Cleveland-Cliffs (CLF) 10-K 8 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 05, 2019	Jun. 30, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	CLEVELAND-CLIFFS INC.
Entity Central Index Key	764,065
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		292,607,474
Trading Symbol	clf
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Public Float			$ 2,487,099,883

Statements Of Condensed Consoli

Statements Of Condensed Consolidated Financial Position - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
CURRENT ASSETS
Cash and cash equivalents	$ 823.2	$ 978.3
Accounts receivable, net	226.7	106.7
Inventories	87.9	138.4
Supplies and other inventories	93.2	88.8
Derivative assets	91.5	37.9
Income tax receivable, current	117.3	13.3
Loans to and accounts receivables from the Canadian Entities	0	51.6
Current assets of discontinued operations	12.4	118.5
Other current assets	27.4	11.1
TOTAL CURRENT ASSETS	1,479.6	1,544.6
PROPERTY, PLANT AND EQUIPMENT, NET	1,286	1,033.8
OTHER ASSETS
Deposits for property, plant and equipment	83	17.8
Income tax receivable, non-current	121.3	235.3
Deferred income taxes	464.8	0
Non-current assets of discontinued operations	0	20.3
Other non-current assets	94.9	101.6
TOTAL ASSETS	3,529.6	2,953.4
CURRENT LIABILITIES
Accounts payable	186.8	99.5
Accrued employment costs	74	52.7
State and local taxes payable	35.5	30.2
Accrued interest	38.4	31.4
Contingent claims	0	55.6
Partnership distribution payable	43.5	44.2
Current liabilities of discontinued operations	6.7	75
Other current liabilities	83.3	63.6
TOTAL CURRENT LIABILITIES	468.2	452.2
POSTEMPLOYMENT BENEFIT LIABILITIES
Pensions	218.4	222.8
Other postretirement benefits	30.3	34.9
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES	248.7	257.7
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	172	167.7
LONG-TERM DEBT	2,092.9	2,304.2
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS	8.3	52.2
OTHER LIABILITIES	115.3	163.5
TOTAL LIABILITIES	3,105.4	3,397.5
COMMITMENTS AND CONTINGENCIES (SEE NOTE 19)
CLIFFS SHAREHOLDERS' EQUITY (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 - 292,611,569 shares (2017 - 297,400,968) shares)	37.7	37.7
Capital in excess of par value of shares	3,916.7	3,933.9
Retained deficit	(3,060.2)	(4,207.3)
Cost of 9,275,225 common shares in treasury (2017 - 4,485,826 shares)	(186.1)	(169.6)
Accumulated other comprehensive loss	(283.9)	(39)
TOTAL CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)	424.2	(444.3)
NONCONTROLLING INTEREST	0	0.2
TOTAL EQUITY (DEFICIT)	424.2	(444.1)
TOTAL LIABILITIES AND EQUITY (DEFICIT)	$ 3,529.6	$ 2,953.4

Statements Of Condensed Conso_2

Statements Of Condensed Consolidated Financial Position (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Preferred stock, par value	$ 0	$ 0
Common shares, par value	$ 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 (in shares)	292,611,569	297,400,968
Common shares in treasury	9,275,225	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 stock, issued and outstanding (in shares)	0	0
Preferred Class B [Member]
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)	4,000,000	4,000,000

Statements Of Condensed Conso_3

Statements Of Condensed Consolidated Operations - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
REVENUES FROM PRODUCT SALES AND SERVICES
Product revenues	$ 2,172.3	$ 1,644.6	$ 1,379.7
Freight and Reimbursement Revenue	160.1	221.4	174.8
TOTAL REVENUES FROM PRODUCT SALES AND SERVICES	2,332.4	1,866	1,554.5
COST OF GOODS SOLD AND OPERATING EXPENSES	(1,522.8)	(1,398.4)	(1,274.4)
SALES MARGIN	809.6	467.6	280.1
OTHER OPERATING INCOME (EXPENSE)
Selling, general and administrative expenses	(116.8)	(102.9)	(115.8)
Miscellaneous - net	(19.6)	25.5	(33.6)
Other operating expense	(136.4)	(77.4)	(149.4)
OPERATING INCOME	673.2	390.2	130.7
OTHER INCOME (EXPENSE)
Interest expense, net	(118.9)	(126.8)	(193.9)
Gain (loss) on extinguishment/restructuring of debt	(6.8)	(165.4)	166.3
Other non-operating income	17.2	10.2	7.3
TOTAL OTHER INCOME (EXPENSE)	(108.5)	(282)	(20.3)
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	564.7	108.2	110.4
INCOME TAX BENEFIT	475.2	252.4	12.2
INCOME FROM CONTINUING OPERATIONS	1,039.9	360.6	122.6
INCOME FROM DISCONTINUED OPERATIONS, net of tax	88.2	2.5	76.7
NET INCOME	1,128.1	363.1	199.3
LOSS (INCOME) ATTRIBUTABLE TO NONCONTROLLING INTEREST	0	3.9	(25.2)
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$ 1,128.1	$ 367	$ 174.1
EARNINGS PER COMMON SHARE ATTRIBUTABLE TO CLIFFS SHAREHOLDERS - BASIC
Continuing operations	$ 3.50	$ 1.27	$ 0.49
Discontinued operations	0.30	0.01	0.39
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Basic:	3.80	1.28	0.88
EARNINGS PER COMMON SHARE ATTRIBUTABLE TO CLIFFS SHAREHOLDERS - DILUTED
Continuing operations	3.42	1.25	0.49
Discontinued operations	0.29	0.01	0.38
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Diluted:	$ 3.71	$ 1.26	$ 0.87
AVERAGE NUMBER OF SHARES (IN THOUSANDS)
Basic	297.2	288.4	197.7
Diluted	304.1	293	200.1

Statements Of Condensed Conso_4

Statements Of Condensed Consolidated Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$ 1,128.1	$ 367	$ 174.1
OTHER COMPREHENSIVE INCOME (LOSS)
Changes in pension and other post-retirement benefits, net of tax	(17.2)	11.5	(19.8)
Changes in foreign currency translation	(225.4)	(13.9)	18.6
Changes in derivative financial instruments, net of tax	(2.3)	(0.5)	(2.6)
OTHER COMPREHENSIVE LOSS	(244.9)	(2.9)	(3.8)
OTHER COMPREHENSIVE LOSS (INCOME) ATTRIBUTABLE TO THE NONCONTROLLING INTEREST	0	(1.1)	0.5
TOTAL COMPREHENSIVE INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$ 883.2	$ 363	$ 170.8

Statements Of Condensed Conso_5

Statements Of Condensed Consolidated Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
OPERATING ACTIVITIES
Net income	$ 1,128.1	$ 363.1	$ 199.3
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	89	87.7	115.4
Deferred income taxes	(460.5)	0	0
Loss (gain) on extinguishment of debt	6.8	165.4	(166.3)
Loss on deconsolidation	0	20.2	17.5
Gain on derivatives	(110.2)	(4.1)	(30.1)
Gain on foreign currency translation	(228.1)	0	0
Other	20.7	25.3	40.1
Changes in operating assets and liabilities:
Receivables and other assets	52.3	(248.7)	43.2
Inventories	42.9	(1.8)	157.8
Payables, accrued expenses and other liabilities	(62.5)	(69)	(73.9)
Net cash provided by operating activities	478.5	338.1	303
INVESTING ACTIVITIES
Purchase of property, plant and equipment	(208.6)	(134.9)	(61.7)
Deposits for property, plant and equipment	(87.5)	(16.8)	(7.4)
Other investing activities	23	(4.3)	11.2
Net cash used by investing activities	(273.1)	(156)	(57.9)
FINANCING ACTIVITIES
Net proceeds from issuance of common shares	0	661.3	287.4
Repurchase of common shares	(47.5)	0	0
Proceeds from issuance of debt	0	1,771.5	0
Debt issuance costs	(1.5)	(28.6)	(5.2)
Borrowings under credit facilities	0	0	105
Repayment under credit facilities	0	0	(105)
Repayments on equipment loans	0	0	(95.6)
Repurchase of debt	(234.5)	(1,720.7)	(305.4)
Acquisition of noncontrolling interest	0	(105)	0
Distributions of partnership equity	(44.2)	(52.9)	(59.9)
Other financing activities	(47.5)	(26.7)	(27.7)
Net cash provided (used) by financing activities	(375.2)	498.9	(206.4)
EFFECT OF EXCHANGE RATE CHANGES ON CASH	(2.3)	3.3	(0.5)
Increase (Decrease) in Cash and Cash Equivalents, Including Cash Classified Within Current Assets of Discontinued Operations	(172.1)	684.3	38.2
LESS: INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS	(17)	18.8	(35.3)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(155.1)	665.5	73.5
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	978.3	312.8	239.3
CASH AND CASH EQUIVALENTS AT END OF YEAR	$ 823.2	$ 978.3	$ 312.8

Statements of Consolidated Chan

Statements of Consolidated Changes in Equity - USD ($) $ in Millions	Total	Depositary Shares [Member]	Common Stock [Member]	Capital in Excess of Par Value of Shares [Member]	Retained Earnings [Member]	Common Shares in Treasury [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interest [Member]
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract]
Preferred Stock, Shares Outstanding		29,300,000
Balance, beginning of period (in shares) at Dec. 31, 2015			153,500,000
Balance, beginning of period at Dec. 31, 2015	$ (1,811.6)	$ 731.3	$ 19.8	$ 2,298.9	$ (4,748.4)	$ (265)	$ (18)	$ 169.8
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract]
NET INCOME	199.3				174.1			25.2
Other Comprehensive Loss	(3.3)						(3.3)
OTHER COMPREHENSIVE INCOME	(3.8)
Pension and OPEB liability, net of tax	(19.8)							(0.5)
Total comprehensive income (loss)	195.5							24.7
Distributions to noncontrolling interest	(3.2)							(3.2)
Distributions of partnership equity	(57.5)							(57.5)
Stock and other incentive plans (in shares)			500,000
Stock and other incentive plans	13.7			(5.8)		19.5
Repurchase of common shares	0
Shares issued for debt exchange			8,200,000
Debt for equity exchange (value)	45.2		$ 1	44.2
Stock Issued During Period, Value, Conversion of Convertible Securities		$ (731.3)	$ 3.5	727.8
Stock Issued During Period, Shares, Conversion of Units		(29,300,000)	26,500,000
Common stock issuance (value)	287.4		$ 5.5	281.9
Balance, end of period (in shares) at Dec. 31, 2016			233,100,000
Balance, end of period at Dec. 31, 2016	(1,330.5)	$ 0	$ 29.8	3,347	(4,574.3)	(245.5)	(21.3)	133.8
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract]
Preferred Stock, Shares Outstanding		0
NET INCOME	363.1				367			(3.9)
Other Comprehensive Loss	(4)						(4)
OTHER COMPREHENSIVE INCOME	(2.9)
Pension and OPEB liability, net of tax	11.5							1.1
Total comprehensive income (loss)	360.2							(2.8)
Adjustments to Additional Paid in Capital, Convertible Debt with Conversion Feature	83.4			83.4
Distributions of partnership equity	(128.8)			(17.3)			5.2	(116.7)
Capital contributions by noncontrolling interest to subsidiary	1.8							1.8
Stock and other incentive plans (in shares)			1,000,000
Stock and other incentive plans	13.5			(62.4)		75.9
Repurchase of common shares	0
Common stock issuance (value)	661.3		$ 7.9	653.4
Acquisition of Noncontrolling Interest	$ (105)			(70.2)			(18.9)	(15.9)
Balance, end of period (in shares) at Dec. 31, 2017	297,400,968		297,400,000
Balance, end of period at Dec. 31, 2017	$ (444.1)	$ 0	$ 37.7	3,933.9	(4,207.3)	(169.6)	(39)	0.2
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract]
Preferred Stock, Shares Outstanding		0
NET INCOME	1,128.1				1,128.1
Other Comprehensive Loss	(244.9)						(244.9)
OTHER COMPREHENSIVE INCOME	(244.9)
Pension and OPEB liability, net of tax	(17.2)
Total comprehensive income (loss)	883.2
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	34				34
Distributions to noncontrolling interest	(0.2)							(0.2)
Stock and other incentive plans (in shares)			600,000
Stock and other incentive plans	$ 13.8			(17.2)		31
Stock Repurchased During Period, Shares	5,400,000		(5,400,000)
Repurchase of common shares	$ (47.5)					(47.5)
Common stock dividends ($0.05 per share)	$ (15)				(15)
Balance, end of period (in shares) at Dec. 31, 2018	292,611,569		292,600,000
Balance, end of period at Dec. 31, 2018	$ 424.2	$ 0	$ 37.7	$ 3,916.7	$ (3,060.2)	$ (186.1)	$ (283.9)	$ 0
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract]
Preferred Stock, Shares Outstanding		0

Statements of Consolidated Ch_2

Statements of Consolidated Changes in Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Stockholders' Equity [Abstract]
Common Stock, Dividends, Per Share, Declared	$ 0.05	$ 0	$ 0

BASIS OF PRESENTATION AND SIGNI

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
BUSINESS SUMMARY AND SIGNIFICANT ACCOUNTING POLICIES	NOTE 1 - BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES Nature of Business Founded in 1847, Cleveland-Cliffs Inc. is the largest and oldest independent iron ore mining company in the United States. We are a major supplier of iron ore pellets to the North American steel industry from our mines and pellet plants located in Michigan and Minnesota. We are currently constructing an HBI production plant in Toledo, Ohio. We expect to complete construction and begin production in 2020. In January 2018, we announced that we would accelerate the time frame for the planned closure of our Asia Pacific Iron Ore mining operations in Australia. In April 2018, we committed to a course of action leading to the permanent closure of our Asia Pacific Iron Ore mining operations and, as planned, completed our final shipment in June 2018. Factors considered in this decision included increasingly discounted prices for lower-iron-content ore and the quality of the remaining iron ore reserves. During 2018, we sold all of the assets of our Asia Pacific Iron Ore business through a series of sales to third parties. As a result of our planned exit, management determined that our Asia Pacific Iron Ore operating segment met the criteria to be classified as held for sale and a discontinued operation under ASC Topic 205, Presentation of Financial Statements . As such, all current and historical Asia Pacific Iron Ore operating segment results are classified within discontinued operations. Refer to NOTE 13 - DISCONTINUED OPERATIONS for further information. In alignment with our strategic goals, we have become a North America-centric business and have updated the names of our operating segments. We are now organized according to our differentiated products. We have two reportable segments – the Mining and Pelletizing segment (formerly known as U.S. Iron Ore) and the Metallics segment. Unless otherwise noted, discussion of our business and results of operations in this Annual Report on Form 10-K refers to our continuing operations. Significant Accounting Policies We consider the following policies to be beneficial in understanding the judgments involved in the preparation of our consolidated financial statements and the uncertainties that could impact our financial condition, results of operations and cash flows. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. The more significant areas requiring the use of management estimates and assumptions relate to mineral reserves future realizable cash flow; environmental, reclamation and closure obligations; valuation of long-lived assets, inventory, tax assets and post-employment, post-retirement and other employee benefit liabilities; reserves for contingencies and litigation; and the fair value of derivative instruments. Actual results could differ from estimates. Management reviews its estimates on an ongoing basis. Changes in facts and circumstances may alter such estimates and affect the results of operations and financial position in future periods. Basis of Consolidation The consolidated financial statements include our accounts and the accounts of our wholly owned subsidiaries, including the following iron ore operations at December 31, 2018 : Name Location Status of Operations Northshore Minnesota Active United Taconite Minnesota Active Tilden Michigan Active Empire Michigan Indefinitely Idled Intercompany transactions and balances are eliminated upon consolidation. Equity Method Investments Investments in unconsolidated ventures that we have the ability to exercise significant influence over, but not control, are accounted for under the equity method. Our 23% ownership interest in Hibbing is recorded as an equity method investment. As of December 31, 2018 and 2017 , our investment in Hibbing was $15.4 million and $11.0 million , respectively, classified in Other liabilities in the Statements of Consolidated Financial Position . Our share of equity income (loss) is eliminated against consolidated product inventory upon production, and against Cost of goods sold and operating expenses when sold. This effectively reduces our cost for our share of the mining ventures' production cost, reflecting the cost-based nature of our participation in unconsolidated ventures. Noncontrolling Interests 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 parties agreed that the net assets were to be distributed in three installments of $44.2 million each, the first of which was paid upon the execution of the agreement, the second of which was paid in August 2018 and the final of which is due August 2019. Upon payment of the first installment, we assumed ArcelorMittal's 21% interest and reflected the ownership percentage change in our consolidated financial statements. During the year ended December 31, 2017 , we accounted for the increase in ownership as an equity transaction, which resulted in a net $12.1 million decrease in equity attributable to Cliffs' shareholders and a $116.7 million decrease in Noncontrolling interest . The net loss and income attributable to the noncontrolling interest of the Empire mining venture was $3.9 million and $25.2 million for the years ended December 31, 2017 and 2016 , respectively. During 2017, we also acquired the remaining 15% equity interest in Tilden owned by U.S. Steel for $105.0 million . With the closing of this transaction, we now have 100% ownership of the mine. During the year ended December 31, 2017 , we accounted for the increase in ownership as an equity transaction, which resulted in an $89.1 million decrease in equity attributable to Cliffs' shareholders and a $15.9 million decrease in Noncontrolling interest . Cash and Cash Equivalents Cash and cash equivalents include cash on hand and on deposit as well as all short-term securities held for the primary purpose of general liquidity. We consider investments in highly liquid debt instruments with an original maturity of three months or less from the date of acquisition and longer maturities when funds can be withdrawn in three months or less without a significant penalty to be cash equivalents. We routinely monitor and evaluate counterparty credit risk related to the financial institutions in which our short-term investment securities are held. Trade Accounts Receivable and Allowance for Doubtful Accounts Trade accounts receivable are recorded at the point control transfers and represents the amount of consideration we expect to receive in exchange for transferred goods and do not bear interest. The allowance for doubtful accounts is our best estimate of the amount of probable credit losses in our existing accounts receivable. We establish provisions for losses on accounts receivable when it is probable that all or part of the outstanding balance will not be collected. We regularly review our accounts receivable balances and establish or adjust the allowance as necessary using the specific identification method. There was no allowance for doubtful accounts at December 31, 2018 and 2017 and no bad debt expense for the years ended December 31, 2018 , 2017 and 2016 . Inventories The Mining and Pelletizing segment product inventories are stated at the lower of cost or market. Cost of iron ore inventories is determined using the LIFO method. Supplies and Other Inventories Supply inventories include replacement parts, fuel, chemicals and other general supplies, which are expected to be used or consumed in normal operations. Supply inventories also include critical spares. Critical spares are replacement parts for equipment that is critical for the continued operation of the mine or processing facilities. Supply inventories are stated at the lower of cost or net realizable value using average cost, less an allowance for obsolete and surplus items. The allowance for obsolete and surplus items was $12.6 million at December 31, 2018 and 2017 . Derivative Financial Instruments and Hedging Activities We are exposed to certain risks related to the ongoing operations of our business, including those caused by changes in commodity prices and energy rates. We have established policies and procedures, including the use of certain derivative instruments, to manage such risks, if deemed necessary. Derivative financial instruments are recognized as either assets or liabilities in the Statements of Consolidated Financial Position and measured at fair value. On the date a qualifying hedging instrument is executed, we designate the hedging instrument as a hedge of the variability of cash flows to be received or paid related to a forecasted transaction (cash flow hedge). We formally document all relationships between hedging instruments and hedged items, as well as our risk-management objective and strategy for undertaking various hedge transactions. This process includes linking all derivatives that are designated as cash flow hedges to specific firm commitments or forecasted transactions. We also formally assess, both at the hedge's inception and on an ongoing basis, whether the derivatives that are used in hedging transactions are highly effective in offsetting changes in cash flows of the related hedged items. When it is determined that a derivative is not highly effective as a hedge or that it has ceased to be a highly effective hedge, we discontinue hedge accounting prospectively and record all future changes in fair value in the period of the instrument's earnings or losses. For derivative instruments that have been designated as cash flow hedges, the changes in fair value are recorded in Accumulated other comprehensive loss . Amounts recorded in Accumulated other comprehensive loss are reclassified to earnings or losses in the period the underlying hedged transaction affects earnings or when the underlying hedged transaction is no longer reasonably possible of occurring. For derivative instruments that have not been designated as cash flow hedges, such as provisional pricing arrangements and supplemental revenue or refunds contained within a customer supply agreement, changes in fair value are recorded in the period of the instrument's earnings or losses. Refer to Revenue Recognition below for discussion of derivatives recorded as a result of pricing terms in our sales contracts. Additionally, refer to NOTE 12 - DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES for further information. Property, Plant and Equipment Our properties are stated at the lower of cost less accumulated depreciation or fair value. Depreciation of plant and equipment is computed principally by the straight-line method based on estimated useful lives, not to exceed the mine lives. Depreciation continues to be recognized when operations are idled temporarily. We use the double-declining balance method of depreciation for certain mining equipment. Depreciation and depletion is provided over the following estimated useful lives: Asset Class Basis Life Office and information technology Straight line 3 to 15 years Buildings Straight line 45 years Mining equipment Straight line/Double declining balance 3 to 20 years Processing equipment Straight line 10 to 45 years Electric power facilities Straight line 10 to 45 years Land improvements Straight line 20 to 45 years Asset retirement obligation Straight line Life of mine Mineral rights Units of production Life of mine Refer to NOTE 5 - PROPERTY, PLANT AND EQUIPMENT for further information. Capitalized Stripping Costs During the development phase, stripping costs are capitalized as a part of the depreciable cost of building, developing and constructing a mine. These capitalized costs are amortized over the productive life of the mine using the units of production method. The production phase does not commence until the removal of more than a de minimis amount of saleable mineral material occurs in conjunction with the removal of overburden or waste material for purposes of obtaining access to an ore body. The stripping costs incurred in the production phase of a mine are variable production costs included in the costs of the inventory produced (extracted) during the period that the stripping costs are incurred. Stripping costs related to expansion of a mining asset of proven and probable reserves are variable production costs that are included in the costs of the inventory produced during the period that the stripping costs are incurred. Other Intangible Assets Our mine permits are subject to periodic amortization on a straight line basis over their estimated useful life, which corresponds with the life of mine. Asset Impairment We monitor conditions that may affect the carrying value of our long-lived tangible and intangible assets when events and circumstances indicate that the carrying value of the asset groups may not be recoverable. In order to determine if assets have been impaired, assets are grouped and tested at the lowest level for which identifiable, independent cash flows are available ("asset group"). An impairment loss exists when projected net undiscounted cash flows are less than the carrying value of the asset group. The measurement of the impairment loss to be recognized is based on the difference between the fair value and the carrying value of the asset group. Fair value can be determined using a market approach, income approach or cost approach. For the years ended December 31, 2018 , 2017 and 2016 , no impairment factors were present that would indicate the carrying value of any of our asset groups may not be recoverable; as a result, no impairment assessments were required. Fair Value Measurements ASC Topic 820, Fair Value Measurements and Disclosures , establishes a three-level valuation hierarchy for classification of fair value measurements. The valuation hierarchy is based upon the transparency of inputs to the valuation of an asset or liability as of the measurement date. Inputs refer broadly to the assumptions that market participants would use in pricing an asset or liability. Inputs may be observable or unobservable. Observable inputs are inputs that reflect the assumptions market participants would use in pricing the asset or liability developed based on market data obtained from independent sources. Unobservable inputs are inputs that reflect our own views about the assumptions market participants would use in pricing the asset or liability developed based on the best information available in the circumstances. The three-tier hierarchy of inputs is summarized below: • Level 1 — Valuation is based upon quoted prices (unadjusted) for identical assets or liabilities in active markets. • Level 2 — Valuation is based upon quoted prices for similar assets and liabilities in active markets, or other inputs that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the financial instrument. • Level 3 — Valuation is based upon other unobservable inputs that are significant to the fair value measurement. The classification of assets and liabilities within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement in its entirety. Refer to NOTE 7 - FAIR VALUE OF FINANCIAL INSTRUMENTS and NOTE 8 - PENSIONS AND OTHER POSTRETIREMENT BENEFITS for further information. Pensions and Other Postretirement Benefits We offer defined benefit pension plans, defined contribution pension plans and other postretirement benefit plans, primarily consisting of retiree healthcare benefits, to most employees in the United States as part of a total compensation and benefits program. We recognize the funded or unfunded status of our postretirement benefit obligations on our December 31, 2018 and 2017 Statements of Consolidated Financial Position based on the difference between the market value of plan assets and the actuarial present value of our retirement obligations on that date, on a plan-by-plan basis. If the plan assets exceed the postretirement benefit obligations, the amount of the surplus is recorded as an asset; if the postretirement benefit obligations exceed the plan assets, the amount of the underfunded obligations is recorded as a liability. Year-end balance sheet adjustments to postretirement assets and obligations are recorded as Accumulated other comprehensive loss in the Statements of Consolidated Financial Position . The actuarial estimates of the PBO and APBO incorporate various assumptions including the discount rates, the rates of increases in compensation, healthcare cost trend rates, mortality, retirement timing and employee turnover. The discount rate is determined based on the prevailing year-end rates for high-grade corporate bonds with a duration matching the expected cash flow timing of the benefit payments from the various plans. The remaining assumptions are based on our estimates of future events by incorporating historical trends and future expectations. The amount of net periodic cost that is recorded in the Statements of Consolidated Operations consists of several components including service cost, interest cost, expected return on plan assets, and amortization of previously unrecognized amounts. Service cost represents the value of the benefits earned in the current year by the participants. Interest cost represents the cost associated with the passage of time. Certain items, such as plan amendments, gains and/or losses resulting from differences between actual and assumed results for demographic and economic factors affecting the obligations and assets of the plans, and changes in other assumptions are subject to deferred recognition for income and expense purposes. The expected return on plan assets is determined utilizing the weighted average of expected returns for plan asset investments in various asset categories based on historical performance, adjusted for current trends. 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/credits, net actuarial gain/loss, and other costs are classified within Other non-operating income . Refer to NOTE 2 - NEW ACCOUNTING STANDARDS and NOTE 8 - PENSIONS AND OTHER POSTRETIREMENT BENEFITS for further information. Asset Retirement Obligations Asset retirement obligations are recognized when incurred and recorded as liabilities at fair value. The fair value of the liability is determined as the discounted value of the expected future cash flows. The asset retirement obligation is accreted over time through periodic charges to earnings. In addition, the asset retirement cost is capitalized and amortized over the life of the related asset. Reclamation costs are adjusted periodically to reflect changes in the estimated present value resulting from the passage of time and revisions to the estimates of either the timing or amount of the reclamation costs. We review, on an annual basis, unless otherwise deemed necessary, the asset retirement obligation at each mine site in accordance with the provisions of ASC Topic 410, Asset Retirement and Environmental Obligations . We perform an in-depth evaluation of the liability every three years in addition to our routine annual assessments. Future reclamation costs for inactive mines are accrued based on management’s best estimate at the end of each period of the costs expected to be incurred at a site. Such cost estimates include, where applicable, ongoing maintenance and monitoring costs. Changes in estimates at inactive mines are reflected in earnings in the period an estimate is revised. See NOTE 11 - ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS for further information. Environmental Remediation Costs We have a formal policy for environmental protection and restoration. Our mining and exploration activities are subject to various laws and regulations governing protection of the environment. We conduct our operations to protect the public health and environment and believe our operations are in compliance with applicable laws and regulations in all material respects. Our environmental liabilities, including obligations for known environmental remediation exposures at active and closed mining operations and other sites, have been recognized based on the estimated cost of investigation and remediation at each site. If the cost can only be estimated as a range of possible amounts with no point in the range being more likely, the minimum of the range is accrued. Future expenditures are not discounted unless the amount and timing of the cash disbursements reasonably can be estimated. It is possible that additional environmental obligations could be incurred, the extent of which cannot be assessed. Potential insurance recoveries have not been reflected in the determination of the liabilities. See NOTE 11 - ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS for further information. Revenue Recognition - Pre-Adoption of Topic 606 Prior to the adoption of Topic 606, revenue was recognized from a sale when persuasive evidence of an arrangement existed, the price was fixed or determinable, the product was delivered in accordance with shipping terms, title and risk of loss were transferred to the customer in accordance with the specified provisions of each supply agreement and collection of the sales price reasonably was assured. Our supply agreements provide that title and risk of loss transfer to the customer either upon loading of the vessel, shipment or when payment is received. Under certain supply agreements, we ship the product to ports on the lower Great Lakes or to the customers’ facilities prior to the transfer of title. Our rationale for shipping iron ore products to certain customers and retaining title until payment is received for these products is to minimize credit risk exposure. Sales were recorded at a sales price specified in the relevant supply agreements resulting in revenue and a receivable at the time of sale. The majority of our contracts have pricing mechanisms that require price estimation at the time of delivery with price finalization at a future period. Upon revenue recognition for provisionally priced sales, a derivative was created for the difference between the sales price used and expected future settlement price. The derivative was adjusted to fair value through Product revenues as a revenue adjustment each reporting period based upon current market data and forward-looking estimates determined by management until the final sales price was determined. The principal risks associated with recognition of sales on a provisional basis include Platts 62% Price, Atlantic Basin pellet premium and index freight fluctuations between the date initially recorded and the date of final settlement. For revenue recognition, we estimated the future settlement rate; however, if significant changes in inputs occurred between the provisional pricing date and the final settlement date, we were required to either return a portion of the sales proceeds received or bill for the additional sales proceeds due based on the provisional sales price. Revenue Recognition - Post-Adoption of Topic 606 We sell a single product, iron ore pellets, in the North American market. With the adoption of Topic 606 as of January 1, 2018, revenue is recognized generally when iron ore is delivered to our customers. Revenue is measured at the point that 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. Refer to NOTE 2 - NEW ACCOUNTING STANDARDS for further information. We enter into supply contracts of varying lengths to provide customers iron ore pellets 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. Most of our 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, Atlantic Basin 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 Topic 815. Refer to NOTE 12 - DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES for further information on how our estimated and final revenue rates are determined. A supply agreement with a customer provides for supplemental revenue or refunds based on the average annual daily market price for hot-rolled coil steel in the year 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 Topic 815. Refer to NOTE 12 - DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES for further information on supplemental revenue or refunds. Included within Revenues from product sales and services is derivative revenue related to Topic 815 of $422.6 million , $120.6 million and $55.9 million for the years ended December 31, 2018 , 2017 and 2016, respectively. As of December 31, 2018 , under the new accounting standard, we had finished goods of 0.8 million long tons in transit or stored at the Port of Toledo to service customers, for which revenue had yet to be recognized. Under the previous accounting standard, we did not recognize revenue and related cost of goods sold until title transferred to the customer, usually when payment was received. As of December 31, 2017, under the previous accounting standard, we had finished goods of 1.5 million long tons stored at ports and customer facilities on the lower Great Lakes to service customers, for which revenue had yet to be recognized. Practical expedients and exemptions We have elected to treat all shipping and handling costs as fulfillment costs because 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: (In Millions) Deferred Revenue (Current) 1 Deferred Revenue (Long-Term) Year Ended Year Ended 2018 2017 2018 2017 Opening balance as of January 1 $ 23.8 $ 16.2 $ 51.4 $ 64.3 Closing balance as of December 31 21.0 22.4 38.5 51.4 Increase (Decrease) $ (2.8 ) $ 6.2 $ (12.9 ) $ (12.9 ) 1 The opening balance for the year ended December 31, 2018 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 pellet supply agreements required supplemental payments to be paid by the customer during the period 2009 through 2012. Installment amounts received under this arrangement in excess of sales were classified as Other current liabilities and Other liabilities in the Statements of 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 December 31, 2018 and December 31, 2017 , installment amounts received in excess of sales totaled $51.3 million and $64.2 million , respectively, related to this agreement. As of December 31, 2018 , and December 31, 2017 , deferred revenue of $12.8 million was recorded in Other current liabilities and $38.5 million and $51.4 million , respectively, was recorded as long-term in Other liabilities in the Statements of 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 deliveries for certain customers. Revenue recognized on these transactions totaling $8.2 million and $9.6 million was deferred and included in Other current liabilities in the Statements of Consolidated Financial Position as of December 31, 2018 and December 31, 2017 , respectively. Cost of Goods Sold Cost of goods sold and operating expenses represents all direct and indirect costs and expenses applicable to the sales from our mining operations. In some circumstances, as requested by the customer, we will coordinate and ship our product via vessel directly to the port nearest to the customer's blast furnace. In this type of contract, the customer will pay one amount inclusive of both product and freight. We recognize revenue for both product revenue and the amount reimbursed for the vessel freight to the final port. We separate these revenue types in the Statements of Consolidated Operations . Accordingly, the revenue we record for freight is offset by an equal amount included in Cost of goods sold and operating expenses for costs we incur for that freight, resulting in no impact on sales margin. Operating expenses represented the portion of the Tilden mining venture costs prior to our 100% ownership; that is, the costs attributable to the share of the mine’s production owned by the other joint venture partner in the Tilden mine until we acquired the remaining 15% noncontrolling interest during 2017. The mining venture functioned as a captive cost company, supplying product only to its owners effectively for the cost of production. Accordingly, the noncontrolling interests’ revenue amounts were stated at cost of production and were offset by an equal amount included in Cost of goods sold and operating expenses resulting in no sales margin reflected for the noncontrolling partner participant. As we were responsible for product fulfillment under the venture, we acted as a principal in the transaction and, accordingly, recorded revenue under these arrangements on a gross basis. The following table is a summary of reimbursements in our operations: (In Millions) Year Ended December 31, 2018 2017 2016 Reimbursements for: Freight $ 160.1 $ 166.7 $ 106.8 Venture partners’ cost — 54.7 68.0 Total reimbursements $ 160.1 $ 221.4 $ 174.8 Where we have joint ownership of a mine, such as Hibbing and up to the point at which we purchased the remaining interest in Tilden, our contracts entitle us to receive management fees or royalties, which we earn as the pellets are produced. Repairs and Maintenance Repairs, maintenance and replacement of components are expensed as incurred. The cost of major equipment overhauls is capitalized and depreciated over the estimated useful life, which is the period until the next scheduled overhaul, generally five years. All other planned and unplanned repairs and maintenance costs are expensed when incurred. Share-Based Compensation 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 its predetermined peer group of mining and metals companies. The fair value assumes that objective will be achieved. The expected te

