)	61.0
Other comprehensive income (loss)	0.8	(17.8)
TOTAL COMPREHENSIVE LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	(66.6)	43.2
Consolidation, Eliminations [Member]
Product	0.0	0.0
Freight and venture partners' cost reimbursements	0.0	0.0
Revenues	0.0	0.0
Cost of Goods and Services Sold	0.0	0.0
Sales margin	0.0	0.0
Selling, General and Administrative Expense	0.0	0.0
Miscellaneous - net	0.0	0.0
Other operating expense	0.0	0.0
Operating Income (Loss)	0.0	0.0
Interest expense, net	0.0	0.0
Loss on extinguishment of debt		0.0
Other non-operating income	0.0	0.0
Other expense	0.0	0.0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	0.0	0.0
Income Tax Expense (Benefit)	0.0	0.0
Equity in income (loss) of subsidiaries	11.2	(103.6)
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	11.2	(103.6)
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX	0.0	0.0
Net Loss		(103.6)
LOSS ATTRIBUTABLE TO NONCONTROLLING INTEREST		0.0
NET LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	11.2	(103.6)
Other comprehensive income (loss)	(6.7)	7.0
TOTAL COMPREHENSIVE LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$ 4.5	$ (96.6)

SUPPLEMENTARY GUARANTOR INFORMATION (Supplementary Statements of Condensed Consolidating Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Net Cash Provided by (Used in) Operating Activities	$ (142.9)	$ (25.1)
Property, Plant and Equipment, Cash Additions	(12.4)	(25.9)
Purchase of property, plant and equipment	(59.0)	(2.0)
Intercompany investments	0.0	0.0
Other investing activities	0.0	0.5
Net Cash Provided by (Used in) Investing Activities	(71.4)	(27.4)
Net proceeds from issuance of common shares	0.0	661.3
Proceeds from issuance of debt	0.0	500.0
Debt issuance costs	(1.5)	(8.5)
Gain (Loss) on Repurchase of Debt Instrument		(1,115.5)
Distributions of partnership equity	0.0	(8.7)
Intercompany financing	0.0	0.0
Other financing activities	(5.5)	(5.6)
Net Cash Provided by (Used in) Financing Activities	(7.0)	23.0
EFFECT OF EXCHANGE RATE CHANGES ON CASH	0.2	1.4
Cash and Cash Equivalents, Period Increase (Decrease)	(221.1)	(28.1)
Cash And Cash Equivalents, At Carrying Value, Including Assets Held For Sale	786.6	295.3	$ 1,007.7	$ 323.4
Reportable Legal Entities [Member] \| Cliffs Shareholders Equity [Member]
Net Cash Provided by (Used in) Operating Activities	(54.7)	(99.5)
Property, Plant and Equipment, Cash Additions	0.0	(0.8)
Purchase of property, plant and equipment	0.0	0.0
Intercompany investments	(137.7)	(56.5)
Other investing activities		0.0
Net Cash Provided by (Used in) Investing Activities	(137.7)	(57.3)
Net proceeds from issuance of common shares		661.3
Proceeds from issuance of debt		500.0
Debt issuance costs	(1.5)	(8.5)
Gain (Loss) on Repurchase of Debt Instrument		(1,115.5)
Distributions of partnership equity		0.0
Intercompany financing	0.0	45.1
Other financing activities	(1.4)	(0.5)
Net Cash Provided by (Used in) Financing Activities	(2.9)	81.9
EFFECT OF EXCHANGE RATE CHANGES ON CASH	0.0	0.0
Cash and Cash Equivalents, Period Increase (Decrease)	(195.3)	(74.9)
Cash And Cash Equivalents, At Carrying Value, Including Assets Held For Sale	753.6	208.5	948.9	283.4
Reportable Legal Entities [Member] \| Guarantor Subsidiaries [Member]
Net Cash Provided by (Used in) Operating Activities	(62.8)	(19.7)
Property, Plant and Equipment, Cash Additions	(8.1)	(24.9)
Purchase of property, plant and equipment	(0.8)	(2.0)
Intercompany investments	(4.8)	(0.5)
Other investing activities		0.5
Net Cash Provided by (Used in) Investing Activities	(13.7)	(26.9)
Net proceeds from issuance of common shares		0.0
Proceeds from issuance of debt		0.0
Debt issuance costs	0.0	0.0
Gain (Loss) on Repurchase of Debt Instrument		0.0
Distributions of partnership equity		(8.7)
Intercompany financing	75.9	55.8
Other financing activities	(0.5)	(0.7)
Net Cash Provided by (Used in) Financing Activities	75.4	46.4
EFFECT OF EXCHANGE RATE CHANGES ON CASH	0.0	0.0
Cash and Cash Equivalents, Period Increase (Decrease)	(1.1)	(0.2)
Cash And Cash Equivalents, At Carrying Value, Including Assets Held For Sale	1.0	2.3	2.1	2.5
Reportable Legal Entities [Member] \| Non-Guarantor Subsidiaries [Member]
Net Cash Provided by (Used in) Operating Activities	(25.4)	94.1
Property, Plant and Equipment, Cash Additions	(4.3)	(0.2)
Purchase of property, plant and equipment	(58.2)	0.0
Intercompany investments	0.0	(45.0)
Other investing activities		0.0
Net Cash Provided by (Used in) Investing Activities	(62.5)	(45.2)
Net proceeds from issuance of common shares		0.0
Proceeds from issuance of debt		0.0
Debt issuance costs	0.0	0.0
Gain (Loss) on Repurchase of Debt Instrument		0.0
Distributions of partnership equity		0.0
Intercompany financing	66.6	1.1
Other financing activities	(3.6)	(4.4)
Net Cash Provided by (Used in) Financing Activities	63.0	(3.3)
EFFECT OF EXCHANGE RATE CHANGES ON CASH	0.2	1.4
Cash and Cash Equivalents, Period Increase (Decrease)	(24.7)	47.0
Cash And Cash Equivalents, At Carrying Value, Including Assets Held For Sale	32.0	84.5	56.7	37.5
Consolidation, Eliminations [Member]
Net Cash Provided by (Used in) Operating Activities	0.0	0.0
Property, Plant and Equipment, Cash Additions	0.0	0.0
Purchase of property, plant and equipment	0.0	0.0
Intercompany investments	142.5	102.0
Other investing activities		0.0
Net Cash Provided by (Used in) Investing Activities	142.5	102.0
Net proceeds from issuance of common shares		0.0
Proceeds from issuance of debt		0.0
Debt issuance costs	0.0	0.0
Gain (Loss) on Repurchase of Debt Instrument		0.0
Distributions of partnership equity		0.0
Intercompany financing	(142.5)	(102.0)
Other financing activities	0.0	0.0
Net Cash Provided by (Used in) Financing Activities	(142.5)	(102.0)
EFFECT OF EXCHANGE RATE CHANGES ON CASH	0.0	0.0
Cash and Cash Equivalents, Period Increase (Decrease)	0.0	0.0
Cash And Cash Equivalents, At Carrying Value, Including Assets Held For Sale	$ 0.0	$ 0.0	$ 0.0	$ 0.0

SUPPLEMENTARY GUARANTOR INFORMATION (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Noncontrolling Interest, Ownership Percentage by Parent	100.00%
$1,075 Million 5.75% 2025 Senior Notes [Member]
Debt Instrument, Par Value	$ 1,075.0	$ 1,075.0
Debt Instrument, Interest Rate, Stated Percentage	5.75%