NEW ACCOUNTING STANDARDS

NEW ACCOUNTING STANDARDS	12 Months Ended
	Dec. 31, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
NEW ACCOUNTING STANDARDS	NOTE 2 - NEW ACCOUNTING STANDARDS Issued and Adopted 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 of $34.0 million to the opening balance of Retained deficit . The comparative period information has not been retrospectively revised and continues to be reported under the accounting standards in effect for those periods. On a prospective basis, we do not expect that the adoption of Topic 606 will have a material impact to our annual net income. Under Topic 606, revenue is generally recognized upon delivery to our 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 in many cases, 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 that 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 2018 and 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 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 $ 978.3 $ — $ 978.3 Accounts receivable, net 106.7 76.6 183.3 Inventories 138.4 (51.4 ) 87.0 Supplies and other inventories 88.8 — 88.8 Derivative assets 37.9 11.6 49.5 Income tax receivable, current 13.3 — 13.3 Loans to and accounts receivables from the Canadian Entities 51.6 — 51.6 Current assets of discontinued operations 118.5 — 118.5 Other current assets 11.1 — 11.1 TOTAL CURRENT ASSETS 1,544.6 36.8 1,581.4 PROPERTY, PLANT AND EQUIPMENT, NET 1,033.8 — 1,033.8 OTHER ASSETS Deposits for property, plant and equipment 17.8 — 17.8 Income tax receivable, non-current 235.3 — 235.3 Non-current assets of discontinued operations 20.3 — 20.3 Other non-current assets 101.6 — 101.6 TOTAL OTHER ASSETS 375.0 — 375.0 TOTAL ASSETS $ 2,953.4 $ 36.8 $ 2,990.2 LIABILITIES CURRENT LIABILITIES Accounts payable $ 99.5 $ 1.4 $ 100.9 Accrued employment costs 52.7 — 52.7 State and local taxes payable 30.2 — 30.2 Accrued interest 31.4 — 31.4 Contingent claims 55.6 — 55.6 Partnership distribution payable 44.2 — 44.2 Current liabilities of discontinued operations 75.0 — 75.0 Other current liabilities 63.6 1.4 65.0 TOTAL CURRENT LIABILITIES 452.2 2.8 455.0 PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES 257.7 — 257.7 ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS 167.7 — 167.7 LONG-TERM DEBT 2,304.2 — 2,304.2 NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS 52.2 — 52.2 OTHER LIABILITIES 163.5 — 163.5 TOTAL LIABILITIES 3,397.5 2.8 3,400.3 EQUITY CLIFFS SHAREHOLDERS' EQUITY (DEFICIT) (444.3 ) 34.0 (410.3 ) NONCONTROLLING INTEREST 0.2 — 0.2 TOTAL EQUITY (DEFICIT) (444.1 ) 34.0 (410.1 ) TOTAL LIABILITIES AND EQUITY (DEFICIT) $ 2,953.4 $ 36.8 $ 2,990.2 The impact of adoption on our Statements of Consolidated Operations and Statements of Consolidated Financial Position is as follows: ($ in Millions) Year Ended December 31, 2018 As Reported Balances without Adoption of Topic 606 Effect of Change REVENUES FROM PRODUCT SALES AND SERVICES Product $ 2,172.3 $ 2,108.1 $ 64.2 Freight and venture partners' cost reimbursements 160.1 156.2 3.9 2,332.4 2,264.3 68.1 COST OF GOODS SOLD AND OPERATING EXPENSES (1,522.8 ) (1,513.2 ) (9.6 ) SALES MARGIN 809.6 751.1 58.5 OTHER OPERATING INCOME (EXPENSE) Selling, general and administrative expenses (116.8 ) (116.8 ) — Miscellaneous - net (19.6 ) (19.6 ) — (136.4 ) (136.4 ) — OPERATING INCOME 673.2 614.7 58.5 OTHER INCOME (EXPENSE) Interest expense, net (118.9 ) (118.9 ) — Loss on extinguishment of debt (6.8 ) (6.8 ) — Other non-operating income 17.2 17.2 — (108.5 ) (108.5 ) — INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES 564.7 506.2 58.5 INCOME TAX BENEFIT 475.2 487.5 (12.3 ) INCOME FROM CONTINUING OPERATIONS 1,039.9 993.7 46.2 INCOME FROM DISCONTINUED OPERATIONS, net of tax 88.2 88.2 — NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 1,128.1 $ 1,081.9 $ 46.2 EARNINGS PER COMMON SHARE ATTRIBUTABLE TO CLIFFS SHAREHOLDERS - BASIC Continuing operations $ 3.50 $ 3.34 $ 0.16 Discontinued operations 0.30 0.30 — $ 3.80 $ 3.64 $ 0.16 EARNINGS PER COMMON SHARE ATTRIBUTABLE TO CLIFFS SHAREHOLDERS - DILUTED Continuing operations $ 3.42 $ 3.27 $ 0.15 Discontinued operations 0.29 0.29 — $ 3.71 $ 3.56 $ 0.15 AVERAGE NUMBER OF SHARES (IN THOUSANDS) Basic 297,176 297,176 Diluted 304,141 304,141 The increased revenue recognized under Topic 606 is due to higher tons shipped and a higher realized revenue rate in December 2018 versus December 2017. Under the previous accounting standard, December 2017 shipments would have been recognized as 2018 sales due to the fact that title and risk of loss does not transfer until payment is received from our customers. (In Millions) December 31, 2018 As Reported Balances without Adoption of Topic 606 Effect of Change ASSETS CURRENT ASSETS Cash and cash equivalents $ 823.2 $ 823.2 $ — Accounts receivable, net 226.7 108.7 118.0 Inventories 87.9 141.3 (53.4 ) Supplies and other inventories 93.2 93.2 — Derivative assets 91.5 60.7 30.8 Income tax receivable, current 117.3 117.3 — Current assets of discontinued operations 12.4 12.4 — Other current assets 27.4 27.4 — TOTAL CURRENT ASSETS 1,479.6 1,384.2 95.4 PROPERTY, PLANT AND EQUIPMENT, NET 1,286.0 1,286.0 — OTHER ASSETS Deposits for property, plant and equipment 83.0 83.0 — Income tax receivable, non-current 121.3 121.3 — Deferred income taxes 464.8 477.1 (12.3 ) Other non-current assets 94.9 94.9 — TOTAL OTHER ASSETS 764.0 776.3 (12.3 ) TOTAL ASSETS $ 3,529.6 $ 3,446.5 $ 83.1 LIABILITIES CURRENT LIABILITIES Accounts payable $ 186.8 $ 184.9 $ 1.9 Accrued employment costs 74.0 74.0 — State and local taxes payable 35.5 35.5 — Accrued interest 38.4 38.4 — Partnership distribution payable 43.5 43.5 — Current liabilities of discontinued operations 6.7 6.7 — Other current liabilities 83.3 83.7 (0.4 ) TOTAL CURRENT LIABILITIES 468.2 466.7 1.5 PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES 248.7 248.7 — ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS 172.0 172.0 — LONG-TERM DEBT 2,092.9 2,092.9 — NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS 8.3 8.3 — OTHER LIABILITIES 115.3 115.3 — TOTAL LIABILITIES 3,105.4 3,103.9 1.5 EQUITY CLIFFS SHAREHOLDERS' EQUITY 424.2 342.6 81.6 TOTAL LIABILITIES AND EQUITY $ 3,529.6 $ 3,446.5 $ 83.1 The adoption of Topic 606 did not have an impact on net cash flows in our Statements of 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 Topic 715, Compensation - Retirement Benefits 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 Consolidated Operations was as follows: (In Millions) Year Ended December 31, 2017 Year Ended December 31, 2016 As Adjusted Without Adoption of ASU 2017-07 Effect of Change As Adjusted Without Adoption of ASU 2017-07 Effect of Change Cost of goods sold and operating expenses $ (1,398.4 ) $ (1,400.7 ) $ 2.3 $ (1,274.4 ) $ (1,278.7 ) $ 4.3 Selling, general and administrative expenses $ (102.9 ) $ (95.1 ) $ (7.8 ) $ (115.8 ) $ (106.3 ) $ (9.5 ) Miscellaneous - net $ 25.5 $ 27.0 $ (1.5 ) $ (33.6 ) $ (32.0 ) $ (1.6 ) Operating income $ 390.2 $ 397.2 $ (7.0 ) $ 130.7 $ 137.5 $ (6.8 ) Other non-operating income $ 10.2 $ 3.2 $ 7.0 $ 7.3 $ 0.5 $ 6.8 Net income $ 363.1 $ 363.1 $ — $ 199.3 $ 199.3 $ — In August 2018, the FASB issued ASU No. 2018-14, Defined Benefit Plans (Topic 715-20) - Changes to the Disclosure Requirements for Defined Benefit Plans . Certain of the existing required disclosures were modified for clarification or removed and additional disclosures were added. We elected to early adopt ASU No. 2018-14 for the year ended December 31, 2018. The effect of the adoption is an overall reduction in our annual disclosures related to defined benefit plans. The adoption of this standard required retrospective adoption, but did not impact prior-period financial results. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820) - Changes to the Disclosure Requirements for Fair Value Measurement . The new standard removes or modifies certain existing disclosure requirements and adds additional disclosure requirements related to fair value measurement. We elected to early adopt ASU No. 2018-13 for the year ended December 31, 2018. The affect of the adoption is an overall reduction in our quarterly and annual disclosures related to fair value measurement. 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 be classified as either operating or finance leases in the Statements of Consolidated Operations . We adopted this standard on its effective date of January 1, 2019 using the optional alternative approach, which requires application of the new guidance at the beginning of the standard's effective date. We have compiled an inventory of our existing leases and have finalized our implementation plan. Based on our analysis, the updated standard will not have a material effect on our consolidated financial statements.

SEGMENT REPORTING

SEGMENT REPORTING	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
SEGMENT REPORTING	NOTE 3 - SEGMENT REPORTING In alignment with our strategic goals, our Company’s continuing operations are organized and managed in two business units according to our differentiated products. The former 'U.S. Iron Ore' segment is now 'Mining and Pelletizing.' Our Mining and Pelletizing 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. In addition, the Toledo HBI business will be categorized under the segment 'Metallics.' In our Metallics segment, we are currently constructing an HBI production plant in Toledo, Ohio. We expect to complete construction and begin production in 2020. We evaluate 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 is 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 Income from continuing operations before income taxes and a reconciliation of Net income to EBITDA and Adjusted EBITDA: 2018 2017 2016 Revenues from product sales and services: Mining and Pelletizing $ 2,332.4 $ 1,866.0 $ 1,554.5 Sales margin: Mining and Pelletizing $ 809.6 $ 467.6 $ 280.1 Other operating expense (136.4 ) (77.4 ) (149.4 ) Other expense (108.5 ) (282.0 ) (20.3 ) Income from continuing operations before income taxes $ 564.7 $ 108.2 $ 110.4 (In Millions) 2018 2017 2016 Net income $ 1,128.1 $ 363.1 $ 199.3 Less: Interest expense, net (121.3 ) (132.0 ) (200.5 ) Income tax benefit 460.3 252.4 12.2 Depreciation, depletion and amortization (89.0 ) (87.7 ) (115.4 ) Total EBITDA $ 878.1 $ 330.4 $ 503.0 Less: Gain (loss) on extinguishment/restructuring of debt $ (6.8 ) $ (165.4 ) $ 166.3 Impact of discontinued operations 120.6 22.0 108.4 Foreign exchange remeasurement (0.9 ) 13.9 (17.8 ) Impairment of long-lived assets (1.1 ) — — Total Adjusted EBITDA $ 766.3 $ 459.9 $ 246.1 EBITDA: Mining and Pelletizing $ 852.9 $ 534.9 $ 342.4 Metallics (3.3 ) (0.4 ) — Corporate and Other 1 28.5 (204.1 ) 160.6 Total EBITDA $ 878.1 $ 330.4 $ 503.0 Adjusted EBITDA: Mining and Pelletizing $ 875.3 $ 559.4 $ 359.6 Metallics (3.3 ) (0.4 ) — Corporate (105.7 ) (99.1 ) (113.5 ) Total Adjusted EBITDA $ 766.3 $ 459.9 $ 246.1 1 Corporate and Other includes activity from discontinued operations. (In Millions) 2018 2017 2016 Depreciation, depletion and amortization: Mining and Pelletizing $ 68.2 $ 66.6 $ 84.0 Corporate 5.6 6.8 6.3 Total depreciation, depletion and amortization $ 73.8 $ 73.4 $ 90.3 Capital additions 1 : Mining and Pelletizing $ 145.0 $ 136.8 $ 62.2 Metallics 248.1 13.7 — Corporate and Other 1.6 2.7 6.1 Total capital additions $ 394.7 $ 153.2 $ 68.3 1 Includes capital lease additions and non-cash accruals. Refer to NOTE 16 - CASH FLOW INFORMATION. A summary of assets by segment is as follows: (In Millions) December 31, December 31, 2017 December 31, 2016 Assets: Mining and Pelletizing $ 1,694.1 $ 1,500.6 $ 1,372.5 Metallics 265.9 13.4 — Total segment assets 1,960.0 1,514.0 1,372.5 Corporate 1,557.2 1,300.6 396.3 Assets of discontinued operations 12.4 138.8 155.1 Total assets $ 3,529.6 $ 2,953.4 $ 1,923.9 Included in the consolidated financial statements are the following amounts relating to geographic location: (In Millions) 2018 2017 2016 Revenues from product sales and services: United States $ 1,847.3 $ 1,504.5 $ 1,236.2 Canada 395.1 206.2 267.1 Other countries 90.0 155.3 51.2 Total revenues from product sales and services $ 2,332.4 $ 1,866.0 $ 1,554.5 Property, plant and equipment, net: United States $ 1,286.0 $ 1,033.8 $ 961.0 Concentrations in Revenue In 2018 and 2017 , three customers individually accounted for more than 10% of our consolidated product revenue and in 2016 , two customers individually accounted for more than 10% of our consolidated product revenue. Total product revenue from those customers represents $2.1 billion , $ 1.5 billion and $ 1.1 billion of our total consolidated product revenue in 2018 , 2017 and 2016 , respectively. The following table represents the percentage of our total Revenues from product sales and services contributed by each category of products and services: 2018 2017 2016 Revenue category: Product 93 % 88 % 89 % Freight and venture partners’ cost reimbursements 7 % 12 % 11 % Total revenues from product sales and services 100 % 100 % 100 %

INVENTORIES

INVENTORIES	12 Months Ended
	Dec. 31, 2018
Inventory Disclosure [Abstract]
Inventories	NOTE 4 - INVENTORIES The following table presents the detail of our Inventories in the Statements of Consolidated Financial Position : (In Millions) December 31, 2018 2017 Finished Goods $ 77.8 $ 127.1 Work-in-Process 10.1 11.3 Total Inventories $ 87.9 $ 138.4 The excess of current cost over LIFO cost of iron ore inventories was $95.6 million and $96.2 million at December 31, 2018 and 2017 , respectively. As of December 31, 2018 , the product inventory balance for the Mining and Pelletizing segment declined, resulting in the liquidation of a LIFO layer in 2018. The effect of the inventory reduction was a decrease in Cost of goods sold and operating expenses of $0.2 million in the Statements of Consolidated Operations for the year ended December 31, 2018 . As of December 31, 2017 , the product inventory balance for the Mining and Pelletizing segment increased, resulting in a LIFO increment in 2017. The effect of the inventory build was an increase in Inventories of $6.2 million in the Statements of Consolidated Financial Position for the year ended December 31, 2017 .

PROPERTY, PLANT AND EQUIPMENT

PROPERTY, PLANT AND EQUIPMENT	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
PROPERTY, PLANT AND EQUIPMENT	NOTE 5 - PROPERTY, PLANT AND EQUIPMENT The following table indicates the carrying value of each of the major classes of our consolidated depreciable assets: (In Millions) December 31, 2018 2017 Land rights and mineral rights $ 549.6 $ 549.6 Office and information technology 70.0 65.8 Buildings 87.2 85.2 Mining equipment 548.5 533.9 Processing equipment 645.8 610.9 Electric power facilities 58.7 56.9 Land improvements 23.8 23.7 Asset retirement obligation 14.8 16.9 Other 25.2 25.2 Construction-in-progress 284.8 32.6 2,308.4 2,000.7 Allowance for depreciation and depletion (1,022.4 ) (966.9 ) $ 1,286.0 $ 1,033.8 We recorded depreciation expense of $65.6 million , $65.8 million and $84.0 million in the Statements of Consolidated Operations for the years ended December 31, 2018 , 2017 and 2016 , respectively. We recorded capitalized interest of $6.5 million into construction-in-progress during the year ended December 31, 2018 . The net book value of the land rights and mineral rights is as follows : (In Millions) December 31, 2018 2017 Land rights $ 12.4 $ 12.4 Mineral rights: Cost $ 537.2 $ 537.2 Depletion (126.5 ) (119.1 ) Net mineral rights $ 410.7 $ 418.1 We recorded depletion expense of $7.4 million , $6.8 million and $3.8 million in the Statements of Consolidated Operations for the years ended December 31, 2018 , 2017 and 2016 , respectively.

DEBT AND CREDIT FACILITIES

DEBT AND CREDIT FACILITIES	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
DEBT AND CREDIT FACILITIES	NOTE 6 - DEBT AND CREDIT FACILITIES The following represents a summary of our long-term debt: (In Millions) December 31, 2018 Debt Instrument Annual Effective Interest Rate Total Principal Amount Debt Issuance Costs Unamortized Discounts Total Debt Senior Secured Notes: $400 Million 4.875% 2024 Senior Notes 5.00% $ 400.0 $ (5.7 ) $ (2.2 ) $ 392.1 Unsecured Notes: $700 Million 4.875% 2021 Senior Notes 4.89% 124.0 (0.2 ) — 123.8 $316.25 Million 1.50% 2025 Convertible Senior Notes 6.26% 316.3 (5.5 ) (75.6 ) 235.2 $1.075 Billion 5.75% 2025 Senior Notes 6.01% 1,073.3 (9.9 ) (14.6 ) 1,048.8 $800 Million 6.25% 2040 Senior Notes 6.34% 298.4 (2.3 ) (3.3 ) 292.8 ABL Facility N/A 450.0 N/A N/A — Fair Value Adjustment to Interest Rate Hedge 0.2 Long-term debt $ 2,092.9 (In Millions) December 31, 2017 Debt Instrument Annual Effective Interest Rate Total Principal Amount Debt Issuance Costs Unamortized Discounts Total Debt Senior 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 Outstanding Senior Secured Notes Our Senior Secured Notes bear interest at a rate of 4.875% per annum, which is payable semi-annually in arrears on January 15 and July 15 of each year. The Senior Secured Notes mature on January 15, 2024 and are secured senior obligations of the Company. Our Senior Secured Notes are jointly and severally and fully and unconditionally guaranteed on a senior secured basis by substantially all of our material domestic subsidiaries and are secured (subject in each case to certain exceptions and permitted liens) by (i) a first-priority lien on substantially all of our assets and the assets of the guarantors, and (ii) a second-priority lien on the ABL Collateral (as defined below), which is junior to a first-priority lien for the benefit of the lenders under our ABL Facility. The terms of the Senior Secured Notes contain certain covenants; however, there are no financial covenants. Upon the occurrence of a change of control triggering event, as defined in the indenture, we will be required to offer to purchase the notes of the applicable series at a purchase price equal to 101% of the principal amount, plus accrued and unpaid interest, if any, to, but not including, the date of purchase. The following is a summary of redemption prices for our 2024 Senior Secured Notes: Redemption Period 1 Redemption Price Restricted Amount Prior to January 15, 2021 - using proceeds of equity issuance 2 104.875 % Up to 35% of original aggregate principal Prior to January 15, 2021 2 100.000 Prior to January 15, 2021 103.000 Up to 10% of original aggregate principal Beginning on January 15, 2021 102.438 Beginning on January 15, 2022 101.219 Beginning on January 15, 2023 100.000 1 Plus accrued and unpaid interest, if any, up to but excluding the redemption date. 2 Plus a "make-whole" premium. Outstanding Unsecured Senior Notes The following represents a summary of our unsecured senior notes' maturity and interest payable due dates: Debt Instrument Maturity Interest Payable (until maturity) $700 Million 4.875% 2021 Senior Notes April 1, 2021 April 1 and October 1 $1.075 Billion 5.75% 2025 Senior Notes March 1, 2025 March 1 and September 1 $800 Million 6.25% 2040 Senior Notes October 1, 2040 April 1 and October 1 The senior notes are unsecured obligations and rank equally in right of payment with all our other existing and future unsecured and unsubordinated indebtedness. There are no subsidiary guarantees of the interest and principal amounts for the 2021 Senior Notes and the 2040 Senior Notes. The 2025 Senior Notes are guaranteed on a senior unsecured basis by our material direct and indirect wholly-owned domestic subsidiaries and, therefore, are structurally senior to any of our existing and future indebtedness that is not guaranteed by such guarantors and are structurally subordinated to all existing and future indebtedness and other liabilities of our subsidiaries that do not guarantee the 2025 Senior Notes. The 2021 Senior Notes and the 2040 Senior Notes may be redeemed any time at our option not less than 30 days nor more than 60 days after prior notice is sent to the holders of the applicable series of notes. The 2021 Senior Notes and the 2040 Senior Notes are redeemable at a redemption price equal to the greater of (1) 100% of the principal amount of the notes to be redeemed or (2) the sum of the present values of the remaining scheduled payments of principal and interest on the notes to be redeemed, discounted to the redemption date on a semi-annual basis at the treasury rate plus 25 basis points with respect to the 2021 Senior Notes and 40 basis points with respect to the 2040 Senior Notes, plus, in each case, accrued and unpaid interest to, but not including, the date of redemption. However, if the 2021 Senior Notes are redeemed on or after the date that is three months prior to their maturity date, the 2021 Senior Notes will be redeemed at a redemption price equal to 100% of the principal amount of the notes to be redeemed plus accrued and unpaid interest to, but not including, the date of redemption. We may redeem the 2025 Senior Notes, in whole or in part, on or after March 1, 2020, at the redemption prices set forth in the indenture, plus accrued and unpaid interest, if any, to, but not including, the date of redemption, and prior to March 1, 2020, at a redemption price equal to 100% of the principal amount thereof plus a “make-whole” premium set forth in the indenture, plus accrued and unpaid interest, if any, to, but not including, the date of redemption. We may also redeem up to 35% of the aggregate principal amount of the 2025 Senior Notes on or prior to March 1, 2020 at a redemption price equal to 105.75% of the principal amount thereof, plus accrued and unpaid interest, if any, to, but not including, the date of redemption with the net cash proceeds of one or more equity offerings. In addition, if a change of control triggering event, as defined in the applicable indenture, occurs with respect to the unsecured notes, we will be required to offer to purchase the notes of the applicable series at a purchase price equal to 101% of the principal amount, plus accrued and unpaid interest, if any, to, but not including, the date of purchase. The terms of the unsecured notes contain certain customary covenants; however, there are no financial covenants. $316.25 Million 1.50% 2025 Convertible Senior Notes The 2025 Convertible Notes bear interest at a rate of 1.50% per year, payable semiannually in arrears on January 15 and July 15 of each year. The 2025 Convertible Notes mature on January 15, 2025. The 2025 Convertible Notes are senior unsecured obligations and rank senior in right of payment to any of our indebtedness that is expressly subordinated in right of payment to the 2025 Convertible Notes; equal in right of payment to any of our unsecured indebtedness that is not so subordinated; effectively junior in right of payment to any of our secured indebtedness to the extent of the value of the assets securing such indebtedness; and structurally junior to all indebtedness and other liabilities (including trade payables) of our subsidiaries. The terms of the 2025 Convertible Notes contain certain customary covenants; however, there are no financial covenants. Holders may convert their 2025 Convertible Notes at their option at any time prior to the close of business on the business day immediately preceding July 15, 2024, only under the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on March 31, 2018, if the last reported sale price of our common shares, par value $0.125 per share, for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day; (2) during the five-business day period after any five-consecutive trading day period (the “measurement period”) in which the trading price per $1,000 principal amount of 2025 Convertible Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of our common shares and the conversion rate on each such trading day; (3) if we call the notes for redemption, at any time prior to the close of business on the scheduled trading day immediately preceding the redemption date; or (4) upon the occurrence of specified corporate events. On or after July 15, 2024 until the close of business on the second scheduled trading day immediately preceding the maturity date, holders may convert their 2025 Convertible Notes at any time, regardless of the foregoing circumstances. Upon conversion, we will pay or deliver, as the case may be, cash, common shares or a combination of cash and common shares, at our election. The conversion rate is 122.4365 common shares per $1,000 principal amount of 2025 Convertible Notes (equivalent to an initial conversion price of $8.17 per common share). The conversion rate will be subject to adjustment in some circumstances but will not be adjusted for any accrued and unpaid interest. In addition, following certain corporate events that occur prior to the maturity date, or if we deliver a notice of redemption, we will, in certain circumstances, increase the conversion rate for a holder who elects to convert its 2025 Convertible Notes in connection with such a corporate event or notice of redemption, as the case may be. We may not redeem the 2025 Convertible Notes prior to January 15, 2022. We may redeem all or any portion of the 2025 Convertible Notes, for cash at our option on or after January 15, 2022 if the last reported sale price of our common shares has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive) during any 30-consecutive trading day period (including the last trading day of such period) ending on, and including, the trading day immediately preceding the date on which we provide notice of redemption at a redemption price equal to 100% of the principal amount of the 2025 Convertible Notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date. It is our current intent to settle conversions through combination settlement. Our ability to settle conversions through combination settlement and cash settlement will be subject to restrictions in the agreement governing our ABL Facility and may be subject to restrictions in agreements governing our future debt. If we undergo a fundamental change as defined in the indenture, holders may require us to repurchase for cash all or any portion of their 2025 Convertible Notes at a fundamental change repurchase price equal to 100% of the principal amount of the 2025 Convertible Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date. In accounting for the issuance of the notes, we separated the 2025 Convertible Notes into liability and equity components. The carrying amount of the liability component was calculated by measuring the fair value of similar liabilities that did not have associated convertible features. The carrying amount of the equity component of $85.9 million representing the conversion option was determined by deducting the fair value of the liability component from the par value of the notes. The difference represents the debt discount that is amortized to interest expense over the term of the notes. The equity component is not remeasured as long as it continues to qualify for equity classification. Debt Extinguishment - 2018 During the year ended December 31, 2018 , we redeemed in full all of our outstanding 5.90% 2020 Senior Notes and 4.80% 2020 Senior Notes with cash on hand. Additionally, we purchased certain of our 4.875% 2021 Senior Notes and 2025 Senior Notes. The following is a summary of the debt extinguished and the respective gain (loss) on extinguishment: (In Millions) Year Ended Debt Extinguished Gain (Loss) on Extinguishment 1 Unsecured Notes: $400 Million 5.90% 2020 Senior Notes $ 88.9 $ (3.3 ) $500 Million 4.80% 2020 Senior Notes 122.4 (3.7 ) $700 Million 4.875% 2021 Senior Notes 14.4 0.1 $1.075 Billion 5.75% 2025 Senior Notes 1.7 0.1 $ 227.4 $ (6.8 ) 1 This includes premiums paid related to the redemption of our notes of $7.1 million. Debt Extinguishment - 2017 During the year ended December 31, 2017, we issued 63.25 million common shares in an underwritten public offering. We received net proceeds of $661.3 million at a public offering price of $10.75 per common share. The net proceeds from the issuance of our common shares and the net proceeds from the issuance of $1.075 billion 2025 Senior Notes were used to redeem in full all of our outstanding 8.25% 2020 First Lien Notes, 8.00% 2020 1.5 Lien Notes and 7.75% 2020 Second Lien Notes. Additionally, through tender offers, we purchased certain of our 5.90% 2020 Senior Notes, our 4.80% 2020 Senior Notes and our 4.875% 2021 Senior Notes. The following is a summary of the debt extinguished and the respective gain (loss) on extinguishment: (In Millions) Year Ended Debt Extinguished Gain (Loss) on Extinguishment 1 Secured Notes: $540 Million 8.25% 2020 First Lien Notes $ 540.0 $ (93.5 ) $218.5 Million 8.00% 2020 1.5 Lien Notes 218.5 45.1 $544.2 Million 7.75% 2020 Second Lien Notes 430.1 (104.5 ) Unsecured Notes: $400 Million 5.90% 2020 Senior Notes 136.7 (7.8 ) $500 Million 4.80% 2020 Senior Notes 114.4 (1.9 ) $700 Million 4.875% 2021 Senior Notes 171.0 (2.8 ) $ 1,610.7 $ (165.4 ) 1 This includes premiums paid related to the redemption of our notes of $110.0 million. Debt Extinguishment/Restructuring - 2016 8.00% 2020 1.5 Lien Notes Exchange On March 2, 2016, we entered into an indenture among the Company, the guarantors party thereto and U.S. Bank National Association, as trustee and notes collateral agent, relating to our issuance of $218.5 million aggregate principal amount of 8.00% 2020 1.5 Lien Notes. The 8.00% 2020 1.5 Lien Notes were issued in exchange offers for certain of our existing senior notes. We accounted for the 8.00% 2020 1.5 Lien Notes exchange as a troubled debt restructuring. For an exchange classified as a troubled debt restructuring, if the future undiscounted cash flows of the newly issued debt are less than the net carrying value of the original debt, the carrying value of the newly issued debt is adjusted to the future undiscounted cash flow amount, a gain is recorded for the difference and no future interest expense is recorded. All future interest payments on the newly issued debt reduce the carrying value. Accordingly, we recognized a gain of $174.3 million in the Gain (loss) on extinguishment/restructuring of debt in the Statements of Consolidated Operations for the year ended December 31, 2016. The following is a summary of the debt exchanged for our $218.5 million 8.00% 2020 1.5 Lien Notes: (In Millions) Debt Extinguished 1.5 Lien Amount Issued Carrying Value 1 Gain on Restructuring 2 $544.2 Million 7.75% 2020 Second Lien Notes $ 114.1 $ 57.0 $ 77.5 $ 6.9 $500 Million 3.95% 2018 Senior Notes 17.6 11.4 15.5 1.8 $400 Million 5.90% 2020 Senior Notes 65.1 26.0 35.4 28.3 $500 Million 4.80% 2020 Senior Notes 44.7 17.9 24.4 19.5 $700 Million 4.875% 2021 Senior Notes 76.3 30.5 41.5 33.3 $800 Million 6.25% 2040 Senior Notes 194.4 75.7 103.0 84.5 $ 512.2 $ 218.5 $ 297.3 $ 174.3 1 Includes undiscounted interest payments 2 Net of amounts expensed for unamortized original issue discount and deferred origination fees Debt-for-Equity Exchanges During the year ended December 31, 2016, we entered into a series of privately negotiated exchange agreements whereby we issued an aggregate of 8.2 million common shares in exchange for $10.0 million aggregate principal amount of our 3.95% 2018 Senior Notes, $20.1 million aggregate principal amount of our 4.80% 2020 Senior Notes and $26.8 million aggregate principal amount of our 4.875% 2021 Senior Notes. There were no exchanges that represented more than 1% of our outstanding common shares during any quarter. Accordingly, we recognized a gain of $11.3 million in Gain (loss) on extinguishment/restructuring of debt in the Statements of Consolidated Operations for the year ended December 31, 2016. Other Debt Repurchases Our 3.95% 2018 Senior Notes were redeemed in whole on September 16, 2016 at a total redemption price of $301.0 million , which included $283.6 million outstanding aggregate principal. As a result, we recorded a $19.9 million pre-tax loss on full retirement of long-term debt in the third quarter of 2016, which consisted of debt redemption premiums of $17.4 million and expenses of $2.5 million related to the write-off of unamortized debt issuance costs, unamortized bond discount and deferred losses on interest rate swaps. The loss was recorded against the Gain (loss) on extinguishment/restructuring of debt in the Statements of Consolidated Operations for the year ended December 31, 2016. During the year ended December 31, 2016, we purchased with cash $5.0 million of our outstanding 4.80% 2020 Senior Notes, which resulted in a gain on extinguishment of $0.6 million . Debt Maturities The following represents a summary of our debt instrument maturities based on the principal amounts outstanding at December 31, 2018 : (In Millions) Maturities of Debt 2019 $ — 2020 — 2021 124.0 2022 — 2023 — 2024 and thereafter 2,088.0 Total maturities of debt $ 2,212.0 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) at the time of closing, 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. On June 19, 2018, the Australian tranche was terminated and reallocated to the U.S. tranche, resulting in a $450.0 million allocation to the U.S. tranche, including a $273.2 million sublimit for the issuance of letters of credit and a $120.0 million sublimit for swingline loans. Availability under the U.S. tranche of the ABL Facility is limited to an eligible U.S. 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. subsidiaries and are required to be guaranteed by certain of our future U.S. subsidiaries. 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”) and (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 ABL Collateral. Borrowings under the ABL Facility bear interest, at our option, at a 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 greater of the federal funds rate plus 0.5% , 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 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 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 December 31, 2018 and 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. The following represents a summary of our borrowing capacity under the ABL Facility: (In Millions) December 31, 2018 December 31, 2017 Available borrowing base on ABL Facility 1 $ 323.7 $ 273.2 Letter of credit obligations and other commitments 2 (55.0 ) (46.5 ) Borrowing capacity available 3 $ 268.7 $ 226.7 1 The ABL Facility has a maximum borrowing base of $450 million, determined by applying customary advance rates to eligible accounts receivable, inventory and certain mobile equipment. 2 We issued standby letters of credit with certain financial institutions in order to support business obligations including, but not limited to, workers compensation, environmental obligations and a Metallics energy supply agreement. 3 As of December 31, 2018 and 2017 we had no loans drawn under the ABL Facility.

FAIR VALUE OF FINANCIAL INSTRUM

FAIR VALUE OF FINANCIAL INSTRUMENTS	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
FAIR VALUE OF FINANCIAL INSTRUMENTS	NOTE 7 - FAIR VALUE OF FINANCIAL INSTRUMENTS The following represents the assets and liabilities measured at fair value: (In Millions) December 31, 2018 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 $ 0.8 $ 542.6 $ — $ 543.4 Derivative assets — 0.1 91.4 91.5 Total $ 0.8 $ 542.7 $ 91.4 $ 634.9 Liabilities: Derivative liabilities $ — $ 3.7 $ — $ 3.7 Total $ — $ 3.7 $ — $ 3.7 (In Millions) December 31, 2017 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 — — 37.9 37.9 Total $ 66.3 $ 550.6 $ 37.9 $ 654.8 Liabilities: Derivative liabilities $ — $ 0.3 $ 1.7 $ 2.0 Total $ — $ 0.3 $ 1.7 $ 2.0 Financial assets classified in Level 1 included money market funds at December 31, 2018 and money market funds and treasury bonds at December 31, 2017 . 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 included commercial paper, certificates of deposit and commodity hedge contracts at December 31, 2018 and commercial paper and certificates of deposits at December 31, 2017 . Level 2 liabilities included commodity hedge contracts at December 31, 2018 and 2017. The Level 3 assets and liabilities include derivative assets that consist of freestanding derivative instruments related to a certain supply agreement and derivative assets and liabilities related to certain provisional pricing arrangements with our customers. The supply agreement included in our Level 3 assets contain provisions for supplemental revenue or refunds based on the average annual daily market price for hot-rolled coil steel in the year 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 derivative instruments to fair value through Product revenues each reporting period until the product is consumed and the amounts are settled. We had assets of $89.3 million and $37.9 million at December 31, 2018 and 2017 , respectively, related to this 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 instruments 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 rates are determined. We had assets of $2.1 million at December 31, 2018 compared to liabilities of $1.7 million related to provisional pricing arrangements at December 31, 2017 . The following table illustrates information about quantitative inputs and assumptions for the derivative assets and derivative liabilities categorized in Level 3 of the fair value hierarchy: Qualitative/Quantitative Information About Level 3 Fair Value Measurements Fair Value at December 31, 2018 (In Millions) Balance Sheet Location Valuation Technique Unobservable Input Point Estimate Customer supply agreement $89.3 Derivative assets Market Approach Management's Estimate of Market Hot-Rolled Coil Steel per net ton $750 Provisional pricing arrangements $2.1 Derivative assets Market Approach Management's Estimate of Platts 62% Price per dry metric ton $68 The significant unobservable input used in the fair value measurement of our customer supply agreement is a forward-looking estimate of the average annual daily market price for hot-rolled coil steel determined by management. 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. 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): Derivative Assets 1 (Level 3) Derivative Liabilities (Level 3) Year Ended Year Ended 2018 2017 2018 2017 Beginning balance - January 1 $ 49.5 $ 30.1 $ (1.7 ) $ — Total gains (losses) Included in earnings 428.7 176.2 (6.1 ) (55.6 ) Settlements (386.8 ) (168.4 ) 7.8 53.9 Ending balance - December 31 $ 91.4 $ 37.9 $ — $ (1.7 ) Total gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) on assets still held at the reporting date $ 91.4 $ 37.9 $ — $ (1.7 ) 1 Beginning balance as of January 1, 2018 includes an $11.6 million adjustment for adoption of Topic 606. The carrying values of certain financial instruments (e.g. Accounts receivable, net , Accounts payable and Other current liabilities ) approximate fair value and, therefore, have been excluded from the table below. A summary of the carrying value and fair value of other financial instruments were as follows: (In Millions) December 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 $ 392.1 $ 370.2 $ 390.3 $ 398.0 Unsecured Notes: $400 Million 5.90% 2020 Senior Notes Level 1 — — 88.6 88.0 $500 Million 4.80% 2020 Senior Notes Level 1 — — 122.0 118.8 $700 Million 4.875% 2021 Senior Notes Level 1 123.8 122.3 138.0 130.8 $316.25 Million 1.50% 2025 Convertible Senior Notes Level 1 235.2 352.4 224.1 352.9 $1.075 Billion 5.75% 2025 Senior Notes Level 1 1,048.8 962.0 1,047.2 1,029.3 $800 Million 6.25% 2040 Senior Notes Level 1 292.8 232.8 292.6 227.1 ABL Facility Level 2 — — — — Fair Value Adjustment to Interest Rate Hedge Level 2 0.2 0.2 1.4 1.4 Total long-term debt $ 2,092.9 $ 2,039.9 $ 2,304.2 $ 2,346.3 The fair value of long-term debt was determined using quoted market prices.

PENSIONS AND OTHER POSTRETIREME

PENSIONS AND OTHER POSTRETIREMENT BENEFITS	12 Months Ended
	Dec. 31, 2018
Postemployment Benefits [Abstract]
PENSIONS AND OTHER POSTRETIREMENT BENEFITS	NOTE 8 - 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 as part of a total compensation and benefits program. The defined benefit pension plans 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. We offer retiree medical coverage to hourly retirees of our USW-represented mines. A new four -year agreement with the USW was entered into on October 12, 2018, and is retroactively effective from October 1, 2018 through September 30, 2022. The 2018 USW agreement established the set fixed monthly medical premiums for participants who retired prior to January 1, 2015. These fixed premiums will expire on December 31, 2020 and revert to increasing premiums based a cost-sharing formula thereafter. The agreement also provides for an OPEB cap that limits the amount of contributions that we have to make toward retiree medical insurance coverage for each retiree and spouse of a retiree per calendar year who retired on or after January 1, 2015. The amount of the annual OPEB cap is based upon the gross plan costs we incurred in 2014. The OPEB cap does not apply to surviving spouses. In lieu of retiree medical coverage, USW-represented employees hired after September 1, 2016 receive a 401(k) contribution of $0.50 per hour worked to a restricted Retiree Health Care Account. Beginning January 1, 2019, the hourly contribution rate increased to $0.60 per hour worked. In addition, we currently provide various levels of retirement health care and OPEB to some full-time employees who meet certain length of service and age requirements (a portion of which is pursuant to collective bargaining agreements). Most plans require retiree contributions and have deductibles, co-pay requirements and benefit limits. Most bargaining unit plans require retiree contributions and co-pays for medical and prescription drug coverage. There is a cap on our cost for medical coverage under the salaried plans. The annual limit applies to each covered participant and equals $7,000 for coverage prior to age 65, with the retiree’s participation adjusted based on the age at which the retiree’s benefits commence. We do not provide OPEB for most salaried employees hired after January 1, 1993. Retiree healthcare coverage is provided through programs administered by insurance companies whose charges are based on benefits paid. The following table summarizes the annual expense (income) recognized related to the retirement plans: (In Millions) 2018 2017 2016 Defined benefit pension plans $ 12.7 $ 18.0 $ 16.5 Defined contribution pension plans 3.1 2.9 2.8 Other postretirement benefits (5.9 ) (6.1 ) (4.0 ) Total $ 9.9 $ 14.8 $ 15.3 Obligations and Funded Status The following tables and information provide additional disclosures: (In Millions) Pension Benefits Other Benefits Change in benefit obligations: 2018 2017 2018 2017 Benefit obligations — beginning of year $ 973.1 $ 931.6 $ 265.9 $ 264.6 Service cost (excluding expenses) 18.7 17.1 2.2 1.8 Interest cost 30.3 30.5 8.3 8.3 Plan amendments 2.2 — 12.8 — Curtailment gain (0.9 ) — — — Actuarial (gain) loss (57.0 ) 54.6 (29.4 ) 7.4 Benefits paid (60.7 ) (60.7 ) (24.4 ) (21.4 ) Participant contributions — — 5.6 4.6 Federal subsidy on benefits paid — — 0.9 0.6 Benefit obligations — end of year $ 905.7 $ 973.1 $ 241.9 $ 265.9 Change in plan assets: Fair value of plan assets — beginning of year $ 749.8 $ 685.8 $ 262.5 $ 253.0 Actual return on plan assets (29.6 ) 100.2 (8.2 ) 24.2 Participant contributions — — 0.5 0.3 Employer contributions 27.6 24.4 3.0 1.7 Asset transfers 0.1 0.1 — — Benefits paid (60.7 ) (60.7 ) (17.6 ) (16.7 ) Fair value of plan assets — end of year $ 687.2 $ 749.8 $ 240.2 $ 262.5 Funded status at December 31: Fair value of plan assets $ 687.2 $ 749.8 $ 240.2 $ 262.5 Benefit obligations (905.7 ) (973.1 ) (241.9 ) (265.9 ) Amount recognized at December 31 $ (218.5 ) $ (223.3 ) $ (1.7 ) $ (3.4 ) Amounts recognized in Statements of Financial Position: Non-current assets $ — $ — $ 32.1 $ 35.4 Current liabilities (0.1 ) (0.5 ) (3.5 ) (3.9 ) Non-current liabilities (218.4 ) (222.8 ) (30.3 ) (34.9 ) Total amount recognized $ (218.5 ) $ (223.3 ) $ (1.7 ) $ (3.4 ) Amounts recognized in accumulated other comprehensive loss: Net actuarial loss $ 330.1 $ 318.7 $ 82.1 $ 88.3 Prior service cost (credit) 8.5 8.8 (9.9 ) (25.6 ) Net amount recognized $ 338.6 $ 327.5 $ 72.2 $ 62.7 (In Millions) 2018 Pension Plans Other Benefits Salaried Hourly Mining SERP Total Salaried Hourly Total Fair value of plan assets $ 249.8 $ 429.4 $ 8.0 $ — $ 687.2 $ — $ 240.2 $ 240.2 Benefit obligation (340.8 ) (548.9 ) (10.7 ) (5.3 ) (905.7 ) (32.9 ) (209.0 ) (241.9 ) Funded status $ (91.0 ) $ (119.5 ) $ (2.7 ) $ (5.3 ) $ (218.5 ) $ (32.9 ) $ 31.2 $ (1.7 ) 2017 Pension Plans Other Benefits Salaried Hourly Mining SERP Total Salaried Hourly Total Fair value of plan assets $ 269.4 $ 473.0 $ 7.4 $ — $ 749.8 $ — $ 262.5 $ 262.5 Benefit obligation (368.0 ) (590.0 ) (10.3 ) (4.8 ) (973.1 ) (37.7 ) (228.2 ) (265.9 ) Funded status $ (98.6 ) $ (117.0 ) $ (2.9 ) $ (4.8 ) $ (223.3 ) $ (37.7 ) $ 34.3 $ (3.4 ) The pension and OPEB plans in 2018 experienced a net actuarial gain of $57.0 million and $29.4 million , respectively. The increase in discount rates due to market conditions was the primary driver, which resulted in gains of $75.7 million and $19.0 million for the pension and OPEB plans, respectively. The net gain was offset partially by losses of $21.7 million for the pensions plans and $2.3 million for the OPEB plans relating to demographic experience. The adoption of the new projection scale resulted in gains totaling $3.0 million for the pension plans and $0.8 million for the OPEB plans. Additionally, an update to the assumed per capita cost of medical benefits resulted in a gain of $11.9 million for the OPEB plans. The pension and OPEB plans in 2017 experienced a net actuarial loss of $54.6 million and $7.4 million , respectively. The decrease in discount rates due to market conditions was the primary driver, which resulted in losses of $46.1 million and $12.6 million for the pension and OPEB plans, respectively. The adoption of the new projection scale resulted in gains totaling $6.1 million for the pension plans and $1.9 million for the OPEB plans. The accumulated benefit obligation for all defined benefit pension plans was $896.8 million and $963.0 million at December 31, 2018 and 2017 , respectively. Components of Net Periodic Benefit Cost (In Millions) Pension Benefits Other Benefits 2018 2017 2016 2018 2017 2016 Service cost $ 18.7 $ 17.1 $ 17.6 $ 2.2 $ 1.8 $ 1.7 Interest cost 30.3 30.5 30.3 8.3 8.3 9.1 Expected return on plan assets (60.0 ) (54.5 ) (54.7 ) (18.4 ) (17.7 ) (17.1 ) Amortization: Prior service costs (credits) 2.2 2.6 2.2 (3.0 ) (3.0 ) (3.7 ) Net actuarial loss 21.2 22.3 21.1 5.0 4.5 6.0 Curtailments 0.3 — — — — — Net periodic benefit cost (credit) $ 12.7 $ 18.0 $ 16.5 $ (5.9 ) $ (6.1 ) $ (4.0 ) Curtailment effects (0.3 ) — — — — — Current year actuarial loss (gain) 31.6 9.3 37.8 (2.9 ) 1.2 (8.1 ) Amortization of net loss (21.2 ) (22.3 ) (21.1 ) (5.0 ) (4.5 ) (6.0 ) Current year prior service cost 2.2 — 5.7 12.8 — 9.8 Amortization of prior service credit (cost) (2.2 ) (2.6 ) (2.2 ) 3.0 3.0 3.7 Total recognized in other comprehensive income (loss) $ 10.1 $ (15.6 ) $ 20.2 $ 7.9 $ (0.3 ) $ (0.6 ) Total recognized in net periodic cost and other comprehensive income (loss) $ 22.8 $ 2.4 $ 36.7 $ 2.0 $ (6.4 ) $ (4.6 ) Assumptions The discount rate for determining PBO is determined individually for each plan as noted in the assumption chart below. The discount rates are determined by matching the projected cash flows used to determine the PBO and APBO to a projected yield curve of 1,101 Aa graded bonds in the 40 th to 90 th percentiles. These bonds are either noncallable or callable with make-whole provisions. On December 31, 2018, the assumed mortality improvement projection was changed from generational scale MP-2017 to generational scale MP-2018. The healthy mortality assumption remains the RP-2014 mortality tables with blue collar adjustments for the Iron Hourly Pension and Hourly OPEB plans, with white collar adjustments for the the Salaried OPEB Plan, and without adjustments for the Salaried and Ore Mining Pension Plans. On December 31, 2017, the assumed mortality improvement projection was changed from generational scale MP-2016 to generational scale MP-2017. Weighted-average assumptions used to determine benefit obligations at December 31 were: Pension Benefits Other Benefits 2018 2017 2018 2017 Discount rate: Iron Hourly Pension Plan 4.31 % 3.60 % N/A % N/A % Salaried Pension Plan 4.21 3.52 N/A N/A Ore Mining Pension Plan 4.33 3.61 N/A N/A Supplemental Executive Retirement Plan 4.22 3.50 N/A N/A Hourly OPEB Plan N/A N/A 4.29 3.60 Salaried OPEB Plan N/A N/A 4.27 3.57 Salaried rate of compensation increase 3.00 3.00 3.00 3.00 Hourly rate of compensation increase 2.00 2.00 N/A N/A Weighted-average assumptions used to determine net benefit cost were: Pension Benefits Other Benefits 2018 2017 2016 2018 2017 2016 Obligation Discount Rate: Iron Hourly Pension Plan 3.61 % 4.02 % 4.27 % N/A % N/A % N/A % Salaried Pension Plan 3.52 3.91 4.13 N/A N/A N/A Ore Mining Pension Plan 3.61 4.04 4.28 N/A N/A N/A Supplemental Executive Retirement Plan 3.54 3.90 4.01 N/A N/A N/A Hourly OPEB Plan N/A N/A N/A 3.60 4.03 4.32 Salaried OPEB Plan N/A N/A N/A 3.57 3.98 4.22 Service Cost Discount Rate: Iron Hourly Pension Plan 3.76 4.30 4.66 N/A N/A N/A Salaried Pension Plan 3.53 3.93 4.14 N/A N/A N/A Ore Mining Pension Plan 3.75 4.27 4.60 N/A N/A N/A Supplemental Executive Retirement Plan 3.43 3.69 3.87 N/A N/A N/A Hourly OPEB Plan N/A N/A N/A 3.73 4.23 4.56 Salaried OPEB Plan N/A N/A N/A 3.76 4.30 4.63 Interest Cost Discount Rate: Iron Hourly Pension Plan 3.21 3.38 3.46 N/A N/A N/A Salaried Pension Plan 3.08 3.21 3.21 N/A N/A N/A Ore Mining Pension Plan 3.22 3.41 3.48 N/A N/A N/A Supplemental Executive Retirement Plan 3.16 3.36 3.30 N/A N/A N/A Hourly OPEB Plan N/A N/A N/A 3.10 3.24 3.48 Salaried OPEB Plan N/A N/A N/A 3.15 3.28 3.31 Expected return on plan assets 8.25 8.25 8.25 7.00 7.00 7.00 Salaried rate of compensation increase 3.00 3.00 3.00 3.00 3.00 3.00 Hourly rate of compensation increase 2.00 2.00 2.00 N/A N/A N/A Assumed health care cost trend rates at December 31 were: 2018 2017 Health care cost trend rate assumed for next year 6.75 % 7.00 % Ultimate health care cost trend rate 5.00 5.00 Year that the ultimate rate is reached 2026 2026 Plan Assets Our financial objectives with respect to our pension and VEBA plan assets are to fully fund the actuarial accrued liability for each of the plans, to maximize investment returns within reasonable and prudent levels of risk, and to maintain sufficient liquidity to meet benefit obligations on a timely basis. Our investment objective is to outperform the expected return on assets assumption used in the plans’ actuarial reports over the life of the plans. The expected return on assets takes into account historical returns and estimated future long-term returns based on capital market assumptions applied to the asset allocation strategy. The expected return is net of investment expenses paid by the plans. In addition, investment performance is monitored on a quarterly basis by benchmarking to various indices and metrics for the one-, three- and five-year periods. The asset allocation strategy is determined through a detailed analysis of assets and liabilities by plan, which defines the overall risk that is acceptable with regard to the expected level and variability of portfolio returns, surplus (assets compared to liabilities), contributions and pension expense. The asset allocation review process involves simulating capital market behaviors including global asset class performance, inflation and interest rates in order to evaluate various asset allocation scenarios and determine the asset mix with the highest likelihood of meeting financial objectives. The process includes factoring in the current funded status and likely future funded status levels of the plans by taking into account expected growth or decline in the contributions over time. The asset allocation strategy varies by plan. The following table reflects the actual asset allocations for pension and VEBA plan assets as of December 31, 2018 and 2017 , as well as the 2019 weighted average target asset allocations. Equity investments include securities in large-cap, mid-cap and small-cap companies located in the U.S. and worldwide. Fixed income investments primarily include corporate bonds and government debt securities. Pension Assets VEBA Assets Asset Category 2019 Target Allocation Percentage of Plan Assets at December 31, 2019 Target Allocation Percentage of Plan Assets at December 31, 2018 2017 2018 2017 Equity securities 45.0 % 38.9 % 43.6 % 8.0 % 8.1 % 8.7 % Fixed income 28.0 % 26.0 % 27.0 % 80.0 % 77.0 % 77.7 % Hedge funds 5.0 % 5.4 % 5.0 % 4.0 % 4.7 % 4.4 % Private equity 7.0 % 6.2 % 5.3 % 3.0 % 1.2 % 1.5 % Structured credit 7.5 % 11.4 % 9.7 % 2.0 % 3.5 % 3.0 % Real estate 7.5 % 10.3 % 8.7 % 3.0 % 5.4 % 4.6 % Cash — % 1.8 % 0.7 % — % 0.1 % 0.1 % Total 100.0 % 100.0 % 100.0 % 100.0 % 100.0 % 100.0 % Following is a description of the inputs and valuation methodologies used to measure the fair value of our plan assets. Equity Securities Equity securities classified as Level 1 investments include U.S. large-, small- and mid-cap investments and international equities. These investments are comprised of securities listed on an exchange, market or automated quotation system for which quotations are readily available. The valuation of these securities is determined using a market approach and is based upon unadjusted quoted prices for identical assets in active markets. Fixed Income Fixed income securities classified as Level 1 investments include bonds and government debt securities. These investments are comprised of securities listed on an exchange, market or automated quotation system for which quotations are readily available. The valuation of these securities is determined using a market approach and is based upon unadjusted quoted prices for identical assets in active markets. Also included in Fixed income is a portfolio of U.S. Treasury STRIPS, which are zero-coupon bearing fixed income securities backed by the full faith and credit of the U.S. government. The securities sell at a discount to par because there are no incremental coupon payments. STRIPS are not issued directly by the Treasury but rather are created by a financial institution, government securities broker or government securities dealer. Liquidity on the issue varies depending on various market conditions; however, in general the STRIPS market is slightly less liquid than that of the U.S. Treasury Bond market. The STRIPS are priced daily through a bond pricing vendor and are classified as Level 2. Hedge Funds Hedge funds are alternative investments comprised of direct or indirect investment in offshore hedge funds with an investment objective to achieve equity-like returns with one half the volatility of equities and moderate correlation. The valuation techniques used to measure fair value attempt to maximize the use of observable inputs and minimize the use of unobservable inputs. Considerable judgment is required to interpret the factors used to develop estimates of fair value. Valuations of the underlying investment funds are obtained and reviewed. The securities that are valued by the funds are interests in the investment funds and not the underlying holdings of such investment funds. Thus, the inputs used to value the investments in each of the underlying funds may differ from the inputs used to value the underlying holdings of such funds. Hedge funds are valued monthly and recorded on a one-month lag. Private Equity Funds Private equity funds are alternative investments that represent direct or indirect investments in partnerships, venture funds or a diversified pool of private investment vehicles (fund of funds). Investment commitments are made in private equity funds based on an asset allocation strategy, and capital calls are made over the life of the funds to fund the commitments. As of December 31, 2018 , remaining commitments total $44.2 million for both our pension and OPEB plans. Committed amounts are funded from plan assets when capital calls are made. Investment commitments are not pre-funded in reserve accounts. Private equity investments are valued quarterly and recorded on a one-quarter lag. For alternative investment values reported on a lag, current market information is reviewed for any material changes in values at the reporting date. Capital distributions for the funds do not occur on a regular frequency. Liquidation of these investments would require sale of the partnership interest. Structured Credit Structured credit investments are alternative investments comprised of collateralized debt obligations and other structured credit investments that are priced based on valuations provided by independent, third-party pricing agents, if available. Such values generally reflect the last reported sales price if the security is actively traded. The third-party pricing agents may also value structured credit investments at an evaluated bid price by employing methodologies that utilize actual market transactions, broker-supplied valuations or other methodologies designed to identify the market value of such securities. Structured credit investments are valued monthly and recorded on a one-month lag. For alternative investment values reported on a lag, current market information is reviewed for any material changes in values at the reporting date. Historically, redemption requests have been considered quarterly, subject to notice of 90 days , although the advisor is currently only requiring notice of 65 days. Real Estate The real estate portfolio for the pension plans is an alternative investment primarily comprised of two funds with strategic categories of real estate investments. All real estate holdings are appraised externally at least annually, and appraisals are conducted by reputable, independent appraisal firms that are members of the Appraisal Institute. All external appraisals are performed in accordance with the Uniform Standards of Professional Appraisal Practices. The property valuations and assumptions about each property are reviewed quarterly by the investment advisor and values are adjusted if there has been a significant change in circumstances relating to the property since the last external appraisal. The fair value of one of the funds is updated monthly, and there is no lag in reported value. Redemption requests are considered on a quarterly basis, subject to notice of 45 days . The real estate fund of funds investment for the Empire-Tilden, Hibbing and United Taconite VEBA plans invests in pooled investment vehicles that in turn invest in commercial real estate properties. Valuations are performed quarterly and financial statements are prepared on a semi-annual basis, with annual audited statements. Asset values for this fund are reported with a one-quarter lag, and current market information is reviewed for any material changes in values at the reporting date. Withdrawals are permitted on the last business day of each quarter subject to a 65 -day prior written notice. Pension The fair value of our pension plan assets by asset category is as follows: (In Millions) December 31, 2018 Asset Category Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Equity securities: U.S. large-cap $ 112.6 $ — $ — $ 112.6 U.S. small/mid-cap 22.5 — — 22.5 International 132.0 — — 132.0 Fixed income 151.1 27.4 — 178.5 Hedge funds — — 37.2 37.2 Private equity — — 42.6 42.6 Structured credit — — 78.8 78.8 Real estate — — 70.5 70.5 Cash 12.5 — — 12.5 Total $ 430.7 $ 27.4 $ 229.1 $ 687.2 (In Millions) December 31, 2017 Asset Category Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Equity securities: U.S. large-cap $ 130.1 $ — $ — $ 130.1 U.S. small/mid-cap 35.5 — — 35.5 International 160.9 — — 160.9 Fixed income 173.6 28.8 — 202.4 Hedge funds — — 37.4 37.4 Private equity — — 39.8 39.8 Structured credit — — 72.9 72.9 Real estate — — 65.5 65.5 Cash 5.3 — — 5.3 Total $ 505.4 $ 28.8 $ 215.6 $ 749.8 The following represents the effect of fair value measurements using significant unobservable inputs (Level 3) on changes in plan assets: (In Millions) Year Ended December 31, 2018 Hedge Funds Private Equity Funds Structured Credit Fund Real Estate Total Beginning balance — January 1, 2018 $ 37.4 $ 39.8 $ 72.9 $ 65.5 $ 215.6 Actual return on plan assets: Relating to assets still held at the reporting date (0.2 ) 1.4 5.9 5.4 12.5 Relating to assets sold during the period — 4.0 — — 4.0 Purchases — 5.2 — — 5.2 Sales — (7.8 ) — (0.4 ) (8.2 ) Ending balance — December 31, 2018 $ 37.2 $ 42.6 $ 78.8 $ 70.5 $ 229.1 (In Millions) Year Ended December 31, 2017 Hedge Funds Private Equity Funds Structured Credit Fund Real Estate Total Beginning balance — January 1, 2017 $ 40.6 $ 36.1 $ 63.8 $ 61.9 $ 202.4 Actual return on plan assets: Relating to assets still held at the reporting date 2.5 0.3 9.1 4.2 16.1 Relating to assets sold during 0.4 4.5 — (0.1 ) 4.8 Purchases 39.0 4.5 — 14.4 57.9 Sales (45.1 ) (5.6 ) — (14.9 ) (65.6 ) Ending balance — December 31, 2017 $ 37.4 $ 39.8 $ 72.9 $ 65.5 $ 215.6 VEBA Assets for OPEB plans include VEBA trusts pursuant to bargaining agreements that are available to fund retired employees’ life insurance obligations and medical benefits. The fair value of our other benefit plan assets by asset category is as follows: (In Millions) December 31, 2018 Asset Category Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Equity securities: U.S. large-cap $ 9.7 $ — $ — $ 9.7 U.S. small/mid-cap 2.4 — — 2.4 International 7.3 — — 7.3 Fixed income 146.8 37.8 — 184.6 Hedge funds — — 11.4 11.4 Private equity — — 3.0 3.0 Structured credit — — 8.5 8.5 Real estate — — 13.1 13.1 Cash 0.2 — — 0.2 Total $ 166.4 $ 37.8 $ 36.0 $ 240.2 (In Millions) December 31, 2017 Asset Category Quoted Prices in Active Significant Other Significant Total Equity securities: U.S. large-cap $ 11.4 $ — $ — $ 11.4 U.S. small/mid-cap 2.8 — — 2.8 International 8.8 — — 8.8 Fixed income 164.1 40.0 — 204.1 Hedge funds — — 11.4 11.4 Private equity — — 3.9 3.9 Structured credit — — 7.9 7.9 Real estate — — 12.0 12.0 Cash 0.2 — — 0.2 Total $ 187.3 $ 40.0 $ 35.2 $ 262.5 The following represents the effect of fair value measurements using significant unobservable inputs (Level 3) on changes in plan assets: (In Millions) Year Ended December 31, 2018 Hedge Funds Private Equity Funds Structured Credit Fund Real Estate Total Beginning balance — January 1, 2018 $ 11.4 $ 3.9 $ 7.9 $ 12.0 $ 35.2 Actual return on plan assets: Relating to assets still held at the reporting date — (0.1 ) 0.6 1.1 1.6 Relating to assets sold during the period — 0.3 — — 0.3 Purchases — — — — — Sales — (1.1 ) — — (1.1 ) Ending balance — December 31, 2018 $ 11.4 $ 3.0 $ 8.5 $ 13.1 $ 36.0 (In Millions) Year Ended December 31, 2017 Hedge Funds Private Equity Funds Structured Credit Fund Real Estate Total Beginning balance — January 1, 2017 $ 11.2 $ 4.3 $ 6.9 $ 11.1 $ 33.5 Actual return on plan assets: Relating to assets still held at the reporting date 0.8 0.9 2.0 3.4 7.1 Relating to assets sold during the period — (0.4 ) (1.0 ) (2.5 ) (3.9 ) Purchases 17.1 1.8 2.1 3.0 24.0 Sales (17.7 ) (2.7 ) (2.1 ) (3.0 ) (25.5 ) Ending balance — December 31, 2017 $ 11.4 $ 3.9 $ 7.9 $ 12.0 $ 35.2 Contributions Annual contributions to the pension plans are made within income tax deductibility restrictions in accordance with statutory regulations. In the event of plan termination, the plan sponsors could be required to fund additional shut down and early retirement obligations that are not included in the pension obligations. Costs for early termination for pensions and other benefits are estimated to be $22.1 million and $3.4 million , respectively. The Company currently has no intention to shut down, terminate or withdraw from any of its employee benefit plans. (In Millions) Pension Benefits Other Benefits Company Contributions VEBA Direct Payments Total 2017 $ 24.4 $ — $ 2.1 $ 2.1 2018 27.6 — 3.8 3.8 2019 (Expected) 1 15.9 — 3.5 3.5 1 Pursuant to the bargaining agreement, benefits can be paid from VEBA trusts that are at least 70% funded (all VEBA trusts are over 70% funded at December 31, 2018). Funding obligations have been suspended as UTAC's, Tilden's and Empire's share of the value of their respective trust assets have reached 90% of their obligation. VEBA plans are not subject to minimum regulatory funding requirements. Amounts contributed are pursuant to bargaining agreements. Contributions by participants to the OPEB plans were $5.6 million for the year ended December 31, 2018 and $4.6 million for the year ended December 31, 2017 . Estimated Cost for 2019 For 2019 , we estimate net periodic benefit cost as follows: (In Millions) Defined benefit pension plans $ 21.5 Other postretirement benefits (2.8 ) Total $ 18.7 Estimated Future Benefit Payments (In Millions) Pension Benefits Other Benefits Gross Company Benefits Less Medicare Subsidy Net Benefit Payments 2019 $ 70.4 $ 18.0 $ (0.8 ) $ 17.2 2020 67.9 17.7 (0.8 ) 16.9 2021 67.5 17.2 (0.9 ) 16.3 2022 67.0 17.0 (0.9 ) 16.1 2023 67.9 16.9 (1.0 ) 15.9 2024-2028 309.7 82.2 (5.4 ) 76.8

STOCK COMPENSATION PLANS

STOCK COMPENSATION PLANS	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
STOCK COMPENSATION PLANS	NOTE 9 - STOCK COMPENSATION PLANS At December 31, 2018 , we have outstanding awards under various share-based compensation plans, which are described below. The compensation cost charged against income from continuing operations for those plans was $15.1 million , $18.2 million and $13.6 million in 2018 , 2017 and 2016 , respectively, which primarily was recorded in Selling, general and administrative expenses in the Statements of Consolidated Operations. There was no income tax benefit recognized for the years ended December 31, 2018 , 2017 and 2016 , due to the full valuation allowance. Employees’ Plans The A&R 2015 Equity Plan was approved by our Board of Directors on February 21, 2017 and by our shareholders on April 25, 2017. The A&R 2015 Equity Plan increased the maximum number of shares that may be issued by 15.0 million common shares. The 2015 Equity Plan was approved by our Board of Directors on March 26, 2015 and by our shareholders on May 19, 2015. The 2015 Equity Plan replaced the 2012 Equity Plan, and allowed for a maximum of 12.9 million common shares to be issued. No additional grants were issued from the 2012 Equity Plan after the date of approval of the 2015 Equity Plan; however, all awards previously granted under the 2012 Amended Equity Plan will continue in full force and effect in accordance with the terms of outstanding awards. Following is a summary of approved grants by the Compensation Committee : Grant Year Vesting Date Plan Issued Under Restricted Stock Units Granted Performance Shares Granted 2018 12/31/2020 A&R 2015 Equity Plan 685,599 675,599 2017 12/31/2019 A&R 2015 Equity Plan 532,358 249,106 2017 12/31/2019 Amended 2015 Equity Plan 553,725 553,725 2016 12/31/2018 2015 Equity Plan 3,406,716 — Performance Shares The outstanding performance shares vest over a period of three years and are intended to be paid out in common shares. Performance is measured on the basis of relative TSR for the period and measured against the constituents of the S&P Metals and Mining ETF Index at the beginning of the relevant performance period. The final payout for the outstanding performance period grants will vary from 0% 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. Following is a summary of our performance share award agreements currently outstanding : Performance Performance Shares Granted Forfeitures to Date Expected to Vest Grant Date Grant Date Fair Value Performance Period 2018 675,599 2,236 673,363 2/21/2018 $ 11.93 1/1/2018 - 12/31/2020 2017 249,106 — 249,106 6/26/2017 $ 10.74 5/31/2017 - 12/31/2019 2017 553,725 51,471 502,254 2/21/2017 $ 19.69 1/1/2017 - 12/31/2019 Restricted Stock Units All of the outstanding restricted stock units are subject to continued employment, are retention based, and are payable in common shares or cash in certain circumstances at a time determined by the Compensation Committee at its discretion. The outstanding restricted stock units that were granted in 2018, 2017, and 2016 cliff vest in three years on December 31, 2020, 2019 and 2018, respectively. Stock Options The 412,710 stock options that were granted during the first quarter of 2015 vested on December 31, 2017, are exercisable at a strike price of $7.70 and expire on January 12, 2025. The 250,000 stock options that were granted in the fourth quarter of 2014 vested in equal thirds on each of December 31, 2015, 2016 and 2017 and are exercisable at a strike price of $13.83 and expire on November 17, 2021. As of December 31, 2018, 563,230 stock options remain outstanding and are exercisable with a weighted average price of $10.42 . Employee Stock Purchase Plan On March 26, 2015, upon recommendation by the Compensation Committee, our Board of Directors approved and adopted, subject to the approval of Cliffs' shareholders at the 2015 Annual Meeting, the Cliffs Natural Resources Inc. 2015 Employee Stock Purchase Plan. This plan was approved by our shareholders at the 2015 Annual Meeting held May 19, 2015. Ten million common shares have been reserved for issuance under this plan; however, as of December 31, 2018, this program has not been made active and no common shares have been purchased. We sought shareholder approval of this plan for the purpose of qualifying the reserved common shares for special tax treatment under Section 423 of the IRC of 1986, as amended. Nonemployee Directors Our nonemployee directors are entitled to receive restricted share awards under the Directors’ Plan. For 2018, 2017 and 2016, nonemployee directors were granted a specified number of restricted shares, with a value equal to $100,000 , $100,000 , and $85,000 , respectively. The number of shares is based on the closing price of our common shares on the date of the Annual Meeting. The awards are subject to any deferral election and pursuant to the terms of the Directors’ Plan and an award agreement. On April 23, 2018, our Governance and Nominating Committee of the Board of Directors approved the acceleration of vesting of the restricted share awards granted to the nonemployee directors prior to April 2018, which were generally subject to three -year vesting. Effective April 30, 2018 and under the terms of the Directors' Plan, the vesting of these outstanding awards was accelerated. The Governance and Nominating Committee also approved a change to the vesting period for all future awards under the Directors' Plan. The nonemployee director restricted awards granted on April 25, 2018 and all future awards are subject to one -year vesting. For the last three years, grants of restricted and/or deferred shares have been awarded to elected or re-elected nonemployee directors as follows: Year of Grant Restricted Shares Deferred Shares 2018 92,718 17,170 2017 93,359 17,289 2016 135,038 29,583 Other Information The following table summarizes the share-based compensation expense that we recorded in continuing operations: (In Millions, except per share amounts) 2018 2017 2016 Cost of goods sold and operating expenses $ 1.7 $ 1.9 $ 1.8 Selling, general and administrative expenses 13.4 16.3 11.8 Reduction of operating income from continuing operations before income taxes 15.1 18.2 13.6 Income tax benefit 1 — — — Reduction of net income from continuing operations attributable to Cliffs shareholders $ 15.1 $ 18.2 $ 13.6 Reduction of continuing operations earnings per common share attributable to Cliffs shareholders: Basic $ 0.05 $ 0.06 $ 0.07 Diluted $ 0.05 $ 0.06 $ 0.07 1 No income tax benefit due to the full valuation allowance. Stock option, restricted stock awards and performance share activity under our long-term equity plans and Directors’ Plans are as follows: 2018 2017 2016 Shares Shares Shares Stock options: Outstanding at beginning of year 599,870 599,870 607,489 Exercised (36,640 ) — — Forfeited/canceled — — (7,619 ) Outstanding at end of year 563,230 599,870 599,870 Restricted awards: Outstanding and restricted at beginning of year 4,776,483 5,461,783 2,338,070 Granted during the year 795,487 1,196,731 3,571,337 Vested and issued (627,567 ) (1,813,315 ) (271,988 ) Forfeited/canceled (140,155 ) (68,716 ) (175,636 ) Outstanding and restricted at end of year 4,804,248 4,776,483 5,461,783 Performance shares: Outstanding at beginning of year 1,848,312 1,368,469 1,496,489 Granted during the year 675,599 802,831 — Vested and issued (489,953 ) — (59,260 ) Forfeited/canceled (609,235 ) (322,988 ) (68,760 ) Outstanding at end of year 1,424,723 1,848,312 1,368,469 Vested or expected to vest as of December 31, 2018 1 6,792,201 Directors’ retainer and voluntary shares: Outstanding at beginning of year — — — Granted during the year 27,300 25,476 — Vested and issued (27,300 ) (25,476 ) — Outstanding at end of year — — — Reserved for future grants or awards at end of year: Employee plans 12,949,420 Directors’ plans 502,378 Total 13,451,798 1 With the adoption of ASU 2016-09, we assume all shares will vest until the date of vesting or forfeiture. A summary of our outstanding share-based awards as of December 31, 2018 is shown below: Shares Weighted Average Grant Date Fair Value Outstanding, beginning of year 7,224,665 $ 6.79 Granted 1,498,386 $ 9.51 Vested and issued (1,181,460 ) $ 7.38 Forfeited/canceled (749,390 ) $ 10.22 Outstanding, end of year 6,792,201 $ 6.90 The total compensation cost related to outstanding awards not yet recognized is $17.1 million at December 31, 2018 . The weighted average remaining period for the awards outstanding at December 31, 2018 is approximately 1.0 year.

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	NOTE 10 - INCOME TAXES Income from continuing operations before income taxes includes the following components: (In Millions) 2018 2017 2016 United States $ 565.0 $ 90.7 $ 124.9 Foreign (0.3 ) 17.5 (14.5 ) $ 564.7 $ 108.2 $ 110.4 The components of the income tax benefit on continuing operations consist of the following: (In Millions) 2018 2017 2016 Current provision (benefit): United States federal $ (0.5 ) $ (252.6 ) $ (11.1 ) United States state & local — (0.1 ) (0.5 ) Foreign 0.7 0.3 (0.1 ) 0.2 (252.4 ) (11.7 ) Deferred benefit: United States federal (475.4 ) — (0.5 ) Total income tax benefit from continuing operations $ (475.2 ) $ (252.4 ) $ (12.2 ) Reconciliation of our income tax attributable to continuing operations computed at the U.S. federal statutory rate is as follows: (In Millions) 2018 2017 2016 Tax at U.S. statutory rate $ 118.6 21.0 % $ 37.9 35.0 % $ 38.6 35.0 % Increase (decrease) due to: Percentage depletion in excess of cost depletion (54.6 ) (9.7 ) (61.6 ) (56.9 ) (36.1 ) (32.7 ) Impact of tax law change - remeasurement of deferred taxes — — 407.5 376.6 149.1 135.1 Dissolution of Luxembourg entities 161.7 28.6 — — — — Prior year adjustments in current year (1.0 ) (0.2 ) (1.1 ) (1.0 ) (11.8 ) (10.7 ) Valuation allowance build (reversal): Tax law change - remeasurement of deferred taxes — — (407.5 ) (376.6 ) (149.1 ) (135.1 ) Current year activity (80.6 ) (14.3 ) (466.3 ) (431.0 ) 122.9 111.3 Release of U.S. valuation allowance (460.5 ) (81.5 ) — — — — Repeal of AMT — — (235.3 ) (217.5 ) — — Dissolution of Luxembourg entities (161.7 ) (28.6 ) — — — — Prior year adjustments in current year 1.0 0.2 (3.5 ) (3.2 ) 9.3 8.4 Tax uncertainties (1.3 ) (0.2 ) (1.4 ) (1.3 ) (11.3 ) (10.2 ) Worthless stock deduction — — — — (73.4 ) (66.5 ) Impact of foreign operations 0.1 — 477.9 441.7 (40.6 ) (36.8 ) Other items, net 3.1 0.6 1.0 0.9 (9.8 ) (8.9 ) Provision for income tax benefit and effective income tax rate including discrete items $ (475.2 ) (84.1 )% $ (252.4 ) (233.3 )% $ (12.2 ) (11.1 )% Our tax provision for the year ended December 31, 2018 was a benefit of $475.2 million and an effective tax rate of negative 84.1% compared with a benefit of $252.4 million and an effective tax rate of negative 233.3% for the prior year. The increase in income tax benefit from the prior year is primarily due to release of the valuation allowance in the U.S. of $460.5 million in the fourth quarter of 2018. Additionally, during 2018, a legal entity reduction initiative was completed resulting in the dissolution of two Luxembourg entities, both of which held net operating loss deferred tax assets. This asset reduction resulted in an expense of $161.7 million which was fully offset by a decrease in valuation allowance. In December 2017, a benefit of $235.3 million was recorded as a result of the repeal of AMT in the 2017 U.S. income tax reform legislation. Additionally, the impact of tax law change - remeasurement of deferred taxes for the year ended December 31, 2017 primarily relates to the statutory rate reduction in the U.S. that decreased the deferred tax assets by $334.1 million , which was fully offset by a decrease in the valuation allowance. Also on December 31, 2017 and 2016, there was a Luxembourg rate reduction that decreased the deferred tax assets by $73.4 million and $149.1 million , respectively. Both of these asset reductions were fully offset by a decrease in valuation allowance. The impact of foreign operations relates to income and losses in foreign jurisdictions where the statutory rates, ranging from 0% to 29.22% , differ from the U.S. statutory rate of 21% for the year ended December 31, 2018 and 35% for the years ended December 31, 2017 and 2016. The components of income taxes for other than continuing operations consisted of the following: (In Millions) 2018 2017 2016 Other comprehensive (income) loss: Postretirement benefit liability $ 3.6 $ — $ — Unrealized net loss on derivative financial instruments 0.7 — — Other — — 0.5 Total $ 4.3 $ — $ 0.5 Significant components of our deferred tax assets and liabilities are as follows: (In Millions) 2018 2017 Deferred tax assets: Operating loss carryforwards $ 2,118.8 $ 2,362.4 Pensions 77.5 76.3 OPEB 25.3 25.6 Deferred income 23.3 24.2 Intangible assets 11.6 13.0 Property, plant and equipment and mineral rights 13.3 — State and local 68.2 74.2 Other liabilities 36.8 30.4 Total deferred tax assets before valuation allowance 2,374.8 2,606.1 Deferred tax asset valuation allowance (1,287.3 ) (1,983.1 ) Net deferred tax assets 1,087.5 623.0 Deferred tax liabilities: Property, plant and equipment and mineral rights — (1.5 ) Investment in ventures (141.2 ) (137.5 ) Intercompany notes (465.7 ) (465.7 ) Other assets (15.8 ) (18.3 ) Total deferred tax liabilities (622.7 ) (623.0 ) Net deferred tax assets $ 464.8 $ — We had gross domestic (including states) and foreign net operating loss carryforwards of $3.6 billion and $6.6 billion , respectively, at December 31, 2018 . We had gross domestic and foreign net operating loss carryforwards at December 31, 2017 of $4.2 billion and $7.2 billion , respectively. The U.S. Federal net operating losses will begin to expire in 2034 and state net operating losses will begin to expire in 2019. The foreign net operating losses can be carried forward indefinitely. We had foreign tax credit carryforwards of $5.8 million at December 31, 2018 and 2017 . The foreign tax credit carryforwards will begin to expire in 2020. We recorded a $695.8 million net decrease in the valuation allowance of certain deferred tax assets in the year ended December 31, 2018 . As of December 31, 2018, our U.S. operations emerged from a three -year cumulative loss position. As the significant negative evidence of cumulative losses has been eliminated, we undertook an evaluation of the continuing need for a valuation allowance on the U.S. deferred tax assets, the majority of which relate to the U.S. tax net operating losses. In completing our evaluation of whether a valuation allowance was still needed, we considered all available positive and negative evidence. Positive evidence considered included the emergence from the three -year cumulative loss position, our long-term customer contracts with minimum tonnage requirements, the global scarcity of iron ore pellets, near term forecasts of strong profitability and the recently revised IRC Section 163(j) interest deduction limitation. Negative evidence included the overall size of the deferred tax asset with limited carryforward and no carryback opportunity, the finite nature of the iron ore resources we mine, the uncertainty of steel tariffs that positively impacted our revenue rates in 2018 and the various market signs that the U.S. economy may be nearing the end of the current expansion. We also considered that future realization of the deferred tax assets depends on the existence of sufficient taxable income of the appropriate character during the carryforward period. In considering sources of taxable income, we identified that a portion of the deferred tax assets would be utilized by existing taxable temporary differences reversing in the same periods as existing deductible temporary differences. In addition, we determined that carryback opportunities and tax planning strategies do not exist as potential sources of future taxable income. Lastly, forecasting future taxable income was considered, but is challenging in a cyclical industry such as ours as it relies heavily on the accuracy of key assumptions, particularly about key pricing benchmarks. Because historical information is verifiable and more objective than forecast information and due to the cyclicality of the industry, we developed an estimate of future income based on our historical earnings through the most recent industry cycle. We adjusted historical earnings for certain non-recurring items as well as to reflect the current corporate structure by eliminating the impact of discontinued operations and extinguished debt (“core earnings”). Additionally, we adjusted core earnings to reflect the impact of the recently revised IRC Section 163(j) interest expense deduction limitation as well as permanent tax adjustments. The IRC Section 163(j) limitation will limit our interest expense deduction, particularly in down years in the industry cycle, resulting in higher taxable income. Based on the core earnings analysis, the Company’s average annual book taxable income through the business cycle is in excess of the estimated $109.0 million taxable income that would be required annually to fully utilize the deferred tax assets within the 19 year carryforward period. We ascribed significant weight in our assessment to the core earnings analysis and the resulting projection of taxable income through the industry cycle. Based on the weight of this positive evidence, and after considering the other available positive and negative evidence, we determined that it was appropriate to release all of the valuation allowance related to U.S. federal deferred tax assets at December 31, 2018 as it is more likely than not that the entire amount of the U.S. deferred tax asset will be realized before the end of the carryforward period. The income tax benefit recorded for the reversal of the valuation allowance against the U.S. deferred tax assets is $460.5 million . During 2018, a legal entity reduction initiative was completed resulting in the dissolution of two Luxembourg entities, both of which held net operating loss deferred tax assets. This asset reduction resulted in an expense of $161.7 million which was fully offset by a decrease in valuation allowance. The remainder of the decrease relates to current year activity. We continue to maintain a full valuation allowance against the remaining Luxembourg subsidiaries net deferred tax assets of approximately $1.2 billion . Our losses in Luxembourg in recent periods represent sufficient negative evidence to require a full valuation allowance against the deferred tax assets in that jurisdiction. We intend to maintain a valuation allowance against the deferred tax assets related to these operating losses, until sufficient positive evidence exists to support the realization of such assets. We also have a valuation allowance recorded against certain state net operating losses and foreign tax credits, which are expected to expire before utilization of approximately $38.3 million and $5.8 million at December 31, 2018 and 2017 , respectively. At December 31, 2018 and 2017 , we had no cumulative undistributed earnings of foreign subsidiaries included in consolidated retained earnings. Accordingly, no provision has been made for U.S. deferred taxes related to future repatriation of earnings. A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: (In Millions) 2018 2017 2016 Unrecognized tax benefits balance as of January 1 $ 33.5 $ 30.7 $ 156.2 Increase (decrease) for tax positions in prior years 0.1 (2.8 ) (61.0 ) Increase for tax positions in current year 3.6 4.5 0.2 Settlements — 1.0 (64.7 ) Lapses in statutes of limitations (8.2 ) — — Other — 0.1 — Unrecognized tax benefits balance as of December 31 $ 29.0 $ 33.5 $ 30.7 At December 31, 2018 and 2017 , we had $29.0 million and $33.5 million , respectively, of unrecognized tax benefits recorded. Of this amount, $4.2 million and $6.1 million , respectively, were recorded in Other liabilities and $24.8 million and $27.4 million , respectively, were recorded as Other non-current assets in the Statements of Consolidated Financial Position for both years. If the $29.0 million were recognized, only $4.2 million would impact the effective tax rate. We do not expect that the amount of unrecognized benefits will change significantly within the next 12 months. At December 31, 2018 and 2017 , we had $2.7 million and $2.1 million , respectively, of accrued interest and penalties related to the unrecognized tax benefits recorded in Other liabilities in the Statements of Consolidated Financial Position. Tax years 2015 and forward remain subject to examination for the U.S. and tax years 2008 and forward remain subject to examination for Canada.

ENVIRONMENTAL AND MINE CLOSURE

ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	12 Months Ended
	Dec. 31, 2018
Environmental Remediation Obligations [Abstract]
Environmental Loss Contingency And Mine Closure Obligation Disclosure [Text Block]	NOTE 11 - ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS The following is a summary of our environmental and mine closure obligations: (In Millions) December 31, 2018 2017 Environmental $ 2.5 $ 2.9 Mine closure 1 172.4 168.4 Total environmental and mine closure obligations 174.9 171.3 Less current portion 2.9 3.6 Long-term environmental and mine closure obligations $ 172.0 $ 167.7 1 Includes our active operating mines, our indefinitely idled Empire mine and a closed mine formerly operating as LTVSMC. Environmental Our mining and exploration activities are subject to various laws and regulations governing the protection of the environment. We conduct our operations to protect the public health and environment and believe our operations are in compliance with applicable laws and regulations in all material respects. Our environmental liabilities include obligations for known environmental remediation exposures at various active and closed mining operations and other sites, and have been recognized based on the estimated cost of investigation and remediation at each site. If the cost can only be estimated as a range of possible amounts with no specific amount being more likely, the minimum of the range is accrued. Future expenditures are not discounted unless the amount and timing of the cash disbursements are readily known. Potential insurance recoveries have not been reflected. Additional environmental obligations could be incurred, the extent of which cannot be assessed. Mine Closure The accrued closure obligation for our mining operations provides for contractual and legal obligations associated with the eventual closure of the mining operations. We performed a detailed assessment of our asset retirement obligations related to our active mining locations in accordance with our accounting policy, under which we perform an in-depth evaluation of the liability every three years in addition to routine annual assessments. In 2017, we employed a third-party specialist to assist in the triennial in-depth evaluation. For the assessments performed, we determined the obligations based on detailed estimates adjusted for factors that a market participant would consider (e.g., inflation, overhead and profit) and then discounted the obligation using the current credit-adjusted risk-free interest rate based on the corresponding life of mine. The estimate also incorporates incremental increases in the closure cost estimates and changes in estimates of mine lives. The closure date for each of our active operating mine sites was determined based on the exhaustion date of the remaining iron ore reserves. The closure date and expected timing of the capital requirements to meet our obligations for our indefinitely idled or closed mines, is determined based on the unique circumstances of each property. For indefinitely idled or closed mines, the accretion of the liability is recognized over the anticipated timing of remediation. The amortization of the related asset and accretion of the liability is recognized over the estimated mine lives for our active operations. The following represents a roll forward of our asset retirement obligation liability for the years ended : (In Millions) December 31, 2018 2017 Asset retirement obligation at beginning of year $ 168.4 $ 187.8 Accretion expense 9.5 13.9 Remediation payments (1.0 ) (5.6 ) Revision in estimated cash flows (4.5 ) (27.7 ) Asset retirement obligation at end of year $ 172.4 $ 168.4 For the year ended December 31, 2017 , the revision of estimated cash flows relates primarily to updates to our estimates resulting from our three-year in-depth review of our 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) average costing data while the current estimate was compiled using a more detailed cost build-up approach.

DERIVATIVE INSTRUMENTS AND HEDG

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES	12 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES	NOTE 12 - DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES The following table presents the fair value of our derivative instruments and the classification of each in the Statements of Consolidated Financial Position : (In Millions) Derivative Assets Derivative Liabilities December 31, 2018 December 31, 2017 December 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 Derivative assets $ 0.1 $ — Other current liabilities $ 3.7 Other current liabilities $ 0.3 Derivatives not designated as hedging instruments under ASC 815: Customer supply agreement Derivative assets 89.3 Derivative assets 37.9 — — Provisional pricing arrangements Derivative assets 2.1 — — Other current liabilities 1.7 Total derivatives not designated as hedging instruments under ASC 815: $ 91.4 $ 37.9 $ — $ 1.7 Total derivatives $ 91.5 $ 37.9 $ 3.7 $ 2.0 Derivatives Designated as Hedging Instruments - Cash Flow Hedges Commodity Contracts The following table presents our outstanding hedge contracts: (Quantities in Millions) December 31, 2018 December 31, 2017 Notional Amount Unit of Measure Varying Maturity Dates Notional Amount Unit of Measure Varying Maturity Dates Natural gas 1.8 MMBtu January 2019 - August 2019 3.5 MMBtu January 2018 - November 2018 Diesel 11.0 Gallons January 2019 - December 2019 — Derivatives Not Designated as Hedging Instruments Customer Supply Agreement A supply agreement with one 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. Historically, prior to the contract that commenced in 2017, this supplemental revenue and refund data source was the customer's average annual realized steel price. The supplemental pricing is characterized as a freestanding derivative and is required to be accounted for separately once control transfers to the customer. The derivative instrument, which is finalized based on a future price, 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 pellets are consumed and the amounts are settled. Provisional Pricing Arrangements Certain of our 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 Atlantic Basin 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. The price adjustment factors have been evaluated to determine if they qualify as 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. Revenue is recognized generally upon delivery to our customers. Revenue is measured at the point that 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 that control transfers through final settlement of contract terms is recorded in accordance with Topic 815 and is characterized as a derivative and accounted for separately. Subsequently, the derivative instruments 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. The 2018 amounts represent the difference between the amount we expected to receive when revenue was initially measured at the point control transfers and our subsequent estimate of the final revenue rate based on the price calculation established in the supply agreements. The 2017 and 2016 amounts represent the difference between the provisional price agreed upon with our customers based on the supply agreement terms and our estimate of the final revenue rate based on the price calculations established in the supply agreements. The following summarizes the effect of our derivatives that are not designated as hedging instruments in the Statements of Consolidated Operations : (In Millions) Derivatives Not Designated as Hedging Instruments Location of Gain (Loss) Recognized in Income on Derivative Year Ended 2018 2017 2016 Customer supply agreements Product revenues $ 425.8 $ 163.3 $ 41.7 Provisional pricing arrangements Product revenues (3.2 ) (42.7 ) 14.2 Commodity contracts Cost of goods sold and operating expenses — (1.3 ) 1.9 Total $ 422.6 $ 119.3 $ 57.8 Refer to NOTE 7 - FAIR VALUE OF FINANCIAL INSTRUMENTS for additional information.

DISCONTINUED OPERATIONS

DISCONTINUED OPERATIONS	12 Months Ended
	Dec. 31, 2018
Discontinued Operations and Disposal Groups [Abstract]
DISCONTINUED OPERATIONS	NOTE 13 - DISCONTINUED OPERATIONS The information below sets forth selected financial information related to operating results of our businesses classified as discontinued operations, which include our former Asia Pacific Iron Ore, North American Coal and Canadian operations. While the reclassification of revenues and expenses related to discontinued operations from prior periods has no impact upon previously reported net income, the Statements of Consolidated Operations present the revenues and expenses that were reclassified from the specified line items to discontinued operations and the Statements of Consolidated Financial Position present the assets and liabilities that were reclassified from the specified line items to assets and liabilities of discontinued operations. The charts below provide an asset group breakout for each financial statement line impacted by discontinued operations. (In Millions) Year Ended December 31, 2018 2017 2016 Income (loss) from discontinued operations, net of tax Asia Pacific Iron Ore $ 118.3 $ 21.2 $ 96.6 North American Coal (3.6 ) 2.6 (2.4 ) Canadian Operations (26.5 ) (21.3 ) (17.5 ) $ 88.2 $ 2.5 $ 76.7 (In Millions) December 31, 2018 December 31, 2017 Asia Pacific Iron Ore North American Coal Total Asia Pacific Iron Ore North American Coal Total Current assets of discontinued operations $ 12.4 $ — $ 12.4 $ 118.5 $ — $ 118.5 Non-current assets of discontinued operations $ — $ — $ — $ 20.3 $ — $ 20.3 Current liabilities of discontinued operations $ 3.8 $ 2.9 $ 6.7 $ 71.8 $ 3.2 $ 75.0 Non-current liabilities of discontinued operations $ 8.3 $ — $ 8.3 $ 52.2 $ — $ 52.2 (In Millions) Year Ended December 31, 2018 2017 2016 Net cash provided (used) by operating activities Asia Pacific Iron Ore $ (81.3 ) $ 79.6 $ 99.8 Canadian Operations (14.6 ) — — $ (95.9 ) $ 79.6 $ 99.8 Net cash provided (used) by investing activities Asia Pacific Iron Ore $ 19.8 $ (2.8 ) $ (0.4 ) Canadian Operations — (7.7 ) 6.8 North American Coal — 2.1 3.6 $ 19.8 $ (8.4 ) $ 10.0 Asia Pacific Iron Ore Operations Background In January 2018, we announced that we would accelerate the time frame for the planned closure of our Asia Pacific Iron Ore mining operations in Australia. In April 2018, we committed to a course of action leading to the permanent closure of our Asia Pacific Iron Ore mining operations and, as planned, completed our final shipment in June 2018. Factors considered in this decision included increasingly discounted prices for lower-iron-content ore and the quality of the remaining iron ore reserves. During 2018, we sold all of the assets of our Asia Pacific Iron Ore business through a series of sales to third parties. As a result of our planned exit, management determined that our Asia Pacific Iron Ore operating segment met the criteria to be classified as held for sale and a discontinued operation under ASC Topic 205, Presentation of Financial Statements . As such, all current and historical Asia Pacific Iron Ore operating segment results are classified within discontinued operations. Income from Discontinued Operations For the reasons discussed above, our previously reported Asia Pacific Iron Ore operating segment results for all periods presented, as well as exit costs, are classified as discontinued operations. (In Millions) Year Ended December 31, Income from Discontinued Operations 2018 2017 2016 Revenues from product sales and services $ 129.1 $ 464.2 $ 554.5 Cost of goods sold and operating expenses (230.7 ) (427.9 ) (440.9 ) Sales margin (101.6 ) 36.3 113.6 Other operating expense (3.3 ) (9.9 ) (10.4 ) Other expense (2.3 ) (5.2 ) (6.6 ) Gain on foreign currency translation 228.1 — — Impairment of long-lived assets (2.6 ) — — Income from discontinued operations, net of tax $ 118.3 $ 21.2 $ 96.6 Recorded Assets and Liabilities (In Millions) Assets and Liabilities of Discontinued Operations December 31, December 31, Cash and cash equivalents $ 12.4 $ 29.4 Accounts receivable, net — 33.9 Inventories — 45.0 Supplies and other inventories — 5.1 Other current assets — 5.1 Total current assets of discontinued operations 12.4 118.5 Property, plant and equipment, net — 17.2 Other non-current assets — 3.1 Total assets of discontinued operations $ 12.4 $ 138.8 Accounts payable $ 3.4 $ 28.2 Accrued liabilities 0.4 28.0 Other current liabilities — 15.6 Total current liabilities of discontinued operations 3.8 71.8 Environmental and mine closure obligations — 28.8 Other liabilities 8.3 23.4 Total liabilities of discontinued operations $ 12.1 $ 124.0 Foreign Currency Historically, the functional currency of our Australian subsidiaries was the Australian dollar. The financial statements of our Australian subsidiaries were previously 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 were recorded as Accumulated other comprehensive loss . Income taxes were not provided for foreign currency translation adjustments. Concurrent with the sale of assets to Mineral Resources Limited in 2018, management determined that there had been significant changes in economic factors related to our Australian subsidiaries. The change in economic factors is a result of the sale and conveyance of substantially all assets and liabilities of our Australian subsidiaries to third parties, representing a significant change in operations. As such, the functional currency for the Australian subsidiaries was changed from the Australian dollar to the U.S. dollar and all remaining Australian denominated monetary balances will be remeasured prospectively through the Statements of Consolidated Operations. In addition, as a result of the liquidation of substantially all of the Australian subsidiaries' net assets, the historical changes in foreign currency translation recorded in Accumulated other comprehensive loss in the Statements of Consolidated Financial Position totaling $228.1 million was reclassified and recognized as a gain in Income from discontinued operations, net of tax in the Statements of Consolidated Operations. North American Coal Operations As of March 31, 2015, management determined that our North American Coal operating segment met the criteria to be classified as held for sale under ASC Topic 205, Presentation of Financial Statements. The North American Coal segment continued to meet the criteria throughout 2015 until we sold our North American Coal operations during the fourth quarter of 2015. As such, all current and historical North American Coal operating segment results are classified as discontinued operations in our financial statements. Historical results also include our CLCC assets, which were sold during the fourth quarter of 2014. We have recognized a tax benefit of $1.0 million for the year ended December 31, 2018 included in Income from discontinued operations, net of tax in the Statements of Consolidated Operations related to a loss on our North American Coal investments. There was no tax expense or benefit recognized for the years ended December 31, 2017 and 2016 . Canadian Operations CCAA Proceedings On January 27, 2015, we announced that the Bloom Lake Group commenced restructuring proceedings in Montreal, Quebec under the CCAA to address the Bloom Lake Group's immediate liquidity issues and to preserve and protect its assets for the benefit of all stakeholders while restructuring and/or sale options were explored. Additionally, on May 20, 2015, the Wabush Group commenced restructuring proceedings in Montreal, Quebec under the CCAA. During March 2018, we entered into a restructuring term sheet that documented the proposed agreed to terms of a plan of compromise or arrangement with the Bloom Lake Group, the Wabush Group and the Monitor in the CCAA proceedings. By order of the Québec Superior Court of Justice (Commercial Division) (the “Court”) dated April 20, 2018, the Bloom Lake Group and the Wabush Group were authorized to file a joint plan of compromise and arrangement dated April 16, 2018 (the “Original Plan”). Following discussions with various stakeholder groups, the Bloom Lake Group and the Wabush Group were authorized by the Court to amend the Original Plan and to file the amended and restated joint plan of compromise and arrangement dated May 16, 2018 (the “Amended Plan”). The Amended Plan was approved by the required majorities of each unsecured creditor class and was sanctioned by the Court by order dated June 29, 2018. In addition, the Bloom Lake Group and the Wabush Group brought a motion before the Court on July 30, 2018 seeking to make further amendments to the Amended Plan to address the manner in which certain distributions under the Amended Plan would be effected. On July 31, 2018, the conditions precedent to the implementation of the Amended Plan were satisfied and the Amended Plan was implemented. Under the terms of the Amended Plan, we and certain of our wholly-owned subsidiaries made a C$19.0 million cash contribution to the Wabush Group pension plans and agreed to contribute into the CCAA estate any remaining distributions or payments we may be entitled to receive as creditors of the Bloom Lake Group and the Wabush Group for distribution to other creditors. The Original Plan did not resolve certain employee claims asserted against us and certain of our affiliates outside of the CCAA proceedings. The Amended Plan resolved those employee claims, all claims by the Bloom Lake Group, the Wabush Group and their respective creditors against us as well as all of our claims against the Bloom Lake Group and the Wabush Group. Loss on Discontinued Operations Our Canadian exit represented a strategic shift in our business. For this reason, our previously reported Eastern Canadian Iron Ore and Ferroalloys operating segment results for all periods prior to the respective deconsolidations, as well as costs to exit, are classified as discontinued operations. The chart below provides a breakout of loss from deconsolidation: (In Millions) Year Ended December 31, 2018 2017 2016 Investment impairment on deconsolidation 1 $ (67.5 ) $ 3.0 $ (17.5 ) Guarantees and contingent liabilities 41.0 (24.3 ) — Total loss from deconsolidation $ (26.5 ) $ (21.3 ) $ (17.5 ) 1 Includes the adjustments to fair value of our remaining interest in the Canadian Entities for the years ended December 31, 2018, 2017 and 2016, and a tax expense resulting from the implementation of the Amended Plan for the year ended December 31, 2018. Investments in the Canadian Entities From the date of deconsolidation until the Amended Plan was approved by the required majorities of each unsecured creditor class and was sanctioned by the Court by order dated June 29, 2018 (the “Sanction Order”), we adjusted our investment in the Canadian Entities to zero with a corresponding charge to Income from discontinued operations, net of tax . Amounts Receivable from the Canadian Entities 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. As of December 31, 2017 we had $51.6 million classified as Loans to and accounts receivables from the Canadian Entities in the Statements of Consolidated Financial Position . Following the approval of the Amended Plan, we reversed our outstanding $51.6 million classified within Loans to and accounts receivables from the Canadian Entities with a corresponding charge to Income from discontinued operations, net of tax in the Statements of Consolidated Financial Position for the year ended December 31, 2018 . Income Tax Expense We have recognized tax expense of $15.9 million for the year ended December 31, 2018 , included in Income from discontinued operations, net of tax related to a gain on our Canadian investments. This expense is primarily the result of the current year receipt of CCAA estate distributions which were immediately contributed back into the CCAA estate as required by the Amended Plan. There was no tax expense or benefit recognized for the years ended December 31, 2017 and 2016 . Guarantees and Contingent Liabilities Under the terms of the approved Amended Plan in 2018 , we and certain of our wholly-owned subsidiaries made a C$19.0 million cash contribution included in Income from discontinued operations, net of tax to the Wabush Group pension plans. During 2017 , we became aware that it was probable the Monitor would assert a preference claim against the Company and/or certain of its affiliates. We estimated a liability of $55.6 million , which included the value of our related-party claims against the Bloom Lake Group and the Wabush Group, classified as Contingent claims in the Statements of Consolidated Financial Position as of December 31, 2017 . Following the approval of the Amended Plan, we reversed our outstanding liability of $55.6 million with a corresponding credit to Income from discontinued operations, net of tax in the Statements of Consolidated Operations for the year ended December 31, 2018 . During 2017 , the Wabush Scully Mine was sold as part of the ongoing CCAA proceedings for the Wabush Group. We previously recorded liabilities of $37.2 million related to guarantees for certain environmental obligations of the Canadian Entities, classified as Other liabilities in the Statements of Consolidated Financial Position as of December 31, 2016 . As part of this transaction, we were required to fund the buyer's financial assurance shortfall of $7.7 million in order to complete the conveyance of the environmental remediation obligations to the buyer, which released us from our guarantees and resulted in a net gain of $31.4 million included in Income from discontinued operations, net of tax in the Statements of Consolidated Operations for the year ended December 31, 2017 .

CAPITAL STOCK

CAPITAL STOCK	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
CAPITAL STOCK	NOTE 14 - CAPITAL STOCK Share Repurchase Program On November 26, 2018, we announced that our Board of Directors authorized a program to repurchase outstanding common shares in the open market or in privately negotiated transactions, up to a maximum of $200 million . We are not obligated to make any purchase and the program may be suspended or discontinued at any time. During 2018, we repurchased 5.4 million common shares at a cost of approximately $47.5 million in aggregate, including commissions and fees, or an average price of approximately $8.78 per share. As of December 31, 2018, there was approximately $152.7 million remaining under the authorization. The share repurchase program is active until December 31, 2019. Dividends On October 18, 2018, the Board of Directors declared a quarterly cash dividend on our common shares of $0.05 per share. As a result, we have recorded $15.0 million in Other current liabilities in the Statements of Consolidated Financial Position for the year ended December 31, 2018 . Subsequent to year end on January 15, 2019, the cash dividend was paid to shareholders of record as of the close of business on January 4, 2019. Common Share Public Offering On February 9, 2017, we issued 63.25 million common shares in an underwritten public offering at a public offering price of $10.75 per common share. We received net proceeds of $661.3 million . The net proceeds from the issuance of our common shares and our issuance of $500 million aggregate principal amount of 2025 Senior Notes were used to redeem in full all of our outstanding 8.00% 2020 1.5 Lien Notes and 7.75% 2020 Second Lien Notes. The aggregate principal amount outstanding of debt redeemed was $648.6 million . Additionally, through tender offers, we purchased $422.2 million in aggregate principal amount of debt, excluding unamortized discounts and deferred charges, of our 5.90% 2020 Senior Notes, our 4.80% 2020 Senior Notes and our 4.875% 2021 Senior Notes. In addition, we redeemed $35.6 million aggregate principal amount of the 8.25% 2020 First Lien Notes with the remaining net proceeds from our common share offering. On August 10, 2016, we issued 44.4 million common shares in an underwritten public offering at a public offering price of $6.75 per common share. We received net proceeds of $287.4 million . The net proceeds from the issuance of our common shares were used to fully redeem our 3.95% 2018 Senior Notes. Preferred Shares Conversion to Common Shares On January 4, 2016, we announced that our Board of Directors determined the final quarterly dividend of our Preferred Shares would not be paid in cash, but instead, pursuant to the terms of the Preferred Shares, the conversion rate was increased such that holders of the Preferred Shares received additional common shares in lieu of the accrued dividend at the time of the mandatory conversion on February 1, 2016. The number of common shares issued on conversion was determined based on the average VWAP per share of our common shares during the 20 trading day period beginning on, and including, the 23 rd scheduled trading day prior to February 1, 2016, subject to customary anti-dilution adjustments. Upon conversion on February 1, 2016, an aggregate of 26.5 million common shares were issued, representing 25.2 million common shares issuable upon conversion and 1.3 million that were issued in lieu of a final cash dividend. Debt-for-Equity Exchanges During the year ended December 31, 2016, we entered into a series of privately negotiated exchange agreements whereby we issued an aggregate of 8.2 million common shares in exchange for $10.0 million aggregate principal amount of our 3.95% 2018 Senior Notes, $20.1 million aggregate principal amount of our 4.80% 2020 Senior Notes and $26.8 million aggregate principal amount of our 4.875% 2021 Senior Notes. There were no exchanges that represented more than 1% of our outstanding common shares during any quarter. Accordingly, we recognized a gain of $11.3 million in Gain (loss) on extinguishment/restructuring of debt in the Statements of Consolidated Operations for the year ended December 31, 2016. The issuances of the common shares in exchange for our senior notes due 2018, 2020 and 2021 were made in reliance on the exemption from registration provided in Section 3(a)(9) of the Securities Act.

ACCUMULATED OTHER COMPREHENSIVE

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Comprehensive Income (Loss) Note [Text Block]	NOTE 15 - ACCUMULATED OTHER COMPREHENSIVE LOSS The components of Accumulated other comprehensive loss within Cliffs shareholders’ equity (deficit) and related tax effects allocated to each are shown below: (In Millions) Pre-tax Amount Tax Benefit After-tax Amount As of December 31, 2018: Postretirement benefit liability $ (408.1 ) $ 127.0 $ (281.1 ) Unrealized net loss on derivative financial instruments (3.5 ) 0.7 (2.8 ) $ (411.6 ) $ 127.7 $ (283.9 ) As of December 31, 2017: Postretirement benefit liability $ (387.3 ) $ 123.4 $ (263.9 ) Foreign currency translation adjustments 225.4 — 225.4 Unrealized net loss on derivative financial instruments (0.5 ) — (0.5 ) $ (162.4 ) $ 123.4 $ (39.0 ) As of December 31, 2016: Postretirement benefit liability $ (384.0 ) $ 123.4 $ (260.6 ) Foreign currency translation adjustments 239.3 — 239.3 $ (144.7 ) $ 123.4 $ (21.3 ) The following tables reflect the changes in Accumulated other comprehensive loss related to Cliffs shareholders’ equity (deficit) for December 31, 2018 , 2017 and 2016: (In Millions) Postretirement Benefit Liability, net of tax Unrealized Net Gain (Loss) on Foreign Currency Translation Net Unrealized Loss on Derivative Financial Instruments, net of tax Accumulated Other Comprehensive Loss Balance December 31, 2017 $ (263.9 ) $ 225.4 $ (0.5 ) $ (39.0 ) Other comprehensive income (loss) before reclassifications (42.9 ) 2.7 (0.6 ) (40.8 ) Net loss (gain) reclassified from accumulated other comprehensive loss 25.7 (228.1 ) (1.7 ) (204.1 ) Balance December 31, 2018 $ (281.1 ) $ — $ (2.8 ) $ (283.9 ) (In Millions) Postretirement Benefit Liability, net of tax Unrealized Net Gain (Loss) on Foreign Currency Translation Net Unrealized Loss on Derivative Financial Instruments, net of tax Accumulated Other Comprehensive Loss Balance December 31, 2016 $ (260.6 ) $ 239.3 $ — $ (21.3 ) Other comprehensive loss before reclassifications (29.8 ) (13.9 ) (0.5 ) (44.2 ) Net loss reclassified from accumulated other comprehensive loss 26.5 — — 26.5 Balance December 31, 2017 $ (263.9 ) $ 225.4 $ (0.5 ) $ (39.0 ) (In Millions) Postretirement Benefit Liability, net of tax Unrealized Net Gain (Loss) on Securities, 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 Balance December 31, 2015 $ (241.4 ) $ 0.1 $ 220.7 $ 2.6 $ (18.0 ) Other comprehensive income (loss) before reclassifications (44.8 ) (0.1 ) 18.4 (3.3 ) (29.8 ) Net loss reclassified from accumulated other comprehensive loss 25.6 — 0.2 0.7 26.5 Balance December 31, 2016 $ (260.6 ) $ — $ 239.3 $ — $ (21.3 ) The following table reflects the details about Accumulated other comprehensive loss components related to Cliffs shareholders’ equity: (In Millions) Details about Accumulated Other Comprehensive Loss Components Amount of (Gain)/Loss Reclassified into Income Affected Line Item in the Statement of Consolidated Operations Year Ended Year Ended Year Ended December 31, 2016 Amortization of pension and postretirement benefit liability: Prior service costs 1 $ (0.8 ) $ (0.4 ) $ (1.5 ) Other non-operating income Net actuarial loss 1 26.2 26.9 27.1 Other non-operating income Curtailments 1 0.3 — — Other non-operating income $ 25.7 $ 26.5 $ 25.6 Net of taxes Changes in foreign currency translation: Unrealized gain on dissolution of entity $ — $ — $ 0.2 Other non-operating income Gain on foreign currency translation 2 (228.1 ) — — Income from discontinued operations, net of tax $ (228.1 ) $ — $ 0.2 Net of taxes Unrealized gain (loss) on derivative financial instruments: Treasury lock $ — $ — $ 1.2 Gain (loss) on extinguishment/restructuring of debt Commodity contracts (1.7 ) — — Cost of goods sold and operating expenses (1.7 ) — 1.2 Total before taxes Income tax expense — — (0.5 ) Income tax benefit $ (1.7 ) $ — $ 0.7 Net of taxes Total reclassifications for the period $ (204.1 ) $ 26.5 $ 26.5 1 These accumulated other comprehensive loss components are included in the computation of net periodic benefit cost. See NOTE 8 - PENSIONS AND OTHER POSTRETIREMENT BENEFITS for further information. 2 Represents Australian accumulated currency translation adjustments due to the liquidation of substantially all of our Australian subsidiaries' net assets. See NOTE 13 - DISCONTINUED OPERATIONS for further information.

CASH FLOW INFORMATION

CASH FLOW INFORMATION	12 Months Ended
	Dec. 31, 2018
Supplemental Cash Flow Information [Abstract]
Cash Flow Information	NOTE 16 - CASH FLOW INFORMATION A reconciliation of capital additions to cash paid for capital expenditures is as follows: (In Millions) Year Ended December 31, 2018 2017 2016 Capital additions 1 $ 394.8 $ 156.0 $ 68.5 Less: Non-cash accruals 93.6 (2.2 ) (0.6 ) Capital leases 7.6 6.5 — Grants (2.5 ) — — Cash paid for capital expenditures including deposits $ 296.1 $ 151.7 $ 69.1 1 Includes capital additions related to discontinued operations of $0.1 million, $2.8 million and $0.2 million for the years ended December 31, 2018, 2017 and 2016, respectively. Cash payments for interest and income taxes are as follows: (In Millions) 2018 2017 2016 Taxes paid on income $ 2.9 $ 1.7 $ 5.9 Income tax refunds $ (11.3 ) $ (7.8 ) $ (5.3 ) Interest paid on debt obligations net of capitalized interest 1 $ 105.7 $ 139.0 $ 184.0 1 Capitalized interest was $6.5 million for the year ended December 31, 2018. Non-Cash Financing Activities - Declared Dividends On October 18, 2018, the Board of Directors declared a quarterly cash dividend on our common shares of $0.05 per share. The cash dividend of $15.0 million was paid on January 15, 2019 to shareholders of record as of the close of business on January 4, 2019.

RELATED PARTIES

RELATED PARTIES	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
RELATED PARTIES	NOTE 17 - RELATED PARTIES One of our four operating mines, Hibbing, is a co-owned joint venture with companies that are integrated steel producers or their subsidiaries. We are the manager of Hibbing 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. The following is a summary of the mine ownership of the co-owned iron ore mine at December 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) Year Ended December 31, 2018 2017 2016 Product revenues from related parties $ 1,234.5 $ 806.7 $ 830.1 Total product revenues $ 2,172.3 $ 1,644.6 $ 1,379.7 Related party product revenue as a percent of total product revenue 56.8 % 49.1 % 60.2 % The following table presents the classification of related party assets and liabilities in the Statements of Consolidated Financial Position : (In Millions) Balance Sheet Location December 31, 2018 December 31, 2017 Accounts receivable, net $ 176.0 $ 68.1 Derivative assets 89.3 37.9 Partnership distribution payable (43.5 ) (44.2 ) Other current liabilities (1.8 ) (12.3 ) Other liabilities — (41.4 ) $ 220.0 $ 8.1 During 2017, our ownership interest in Empire increased to 100% when 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, the second of which was paid in August 2018, and the final of which is due in August 2019. The remaining installment is reflected in Partnership distribution payable in the Statements of Consolidated Financial Position as of December 31, 2018 . A supply agreement with one 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 12 - DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES for further information.

EARNINGS PER SHARE

EARNINGS PER SHARE	12 Months Ended
	Dec. 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 per share: (In Millions, Except Per Share Amounts) Year Ended 2018 2017 2016 Income from continuing operations $ 1,039.9 $ 360.6 $ 122.6 Loss (income) from continuing operations attributable to — 3.9 (25.2 ) Net income from continuing operations $ 1,039.9 $ 364.5 $ 97.4 Income from discontinued operations, net of tax 88.2 2.5 76.7 Net income attributable to Cliffs shareholders $ 1,128.1 $ 367.0 $ 174.1 Weighted average number of shares: Basic 297.2 288.4 197.7 $316.25 million 1.50% 2025 Convertible Senior Notes 3.4 — — Employee stock plans 3.5 4.6 2.4 Diluted 304.1 293.0 200.1 Earnings per common share attributable to Continuing operations $ 3.50 $ 1.27 $ 0.49 Discontinued operations 0.30 0.01 0.39 $ 3.80 $ 1.28 $ 0.88 Earnings per common share attributable to Continuing operations $ 3.42 $ 1.25 $ 0.49 Discontinued operations 0.29 0.01 0.38 $ 3.71 $ 1.26 $ 0.87 The dilutive impact of 2025 Convertible Notes that were issued in December 2017 is calculated based on the treasury-stock method with the number of dilutive shares being calculated based on the difference in the average share price and the conversion price. There was no dilution during 2017 related to the common share equivalents for the 2025 Convertible Notes as our common shares average price did not rise in value above the conversion price.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	NOTE 19 - COMMITMENTS AND CONTINGENCIES Purchase Commitments In 2017, we began to incur capital commitments related to the construction of our HBI production plant in Toledo, Ohio. We expect to spend approximately $830 million on the HBI production plant, exclusive of construction-related contingencies and capitalized interest through 2020. Through December 31, 2018, we have entered into contracts and purchase orders for approximately $580 million of the total capital investment for the HBI production plant, of which a total of approximately $180 million has been expended project-to-date, including deposits. Of the remaining committed capital, expenditures of approximately $425 million and $225 million are expected to be made during 2019 and 2020, respectively. 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. 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 have a material effect on our financial position, results of operations or cash flows. We previously recorded a liability in the Statements of Consolidated Financial Position related to the CCAA proceedings, in which a settlement was reached during the period ended June 30, 2018. Refer to NOTE 13 - DISCONTINUED OPERATIONS for information on the CCAA proceedings. Environmental Matters We had environmental liabilities of $2.5 million and $2.9 million at December 31, 2018 and 2017 , respectively, including obligations for known environmental remediation exposures at active and closed mining operations and other sites. These amounts have been recognized based on the estimated cost of investigation and remediation at each site, and include site studies, design and implementation of remediation plans, legal and consulting fees, and post-remediation monitoring and related activities. Future expenditures are not discounted unless the amount and timing of the cash disbursements are readily known. Potential insurance recoveries have not been reflected. Additional environmental obligations could be incurred, the extent of which cannot be assessed. The amount of our ultimate liability with respect to these matters may be affected by several uncertainties, primarily the ultimate cost of required remediation and the extent to which other responsible parties contribute. Refer to NOTE 11 - ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS for further information. Tax Matters The calculation of our tax liabilities involves dealing with uncertainties in the application of complex tax regulations. We recognize liabilities for anticipated tax audit issues based on our estimate of whether, and the extent to which, additional taxes will be due. If we ultimately determine that payment of these amounts is unnecessary, we reverse the liability and recognize a tax benefit during the period in which we determine that the liability is no longer necessary. We also recognize tax benefits to the extent that it is more likely than not that our positions will be sustained when challenged by the taxing authorities. To the extent we prevail in matters for which liabilities have been established, or are required to pay amounts in excess of our liabilities, our effective tax rate in a given period could be materially affected. An unfavorable tax settlement would require use of our cash and result in an increase in our effective tax rate in the year of resolution. A favorable tax settlement would be recognized as a reduction in our effective tax rate in the year of resolution. Refer to NOTE 10 - INCOME TAXES for further information.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	12 Months Ended
	Dec. 31, 2018
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	NOTE 20 - SUBSEQUENT EVENTS We have evaluated subsequent events through the date of financial statement issuance.

QUARTERLY RESULTS OF OPERATIONS

QUARTERLY RESULTS OF OPERATIONS - (UNAUDITED)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information [Text Block]	The sum of quarterly EPS may not equal EPS for the year due to discrete quarterly calculations. (In Millions, Except Per Share Amounts) 1 2018 Quarters First Second Third Fourth Year Revenues from product sales and services $ 180.0 $ 714.3 $ 741.8 $ 696.3 $ 2,332.4 Sales margin 61.5 284.5 261.6 202.0 809.6 Net income (loss) from continuing operations attributable to Cliffs shareholders (13.4 ) 229.4 199.8 624.1 1,039.9 Income (loss) from discontinued operations, net of tax (70.9 ) (64.3 ) 238.0 (14.6 ) 88.2 Net income (loss) attributable to Cliffs common shareholders $ (84.3 ) $ 165.1 $ 437.8 $ 609.5 $ 1,128.1 Earnings (loss) per common share attributable to Continuing operations $ (0.05 ) $ 0.77 $ 0.67 $ 2.11 $ 3.50 Discontinued operations (0.24 ) (0.22 ) 0.80 (0.05 ) 0.30 $ (0.29 ) $ 0.55 $ 1.47 $ 2.06 $ 3.80 Earnings (loss) per common share attributable to Continuing operations $ (0.05 ) $ 0.76 $ 0.64 $ 2.03 $ 3.42 Discontinued operations (0.24 ) (0.21 ) 0.77 (0.05 ) 0.29 $ (0.29 ) $ 0.55 $ 1.41 $ 1.98 $ 3.71 1 On January 1, 2018, we adopted Topic 606 and applied it to all contracts that were not completed using the modified retrospective method. The comparative period information has not been retrospectively revised and continues to be reported under the accounting standards in effect for those periods. Refer to NOTE 2 - NEW ACCOUNTING STANDARDS for information regarding the adoption of Topic 606. The diluted earnings per share calculation for the first quarter of 2018 excludes equity plan awards of 3.8 million that were anti-dilutive. (In Millions, Except Per Share Amounts) 2017 Quarters First Second Third Fourth Year Revenues from product sales and services $ 286.2 $ 471.3 $ 596.7 $ 511.8 $ 1,866.0 Sales margin 49.0 144.7 157.8 116.1 467.6 Income (loss) from continuing operations $ (78.5 ) $ 83.8 $ 22.3 $ 333.0 $ 360.6 Loss (income) from continuing operations attributable to noncontrolling interest 1.7 1.7 0.5 — 3.9 Net income (loss) from continuing operations attributable to Cliffs shareholders $ (76.8 ) $ 85.5 $ 22.8 $ 333.0 $ 364.5 Income (loss) from discontinued operations, net of tax 48.7 (53.7 ) 30.6 (23.1 ) 2.5 Net income (loss) attributable to Cliffs common shareholders $ (28.1 ) $ 31.8 $ 53.4 $ 309.9 $ 367.0 Earnings (loss) per common share attributable to Continuing operations $ (0.29 ) $ 0.28 $ 0.08 $ 1.12 $ 1.27 Discontinued operations 0.18 (0.18 ) 0.10 (0.08 ) 0.01 $ (0.11 ) $ 0.10 $ 0.18 $ 1.04 $ 1.28 Earnings (loss) per common share attributable to Continuing operations $ (0.29 ) $ 0.28 $ 0.08 $ 1.11 $ 1.25 Discontinued operations 0.18 (0.18 ) 0.10 (0.08 ) 0.01 $ (0.11 ) $ 0.10 $ 0.18 $ 1.03 $ 1.26

SUPPLEMENTARY GUARANTOR INFORMA

SUPPLEMENTARY GUARANTOR INFORMATION	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
SUPPLEMENTARY GUARANTOR INFORMATION	NOTE 22 - SUPPLEMENTARY GUARANTOR INFORMATION The accompanying 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 have guaranteed the obligations under the $1.075 billion 5.75% 2025 Senior Notes issued by Cleveland-Cliffs Inc. See NOTE 6 - DEBT AND CREDIT FACILITIES for further information. The following presents the 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 December 31, 2018. The condensed consolidating financial information is presented as if the Guarantor structure at December 31, 2018 existed for all years presented. As a result, the Guarantor subsidiaries within the condensed consolidating financial information as of December 31, 2018 and 2017 and for the years ended December 31, 2018, 2017 and 2016 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 consolidating financial information follows the same accounting policies as described in the consolidated financial statements. The accompanying 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. Condensed Consolidating Statement of Financial Position As of December 31, 2018 (In Millions) Cleveland-Cliffs Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations Consolidated ASSETS CURRENT ASSETS Cash and cash equivalents $ 819.8 $ 0.7 $ 2.7 $ — $ 823.2 Accounts receivable, net 9.2 221.3 0.3 (4.1 ) 226.7 Inventories — 87.9 — — 87.9 Supplies and other inventories — 93.2 — — 93.2 Derivative assets 0.1 91.4 — — 91.5 Income tax receivable, current 117.3 — — — 117.3 Current assets of discontinued operations — — 12.4 — 12.4 Other current assets 10.0 16.9 0.5 — 27.4 TOTAL CURRENT ASSETS 956.4 511.4 15.9 (4.1 ) 1,479.6 PROPERTY, PLANT AND EQUIPMENT, NET 13.3 1,221.9 50.8 — 1,286.0 OTHER ASSETS Deposits for property, plant and equipment — 68.4 14.6 — 83.0 Income tax receivable, non-current 117.2 4.1 — — 121.3 Deferred income taxes 463.6 — 1.2 — 464.8 Investment in subsidiaries 1,262.3 50.8 — (1,313.1 ) — Long-term intercompany notes — — 121.3 (121.3 ) — Other non-current assets 8.0 85.4 1.5 — 94.9 TOTAL OTHER ASSETS 1,851.1 208.7 138.6 (1,434.4 ) 764.0 TOTAL ASSETS $ 2,820.8 $ 1,942.0 $ 205.3 $ (1,438.5 ) $ 3,529.6 LIABILITIES CURRENT LIABILITIES Accounts payable $ 5.3 $ 181.4 $ 4.2 $ (4.1 ) $ 186.8 Accrued employment costs 28.5 45.4 0.1 — 74.0 State and local taxes payable — 35.4 0.1 — 35.5 Accrued interest 38.4 — — — 38.4 Partnership distribution payable — 43.5 — — 43.5 Current liabilities of discontinued operations — — 6.7 — 6.7 Other current liabilities 30.6 51.3 1.4 — 83.3 TOTAL CURRENT LIABILITIES 102.8 357.0 12.5 (4.1 ) 468.2 POSTEMPLOYMENT BENEFIT LIABILITIES Pensions 58.3 390.5 (230.4 ) — 218.4 Other postretirement benefits 6.0 23.9 0.4 — 30.3 TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES 64.3 414.4 (230.0 ) — 248.7 ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS — 152.1 19.9 — 172.0 LONG-TERM DEBT 2,092.9 — — — 2,092.9 LONG-TERM INTERCOMPANY NOTES 121.3 — — (121.3 ) — NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS — — 8.3 — 8.3 OTHER LIABILITIES 15.3 99.5 0.5 — 115.3 TOTAL LIABILITIES 2,396.6 1,023.0 (188.8 ) (125.4 ) 3,105.4 COMMITMENTS AND CONTINGENCIES EQUITY TOTAL EQUITY 424.2 919.0 394.1 (1,313.1 ) 424.2 TOTAL LIABILITIES AND EQUITY $ 2,820.8 $ 1,942.0 $ 205.3 $ (1,438.5 ) $ 3,529.6 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 $ 27.3 $ — $ 978.3 Accounts receivable, net 4.5 102.9 — (0.7 ) 106.7 Inventories — 138.4 — — 138.4 Supplies and other inventories — 88.8 — — 88.8 Derivative assets — 37.9 — — 37.9 Income tax receivable, current 11.4 1.9 — — 13.3 Loans to and accounts receivables from the Canadian Entities 44.7 6.9 — — 51.6 Current assets of discontinued operations — — 118.5 — 118.5 Other current assets 5.0 5.6 0.5 — 11.1 TOTAL CURRENT ASSETS 1,014.5 384.5 146.3 (0.7 ) 1,544.6 PROPERTY, PLANT AND EQUIPMENT, NET 17.5 965.5 50.8 — 1,033.8 OTHER ASSETS Deposits for property, plant and equipment — 8.2 9.6 — 17.8 Income tax receivable, non-current 235.3 — — — 235.3 Investment in subsidiaries 1,024.3 29.9 — (1,054.2 ) — Long-term intercompany notes — — 242.0 (242.0 ) — Non-current assets of discontinued operations — — 20.3 — 20.3 Other non-current assets 7.8 91.8 2.0 — 101.6 TOTAL OTHER ASSETS 1,267.4 129.9 273.9 (1,296.2 ) 375.0 TOTAL ASSETS $ 2,299.4 $ 1,479.9 $ 471.0 $ (1,296.9 ) $ 2,953.4 LIABILITIES CURRENT LIABILITIES Accounts payable $ 7.1 $ 92.3 $ 0.8 $ (0.7 ) $ 99.5 Accrued employment costs 13.7 38.9 0.1 — 52.7 State and local taxes payable — 30.0 0.2 — 30.2 Accrued interest 31.4 — — — 31.4 Contingent claims 55.6 — — — 55.6 Partnership distribution payable — 44.2 — — 44.2 Current liabilities of discontinued operations — — 75.0 — 75.0 Other current liabilities 7.4 54.5 1.7 — 63.6 TOTAL CURRENT LIABILITIES 115.2 259.9 77.8 (0.7 ) 452.2 POSTEMPLOYMENT BENEFIT LIABILITIES Pensions 59.2 403.6 (240.0 ) — 222.8 Other postretirement benefits 7.2 27.0 0.7 — 34.9 TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES 66.4 430.6 (239.3 ) — 257.7 ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS — 140.6 27.1 — 167.7 LONG-TERM DEBT 2,304.2 — — — 2,304.2 LONG-TERM INTERCOMPANY NOTES 242.0 — — (242.0 ) — NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS — — 52.2 — 52.2 OTHER LIABILITIES 15.7 147.2 0.6 — 163.5 TOTAL LIABILITIES 2,743.5 978.3 (81.6 ) (242.7 ) 3,397.5 COMMITMENTS AND CONTINGENCIES EQUITY TOTAL CLIFFS SHAREHOLDERS' EQUITY (DEFICIT) (444.1 ) 501.6 552.4 (1,054.2 ) (444.3 ) NONCONTROLLING INTEREST — — 0.2 — 0.2 TOTAL DEFICIT (444.1 ) 501.6 552.6 (1,054.2 ) (444.1 ) TOTAL LIABILITIES AND DEFICIT $ 2,299.4 $ 1,479.9 $ 471.0 $ (1,296.9 ) $ 2,953.4 Condensed Consolidating Statement of Operations and Comprehensive Income For the Year Ended December 31, 2018 (In Millions) Cleveland-Cliffs Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations Consolidated REVENUES FROM PRODUCT SALES AND SERVICES Product $ — $ 2,172.3 $ — $ — $ 2,172.3 Freight and venture partners' cost reimbursements — 160.1 — — 160.1 — 2,332.4 — — 2,332.4 COST OF GOODS SOLD AND OPERATING EXPENSES — (1,522.8 ) — — (1,522.8 ) SALES MARGIN — 809.6 — — 809.6 OTHER OPERATING INCOME (EXPENSE) Selling, general and administrative expenses (86.1 ) (30.4 ) (0.3 ) — (116.8 ) Miscellaneous - net (0.3 ) (23.6 ) 4.3 — (19.6 ) (86.4 ) (54.0 ) 4.0 — (136.4 ) OPERATING INCOME (LOSS) (86.4 ) 755.6 4.0 — 673.2 OTHER INCOME (EXPENSE) Interest expense, net (117.6 ) (2.1 ) 0.8 — (118.9 ) Loss on extinguishment of debt (6.8 ) — — — (6.8 ) Other non-operating income (loss) (3.5 ) 0.9 19.8 — 17.2 (127.9 ) (1.2 ) 20.6 — (108.5 ) INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES (214.3 ) 754.4 24.6 — 564.7 INCOME TAX BENEFIT 474.7 — 0.5 — 475.2 EQUITY IN INCOME OF SUBSIDIARIES 858.2 25.5 — (883.7 ) — INCOME FROM CONTINUING OPERATIONS 1,118.6 779.9 25.1 (883.7 ) 1,039.9 INCOME FROM DISCONTINUED OPERATIONS, net of tax 9.5 12.3 66.4 — 88.2 NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 1,128.1 $ 792.2 $ 91.5 $ (883.7 ) $ 1,128.1 OTHER COMPREHENSIVE LOSS (244.9 ) (24.1 ) (256.7 ) 280.8 (244.9 ) TOTAL COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 883.2 $ 768.1 $ (165.2 ) $ (602.9 ) $ 883.2 Condensed Consolidating Statement of Operations and Comprehensive Income For the Year Ended December 31, 2017 (In Millions) Cleveland-Cliffs Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations Consolidated REVENUES FROM PRODUCT SALES AND SERVICES Product $ — $ 1,644.6 $ — $ — $ 1,644.6 Freight and venture partners' cost reimbursements — 221.4 — — 221.4 — 1,866.0 — — 1,866.0 COST OF GOODS SOLD AND OPERATING EXPENSES — (1,398.4 ) — — (1,398.4 ) SALES MARGIN — 467.6 — — 467.6 OTHER OPERATING INCOME (EXPENSE) Selling, general and administrative expenses (77.2 ) (19.9 ) (5.8 ) — (102.9 ) Miscellaneous - net (2.3 ) 11.0 16.8 — 25.5 (79.5 ) (8.9 ) 11.0 — (77.4 ) OPERATING INCOME (LOSS) (79.5 ) 458.7 11.0 — 390.2 OTHER INCOME (EXPENSE) Interest expense, net (126.8 ) (1.0 ) 1.0 — (126.8 ) Loss on extinguishment of debt (165.4 ) — — — (165.4 ) Other non-operating income (expense) (4.0 ) (3.0 ) 17.2 — 10.2 (296.2 ) (4.0 ) 18.2 — (282.0 ) INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES (375.7 ) 454.7 29.2 — 108.2 INCOME TAX BENEFIT (EXPENSE) 251.4 1.3 (0.3 ) — 252.4 EQUITY IN INCOME OF SUBSIDIARIES 512.6 11.8 — (524.4 ) — INCOME FROM CONTINUING OPERATIONS 388.3 467.8 28.9 (524.4 ) 360.6 INCOME (LOSS) FROM DISCONTINUED OPERATIONS, net of tax (21.3 ) 1.7 22.1 — 2.5 NET INCOME 367.0 469.5 51.0 (524.4 ) 363.1 INCOME ATTRIBUTABLE TO NONCONTROLLING INTEREST — 3.9 — — 3.9 NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 367.0 $ 473.4 $ 51.0 $ (524.4 ) $ 367.0 OTHER COMPREHENSIVE INCOME (LOSS) (4.0 ) 12.9 (4.8 ) (8.1 ) (4.0 ) TOTAL COMPREHENSIVE INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 363.0 $ 486.3 $ 46.2 $ (532.5 ) $ 363.0 Condensed Consolidating Statement of Operations and Comprehensive Income For the Year Ended December 31, 2016 (In Millions) Cleveland-Cliffs Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations Consolidated REVENUES FROM PRODUCT SALES AND SERVICES Product $ — $ 1,379.7 $ — $ — $ 1,379.7 Freight and venture partners' cost reimbursements — 174.8 — — 174.8 — 1,554.5 — — 1,554.5 COST OF GOODS SOLD AND OPERATING EXPENSES — (1,274.4 ) — — (1,274.4 ) SALES MARGIN — 280.1 — — 280.1 OTHER OPERATING INCOME (EXPENSE) Selling, general and administrative expenses (94.3 ) (18.0 ) (3.5 ) — (115.8 ) Miscellaneous - net (5.6 ) (12.4 ) (15.6 ) — (33.6 ) (99.9 ) (30.4 ) (19.1 ) — (149.4 ) OPERATING INCOME (LOSS) (99.9 ) 249.7 (19.1 ) — 130.7 OTHER INCOME (EXPENSE) Interest expense, net (194.5 ) 0.1 0.5 — (193.9 ) Gain on extinguishment/restructuring of debt 166.3 — — — 166.3 Other non-operating income (expense) (4.1 ) (5.0 ) 16.4 — 7.3 (32.3 ) (4.9 ) 16.9 — (20.3 ) INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES (132.2 ) 244.8 (2.2 ) — 110.4 INCOME TAX BENEFIT 4.3 3.0 4.9 — 12.2 EQUITY IN INCOME OF SUBSIDIARIES 319.1 13.7 — (332.8 ) — INCOME FROM CONTINUING OPERATIONS 191.2 261.5 2.7 (332.8 ) 122.6 INCOME (LOSS) FROM DISCONTINUED OPERATIONS, net of tax (17.1 ) 2.6 91.2 — 76.7 NET INCOME (LOSS) 174.1 264.1 93.9 (332.8 ) 199.3 INCOME ATTRIBUTABLE TO NONCONTROLLING INTEREST — (25.2 ) — — (25.2 ) NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 174.1 $ 238.9 $ 93.9 $ (332.8 ) $ 174.1 OTHER COMPREHENSIVE INCOME (LOSS) (3.3 ) (20.7 ) 15.4 5.3 (3.3 ) TOTAL COMPREHENSIVE INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 170.8 $ 218.2 $ 109.3 $ (327.5 ) $ 170.8 Condensed Consolidating Statement of Cash Flows For the Year Ended December 31, 2018 (In Millions) Cleveland-Cliffs Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations Consolidated Net cash provided (used) by operating activities $ (120.7 ) $ 741.0 $ (141.8 ) $ — $ 478.5 INVESTING ACTIVITIES Purchase of property, plant and equipment (1.2 ) (207.3 ) (0.1 ) — (208.6 ) Deposits for property, plant and equipment — (82.3 ) (5.2 ) — (87.5 ) Intercompany investing 399.1 (7.1 ) 120.7 (512.7 ) — Other investing activities — 3.1 19.9 — 23.0 Net cash provided (used) in investing activities 397.9 (293.6 ) 135.3 (512.7 ) (273.1 ) FINANCING ACTIVITIES Repurchase of common shares (47.5 ) — — — (47.5 ) Debt issuance costs (1.5 ) — — — (1.5 ) Repurchase of debt (234.5 ) — — — (234.5 ) Distributions of partnership equity — (44.2 ) — — (44.2 ) Intercompany financing (120.7 ) (402.4 ) 10.4 512.7 — Other financing activities (2.1 ) (2.2 ) (43.2 ) — (47.5 ) Net cash used by financing activities (406.3 ) (448.8 ) (32.8 ) 512.7 (375.2 ) EFFECT OF EXCHANGE RATE CHANGES ON CASH — — (2.3 ) — (2.3 ) DECREASE IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS (129.1 ) (1.4 ) (41.6 ) — (172.1 ) LESS: DECREASE IN CASH AND CASH EQUIVALENTS CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS — — (17.0 ) — (17.0 ) NET DECREASE IN CASH AND CASH EQUIVALENTS (129.1 ) (1.4 ) (24.6 ) — (155.1 ) CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR 948.9 2.1 27.3 — 978.3 CASH AND CASH EQUIVALENTS AT END OF YEAR $ 819.8 $ 0.7 $ 2.7 $ — $ 823.2 Condensed Consolidating Statement of Cash Flows For the Year Ended December 31, 2017 (In Millions) Cleveland-Cliffs Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations Consolidated Net cash provided (used) by operating activities $ (166.8 ) $ 430.0 $ 74.9 $ — $ 338.1 INVESTING ACTIVITIES Purchase of property, plant and equipment (3.4 ) (79.8 ) (51.7 ) — (134.9 ) Deposits for property, plant and equipment — (11.7 ) (5.1 ) — (16.8 ) Intercompany investing 225.7 (7.3 ) (45.1 ) (173.3 ) — Other investing activities (7.7 ) 3.4 — — (4.3 ) Net cash provided (used) by investing activities 214.6 (95.4 ) (101.9 ) (173.3 ) (156.0 ) FINANCING ACTIVITIES Net proceeds from issuance of common shares 661.3 — — — 661.3 Proceeds from issuance of debt 1,771.5 — — — 1,771.5 Debt issuance costs (28.6 ) — — — (28.6 ) Repurchase of debt (1,720.7 ) — — — (1,720.7 ) Acquisition of noncontrolling interest (105.0 ) — — — (105.0 ) Distributions of partnership equity — (52.9 ) — — (52.9 ) Intercompany financing 45.0 (277.6 ) 59.3 173.3 — Other financing activities (5.8 ) (4.5 ) (16.4 ) — (26.7 ) Net cash provided (used) by financing activities 617.7 (335.0 ) 42.9 173.3 498.9 EFFECT OF EXCHANGE RATE CHANGES ON CASH — — 3.3 — 3.3 INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS 665.5 (0.4 ) 19.2 — 684.3 LESS: INCREASE IN CASH AND CASH EQUIVALENTS CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS — — 18.8 — 18.8 NET INCREASE IN CASH AND CASH EQUIVALENTS 665.5 (0.4 ) 0.4 — 665.5 CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR 283.4 2.5 26.9 — 312.8 CASH AND CASH EQUIVALENTS AT END OF YEAR $ 948.9 $ 2.1 $ 27.3 $ — $ 978.3 Condensed Consolidating Statement of Cash Flows For the Year Ended December 31, 2016 (In Millions) Cleveland-Cliffs Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations Consolidated Net cash provided (used) by operating activities $ (275.7 ) $ 462.9 $ 115.8 $ — $ 303.0 INVESTING ACTIVITIES Purchase of property, plant and equipment (6.2 ) (55.1 ) (0.4 ) — (61.7 ) Deposits for property, plant and equipment — (4.9 ) (2.5 ) — (7.4 ) Intercompany investments 356.6 (3.3 ) (117.0 ) (236.3 ) — Other investing activities 0.4 10.8 — — 11.2 Net cash provided (used) by investing activities 350.8 (52.5 ) (119.9 ) (236.3 ) (57.9 ) FINANCING ACTIVITIES Net proceeds from issuance of common shares 287.4 — — — 287.4 Debt issuance costs (5.2 ) — — — (5.2 ) Borrowings under credit facilities 105.0 — — — 105.0 Repayments on credit facilities (105.0 ) — — — (105.0 ) Repayments on equipment loans (95.6 ) — — — (95.6 ) Repurchase of debt (305.4 ) — — — (305.4 ) Distributions of partnership equity — (59.9 ) — — (59.9 ) Intercompany financing 117.0 (339.9 ) (13.4 ) 236.3 — Other financing activities (0.6 ) (9.9 ) (17.2 ) — (27.7 ) Net cash used by financing activities (2.4 ) (409.7 ) (30.6 ) 236.3 (206.4 ) EFFECT OF EXCHANGE RATE CHANGES ON CASH — — (0.5 ) — (0.5 ) INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS 72.7 0.7 (35.2 ) — 38.2 LESS: DECREASE IN CASH AND CASH EQUIVALENTS CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS — — (35.3 ) — (35.3 ) NET INCREASE IN CASH AND CASH EQUIVALENTS 72.7 0.7 0.1 — 73.5 CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR 210.7 1.8 26.8 — 239.3 CASH AND CASH EQUIVALENTS AT END OF YEAR $ 283.4 $ 2.5 $ 26.9 $ — $ 312.8

SCHEDULE II - VALUATION AND QUA

SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS (Notes)	12 Months Ended
	Dec. 31, 2018
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block]	Cleveland-Cliffs Inc. and Subsidiaries Schedule II – Valuation and Qualifying Accounts (In Millions) Additions Balance at Beginning of Year Charged to Cost and Expenses Charged to Other Accounts Balance at End of Year Classification Acquisition Deductions Year Ended December 31, 2018: Deferred Tax Valuation Allowance $ 1,983.1 $ (691.3 ) $ (4.5 ) $ — $ — $ 1,287.3 Year Ended December 31, 2017: Deferred Tax Valuation Allowance $ 3,095.1 $ (1,120.0 ) $ (9.8 ) $ 17.8 $ — $ 1,983.1 Year Ended December 31, 2016: Deferred Tax Valuation Allowance $ 3,099.8 $ (7.6 ) $ 5.1 $ — $ 2.2 $ 3,095.1 Accounts Receivable Allowance $ 7.1 $ — $ (7.1 ) $ — $ — $ —

BASIS OF PRESENTATION AND SIG_2

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. The more significant areas requiring the use of management estimates and assumptions relate to mineral reserves future realizable cash flow; environmental, reclamation and closure obligations; valuation of long-lived assets, inventory, tax assets and post-employment, post-retirement and other employee benefit liabilities; reserves for contingencies and litigation; and the fair value of derivative instruments. Actual results could differ from estimates. Management reviews its estimates on an ongoing basis. Changes in facts and circumstances may alter such estimates and affect the results of operations and financial position in future periods.
Basis Of Consolidation	Basis of Consolidation The consolidated financial statements include our accounts and the accounts of our wholly owned subsidiaries, including the following iron ore operations at December 31, 2018 : Name Location Status of Operations Northshore Minnesota Active United Taconite Minnesota Active Tilden Michigan Active Empire Michigan Indefinitely Idled Intercompany transactions and balances are eliminated upon consolidation.
Equity Method Investments	Equity Method Investments Investments in unconsolidated ventures that we have the ability to exercise significant influence over, but not control, are accounted for under the equity method. Our 23% ownership interest in Hibbing is recorded as an equity method investment. As of December 31, 2018 and 2017 , our investment in Hibbing was $15.4 million and $11.0 million , respectively, classified in Other liabilities in the Statements of Consolidated Financial Position . Our share of equity income (loss) is eliminated against consolidated product inventory upon production, and against Cost of goods sold and operating expenses when sold. This effectively reduces our cost for our share of the mining ventures' production cost, reflecting the cost-based nature of our participation in unconsolidated ventures.
Noncontrolling Interests	Noncontrolling Interests 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 parties agreed that the net assets were to be distributed in three installments of $44.2 million each, the first of which was paid upon the execution of the agreement, the second of which was paid in August 2018 and the final of which is due August 2019. Upon payment of the first installment, we assumed ArcelorMittal's 21% interest and reflected the ownership percentage change in our consolidated financial statements. During the year ended December 31, 2017 , we accounted for the increase in ownership as an equity transaction, which resulted in a net $12.1 million decrease in equity attributable to Cliffs' shareholders and a $116.7 million decrease in Noncontrolling interest . The net loss and income attributable to the noncontrolling interest of the Empire mining venture was $3.9 million and $25.2 million for the years ended December 31, 2017 and 2016 , respectively. During 2017, we also acquired the remaining 15% equity interest in Tilden owned by U.S. Steel for $105.0 million . With the closing of this transaction, we now have 100% ownership of the mine. During the year ended December 31, 2017 , we accounted for the increase in ownership as an equity transaction, which resulted in an $89.1 million decrease in equity attributable to Cliffs' shareholders and a $15.9 million decrease in Noncontrolling interest .
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents include cash on hand and on deposit as well as all short-term securities held for the primary purpose of general liquidity. We consider investments in highly liquid debt instruments with an original maturity of three months or less from the date of acquisition and longer maturities when funds can be withdrawn in three months or less without a significant penalty to be cash equivalents. We routinely monitor and evaluate counterparty credit risk related to the financial institutions in which our short-term investment securities are held.
Trade and Other Accounts Receivable	Trade Accounts Receivable and Allowance for Doubtful Accounts Trade accounts receivable are recorded at the point control transfers and represents the amount of consideration we expect to receive in exchange for transferred goods and do not bear interest. The allowance for doubtful accounts is our best estimate of the amount of probable credit losses in our existing accounts receivable. We establish provisions for losses on accounts receivable when it is probable that all or part of the outstanding balance will not be collected. We regularly review our accounts receivable balances and establish or adjust the allowance as necessary using the specific identification method. There was no allowance for doubtful accounts at December 31, 2018 and 2017 and no bad debt expense for the years ended December 31, 2018 , 2017 and 2016 .
Inventory	Inventories The Mining and Pelletizing segment product inventories are stated at the lower of cost or market. Cost of iron ore inventories is determined using the LIFO method.
Inventory Supplies	Supplies and Other Inventories Supply inventories include replacement parts, fuel, chemicals and other general supplies, which are expected to be used or consumed in normal operations. Supply inventories also include critical spares. Critical spares are replacement parts for equipment that is critical for the continued operation of the mine or processing facilities. Supply inventories are stated at the lower of cost or net realizable value using average cost, less an allowance for obsolete and surplus items. The allowance for obsolete and surplus items was $12.6 million at December 31, 2018 and 2017 .
Derivatives	Derivative Financial Instruments and Hedging Activities We are exposed to certain risks related to the ongoing operations of our business, including those caused by changes in commodity prices and energy rates. We have established policies and procedures, including the use of certain derivative instruments, to manage such risks, if deemed necessary. Derivative financial instruments are recognized as either assets or liabilities in the Statements of Consolidated Financial Position and measured at fair value. On the date a qualifying hedging instrument is executed, we designate the hedging instrument as a hedge of the variability of cash flows to be received or paid related to a forecasted transaction (cash flow hedge). We formally document all relationships between hedging instruments and hedged items, as well as our risk-management objective and strategy for undertaking various hedge transactions. This process includes linking all derivatives that are designated as cash flow hedges to specific firm commitments or forecasted transactions. We also formally assess, both at the hedge's inception and on an ongoing basis, whether the derivatives that are used in hedging transactions are highly effective in offsetting changes in cash flows of the related hedged items. When it is determined that a derivative is not highly effective as a hedge or that it has ceased to be a highly effective hedge, we discontinue hedge accounting prospectively and record all future changes in fair value in the period of the instrument's earnings or losses. For derivative instruments that have been designated as cash flow hedges, the changes in fair value are recorded in Accumulated other comprehensive loss . Amounts recorded in Accumulated other comprehensive loss are reclassified to earnings or losses in the period the underlying hedged transaction affects earnings or when the underlying hedged transaction is no longer reasonably possible of occurring. For derivative instruments that have not been designated as cash flow hedges, such as provisional pricing arrangements and supplemental revenue or refunds contained within a customer supply agreement, changes in fair value are recorded in the period of the instrument's earnings or losses. Refer to Revenue Recognition below for discussion of derivatives recorded as a result of pricing terms in our sales contracts. Additionally, refer to NOTE 12 - DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES for further information.
Property, Plant and Equipment	Property, Plant and Equipment Our properties are stated at the lower of cost less accumulated depreciation or fair value. Depreciation of plant and equipment is computed principally by the straight-line method based on estimated useful lives, not to exceed the mine lives. Depreciation continues to be recognized when operations are idled temporarily. We use the double-declining balance method of depreciation for certain mining equipment. Depreciation and depletion is provided over the following estimated useful lives: Asset Class Basis Life Office and information technology Straight line 3 to 15 years Buildings Straight line 45 years Mining equipment Straight line/Double declining balance 3 to 20 years Processing equipment Straight line 10 to 45 years Electric power facilities Straight line 10 to 45 years Land improvements Straight line 20 to 45 years Asset retirement obligation Straight line Life of mine Mineral rights Units of production Life of mine Refer to NOTE 5 - PROPERTY, PLANT AND EQUIPMENT for further information.
Capitalized Stripping Costs	Capitalized Stripping Costs During the development phase, stripping costs are capitalized as a part of the depreciable cost of building, developing and constructing a mine. These capitalized costs are amortized over the productive life of the mine using the units of production method. The production phase does not commence until the removal of more than a de minimis amount of saleable mineral material occurs in conjunction with the removal of overburden or waste material for purposes of obtaining access to an ore body. The stripping costs incurred in the production phase of a mine are variable production costs included in the costs of the inventory produced (extracted) during the period that the stripping costs are incurred. Stripping costs related to expansion of a mining asset of proven and probable reserves are variable production costs that are included in the costs of the inventory produced during the period that the stripping costs are incurred.
Other Intangible Assets and Liabilities	Other Intangible Assets Our mine permits are subject to periodic amortization on a straight line basis over their estimated useful life, which corresponds with the life of mine.
Impairment or Disposal of Long-Lived Assets	Asset Impairment We monitor conditions that may affect the carrying value of our long-lived tangible and intangible assets when events and circumstances indicate that the carrying value of the asset groups may not be recoverable. In order to determine if assets have been impaired, assets are grouped and tested at the lowest level for which identifiable, independent cash flows are available ("asset group"). An impairment loss exists when projected net undiscounted cash flows are less than the carrying value of the asset group. The measurement of the impairment loss to be recognized is based on the difference between the fair value and the carrying value of the asset group. Fair value can be determined using a market approach, income approach or cost approach. For the years ended December 31, 2018 , 2017 and 2016 , no impairment factors were present that would indicate the carrying value of any of our asset groups may not be recoverable; as a result, no impairment assessments were required.
Fair Value of Financial Instruments	Fair Value Measurements ASC Topic 820, Fair Value Measurements and Disclosures , establishes a three-level valuation hierarchy for classification of fair value measurements. The valuation hierarchy is based upon the transparency of inputs to the valuation of an asset or liability as of the measurement date. Inputs refer broadly to the assumptions that market participants would use in pricing an asset or liability. Inputs may be observable or unobservable. Observable inputs are inputs that reflect the assumptions market participants would use in pricing the asset or liability developed based on market data obtained from independent sources. Unobservable inputs are inputs that reflect our own views about the assumptions market participants would use in pricing the asset or liability developed based on the best information available in the circumstances. The three-tier hierarchy of inputs is summarized below: • Level 1 — Valuation is based upon quoted prices (unadjusted) for identical assets or liabilities in active markets. • Level 2 — Valuation is based upon quoted prices for similar assets and liabilities in active markets, or other inputs that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the financial instrument. • Level 3 — Valuation is based upon other unobservable inputs that are significant to the fair value measurement. The classification of assets and liabilities within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement in its entirety. Refer to NOTE 7 - FAIR VALUE OF FINANCIAL INSTRUMENTS and NOTE 8 - PENSIONS AND OTHER POSTRETIREMENT BENEFITS for further information.
Pension and Other Postretirement Plans	Pensions and Other Postretirement Benefits We offer defined benefit pension plans, defined contribution pension plans and other postretirement benefit plans, primarily consisting of retiree healthcare benefits, to most employees in the United States as part of a total compensation and benefits program. We recognize the funded or unfunded status of our postretirement benefit obligations on our December 31, 2018 and 2017 Statements of Consolidated Financial Position based on the difference between the market value of plan assets and the actuarial present value of our retirement obligations on that date, on a plan-by-plan basis. If the plan assets exceed the postretirement benefit obligations, the amount of the surplus is recorded as an asset; if the postretirement benefit obligations exceed the plan assets, the amount of the underfunded obligations is recorded as a liability. Year-end balance sheet adjustments to postretirement assets and obligations are recorded as Accumulated other comprehensive loss in the Statements of Consolidated Financial Position . The actuarial estimates of the PBO and APBO incorporate various assumptions including the discount rates, the rates of increases in compensation, healthcare cost trend rates, mortality, retirement timing and employee turnover. The discount rate is determined based on the prevailing year-end rates for high-grade corporate bonds with a duration matching the expected cash flow timing of the benefit payments from the various plans. The remaining assumptions are based on our estimates of future events by incorporating historical trends and future expectations. The amount of net periodic cost that is recorded in the Statements of Consolidated Operations consists of several components including service cost, interest cost, expected return on plan assets, and amortization of previously unrecognized amounts. Service cost represents the value of the benefits earned in the current year by the participants. Interest cost represents the cost associated with the passage of time. Certain items, such as plan amendments, gains and/or losses resulting from differences between actual and assumed results for demographic and economic factors affecting the obligations and assets of the plans, and changes in other assumptions are subject to deferred recognition for income and expense purposes. The expected return on plan assets is determined utilizing the weighted average of expected returns for plan asset investments in various asset categories based on historical performance, adjusted for current trends. 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/credits, net actuarial gain/loss, and other costs are classified within Other non-operating income . Refer to NOTE 2 - NEW ACCOUNTING STANDARDS and NOTE 8 - PENSIONS AND OTHER POSTRETIREMENT BENEFITS for further information.
Asset Retirement Obligations	Asset Retirement Obligations Asset retirement obligations are recognized when incurred and recorded as liabilities at fair value. The fair value of the liability is determined as the discounted value of the expected future cash flows. The asset retirement obligation is accreted over time through periodic charges to earnings. In addition, the asset retirement cost is capitalized and amortized over the life of the related asset. Reclamation costs are adjusted periodically to reflect changes in the estimated present value resulting from the passage of time and revisions to the estimates of either the timing or amount of the reclamation costs. We review, on an annual basis, unless otherwise deemed necessary, the asset retirement obligation at each mine site in accordance with the provisions of ASC Topic 410, Asset Retirement and Environmental Obligations . We perform an in-depth evaluation of the liability every three years in addition to our routine annual assessments. Future reclamation costs for inactive mines are accrued based on management’s best estimate at the end of each period of the costs expected to be incurred at a site. Such cost estimates include, where applicable, ongoing maintenance and monitoring costs. Changes in estimates at inactive mines are reflected in earnings in the period an estimate is revised. See NOTE 11 - ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS for further information.
Environmental Costs	Environmental Remediation Costs We have a formal policy for environmental protection and restoration. Our mining and exploration activities are subject to various laws and regulations governing protection of the environment. We conduct our operations to protect the public health and environment and believe our operations are in compliance with applicable laws and regulations in all material respects. Our environmental liabilities, including obligations for known environmental remediation exposures at active and closed mining operations and other sites, have been recognized based on the estimated cost of investigation and remediation at each site. If the cost can only be estimated as a range of possible amounts with no point in the range being more likely, the minimum of the range is accrued. Future expenditures are not discounted unless the amount and timing of the cash disbursements reasonably can be estimated. It is possible that additional environmental obligations could be incurred, the extent of which cannot be assessed. Potential insurance recoveries have not been reflected in the determination of the liabilities. See NOTE 11 - ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS for further information.
Revenue Recognition - Pre and Post Adoption of Topic 606 and Deferred Revenue	Revenue Recognition - Pre-Adoption of Topic 606 Prior to the adoption of Topic 606, revenue was recognized from a sale when persuasive evidence of an arrangement existed, the price was fixed or determinable, the product was delivered in accordance with shipping terms, title and risk of loss were transferred to the customer in accordance with the specified provisions of each supply agreement and collection of the sales price reasonably was assured. Our supply agreements provide that title and risk of loss transfer to the customer either upon loading of the vessel, shipment or when payment is received. Under certain supply agreements, we ship the product to ports on the lower Great Lakes or to the customers’ facilities prior to the transfer of title. Our rationale for shipping iron ore products to certain customers and retaining title until payment is received for these products is to minimize credit risk exposure. Sales were recorded at a sales price specified in the relevant supply agreements resulting in revenue and a receivable at the time of sale. The majority of our contracts have pricing mechanisms that require price estimation at the time of delivery with price finalization at a future period. Upon revenue recognition for provisionally priced sales, a derivative was created for the difference between the sales price used and expected future settlement price. The derivative was adjusted to fair value through Product revenues as a revenue adjustment each reporting period based upon current market data and forward-looking estimates determined by management until the final sales price was determined. The principal risks associated with recognition of sales on a provisional basis include Platts 62% Price, Atlantic Basin pellet premium and index freight fluctuations between the date initially recorded and the date of final settlement. For revenue recognition, we estimated the future settlement rate; however, if significant changes in inputs occurred between the provisional pricing date and the final settlement date, we were required to either return a portion of the sales proceeds received or bill for the additional sales proceeds due based on the provisional sales price. Revenue Recognition - Post-Adoption of Topic 606 We sell a single product, iron ore pellets, in the North American market. With the adoption of Topic 606 as of January 1, 2018, revenue is recognized generally when iron ore is delivered to our customers. Revenue is measured at the point that 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. Refer to NOTE 2 - NEW ACCOUNTING STANDARDS for further information. We enter into supply contracts of varying lengths to provide customers iron ore pellets 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. Most of our 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, Atlantic Basin 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 Topic 815. Refer to NOTE 12 - DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES for further information on how our estimated and final revenue rates are determined. A supply agreement with a customer provides for supplemental revenue or refunds based on the average annual daily market price for hot-rolled coil steel in the year 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 Topic 815. Refer to NOTE 12 - DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES for further information on supplemental revenue or refunds. Included within Revenues from product sales and services is derivative revenue related to Topic 815 of $422.6 million , $120.6 million and $55.9 million for the years ended December 31, 2018 , 2017 and 2016, respectively. As of December 31, 2018 , under the new accounting standard, we had finished goods of 0.8 million long tons in transit or stored at the Port of Toledo to service customers, for which revenue had yet to be recognized. Under the previous accounting standard, we did not recognize revenue and related cost of goods sold until title transferred to the customer, usually when payment was received. As of December 31, 2017, under the previous accounting standard, we had finished goods of 1.5 million long tons stored at ports and customer facilities on the lower Great Lakes to service customers, for which revenue had yet to be recognized. Practical expedients and exemptions We have elected to treat all shipping and handling costs as fulfillment costs because 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: (In Millions) Deferred Revenue (Current) 1 Deferred Revenue (Long-Term) Year Ended Year Ended 2018 2017 2018 2017 Opening balance as of January 1 $ 23.8 $ 16.2 $ 51.4 $ 64.3 Closing balance as of December 31 21.0 22.4 38.5 51.4 Increase (Decrease) $ (2.8 ) $ 6.2 $ (12.9 ) $ (12.9 ) 1 The opening balance for the year ended December 31, 2018 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 pellet supply agreements required supplemental payments to be paid by the customer during the period 2009 through 2012. Installment amounts received under this arrangement in excess of sales were classified as Other current liabilities and Other liabilities in the Statements of 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 December 31, 2018 and December 31, 2017 , installment amounts received in excess of sales totaled $51.3 million and $64.2 million , respectively, related to this agreement. As of December 31, 2018 , and December 31, 2017 , deferred revenue of $12.8 million was recorded in Other current liabilities and $38.5 million and $51.4 million , respectively, was recorded as long-term in Other liabilities in the Statements of 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 deliveries for certain customers. Revenue recognized on these transactions totaling $8.2 million and $9.6 million was deferred and included in Other current liabilities in the Statements of Consolidated Financial Position as of December 31, 2018 and December 31, 2017 , respectively.
Cost of Sales	Cost of Goods Sold Cost of goods sold and operating expenses represents all direct and indirect costs and expenses applicable to the sales from our mining operations. In some circumstances, as requested by the customer, we will coordinate and ship our product via vessel directly to the port nearest to the customer's blast furnace. In this type of contract, the customer will pay one amount inclusive of both product and freight. We recognize revenue for both product revenue and the amount reimbursed for the vessel freight to the final port. We separate these revenue types in the Statements of Consolidated Operations . Accordingly, the revenue we record for freight is offset by an equal amount included in Cost of goods sold and operating expenses for costs we incur for that freight, resulting in no impact on sales margin. Operating expenses represented the portion of the Tilden mining venture costs prior to our 100% ownership; that is, the costs attributable to the share of the mine’s production owned by the other joint venture partner in the Tilden mine until we acquired the remaining 15% noncontrolling interest during 2017. The mining venture functioned as a captive cost company, supplying product only to its owners effectively for the cost of production. Accordingly, the noncontrolling interests’ revenue amounts were stated at cost of production and were offset by an equal amount included in Cost of goods sold and operating expenses resulting in no sales margin reflected for the noncontrolling partner participant. As we were responsible for product fulfillment under the venture, we acted as a principal in the transaction and, accordingly, recorded revenue under these arrangements on a gross basis. The following table is a summary of reimbursements in our operations: (In Millions) Year Ended December 31, 2018 2017 2016 Reimbursements for: Freight $ 160.1 $ 166.7 $ 106.8 Venture partners’ cost — 54.7 68.0 Total reimbursements $ 160.1 $ 221.4 $ 174.8 Where we have joint ownership of a mine, such as Hibbing and up to the point at which we purchased the remaining interest in Tilden, our contracts entitle us to receive management fees or royalties, which we earn as the pellets are produced.
Repairs And Maintenance	Repairs and Maintenance Repairs, maintenance and replacement of components are expensed as incurred. The cost of major equipment overhauls is capitalized and depreciated over the estimated useful life, which is the period until the next scheduled overhaul, generally five years. All other planned and unplanned repairs and maintenance costs are expensed when incurred.
Share-based Compensation, Option and Incentive Plans	Share-Based Compensation 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 its predetermined peer group of mining and metals companies. The fair value assumes that objective 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 performance period. The fair value of the restricted stock units is determined based on the closing price of our common shares on the grant date. Upon vesting of share-based compensation awards, we issue shares from treasury shares before issuing new shares. Forfeitures are recognized when they occur. The fair value of stock options is estimated on the date of grant using a Black-Scholes model using the grant date price of our common shares and option exercise price, and assumptions regarding the option’s expected term, the volatility of our common shares, the risk-free interest rate, and the dividend yield over the option’s expected term. Refer to NOTE 9 - STOCK COMPENSATION PLANS for additional information.
Income Tax	Income Taxes Income taxes are based on income for financial reporting purposes, calculated using tax rates by jurisdiction, and reflect a current tax liability or asset for the estimated taxes payable or recoverable on the current year tax return and expected annual changes in deferred taxes. Any interest or penalties on income tax are recognized as a component of Income tax benefit . We account for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized within Net income in the period that includes the enactment date. We record net deferred tax assets to the extent we believe these assets will more likely than not be realized. In making such determination, we consider all available positive and negative evidence, including scheduled reversals of deferred tax liabilities, projected future taxable income, tax planning strategies and recent financial results of operations. Accounting for uncertainty in income taxes recognized in the financial statements requires that a tax benefit from an uncertain tax position be recognized when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, based on technical merits. See NOTE 10 - INCOME TAXES for further information.
Discontinued Operations	Discontinued Operations Asia Pacific Iron Ore Operations In January 2018, we announced that we would accelerate the time frame for the planned closure of our Asia Pacific Iron Ore mining operations in Australia. In April 2018, we committed to a course of action leading to the permanent closure of our Asia Pacific Iron Ore mining operations and, as planned, completed our final shipment in June 2018. Factors considered in this decision included increasingly discounted prices for lower-iron-content ore and the quality of the remaining iron ore reserves. As a result of our planned exit, management determined that our Asia Pacific Iron Ore operating segment met the criteria to be classified as held for sale and a discontinued operation under ASC Topic 205, Presentation of Financial Statements . As such, all current and historical Asia Pacific Iron Ore operating segment results are classified within discontinued operations. Refer to NOTE 13 - DISCONTINUED OPERATIONS for further discussion of the Asia Pacific Iron Ore segment discontinued operations. Canadian Operations As more fully described in NOTE 13 - DISCONTINUED OPERATIONS , in January 2015, we announced that the Bloom Lake Group commenced restructuring proceedings in Montreal, Quebec under the CCAA. At that time, we had suspended Bloom Lake operations and for several months had been exploring options to sell certain of our Canadian assets, among other initiatives. 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 restructuring proceedings in Montreal, Quebec under the CCAA which resulted in the deconsolidation of the remaining Wabush Group entities that were not previously deconsolidated. The Wabush Group was no longer generating revenues and was not able to meet its obligations as they came due. 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. Our Canadian exit represented a strategic shift in our business. For this reason, all Eastern Canadian Iron Ore and Ferroalloys costs to exit are classified as discontinued operations.
Foreign Currency Transactions and Translations	Foreign Currency Our financial statements are prepared with the U.S. dollar as the reporting currency. Historically, the functional currency of our Australian subsidiaries was the Australian dollar. Concurrent with the sale of assets to Mineral Resources Limited in August 2018, management determined that there were significant changes in economic factors related to our Australian subsidiaries. The change in economic factors was a result of the sale and conveyance of substantially all assets and liabilities of our Australian subsidiaries to third parties, representing a significant change in operations. As such, the functional currency for the Australian subsidiaries changed from the Australian dollar to the U.S. dollar and all remaining Australian denominated monetary balances will be remeasured prospectively through the Statements of Consolidated Operations . In addition, as a result of the liquidation of substantially all of the Australian subsidiaries' assets, the historical impact of foreign currency translation recorded in Accumulated other comprehensive loss in the Statements of Consolidated Financial Position of $228.1 million was reclassified and recognized as a gain in Income from discontinued operations, net of tax in the Statements of Consolidated Operations . Refer to NOTE 13 - DISCONTINUED OPERATIONS for further information regarding our Australian subsidiaries. The functional currency of all other subsidiaries is the U.S. dollar. 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 Consolidated Operations . Transaction gains and losses resulting from remeasurement of intercompany loans are included in Miscellaneous - net in our Statements of Consolidated Operations . The following represents the net gain (loss) related to impact of transaction gains and losses from continuing operations resulting from remeasurement: (In Millions) 2018 2017 2016 Remeasurement of intercompany loans $ (0.7 ) $ 16.6 $ (16.6 ) Other remeasurement (0.2 ) (2.7 ) (1.2 ) Total $ (0.9 ) $ 13.9 $ (17.8 )
Earnings Per Share	Earnings Per Share We present both basic and diluted earnings per share amounts for continuing operations and discontinued operations. Total basic earnings per share amounts are calculated by dividing Net income attributable to Cliffs shareholders by the weighted average number of common shares outstanding during the period presented. Total diluted earnings per share amounts are calculated by dividing Net income attributable to Cliffs shareholders by the weighted average number of common shares, common share equivalents under stock plans using the treasury-stock method and the calculated common share equivalents in excess of the conversion rate related to our 2025 Convertible Senior Notes using the treasury-stock method. Common share equivalents are excluded from EPS computations in the periods in which they have an anti-dilutive effect. Holders of the 2025 Convertible Senior Notes may convert their notes during any quarter between April 1, 2018 and July 15, 2024 where our share price exceeds 130% of the conversion price for 20 trading days during a 30 trading day period. Holders of the 2025 Convertible Senior Notes may also convert their notes during any quarter between April 1, 2018 and July 15, 2024 during the five business day period after any five consecutive trading day period in which the trading price per $1,000 principal amount of notes, for each trading day of the measurement period was less than 98% of the product of the last reported sale price of our common shares and the conversion price on each such trading day. If our common shares rise in value above the conversion price, diluted EPS will be calculated based on the treasury-stock method with the number of dilutive shares being calculated based on the difference in the average share price and the conversion price. See NOTE 18 - EARNINGS PER SHARE for further information.

BASIS OF PRESENTATION AND SIG_3

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2018
Schedule Of Subsidiaries	The consolidated financial statements include our accounts and the accounts of our wholly owned subsidiaries, including the following iron ore operations at December 31, 2018 : Name Location Status of Operations Northshore Minnesota Active United Taconite Minnesota Active Tilden Michigan Active Empire Michigan Indefinitely Idled
Depreciation Disclosure [Table Text Block]	Depreciation and depletion is provided over the following estimated useful lives: Asset Class Basis Life Office and information technology Straight line 3 to 15 years Buildings Straight line 45 years Mining equipment Straight line/Double declining balance 3 to 20 years Processing equipment Straight line 10 to 45 years Electric power facilities Straight line 10 to 45 years Land improvements Straight line 20 to 45 years Asset retirement obligation Straight line Life of mine Mineral rights Units of production Life of mine
Estimated Useful Lives Of Intangible Assets Subject To Periodic Amortization On Straight Line Basis Table [Text Block]	Our mine permits are subject to periodic amortization on a straight line basis over their estimated useful life, which corresponds with the life of mine.
Contract with Customer, Asset and Liability [Table Text Block]	The table below summarizes our deferred revenue balances: (In Millions) Deferred Revenue (Current) 1 Deferred Revenue (Long-Term) Year Ended Year Ended 2018 2017 2018 2017 Opening balance as of January 1 $ 23.8 $ 16.2 $ 51.4 $ 64.3 Closing balance as of December 31 21.0 22.4 38.5 51.4 Increase (Decrease) $ (2.8 ) $ 6.2 $ (12.9 ) $ (12.9 ) 1 The opening balance for the year ended December 31, 2018 includes a $1.4 million adjustment from the December 31, 2017 balance due to the adoption of Topic 606.
Reimbursements Revenue Disclosure [Table Text Block]	The following table is a summary of reimbursements in our operations: (In Millions) Year Ended December 31, 2018 2017 2016 Reimbursements for: Freight $ 160.1 $ 166.7 $ 106.8 Venture partners’ cost — 54.7 68.0 Total reimbursements $ 160.1 $ 221.4 $ 174.8
Foreign Currency Transaction [Table Text Block]	The following represents the net gain (loss) related to impact of transaction gains and losses from continuing operations resulting from remeasurement: (In Millions) 2018 2017 2016 Remeasurement of intercompany loans $ (0.7 ) $ 16.6 $ (16.6 ) Other remeasurement (0.2 ) (2.7 ) (1.2 ) Total $ (0.9 ) $ 13.9 $ (17.8 )

NEW ACCOUNTING STANDARDS (Table

NEW ACCOUNTING STANDARDS (Tables)	12 Months Ended
	Dec. 31, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles	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 Consolidated Operations was as follows: (In Millions) Year Ended December 31, 2017 Year Ended December 31, 2016 As Adjusted Without Adoption of ASU 2017-07 Effect of Change As Adjusted Without Adoption of ASU 2017-07 Effect of Change Cost of goods sold and operating expenses $ (1,398.4 ) $ (1,400.7 ) $ 2.3 $ (1,274.4 ) $ (1,278.7 ) $ 4.3 Selling, general and administrative expenses $ (102.9 ) $ (95.1 ) $ (7.8 ) $ (115.8 ) $ (106.3 ) $ (9.5 ) Miscellaneous - net $ 25.5 $ 27.0 $ (1.5 ) $ (33.6 ) $ (32.0 ) $ (1.6 ) Operating income $ 390.2 $ 397.2 $ (7.0 ) $ 130.7 $ 137.5 $ (6.8 ) Other non-operating income $ 10.2 $ 3.2 $ 7.0 $ 7.3 $ 0.5 $ 6.8 Net income $ 363.1 $ 363.1 $ — $ 199.3 $ 199.3 $ — 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 $ 978.3 $ — $ 978.3 Accounts receivable, net 106.7 76.6 183.3 Inventories 138.4 (51.4 ) 87.0 Supplies and other inventories 88.8 — 88.8 Derivative assets 37.9 11.6 49.5 Income tax receivable, current 13.3 — 13.3 Loans to and accounts receivables from the Canadian Entities 51.6 — 51.6 Current assets of discontinued operations 118.5 — 118.5 Other current assets 11.1 — 11.1 TOTAL CURRENT ASSETS 1,544.6 36.8 1,581.4 PROPERTY, PLANT AND EQUIPMENT, NET 1,033.8 — 1,033.8 OTHER ASSETS Deposits for property, plant and equipment 17.8 — 17.8 Income tax receivable, non-current 235.3 — 235.3 Non-current assets of discontinued operations 20.3 — 20.3 Other non-current assets 101.6 — 101.6 TOTAL OTHER ASSETS 375.0 — 375.0 TOTAL ASSETS $ 2,953.4 $ 36.8 $ 2,990.2 LIABILITIES CURRENT LIABILITIES Accounts payable $ 99.5 $ 1.4 $ 100.9 Accrued employment costs 52.7 — 52.7 State and local taxes payable 30.2 — 30.2 Accrued interest 31.4 — 31.4 Contingent claims 55.6 — 55.6 Partnership distribution payable 44.2 — 44.2 Current liabilities of discontinued operations 75.0 — 75.0 Other current liabilities 63.6 1.4 65.0 TOTAL CURRENT LIABILITIES 452.2 2.8 455.0 PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES 257.7 — 257.7 ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS 167.7 — 167.7 LONG-TERM DEBT 2,304.2 — 2,304.2 NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS 52.2 — 52.2 OTHER LIABILITIES 163.5 — 163.5 TOTAL LIABILITIES 3,397.5 2.8 3,400.3 EQUITY CLIFFS SHAREHOLDERS' EQUITY (DEFICIT) (444.3 ) 34.0 (410.3 ) NONCONTROLLING INTEREST 0.2 — 0.2 TOTAL EQUITY (DEFICIT) (444.1 ) 34.0 (410.1 ) TOTAL LIABILITIES AND EQUITY (DEFICIT) $ 2,953.4 $ 36.8 $ 2,990.2 The impact of adoption on our Statements of Consolidated Operations and Statements of Consolidated Financial Position is as follows: ($ in Millions) Year Ended December 31, 2018 As Reported Balances without Adoption of Topic 606 Effect of Change REVENUES FROM PRODUCT SALES AND SERVICES Product $ 2,172.3 $ 2,108.1 $ 64.2 Freight and venture partners' cost reimbursements 160.1 156.2 3.9 2,332.4 2,264.3 68.1 COST OF GOODS SOLD AND OPERATING EXPENSES (1,522.8 ) (1,513.2 ) (9.6 ) SALES MARGIN 809.6 751.1 58.5 OTHER OPERATING INCOME (EXPENSE) Selling, general and administrative expenses (116.8 ) (116.8 ) — Miscellaneous - net (19.6 ) (19.6 ) — (136.4 ) (136.4 ) — OPERATING INCOME 673.2 614.7 58.5 OTHER INCOME (EXPENSE) Interest expense, net (118.9 ) (118.9 ) — Loss on extinguishment of debt (6.8 ) (6.8 ) — Other non-operating income 17.2 17.2 — (108.5 ) (108.5 ) — INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES 564.7 506.2 58.5 INCOME TAX BENEFIT 475.2 487.5 (12.3 ) INCOME FROM CONTINUING OPERATIONS 1,039.9 993.7 46.2 INCOME FROM DISCONTINUED OPERATIONS, net of tax 88.2 88.2 — NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 1,128.1 $ 1,081.9 $ 46.2 EARNINGS PER COMMON SHARE ATTRIBUTABLE TO CLIFFS SHAREHOLDERS - BASIC Continuing operations $ 3.50 $ 3.34 $ 0.16 Discontinued operations 0.30 0.30 — $ 3.80 $ 3.64 $ 0.16 EARNINGS PER COMMON SHARE ATTRIBUTABLE TO CLIFFS SHAREHOLDERS - DILUTED Continuing operations $ 3.42 $ 3.27 $ 0.15 Discontinued operations 0.29 0.29 — $ 3.71 $ 3.56 $ 0.15 AVERAGE NUMBER OF SHARES (IN THOUSANDS) Basic 297,176 297,176 Diluted 304,141 304,141 The increased revenue recognized under Topic 606 is due to higher tons shipped and a higher realized revenue rate in December 2018 versus December 2017. Under the previous accounting standard, December 2017 shipments would have been recognized as 2018 sales due to the fact that title and risk of loss does not transfer until payment is received from our customers. (In Millions) December 31, 2018 As Reported Balances without Adoption of Topic 606 Effect of Change ASSETS CURRENT ASSETS Cash and cash equivalents $ 823.2 $ 823.2 $ — Accounts receivable, net 226.7 108.7 118.0 Inventories 87.9 141.3 (53.4 ) Supplies and other inventories 93.2 93.2 — Derivative assets 91.5 60.7 30.8 Income tax receivable, current 117.3 117.3 — Current assets of discontinued operations 12.4 12.4 — Other current assets 27.4 27.4 — TOTAL CURRENT ASSETS 1,479.6 1,384.2 95.4 PROPERTY, PLANT AND EQUIPMENT, NET 1,286.0 1,286.0 — OTHER ASSETS Deposits for property, plant and equipment 83.0 83.0 — Income tax receivable, non-current 121.3 121.3 — Deferred income taxes 464.8 477.1 (12.3 ) Other non-current assets 94.9 94.9 — TOTAL OTHER ASSETS 764.0 776.3 (12.3 ) TOTAL ASSETS $ 3,529.6 $ 3,446.5 $ 83.1 LIABILITIES CURRENT LIABILITIES Accounts payable $ 186.8 $ 184.9 $ 1.9 Accrued employment costs 74.0 74.0 — State and local taxes payable 35.5 35.5 — Accrued interest 38.4 38.4 — Partnership distribution payable 43.5 43.5 — Current liabilities of discontinued operations 6.7 6.7 — Other current liabilities 83.3 83.7 (0.4 ) TOTAL CURRENT LIABILITIES 468.2 466.7 1.5 PENSION AND POSTEMPLOYMENT BENEFIT LIABILITIES 248.7 248.7 — ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS 172.0 172.0 — LONG-TERM DEBT 2,092.9 2,092.9 — NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS 8.3 8.3 — OTHER LIABILITIES 115.3 115.3 — TOTAL LIABILITIES 3,105.4 3,103.9 1.5 EQUITY CLIFFS SHAREHOLDERS' EQUITY 424.2 342.6 81.6 TOTAL LIABILITIES AND EQUITY $ 3,529.6 $ 3,446.5 $ 83.1

SEGMENT REPORTING (Tables)

SEGMENT REPORTING (Tables)	12 Months Ended
	Dec. 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 Income from continuing operations before income taxes and a reconciliation of Net income to EBITDA and Adjusted EBITDA: 2018 2017 2016 Revenues from product sales and services: Mining and Pelletizing $ 2,332.4 $ 1,866.0 $ 1,554.5 Sales margin: Mining and Pelletizing $ 809.6 $ 467.6 $ 280.1 Other operating expense (136.4 ) (77.4 ) (149.4 ) Other expense (108.5 ) (282.0 ) (20.3 ) Income from continuing operations before income taxes $ 564.7 $ 108.2 $ 110.4 (In Millions) 2018 2017 2016 Net income $ 1,128.1 $ 363.1 $ 199.3 Less: Interest expense, net (121.3 ) (132.0 ) (200.5 ) Income tax benefit 460.3 252.4 12.2 Depreciation, depletion and amortization (89.0 ) (87.7 ) (115.4 ) Total EBITDA $ 878.1 $ 330.4 $ 503.0 Less: Gain (loss) on extinguishment/restructuring of debt $ (6.8 ) $ (165.4 ) $ 166.3 Impact of discontinued operations 120.6 22.0 108.4 Foreign exchange remeasurement (0.9 ) 13.9 (17.8 ) Impairment of long-lived assets (1.1 ) — — Total Adjusted EBITDA $ 766.3 $ 459.9 $ 246.1 EBITDA: Mining and Pelletizing $ 852.9 $ 534.9 $ 342.4 Metallics (3.3 ) (0.4 ) — Corporate and Other 1 28.5 (204.1 ) 160.6 Total EBITDA $ 878.1 $ 330.4 $ 503.0 Adjusted EBITDA: Mining and Pelletizing $ 875.3 $ 559.4 $ 359.6 Metallics (3.3 ) (0.4 ) — Corporate (105.7 ) (99.1 ) (113.5 ) Total Adjusted EBITDA $ 766.3 $ 459.9 $ 246.1 1 Corporate and Other includes activity from discontinued operations. (In Millions) 2018 2017 2016 Depreciation, depletion and amortization: Mining and Pelletizing $ 68.2 $ 66.6 $ 84.0 Corporate 5.6 6.8 6.3 Total depreciation, depletion and amortization $ 73.8 $ 73.4 $ 90.3 Capital additions 1 : Mining and Pelletizing $ 145.0 $ 136.8 $ 62.2 Metallics 248.1 13.7 — Corporate and Other 1.6 2.7 6.1 Total capital additions $ 394.7 $ 153.2 $ 68.3 1 Includes capital lease additions and non-cash accruals. Refer to NOTE 16 - CASH FLOW INFORMATION.
Summary of Assets by Segment	A summary of assets by segment is as follows: (In Millions) December 31, December 31, 2017 December 31, 2016 Assets: Mining and Pelletizing $ 1,694.1 $ 1,500.6 $ 1,372.5 Metallics 265.9 13.4 — Total segment assets 1,960.0 1,514.0 1,372.5 Corporate 1,557.2 1,300.6 396.3 Assets of discontinued operations 12.4 138.8 155.1 Total assets $ 3,529.6 $ 2,953.4 $ 1,923.9
Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas	Included in the consolidated financial statements are the following amounts relating to geographic location: (In Millions) 2018 2017 2016 Revenues from product sales and services: United States $ 1,847.3 $ 1,504.5 $ 1,236.2 Canada 395.1 206.2 267.1 Other countries 90.0 155.3 51.2 Total revenues from product sales and services $ 2,332.4 $ 1,866.0 $ 1,554.5 Property, plant and equipment, net: United States $ 1,286.0 $ 1,033.8 $ 961.0
Revenue from External Customers by Products and Services	The following table represents the percentage of our total Revenues from product sales and services contributed by each category of products and services: 2018 2017 2016 Revenue category: Product 93 % 88 % 89 % Freight and venture partners’ cost reimbursements 7 % 12 % 11 % Total revenues from product sales and services 100 % 100 % 100 %

INVENTORIES (Tables)

INVENTORIES (Tables)	12 Months Ended
	Dec. 31, 2018
Inventory Disclosure [Abstract]
Schedule Of Inventories	The following table presents the detail of our Inventories in the Statements of Consolidated Financial Position : (In Millions) December 31, 2018 2017 Finished Goods $ 77.8 $ 127.1 Work-in-Process 10.1 11.3 Total Inventories $ 87.9 $ 138.4

PROPERTY, PLANT AND EQUIPMENT (

PROPERTY, PLANT AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Value Of Each Of The Major Classes Of Consolidated Depreciable Assets	The following table indicates the carrying value of each of the major classes of our consolidated depreciable assets: (In Millions) December 31, 2018 2017 Land rights and mineral rights $ 549.6 $ 549.6 Office and information technology 70.0 65.8 Buildings 87.2 85.2 Mining equipment 548.5 533.9 Processing equipment 645.8 610.9 Electric power facilities 58.7 56.9 Land improvements 23.8 23.7 Asset retirement obligation 14.8 16.9 Other 25.2 25.2 Construction-in-progress 284.8 32.6 2,308.4 2,000.7 Allowance for depreciation and depletion (1,022.4 ) (966.9 ) $ 1,286.0 $ 1,033.8
Book Value of Land and Mineral Rights Disclosure [Table Text Block]	The net book value of the land rights and mineral rights is as follows : (In Millions) December 31, 2018 2017 Land rights $ 12.4 $ 12.4 Mineral rights: Cost $ 537.2 $ 537.2 Depletion (126.5 ) (119.1 ) Net mineral rights $ 410.7 $ 418.1

DEBT AND CREDIT FACILITIES (Tab

DEBT AND CREDIT FACILITIES (Tables)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Line of Credit Facility [Line Items]
Schedule of Line of Credit Facilities [Table Text Block]	The following represents a summary of our borrowing capacity under the ABL Facility: (In Millions) December 31, 2018 December 31, 2017 Available borrowing base on ABL Facility 1 $ 323.7 $ 273.2 Letter of credit obligations and other commitments 2 (55.0 ) (46.5 ) Borrowing capacity available 3 $ 268.7 $ 226.7 1 The ABL Facility has a maximum borrowing base of $450 million, determined by applying customary advance rates to eligible accounts receivable, inventory and certain mobile equipment. 2 We issued standby letters of credit with certain financial institutions in order to support business obligations including, but not limited to, workers compensation, environmental obligations and a Metallics energy supply agreement. 3 As of December 31, 2018 and 2017 we had no loans drawn under the ABL Facility.
Schedule Of Long-Term Debt	The following represents a summary of our long-term debt: (In Millions) December 31, 2018 Debt Instrument Annual Effective Interest Rate Total Principal Amount Debt Issuance Costs Unamortized Discounts Total Debt Senior Secured Notes: $400 Million 4.875% 2024 Senior Notes 5.00% $ 400.0 $ (5.7 ) $ (2.2 ) $ 392.1 Unsecured Notes: $700 Million 4.875% 2021 Senior Notes 4.89% 124.0 (0.2 ) — 123.8 $316.25 Million 1.50% 2025 Convertible Senior Notes 6.26% 316.3 (5.5 ) (75.6 ) 235.2 $1.075 Billion 5.75% 2025 Senior Notes 6.01% 1,073.3 (9.9 ) (14.6 ) 1,048.8 $800 Million 6.25% 2040 Senior Notes 6.34% 298.4 (2.3 ) (3.3 ) 292.8 ABL Facility N/A 450.0 N/A N/A — Fair Value Adjustment to Interest Rate Hedge 0.2 Long-term debt $ 2,092.9 (In Millions) December 31, 2017 Debt Instrument Annual Effective Interest Rate Total Principal Amount Debt Issuance Costs Unamortized Discounts Total Debt Senior 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 Extinguishment of Debt [Table Text Block]	The following is a summary of the debt extinguished and the respective gain (loss) on extinguishment: (In Millions) Year Ended Debt Extinguished Gain (Loss) on Extinguishment 1 Unsecured Notes: $400 Million 5.90% 2020 Senior Notes $ 88.9 $ (3.3 ) $500 Million 4.80% 2020 Senior Notes 122.4 (3.7 ) $700 Million 4.875% 2021 Senior Notes 14.4 0.1 $1.075 Billion 5.75% 2025 Senior Notes 1.7 0.1 $ 227.4 $ (6.8 ) 1 This includes premiums paid related to the redemption of our notes of $7.1 million.	The following is a summary of the debt extinguished and the respective gain (loss) on extinguishment: (In Millions) Year Ended Debt Extinguished Gain (Loss) on Extinguishment 1 Secured Notes: $540 Million 8.25% 2020 First Lien Notes $ 540.0 $ (93.5 ) $218.5 Million 8.00% 2020 1.5 Lien Notes 218.5 45.1 $544.2 Million 7.75% 2020 Second Lien Notes 430.1 (104.5 ) Unsecured Notes: $400 Million 5.90% 2020 Senior Notes 136.7 (7.8 ) $500 Million 4.80% 2020 Senior Notes 114.4 (1.9 ) $700 Million 4.875% 2021 Senior Notes 171.0 (2.8 ) $ 1,610.7 $ (165.4 ) 1 This includes premiums paid related to the redemption of our notes of $110.0 million.	The following is a summary of the debt exchanged for our $218.5 million 8.00% 2020 1.5 Lien Notes: (In Millions) Debt Extinguished 1.5 Lien Amount Issued Carrying Value 1 Gain on Restructuring 2 $544.2 Million 7.75% 2020 Second Lien Notes $ 114.1 $ 57.0 $ 77.5 $ 6.9 $500 Million 3.95% 2018 Senior Notes 17.6 11.4 15.5 1.8 $400 Million 5.90% 2020 Senior Notes 65.1 26.0 35.4 28.3 $500 Million 4.80% 2020 Senior Notes 44.7 17.9 24.4 19.5 $700 Million 4.875% 2021 Senior Notes 76.3 30.5 41.5 33.3 $800 Million 6.25% 2040 Senior Notes 194.4 75.7 103.0 84.5 $ 512.2 $ 218.5 $ 297.3 $ 174.3 1 Includes undiscounted interest payments 2 Net of amounts expensed for unamortized original issue discount and deferred origination fees
Schedule of Maturities of Long-term Debt [Table Text Block]	The following represents a summary of our debt instrument maturities based on the principal amounts outstanding at December 31, 2018 : (In Millions) Maturities of Debt 2019 $ — 2020 — 2021 124.0 2022 — 2023 — 2024 and thereafter 2,088.0 Total maturities of debt $ 2,212.0

DEBT AND CREDIT FACILITIES Debt

DEBT AND CREDIT FACILITIES Debt Extinguishment (Tables)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Extinguishment of Debt [Line Items]
Schedule of Extinguishment of Debt [Table Text Block]	The following is a summary of the debt extinguished and the respective gain (loss) on extinguishment: (In Millions) Year Ended Debt Extinguished Gain (Loss) on Extinguishment 1 Unsecured Notes: $400 Million 5.90% 2020 Senior Notes $ 88.9 $ (3.3 ) $500 Million 4.80% 2020 Senior Notes 122.4 (3.7 ) $700 Million 4.875% 2021 Senior Notes 14.4 0.1 $1.075 Billion 5.75% 2025 Senior Notes 1.7 0.1 $ 227.4 $ (6.8 ) 1 This includes premiums paid related to the redemption of our notes of $7.1 million.	The following is a summary of the debt extinguished and the respective gain (loss) on extinguishment: (In Millions) Year Ended Debt Extinguished Gain (Loss) on Extinguishment 1 Secured Notes: $540 Million 8.25% 2020 First Lien Notes $ 540.0 $ (93.5 ) $218.5 Million 8.00% 2020 1.5 Lien Notes 218.5 45.1 $544.2 Million 7.75% 2020 Second Lien Notes 430.1 (104.5 ) Unsecured Notes: $400 Million 5.90% 2020 Senior Notes 136.7 (7.8 ) $500 Million 4.80% 2020 Senior Notes 114.4 (1.9 ) $700 Million 4.875% 2021 Senior Notes 171.0 (2.8 ) $ 1,610.7 $ (165.4 ) 1 This includes premiums paid related to the redemption of our notes of $110.0 million.	The following is a summary of the debt exchanged for our $218.5 million 8.00% 2020 1.5 Lien Notes: (In Millions) Debt Extinguished 1.5 Lien Amount Issued Carrying Value 1 Gain on Restructuring 2 $544.2 Million 7.75% 2020 Second Lien Notes $ 114.1 $ 57.0 $ 77.5 $ 6.9 $500 Million 3.95% 2018 Senior Notes 17.6 11.4 15.5 1.8 $400 Million 5.90% 2020 Senior Notes 65.1 26.0 35.4 28.3 $500 Million 4.80% 2020 Senior Notes 44.7 17.9 24.4 19.5 $700 Million 4.875% 2021 Senior Notes 76.3 30.5 41.5 33.3 $800 Million 6.25% 2040 Senior Notes 194.4 75.7 103.0 84.5 $ 512.2 $ 218.5 $ 297.3 $ 174.3 1 Includes undiscounted interest payments 2 Net of amounts expensed for unamortized original issue discount and deferred origination fees

FAIR VALUE OF FINANCIAL INSTR_2

FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value, by Balance Sheet Grouping [Table Text Block]	The following represents the assets and liabilities measured at fair value: (In Millions) December 31, 2018 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 $ 0.8 $ 542.6 $ — $ 543.4 Derivative assets — 0.1 91.4 91.5 Total $ 0.8 $ 542.7 $ 91.4 $ 634.9 Liabilities: Derivative liabilities $ — $ 3.7 $ — $ 3.7 Total $ — $ 3.7 $ — $ 3.7 (In Millions) December 31, 2017 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 — — 37.9 37.9 Total $ 66.3 $ 550.6 $ 37.9 $ 654.8 Liabilities: Derivative liabilities $ — $ 0.3 $ 1.7 $ 2.0 Total $ — $ 0.3 $ 1.7 $ 2.0
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Recurring and Nonrecurring, Valuation Techniques	The following table illustrates information about quantitative inputs and assumptions for the derivative assets and derivative liabilities categorized in Level 3 of the fair value hierarchy: Qualitative/Quantitative Information About Level 3 Fair Value Measurements Fair Value at December 31, 2018 (In Millions) Balance Sheet Location Valuation Technique Unobservable Input Point Estimate Customer supply agreement $89.3 Derivative assets Market Approach Management's Estimate of Market Hot-Rolled Coil Steel per net ton $750 Provisional pricing arrangements $2.1 Derivative assets Market Approach Management's Estimate of Platts 62% Price per dry metric ton $68
Fair Value, Assets Measured On Recurring Basis, Unobservable Input Reconciliation	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): Derivative Assets 1 (Level 3) Derivative Liabilities (Level 3) Year Ended Year Ended 2018 2017 2018 2017 Beginning balance - January 1 $ 49.5 $ 30.1 $ (1.7 ) $ — Total gains (losses) Included in earnings 428.7 176.2 (6.1 ) (55.6 ) Settlements (386.8 ) (168.4 ) 7.8 53.9 Ending balance - December 31 $ 91.4 $ 37.9 $ — $ (1.7 ) Total gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) on assets still held at the reporting date $ 91.4 $ 37.9 $ — $ (1.7 ) 1 Beginning balance as of January 1, 2018 includes an $11.6 million adjustment for adoption of Topic 606.
Schedule Of Carrying Value And Fair Value Of Financial Instruments	A summary of the carrying value and fair value of other financial instruments were as follows: (In Millions) December 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 $ 392.1 $ 370.2 $ 390.3 $ 398.0 Unsecured Notes: $400 Million 5.90% 2020 Senior Notes Level 1 — — 88.6 88.0 $500 Million 4.80% 2020 Senior Notes Level 1 — — 122.0 118.8 $700 Million 4.875% 2021 Senior Notes Level 1 123.8 122.3 138.0 130.8 $316.25 Million 1.50% 2025 Convertible Senior Notes Level 1 235.2 352.4 224.1 352.9 $1.075 Billion 5.75% 2025 Senior Notes Level 1 1,048.8 962.0 1,047.2 1,029.3 $800 Million 6.25% 2040 Senior Notes Level 1 292.8 232.8 292.6 227.1 ABL Facility Level 2 — — — — Fair Value Adjustment to Interest Rate Hedge Level 2 0.2 0.2 1.4 1.4 Total long-term debt $ 2,092.9 $ 2,039.9 $ 2,304.2 $ 2,346.3

PENSIONS AND OTHER POSTRETIRE_2

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Tables)	12 Months Ended
	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Retirement And Defined Compensation Plans Disclosures [Table Text Block]	The following table summarizes the annual expense (income) recognized related to the retirement plans: (In Millions) 2018 2017 2016 Defined benefit pension plans $ 12.7 $ 18.0 $ 16.5 Defined contribution pension plans 3.1 2.9 2.8 Other postretirement benefits (5.9 ) (6.1 ) (4.0 ) Total $ 9.9 $ 14.8 $ 15.3
Obligations and Funded Status	The following tables and information provide additional disclosures: (In Millions) Pension Benefits Other Benefits Change in benefit obligations: 2018 2017 2018 2017 Benefit obligations — beginning of year $ 973.1 $ 931.6 $ 265.9 $ 264.6 Service cost (excluding expenses) 18.7 17.1 2.2 1.8 Interest cost 30.3 30.5 8.3 8.3 Plan amendments 2.2 — 12.8 — Curtailment gain (0.9 ) — — — Actuarial (gain) loss (57.0 ) 54.6 (29.4 ) 7.4 Benefits paid (60.7 ) (60.7 ) (24.4 ) (21.4 ) Participant contributions — — 5.6 4.6 Federal subsidy on benefits paid — — 0.9 0.6 Benefit obligations — end of year $ 905.7 $ 973.1 $ 241.9 $ 265.9 Change in plan assets: Fair value of plan assets — beginning of year $ 749.8 $ 685.8 $ 262.5 $ 253.0 Actual return on plan assets (29.6 ) 100.2 (8.2 ) 24.2 Participant contributions — — 0.5 0.3 Employer contributions 27.6 24.4 3.0 1.7 Asset transfers 0.1 0.1 — — Benefits paid (60.7 ) (60.7 ) (17.6 ) (16.7 ) Fair value of plan assets — end of year $ 687.2 $ 749.8 $ 240.2 $ 262.5 Funded status at December 31: Fair value of plan assets $ 687.2 $ 749.8 $ 240.2 $ 262.5 Benefit obligations (905.7 ) (973.1 ) (241.9 ) (265.9 ) Amount recognized at December 31 $ (218.5 ) $ (223.3 ) $ (1.7 ) $ (3.4 ) Amounts recognized in Statements of Financial Position: Non-current assets $ — $ — $ 32.1 $ 35.4 Current liabilities (0.1 ) (0.5 ) (3.5 ) (3.9 ) Non-current liabilities (218.4 ) (222.8 ) (30.3 ) (34.9 ) Total amount recognized $ (218.5 ) $ (223.3 ) $ (1.7 ) $ (3.4 ) Amounts recognized in accumulated other comprehensive loss: Net actuarial loss $ 330.1 $ 318.7 $ 82.1 $ 88.3 Prior service cost (credit) 8.5 8.8 (9.9 ) (25.6 ) Net amount recognized $ 338.6 $ 327.5 $ 72.2 $ 62.7
Fair Value Of Plan Assets, Benefit Obligation And Funded Status	(In Millions) 2018 Pension Plans Other Benefits Salaried Hourly Mining SERP Total Salaried Hourly Total Fair value of plan assets $ 249.8 $ 429.4 $ 8.0 $ — $ 687.2 $ — $ 240.2 $ 240.2 Benefit obligation (340.8 ) (548.9 ) (10.7 ) (5.3 ) (905.7 ) (32.9 ) (209.0 ) (241.9 ) Funded status $ (91.0 ) $ (119.5 ) $ (2.7 ) $ (5.3 ) $ (218.5 ) $ (32.9 ) $ 31.2 $ (1.7 ) 2017 Pension Plans Other Benefits Salaried Hourly Mining SERP Total Salaried Hourly Total Fair value of plan assets $ 269.4 $ 473.0 $ 7.4 $ — $ 749.8 $ — $ 262.5 $ 262.5 Benefit obligation (368.0 ) (590.0 ) (10.3 ) (4.8 ) (973.1 ) (37.7 ) (228.2 ) (265.9 ) Funded status $ (98.6 ) $ (117.0 ) $ (2.9 ) $ (4.8 ) $ (223.3 ) $ (37.7 ) $ 34.3 $ (3.4 )
Components Of Net Periodic Benefit Cost	Components of Net Periodic Benefit Cost (In Millions) Pension Benefits Other Benefits 2018 2017 2016 2018 2017 2016 Service cost $ 18.7 $ 17.1 $ 17.6 $ 2.2 $ 1.8 $ 1.7 Interest cost 30.3 30.5 30.3 8.3 8.3 9.1 Expected return on plan assets (60.0 ) (54.5 ) (54.7 ) (18.4 ) (17.7 ) (17.1 ) Amortization: Prior service costs (credits) 2.2 2.6 2.2 (3.0 ) (3.0 ) (3.7 ) Net actuarial loss 21.2 22.3 21.1 5.0 4.5 6.0 Curtailments 0.3 — — — — — Net periodic benefit cost (credit) $ 12.7 $ 18.0 $ 16.5 $ (5.9 ) $ (6.1 ) $ (4.0 ) Curtailment effects (0.3 ) — — — — — Current year actuarial loss (gain) 31.6 9.3 37.8 (2.9 ) 1.2 (8.1 ) Amortization of net loss (21.2 ) (22.3 ) (21.1 ) (5.0 ) (4.5 ) (6.0 ) Current year prior service cost 2.2 — 5.7 12.8 — 9.8 Amortization of prior service credit (cost) (2.2 ) (2.6 ) (2.2 ) 3.0 3.0 3.7 Total recognized in other comprehensive income (loss) $ 10.1 $ (15.6 ) $ 20.2 $ 7.9 $ (0.3 ) $ (0.6 ) Total recognized in net periodic cost and other comprehensive income (loss) $ 22.8 $ 2.4 $ 36.7 $ 2.0 $ (6.4 ) $ (4.6 )
Weighted-Average Assumptions Used to Determine Benefit Obligations	Weighted-average assumptions used to determine benefit obligations at December 31 were: Pension Benefits Other Benefits 2018 2017 2018 2017 Discount rate: Iron Hourly Pension Plan 4.31 % 3.60 % N/A % N/A % Salaried Pension Plan 4.21 3.52 N/A N/A Ore Mining Pension Plan 4.33 3.61 N/A N/A Supplemental Executive Retirement Plan 4.22 3.50 N/A N/A Hourly OPEB Plan N/A N/A 4.29 3.60 Salaried OPEB Plan N/A N/A 4.27 3.57 Salaried rate of compensation increase 3.00 3.00 3.00 3.00 Hourly rate of compensation increase 2.00 2.00 N/A N/A
Weighted-Average Assumptions Used To Determine Net Benefit Costs	Weighted-average assumptions used to determine net benefit cost were: Pension Benefits Other Benefits 2018 2017 2016 2018 2017 2016 Obligation Discount Rate: Iron Hourly Pension Plan 3.61 % 4.02 % 4.27 % N/A % N/A % N/A % Salaried Pension Plan 3.52 3.91 4.13 N/A N/A N/A Ore Mining Pension Plan 3.61 4.04 4.28 N/A N/A N/A Supplemental Executive Retirement Plan 3.54 3.90 4.01 N/A N/A N/A Hourly OPEB Plan N/A N/A N/A 3.60 4.03 4.32 Salaried OPEB Plan N/A N/A N/A 3.57 3.98 4.22 Service Cost Discount Rate: Iron Hourly Pension Plan 3.76 4.30 4.66 N/A N/A N/A Salaried Pension Plan 3.53 3.93 4.14 N/A N/A N/A Ore Mining Pension Plan 3.75 4.27 4.60 N/A N/A N/A Supplemental Executive Retirement Plan 3.43 3.69 3.87 N/A N/A N/A Hourly OPEB Plan N/A N/A N/A 3.73 4.23 4.56 Salaried OPEB Plan N/A N/A N/A 3.76 4.30 4.63 Interest Cost Discount Rate: Iron Hourly Pension Plan 3.21 3.38 3.46 N/A N/A N/A Salaried Pension Plan 3.08 3.21 3.21 N/A N/A N/A Ore Mining Pension Plan 3.22 3.41 3.48 N/A N/A N/A Supplemental Executive Retirement Plan 3.16 3.36 3.30 N/A N/A N/A Hourly OPEB Plan N/A N/A N/A 3.10 3.24 3.48 Salaried OPEB Plan N/A N/A N/A 3.15 3.28 3.31 Expected return on plan assets 8.25 8.25 8.25 7.00 7.00 7.00 Salaried rate of compensation increase 3.00 3.00 3.00 3.00 3.00 3.00 Hourly rate of compensation increase 2.00 2.00 2.00 N/A N/A N/A
Assumed Health Care Cost Trend Rates	Assumed health care cost trend rates at December 31 were: 2018 2017 Health care cost trend rate assumed for next year 6.75 % 7.00 % Ultimate health care cost trend rate 5.00 5.00 Year that the ultimate rate is reached 2026 2026
Plan Assets and Asset Allocation	The following table reflects the actual asset allocations for pension and VEBA plan assets as of December 31, 2018 and 2017 , as well as the 2019 weighted average target asset allocations. Equity investments include securities in large-cap, mid-cap and small-cap companies located in the U.S. and worldwide. Fixed income investments primarily include corporate bonds and government debt securities. Pension Assets VEBA Assets Asset Category 2019 Target Allocation Percentage of Plan Assets at December 31, 2019 Target Allocation Percentage of Plan Assets at December 31, 2018 2017 2018 2017 Equity securities 45.0 % 38.9 % 43.6 % 8.0 % 8.1 % 8.7 % Fixed income 28.0 % 26.0 % 27.0 % 80.0 % 77.0 % 77.7 % Hedge funds 5.0 % 5.4 % 5.0 % 4.0 % 4.7 % 4.4 % Private equity 7.0 % 6.2 % 5.3 % 3.0 % 1.2 % 1.5 % Structured credit 7.5 % 11.4 % 9.7 % 2.0 % 3.5 % 3.0 % Real estate 7.5 % 10.3 % 8.7 % 3.0 % 5.4 % 4.6 % Cash — % 1.8 % 0.7 % — % 0.1 % 0.1 % Total 100.0 % 100.0 % 100.0 % 100.0 % 100.0 % 100.0 %
Fair Value, Assets and Liabilities Measured on Recurring Basis	Pension The fair value of our pension plan assets by asset category is as follows: (In Millions) December 31, 2018 Asset Category Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Equity securities: U.S. large-cap $ 112.6 $ — $ — $ 112.6 U.S. small/mid-cap 22.5 — — 22.5 International 132.0 — — 132.0 Fixed income 151.1 27.4 — 178.5 Hedge funds — — 37.2 37.2 Private equity — — 42.6 42.6 Structured credit — — 78.8 78.8 Real estate — — 70.5 70.5 Cash 12.5 — — 12.5 Total $ 430.7 $ 27.4 $ 229.1 $ 687.2 (In Millions) December 31, 2017 Asset Category Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Equity securities: U.S. large-cap $ 130.1 $ — $ — $ 130.1 U.S. small/mid-cap 35.5 — — 35.5 International 160.9 — — 160.9 Fixed income 173.6 28.8 — 202.4 Hedge funds — — 37.4 37.4 Private equity — — 39.8 39.8 Structured credit — — 72.9 72.9 Real estate — — 65.5 65.5 Cash 5.3 — — 5.3 Total $ 505.4 $ 28.8 $ 215.6 $ 749.8
Effect of Fair Value Measurements Using Significant Unobservable Inputs on Changes in Plan Assets	The following represents the effect of fair value measurements using significant unobservable inputs (Level 3) on changes in plan assets: (In Millions) Year Ended December 31, 2018 Hedge Funds Private Equity Funds Structured Credit Fund Real Estate Total Beginning balance — January 1, 2018 $ 37.4 $ 39.8 $ 72.9 $ 65.5 $ 215.6 Actual return on plan assets: Relating to assets still held at the reporting date (0.2 ) 1.4 5.9 5.4 12.5 Relating to assets sold during the period — 4.0 — — 4.0 Purchases — 5.2 — — 5.2 Sales — (7.8 ) — (0.4 ) (8.2 ) Ending balance — December 31, 2018 $ 37.2 $ 42.6 $ 78.8 $ 70.5 $ 229.1 (In Millions) Year Ended December 31, 2017 Hedge Funds Private Equity Funds Structured Credit Fund Real Estate Total Beginning balance — January 1, 2017 $ 40.6 $ 36.1 $ 63.8 $ 61.9 $ 202.4 Actual return on plan assets: Relating to assets still held at the reporting date 2.5 0.3 9.1 4.2 16.1 Relating to assets sold during 0.4 4.5 — (0.1 ) 4.8 Purchases 39.0 4.5 — 14.4 57.9 Sales (45.1 ) (5.6 ) — (14.9 ) (65.6 ) Ending balance — December 31, 2017 $ 37.4 $ 39.8 $ 72.9 $ 65.5 $ 215.6 VEBA Assets fo
Schedule Of Annual Contributions	(In Millions) Pension Benefits Other Benefits Company Contributions VEBA Direct Payments Total 2017 $ 24.4 $ — $ 2.1 $ 2.1 2018 27.6 — 3.8 3.8 2019 (Expected) 1 15.9 — 3.5 3.5 1 Pursuant to the bargaining agreement, benefits can be paid from VEBA trusts that are at least 70% funded (all VEBA trusts are over 70% funded at December 31, 2018). Funding obligations have been suspended as UTAC's, Tilden's and Empire's share of the value of their respective trust assets have reached 90% of their obligation.
Estimated Net Periodic Benefit Cost	Estimated Cost for 2019 For 2019 , we estimate net periodic benefit cost as follows: (In Millions) Defined benefit pension plans $ 21.5 Other postretirement benefits (2.8 ) Total $ 18.7
Estimated Future Benefit Payments	Estimated Future Benefit Payments (In Millions) Pension Benefits Other Benefits Gross Company Benefits Less Medicare Subsidy Net Benefit Payments 2019 $ 70.4 $ 18.0 $ (0.8 ) $ 17.2 2020 67.9 17.7 (0.8 ) 16.9 2021 67.5 17.2 (0.9 ) 16.3 2022 67.0 17.0 (0.9 ) 16.1 2023 67.9 16.9 (1.0 ) 15.9 2024-2028 309.7 82.2 (5.4 ) 76.8
Veba Trust [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Assets and Liabilities Measured on Recurring Basis	The fair value of our other benefit plan assets by asset category is as follows: (In Millions) December 31, 2018 Asset Category Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Equity securities: U.S. large-cap $ 9.7 $ — $ — $ 9.7 U.S. small/mid-cap 2.4 — — 2.4 International 7.3 — — 7.3 Fixed income 146.8 37.8 — 184.6 Hedge funds — — 11.4 11.4 Private equity — — 3.0 3.0 Structured credit — — 8.5 8.5 Real estate — — 13.1 13.1 Cash 0.2 — — 0.2 Total $ 166.4 $ 37.8 $ 36.0 $ 240.2 (In Millions) December 31, 2017 Asset Category Quoted Prices in Active Significant Other Significant Total Equity securities: U.S. large-cap $ 11.4 $ — $ — $ 11.4 U.S. small/mid-cap 2.8 — — 2.8 International 8.8 — — 8.8 Fixed income 164.1 40.0 — 204.1 Hedge funds — — 11.4 11.4 Private equity — — 3.9 3.9 Structured credit — — 7.9 7.9 Real estate — — 12.0 12.0 Cash 0.2 — — 0.2 Total $ 187.3 $ 40.0 $ 35.2 $ 262.5
Effect of Fair Value Measurements Using Significant Unobservable Inputs on Changes in Plan Assets	The following represents the effect of fair value measurements using significant unobservable inputs (Level 3) on changes in plan assets: (In Millions) Year Ended December 31, 2018 Hedge Funds Private Equity Funds Structured Credit Fund Real Estate Total Beginning balance — January 1, 2018 $ 11.4 $ 3.9 $ 7.9 $ 12.0 $ 35.2 Actual return on plan assets: Relating to assets still held at the reporting date — (0.1 ) 0.6 1.1 1.6 Relating to assets sold during the period — 0.3 — — 0.3 Purchases — — — — — Sales — (1.1 ) — — (1.1 ) Ending balance — December 31, 2018 $ 11.4 $ 3.0 $ 8.5 $ 13.1 $ 36.0 (In Millions) Year Ended December 31, 2017 Hedge Funds Private Equity Funds Structured Credit Fund Real Estate Total Beginning balance — January 1, 2017 $ 11.2 $ 4.3 $ 6.9 $ 11.1 $ 33.5 Actual return on plan assets: Relating to assets still held at the reporting date 0.8 0.9 2.0 3.4 7.1 Relating to assets sold during the period — (0.4 ) (1.0 ) (2.5 ) (3.9 ) Purchases 17.1 1.8 2.1 3.0 24.0 Sales (17.7 ) (2.7 ) (2.1 ) (3.0 ) (25.5 ) Ending balance — December 31, 2017 $ 11.4 $ 3.9 $ 7.9 $ 12.0 $ 35.2 Contributions

STOCK COMPENSATION PLANS (Table

STOCK COMPENSATION PLANS (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Approved Grants Equity Plans [Table Text Block]	Following is a summary of approved grants by the Compensation Committee : Grant Year Vesting Date Plan Issued Under Restricted Stock Units Granted Performance Shares Granted 2018 12/31/2020 A&R 2015 Equity Plan 685,599 675,599 2017 12/31/2019 A&R 2015 Equity Plan 532,358 249,106 2017 12/31/2019 Amended 2015 Equity Plan 553,725 553,725 2016 12/31/2018 2015 Equity Plan 3,406,716 —
Stock Incentive Plans Disclosure [Table Text Block]	Following is a summary of our performance share award agreements currently outstanding : Performance Performance Shares Granted Forfeitures to Date Expected to Vest Grant Date Grant Date Fair Value Performance Period 2018 675,599 2,236 673,363 2/21/2018 $ 11.93 1/1/2018 - 12/31/2020 2017 249,106 — 249,106 6/26/2017 $ 10.74 5/31/2017 - 12/31/2019 2017 553,725 51,471 502,254 2/21/2017 $ 19.69 1/1/2017 - 12/31/2019
Incentive Compensation and Other Benefit Plans for Employees and Directors [Table Text Block]	For the last three years, grants of restricted and/or deferred shares have been awarded to elected or re-elected nonemployee directors as follows: Year of Grant Restricted Shares Deferred Shares 2018 92,718 17,170 2017 93,359 17,289 2016 135,038 29,583
Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block]	The following table summarizes the share-based compensation expense that we recorded in continuing operations: (In Millions, except per share amounts) 2018 2017 2016 Cost of goods sold and operating expenses $ 1.7 $ 1.9 $ 1.8 Selling, general and administrative expenses 13.4 16.3 11.8 Reduction of operating income from continuing operations before income taxes 15.1 18.2 13.6 Income tax benefit 1 — — — Reduction of net income from continuing operations attributable to Cliffs shareholders $ 15.1 $ 18.2 $ 13.6 Reduction of continuing operations earnings per common share attributable to Cliffs shareholders: Basic $ 0.05 $ 0.06 $ 0.07 Diluted $ 0.05 $ 0.06 $ 0.07 1 No income tax benefit due to the full valuation allowance.
Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]	Stock option, restricted stock awards and performance share activity under our long-term equity plans and Directors’ Plans are as follows: 2018 2017 2016 Shares Shares Shares Stock options: Outstanding at beginning of year 599,870 599,870 607,489 Exercised (36,640 ) — — Forfeited/canceled — — (7,619 ) Outstanding at end of year 563,230 599,870 599,870 Restricted awards: Outstanding and restricted at beginning of year 4,776,483 5,461,783 2,338,070 Granted during the year 795,487 1,196,731 3,571,337 Vested and issued (627,567 ) (1,813,315 ) (271,988 ) Forfeited/canceled (140,155 ) (68,716 ) (175,636 ) Outstanding and restricted at end of year 4,804,248 4,776,483 5,461,783 Performance shares: Outstanding at beginning of year 1,848,312 1,368,469 1,496,489 Granted during the year 675,599 802,831 — Vested and issued (489,953 ) — (59,260 ) Forfeited/canceled (609,235 ) (322,988 ) (68,760 ) Outstanding at end of year 1,424,723 1,848,312 1,368,469 Vested or expected to vest as of December 31, 2018 1 6,792,201 Directors’ retainer and voluntary shares: Outstanding at beginning of year — — — Granted during the year 27,300 25,476 — Vested and issued (27,300 ) (25,476 ) — Outstanding at end of year — — — Reserved for future grants or awards at end of year: Employee plans 12,949,420 Directors’ plans 502,378 Total 13,451,798 1 With the adoption of ASU 2016-09, we assume all shares will vest until the date of vesting or forfeiture.
Employee Stock Awards Outstanding [Table Text Block]	A summary of our outstanding share-based awards as of December 31, 2018 is shown below: Shares Weighted Average Grant Date Fair Value Outstanding, beginning of year 7,224,665 $ 6.79 Granted 1,498,386 $ 9.51 Vested and issued (1,181,460 ) $ 7.38 Forfeited/canceled (749,390 ) $ 10.22 Outstanding, end of year 6,792,201 $ 6.90

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Contingency [Line Items]
Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block]	Income from continuing operations before income taxes includes the following components: (In Millions) 2018 2017 2016 United States $ 565.0 $ 90.7 $ 124.9 Foreign (0.3 ) 17.5 (14.5 ) $ 564.7 $ 108.2 $ 110.4
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	The components of the income tax benefit on continuing operations consist of the following: (In Millions) 2018 2017 2016 Current provision (benefit): United States federal $ (0.5 ) $ (252.6 ) $ (11.1 ) United States state & local — (0.1 ) (0.5 ) Foreign 0.7 0.3 (0.1 ) 0.2 (252.4 ) (11.7 ) Deferred benefit: United States federal (475.4 ) — (0.5 ) Total income tax benefit from continuing operations $ (475.2 ) $ (252.4 ) $ (12.2 )
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	Reconciliation of our income tax attributable to continuing operations computed at the U.S. federal statutory rate is as follows: (In Millions) 2018 2017 2016 Tax at U.S. statutory rate $ 118.6 21.0 % $ 37.9 35.0 % $ 38.6 35.0 % Increase (decrease) due to: Percentage depletion in excess of cost depletion (54.6 ) (9.7 ) (61.6 ) (56.9 ) (36.1 ) (32.7 ) Impact of tax law change - remeasurement of deferred taxes — — 407.5 376.6 149.1 135.1 Dissolution of Luxembourg entities 161.7 28.6 — — — — Prior year adjustments in current year (1.0 ) (0.2 ) (1.1 ) (1.0 ) (11.8 ) (10.7 ) Valuation allowance build (reversal): Tax law change - remeasurement of deferred taxes — — (407.5 ) (376.6 ) (149.1 ) (135.1 ) Current year activity (80.6 ) (14.3 ) (466.3 ) (431.0 ) 122.9 111.3 Release of U.S. valuation allowance (460.5 ) (81.5 ) — — — — Repeal of AMT — — (235.3 ) (217.5 ) — — Dissolution of Luxembourg entities (161.7 ) (28.6 ) — — — — Prior year adjustments in current year 1.0 0.2 (3.5 ) (3.2 ) 9.3 8.4 Tax uncertainties (1.3 ) (0.2 ) (1.4 ) (1.3 ) (11.3 ) (10.2 ) Worthless stock deduction — — — — (73.4 ) (66.5 ) Impact of foreign operations 0.1 — 477.9 441.7 (40.6 ) (36.8 ) Other items, net 3.1 0.6 1.0 0.9 (9.8 ) (8.9 ) Provision for income tax benefit and effective income tax rate including discrete items $ (475.2 ) (84.1 )% $ (252.4 ) (233.3 )% $ (12.2 ) (11.1 )%
Income Taxes Other Than Continuing Operations Disclosure Text Block [Table Text Block]	The components of income taxes for other than continuing operations consisted of the following: (In Millions) 2018 2017 2016 Other comprehensive (income) loss: Postretirement benefit liability $ 3.6 $ — $ — Unrealized net loss on derivative financial instruments 0.7 — — Other — — 0.5 Total $ 4.3 $ — $ 0.5
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	Significant components of our deferred tax assets and liabilities are as follows: (In Millions) 2018 2017 Deferred tax assets: Operating loss carryforwards $ 2,118.8 $ 2,362.4 Pensions 77.5 76.3 OPEB 25.3 25.6 Deferred income 23.3 24.2 Intangible assets 11.6 13.0 Property, plant and equipment and mineral rights 13.3 — State and local 68.2 74.2 Other liabilities 36.8 30.4 Total deferred tax assets before valuation allowance 2,374.8 2,606.1 Deferred tax asset valuation allowance (1,287.3 ) (1,983.1 ) Net deferred tax assets 1,087.5 623.0 Deferred tax liabilities: Property, plant and equipment and mineral rights — (1.5 ) Investment in ventures (141.2 ) (137.5 ) Intercompany notes (465.7 ) (465.7 ) Other assets (15.8 ) (18.3 ) Total deferred tax liabilities (622.7 ) (623.0 ) Net deferred tax assets $ 464.8 $ —
Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block]	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: (In Millions) 2018 2017 2016 Unrecognized tax benefits balance as of January 1 $ 33.5 $ 30.7 $ 156.2 Increase (decrease) for tax positions in prior years 0.1 (2.8 ) (61.0 ) Increase for tax positions in current year 3.6 4.5 0.2 Settlements — 1.0 (64.7 ) Lapses in statutes of limitations (8.2 ) — — Other — 0.1 — Unrecognized tax benefits balance as of December 31 $ 29.0 $ 33.5 $ 30.7

ENVIRONMENTAL AND MINE CLOSUR_2

ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Tables)	12 Months Ended
	Dec. 31, 2018
Environmental Remediation Obligations [Abstract]
Schedule of Environmental Loss Contingencies and Asset Retirement Obligations [Table Text Block]	The following is a summary of our environmental and mine closure obligations: (In Millions) December 31, 2018 2017 Environmental $ 2.5 $ 2.9 Mine closure 1 172.4 168.4 Total environmental and mine closure obligations 174.9 171.3 Less current portion 2.9 3.6 Long-term environmental and mine closure obligations $ 172.0 $ 167.7 1 Includes our active operating mines, our indefinitely idled Empire mine and a closed mine formerly operating as LTVSMC.
Asset Retirement Obligations	The following represents a roll forward of our asset retirement obligation liability for the years ended : (In Millions) December 31, 2018 2017 Asset retirement obligation at beginning of year $ 168.4 $ 187.8 Accretion expense 9.5 13.9 Remediation payments (1.0 ) (5.6 ) Revision in estimated cash flows (4.5 ) (27.7 ) Asset retirement obligation at end of year $ 172.4 $ 168.4

DERIVATIVE INSTRUMENTS AND HE_2

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Tables)	12 Months Ended
	Dec. 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 Consolidated Financial Position : (In Millions) Derivative Assets Derivative Liabilities December 31, 2018 December 31, 2017 December 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 Derivative assets $ 0.1 $ — Other current liabilities $ 3.7 Other current liabilities $ 0.3 Derivatives not designated as hedging instruments under ASC 815: Customer supply agreement Derivative assets 89.3 Derivative assets 37.9 — — Provisional pricing arrangements Derivative assets 2.1 — — Other current liabilities 1.7 Total derivatives not designated as hedging instruments under ASC 815: $ 91.4 $ 37.9 $ — $ 1.7 Total derivatives $ 91.5 $ 37.9 $ 3.7 $ 2.0
Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block]	The following table presents our outstanding hedge contracts: (Quantities in Millions) December 31, 2018 December 31, 2017 Notional Amount Unit of Measure Varying Maturity Dates Notional Amount Unit of Measure Varying Maturity Dates Natural gas 1.8 MMBtu January 2019 - August 2019 3.5 MMBtu January 2018 - November 2018 Diesel 11.0 Gallons January 2019 - December 2019 —
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 Consolidated Operations : (In Millions) Derivatives Not Designated as Hedging Instruments Location of Gain (Loss) Recognized in Income on Derivative Year Ended 2018 2017 2016 Customer supply agreements Product revenues $ 425.8 $ 163.3 $ 41.7 Provisional pricing arrangements Product revenues (3.2 ) (42.7 ) 14.2 Commodity contracts Cost of goods sold and operating expenses — (1.3 ) 1.9 Total $ 422.6 $ 119.3 $ 57.8

DISCONTINUED OPERATIONS (Tables

DISCONTINUED OPERATIONS (Tables)	12 Months Ended
	Dec. 31, 2018
Discontinued Operations and Disposal Groups [Abstract]
Schedule of Disposal Groups, Including Discontinued Operations, Income Statement, Balance Sheet and Additional Disclosures [Table Text Block]	The charts below provide an asset group breakout for each financial statement line impacted by discontinued operations. (In Millions) Year Ended December 31, 2018 2017 2016 Income (loss) from discontinued operations, net of tax Asia Pacific Iron Ore $ 118.3 $ 21.2 $ 96.6 North American Coal (3.6 ) 2.6 (2.4 ) Canadian Operations (26.5 ) (21.3 ) (17.5 ) $ 88.2 $ 2.5 $ 76.7 (In Millions) December 31, 2018 December 31, 2017 Asia Pacific Iron Ore North American Coal Total Asia Pacific Iron Ore North American Coal Total Current assets of discontinued operations $ 12.4 $ — $ 12.4 $ 118.5 $ — $ 118.5 Non-current assets of discontinued operations $ — $ — $ — $ 20.3 $ — $ 20.3 Current liabilities of discontinued operations $ 3.8 $ 2.9 $ 6.7 $ 71.8 $ 3.2 $ 75.0 Non-current liabilities of discontinued operations $ 8.3 $ — $ 8.3 $ 52.2 $ — $ 52.2 (In Millions) Year Ended December 31, 2018 2017 2016 Net cash provided (used) by operating activities Asia Pacific Iron Ore $ (81.3 ) $ 79.6 $ 99.8 Canadian Operations (14.6 ) — — $ (95.9 ) $ 79.6 $ 99.8 Net cash provided (used) by investing activities Asia Pacific Iron Ore $ 19.8 $ (2.8 ) $ (0.4 ) Canadian Operations — (7.7 ) 6.8 North American Coal — 2.1 3.6 $ 19.8 $ (8.4 ) $ 10.0
Schedule of Disposal Groups, including Discontinued Operations, Income Statement [Table Text Block]	For the reasons discussed above, our previously reported Asia Pacific Iron Ore operating segment results for all periods presented, as well as exit costs, are classified as discontinued operations. (In Millions) Year Ended December 31, Income from Discontinued Operations 2018 2017 2016 Revenues from product sales and services $ 129.1 $ 464.2 $ 554.5 Cost of goods sold and operating expenses (230.7 ) (427.9 ) (440.9 ) Sales margin (101.6 ) 36.3 113.6 Other operating expense (3.3 ) (9.9 ) (10.4 ) Other expense (2.3 ) (5.2 ) (6.6 ) Gain on foreign currency translation 228.1 — — Impairment of long-lived assets (2.6 ) — — Income from discontinued operations, net of tax $ 118.3 $ 21.2 $ 96.6
Schedule of Disposal Groups, Including Discontinued Operations, Assets and Liabilities [Table Text Block]	Recorded Assets and Liabilities (In Millions) Assets and Liabilities of Discontinued Operations December 31, December 31, Cash and cash equivalents $ 12.4 $ 29.4 Accounts receivable, net — 33.9 Inventories — 45.0 Supplies and other inventories — 5.1 Other current assets — 5.1 Total current assets of discontinued operations 12.4 118.5 Property, plant and equipment, net — 17.2 Other non-current assets — 3.1 Total assets of discontinued operations $ 12.4 $ 138.8 Accounts payable $ 3.4 $ 28.2 Accrued liabilities 0.4 28.0 Other current liabilities — 15.6 Total current liabilities of discontinued operations 3.8 71.8 Environmental and mine closure obligations — 28.8 Other liabilities 8.3 23.4 Total liabilities of discontinued operations $ 12.1 $ 124.0
PreTax Exit Costs [Table Text Block]	The chart below provides a breakout of loss from deconsolidation: (In Millions) Year Ended December 31, 2018 2017 2016 Investment impairment on deconsolidation 1 $ (67.5 ) $ 3.0 $ (17.5 ) Guarantees and contingent liabilities 41.0 (24.3 ) — Total loss from deconsolidation $ (26.5 ) $ (21.3 ) $ (17.5 ) 1 Includes the adjustments to fair value of our remaining interest in the Canadian Entities for the years ended December 31, 2018, 2017 and 2016, and a tax expense resulting from the implementation of the Amended Plan for the year ended December 31, 2018.

ACCUMULATED OTHERCOMPREHENSIVE

ACCUMULATED OTHERCOMPREHENSIVE INCOME (LOSS) (Tables)	12 Months Ended
	Dec. 31, 2018
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	The components of Accumulated other comprehensive loss within Cliffs shareholders’ equity (deficit) and related tax effects allocated to each are shown below: (In Millions) Pre-tax Amount Tax Benefit After-tax Amount As of December 31, 2018: Postretirement benefit liability $ (408.1 ) $ 127.0 $ (281.1 ) Unrealized net loss on derivative financial instruments (3.5 ) 0.7 (2.8 ) $ (411.6 ) $ 127.7 $ (283.9 ) As of December 31, 2017: Postretirement benefit liability $ (387.3 ) $ 123.4 $ (263.9 ) Foreign currency translation adjustments 225.4 — 225.4 Unrealized net loss on derivative financial instruments (0.5 ) — (0.5 ) $ (162.4 ) $ 123.4 $ (39.0 ) As of December 31, 2016: Postretirement benefit liability $ (384.0 ) $ 123.4 $ (260.6 ) Foreign currency translation adjustments 239.3 — 239.3 $ (144.7 ) $ 123.4 $ (21.3 ) The following tables reflect the changes in Accumulated other comprehensive loss related to Cliffs shareholders’ equity (deficit) for December 31, 2018 , 2017 and 2016: (In Millions) Postretirement Benefit Liability, net of tax Unrealized Net Gain (Loss) on Foreign Currency Translation Net Unrealized Loss on Derivative Financial Instruments, net of tax Accumulated Other Comprehensive Loss Balance December 31, 2017 $ (263.9 ) $ 225.4 $ (0.5 ) $ (39.0 ) Other comprehensive income (loss) before reclassifications (42.9 ) 2.7 (0.6 ) (40.8 ) Net loss (gain) reclassified from accumulated other comprehensive loss 25.7 (228.1 ) (1.7 ) (204.1 ) Balance December 31, 2018 $ (281.1 ) $ — $ (2.8 ) $ (283.9 ) (In Millions) Postretirement Benefit Liability, net of tax Unrealized Net Gain (Loss) on Foreign Currency Translation Net Unrealized Loss on Derivative Financial Instruments, net of tax Accumulated Other Comprehensive Loss Balance December 31, 2016 $ (260.6 ) $ 239.3 $ — $ (21.3 ) Other comprehensive loss before reclassifications (29.8 ) (13.9 ) (0.5 ) (44.2 ) Net loss reclassified from accumulated other comprehensive loss 26.5 — — 26.5 Balance December 31, 2017 $ (263.9 ) $ 225.4 $ (0.5 ) $ (39.0 ) (In Millions) Postretirement Benefit Liability, net of tax Unrealized Net Gain (Loss) on Securities, 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 Balance December 31, 2015 $ (241.4 ) $ 0.1 $ 220.7 $ 2.6 $ (18.0 ) Other comprehensive income (loss) before reclassifications (44.8 ) (0.1 ) 18.4 (3.3 ) (29.8 ) Net loss reclassified from accumulated other comprehensive loss 25.6 — 0.2 0.7 26.5 Balance December 31, 2016 $ (260.6 ) $ — $ 239.3 $ — $ (21.3 )
ACCUMLATED OTHER COMPREHENSIVE INCOME (LOSS)	The following table reflects the details about Accumulated other comprehensive loss components related to Cliffs shareholders’ equity: (In Millions) Details about Accumulated Other Comprehensive Loss Components Amount of (Gain)/Loss Reclassified into Income Affected Line Item in the Statement of Consolidated Operations Year Ended Year Ended Year Ended December 31, 2016 Amortization of pension and postretirement benefit liability: Prior service costs 1 $ (0.8 ) $ (0.4 ) $ (1.5 ) Other non-operating income Net actuarial loss 1 26.2 26.9 27.1 Other non-operating income Curtailments 1 0.3 — — Other non-operating income $ 25.7 $ 26.5 $ 25.6 Net of taxes Changes in foreign currency translation: Unrealized gain on dissolution of entity $ — $ — $ 0.2 Other non-operating income Gain on foreign currency translation 2 (228.1 ) — — Income from discontinued operations, net of tax $ (228.1 ) $ — $ 0.2 Net of taxes Unrealized gain (loss) on derivative financial instruments: Treasury lock $ — $ — $ 1.2 Gain (loss) on extinguishment/restructuring of debt Commodity contracts (1.7 ) — — Cost of goods sold and operating expenses (1.7 ) — 1.2 Total before taxes Income tax expense — — (0.5 ) Income tax benefit $ (1.7 ) $ — $ 0.7 Net of taxes Total reclassifications for the period $ (204.1 ) $ 26.5 $ 26.5 1 These accumulated other comprehensive loss components are included in the computation of net periodic benefit cost. See NOTE 8 - PENSIONS AND OTHER POSTRETIREMENT BENEFITS for further information. 2 Represents Australian accumulated currency translation adjustments due to the liquidation of substantially all of our Australian subsidiaries' net assets. See NOTE 13 - DISCONTINUED OPERATIONS for further information.

CASH FLOW INFORMATION (Tables)

CASH FLOW INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2018
Supplemental Cash Flow Information [Abstract]
Supplemental Cash Flow Disclosures	Cash payments for interest and income taxes are as follows: (In Millions) 2018 2017 2016 Taxes paid on income $ 2.9 $ 1.7 $ 5.9 Income tax refunds $ (11.3 ) $ (7.8 ) $ (5.3 ) Interest paid on debt obligations net of capitalized interest 1 $ 105.7 $ 139.0 $ 184.0 1 Capitalized interest was $6.5 million for the year ended December 31, 2018. A reconciliation of capital additions to cash paid for capital expenditures is as follows: (In Millions) Year Ended December 31, 2018 2017 2016 Capital additions 1 $ 394.8 $ 156.0 $ 68.5 Less: Non-cash accruals 93.6 (2.2 ) (0.6 ) Capital leases 7.6 6.5 — Grants (2.5 ) — — Cash paid for capital expenditures including deposits $ 296.1 $ 151.7 $ 69.1 1 Includes capital additions related to discontinued operations of $0.1 million, $2.8 million and $0.2 million for the years ended December 31, 2018, 2017 and 2016, respectively.

RELATED PARTIES (Tables)

RELATED PARTIES (Tables)	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Summary Of Other Ownership Interests	The following is a summary of the mine ownership of the co-owned iron ore mine at December 31, 2018 : Mine Cleveland-Cliffs Inc. ArcelorMittal U.S. Steel Hibbing 23.0% 62.3% 14.7%
Summary Of Related Party Transactions Table Disclosure	Product revenues from related parties were as follows: (In Millions) Year Ended December 31, 2018 2017 2016 Product revenues from related parties $ 1,234.5 $ 806.7 $ 830.1 Total product revenues $ 2,172.3 $ 1,644.6 $ 1,379.7 Related party product revenue as a percent of total product revenue 56.8 % 49.1 % 60.2 %
Summary of Balance Sheet Presentation [Table Text Block]	The following table presents the classification of related party assets and liabilities in the Statements of Consolidated Financial Position : (In Millions) Balance Sheet Location December 31, 2018 December 31, 2017 Accounts receivable, net $ 176.0 $ 68.1 Derivative assets 89.3 37.9 Partnership distribution payable (43.5 ) (44.2 ) Other current liabilities (1.8 ) (12.3 ) Other liabilities — (41.4 ) $ 220.0 $ 8.1

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Earnings Per Share Computation	The following table summarizes the computation of basic and diluted earnings per share: (In Millions, Except Per Share Amounts) Year Ended 2018 2017 2016 Income from continuing operations $ 1,039.9 $ 360.6 $ 122.6 Loss (income) from continuing operations attributable to — 3.9 (25.2 ) Net income from continuing operations $ 1,039.9 $ 364.5 $ 97.4 Income from discontinued operations, net of tax 88.2 2.5 76.7 Net income attributable to Cliffs shareholders $ 1,128.1 $ 367.0 $ 174.1 Weighted average number of shares: Basic 297.2 288.4 197.7 $316.25 million 1.50% 2025 Convertible Senior Notes 3.4 — — Employee stock plans 3.5 4.6 2.4 Diluted 304.1 293.0 200.1 Earnings per common share attributable to Continuing operations $ 3.50 $ 1.27 $ 0.49 Discontinued operations 0.30 0.01 0.39 $ 3.80 $ 1.28 $ 0.88 Earnings per common share attributable to Continuing operations $ 3.42 $ 1.25 $ 0.49 Discontinued operations 0.29 0.01 0.38 $ 3.71 $ 1.26 $ 0.87

QUARTERLY RESULTS OF OPERATIO_2

QUARTERLY RESULTS OF OPERATIONS (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information [Table Text Block]	NOTE 21 - QUARTERLY RESULTS OF OPERATIONS (UNAUDITED) The sum of quarterly EPS may not equal EPS for the year due to discrete quarterly calculations. (In Millions, Except Per Share Amounts) 1 2018 Quarters First Second Third Fourth Year Revenues from product sales and services $ 180.0 $ 714.3 $ 741.8 $ 696.3 $ 2,332.4 Sales margin 61.5 284.5 261.6 202.0 809.6 Net income (loss) from continuing operations attributable to Cliffs shareholders (13.4 ) 229.4 199.8 624.1 1,039.9 Income (loss) from discontinued operations, net of tax (70.9 ) (64.3 ) 238.0 (14.6 ) 88.2 Net income (loss) attributable to Cliffs common shareholders $ (84.3 ) $ 165.1 $ 437.8 $ 609.5 $ 1,128.1 Earnings (loss) per common share attributable to Continuing operations $ (0.05 ) $ 0.77 $ 0.67 $ 2.11 $ 3.50 Discontinued operations (0.24 ) (0.22 ) 0.80 (0.05 ) 0.30 $ (0.29 ) $ 0.55 $ 1.47 $ 2.06 $ 3.80 Earnings (loss) per common share attributable to Continuing operations $ (0.05 ) $ 0.76 $ 0.64 $ 2.03 $ 3.42 Discontinued operations (0.24 ) (0.21 ) 0.77 (0.05 ) 0.29 $ (0.29 ) $ 0.55 $ 1.41 $ 1.98 $ 3.71 1 On January 1, 2018, we adopted Topic 606 and applied it to all contracts that were not completed using the modified retrospective method. The comparative period information has not been retrospectively revised and continues to be reported under the accounting standards in effect for those periods. Refer to NOTE 2 - NEW ACCOUNTING STANDARDS for information regarding the adoption of Topic 606. The diluted earnings per share calculation for the first quarter of 2018 excludes equity plan awards of 3.8 million that were anti-dilutive. (In Millions, Except Per Share Amounts) 2017 Quarters First Second Third Fourth Year Revenues from product sales and services $ 286.2 $ 471.3 $ 596.7 $ 511.8 $ 1,866.0 Sales margin 49.0 144.7 157.8 116.1 467.6 Income (loss) from continuing operations $ (78.5 ) $ 83.8 $ 22.3 $ 333.0 $ 360.6 Loss (income) from continuing operations attributable to noncontrolling interest 1.7 1.7 0.5 — 3.9 Net income (loss) from continuing operations attributable to Cliffs shareholders $ (76.8 ) $ 85.5 $ 22.8 $ 333.0 $ 364.5 Income (loss) from discontinued operations, net of tax 48.7 (53.7 ) 30.6 (23.1 ) 2.5 Net income (loss) attributable to Cliffs common shareholders $ (28.1 ) $ 31.8 $ 53.4 $ 309.9 $ 367.0 Earnings (loss) per common share attributable to Continuing operations $ (0.29 ) $ 0.28 $ 0.08 $ 1.12 $ 1.27 Discontinued operations 0.18 (0.18 ) 0.10 (0.08 ) 0.01 $ (0.11 ) $ 0.10 $ 0.18 $ 1.04 $ 1.28 Earnings (loss) per common share attributable to Continuing operations $ (0.29 ) $ 0.28 $ 0.08 $ 1.11 $ 1.25 Discontinued operations 0.18 (0.18 ) 0.10 (0.08 ) 0.01 $ (0.11 ) $ 0.10 $ 0.18 $ 1.03 $ 1.26 The diluted earnings per share calculation for the first quarter of 2017 excludes equity plan awards of 4.6 million that were anti-dilutive.

SUPPLEMENTARY GUARANTOR INFOR_2

SUPPLEMENTARY GUARANTOR INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Supplemental Condensed Consolidating Financial Position	Condensed Consolidating Statement of Financial Position As of December 31, 2018 (In Millions) Cleveland-Cliffs Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations Consolidated ASSETS CURRENT ASSETS Cash and cash equivalents $ 819.8 $ 0.7 $ 2.7 $ — $ 823.2 Accounts receivable, net 9.2 221.3 0.3 (4.1 ) 226.7 Inventories — 87.9 — — 87.9 Supplies and other inventories — 93.2 — — 93.2 Derivative assets 0.1 91.4 — — 91.5 Income tax receivable, current 117.3 — — — 117.3 Current assets of discontinued operations — — 12.4 — 12.4 Other current assets 10.0 16.9 0.5 — 27.4 TOTAL CURRENT ASSETS 956.4 511.4 15.9 (4.1 ) 1,479.6 PROPERTY, PLANT AND EQUIPMENT, NET 13.3 1,221.9 50.8 — 1,286.0 OTHER ASSETS Deposits for property, plant and equipment — 68.4 14.6 — 83.0 Income tax receivable, non-current 117.2 4.1 — — 121.3 Deferred income taxes 463.6 — 1.2 — 464.8 Investment in subsidiaries 1,262.3 50.8 — (1,313.1 ) — Long-term intercompany notes — — 121.3 (121.3 ) — Other non-current assets 8.0 85.4 1.5 — 94.9 TOTAL OTHER ASSETS 1,851.1 208.7 138.6 (1,434.4 ) 764.0 TOTAL ASSETS $ 2,820.8 $ 1,942.0 $ 205.3 $ (1,438.5 ) $ 3,529.6 LIABILITIES CURRENT LIABILITIES Accounts payable $ 5.3 $ 181.4 $ 4.2 $ (4.1 ) $ 186.8 Accrued employment costs 28.5 45.4 0.1 — 74.0 State and local taxes payable — 35.4 0.1 — 35.5 Accrued interest 38.4 — — — 38.4 Partnership distribution payable — 43.5 — — 43.5 Current liabilities of discontinued operations — — 6.7 — 6.7 Other current liabilities 30.6 51.3 1.4 — 83.3 TOTAL CURRENT LIABILITIES 102.8 357.0 12.5 (4.1 ) 468.2 POSTEMPLOYMENT BENEFIT LIABILITIES Pensions 58.3 390.5 (230.4 ) — 218.4 Other postretirement benefits 6.0 23.9 0.4 — 30.3 TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES 64.3 414.4 (230.0 ) — 248.7 ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS — 152.1 19.9 — 172.0 LONG-TERM DEBT 2,092.9 — — — 2,092.9 LONG-TERM INTERCOMPANY NOTES 121.3 — — (121.3 ) — NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS — — 8.3 — 8.3 OTHER LIABILITIES 15.3 99.5 0.5 — 115.3 TOTAL LIABILITIES 2,396.6 1,023.0 (188.8 ) (125.4 ) 3,105.4 COMMITMENTS AND CONTINGENCIES EQUITY TOTAL EQUITY 424.2 919.0 394.1 (1,313.1 ) 424.2 TOTAL LIABILITIES AND EQUITY $ 2,820.8 $ 1,942.0 $ 205.3 $ (1,438.5 ) $ 3,529.6 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 $ 27.3 $ — $ 978.3 Accounts receivable, net 4.5 102.9 — (0.7 ) 106.7 Inventories — 138.4 — — 138.4 Supplies and other inventories — 88.8 — — 88.8 Derivative assets — 37.9 — — 37.9 Income tax receivable, current 11.4 1.9 — — 13.3 Loans to and accounts receivables from the Canadian Entities 44.7 6.9 — — 51.6 Current assets of discontinued operations — — 118.5 — 118.5 Other current assets 5.0 5.6 0.5 — 11.1 TOTAL CURRENT ASSETS 1,014.5 384.5 146.3 (0.7 ) 1,544.6 PROPERTY, PLANT AND EQUIPMENT, NET 17.5 965.5 50.8 — 1,033.8 OTHER ASSETS Deposits for property, plant and equipment — 8.2 9.6 — 17.8 Income tax receivable, non-current 235.3 — — — 235.3 Investment in subsidiaries 1,024.3 29.9 — (1,054.2 ) — Long-term intercompany notes — — 242.0 (242.0 ) — Non-current assets of discontinued operations — — 20.3 — 20.3 Other non-current assets 7.8 91.8 2.0 — 101.6 TOTAL OTHER ASSETS 1,267.4 129.9 273.9 (1,296.2 ) 375.0 TOTAL ASSETS $ 2,299.4 $ 1,479.9 $ 471.0 $ (1,296.9 ) $ 2,953.4 LIABILITIES CURRENT LIABILITIES Accounts payable $ 7.1 $ 92.3 $ 0.8 $ (0.7 ) $ 99.5 Accrued employment costs 13.7 38.9 0.1 — 52.7 State and local taxes payable — 30.0 0.2 — 30.2 Accrued interest 31.4 — — — 31.4 Contingent claims 55.6 — — — 55.6 Partnership distribution payable — 44.2 — — 44.2 Current liabilities of discontinued operations — — 75.0 — 75.0 Other current liabilities 7.4 54.5 1.7 — 63.6 TOTAL CURRENT LIABILITIES 115.2 259.9 77.8 (0.7 ) 452.2 POSTEMPLOYMENT BENEFIT LIABILITIES Pensions 59.2 403.6 (240.0 ) — 222.8 Other postretirement benefits 7.2 27.0 0.7 — 34.9 TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES 66.4 430.6 (239.3 ) — 257.7 ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS — 140.6 27.1 — 167.7 LONG-TERM DEBT 2,304.2 — — — 2,304.2 LONG-TERM INTERCOMPANY NOTES 242.0 — — (242.0 ) — NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS — — 52.2 — 52.2 OTHER LIABILITIES 15.7 147.2 0.6 — 163.5 TOTAL LIABILITIES 2,743.5 978.3 (81.6 ) (242.7 ) 3,397.5 COMMITMENTS AND CONTINGENCIES EQUITY TOTAL CLIFFS SHAREHOLDERS' EQUITY (DEFICIT) (444.1 ) 501.6 552.4 (1,054.2 ) (444.3 ) NONCONTROLLING INTEREST — — 0.2 — 0.2 TOTAL DEFICIT (444.1 ) 501.6 552.6 (1,054.2 ) (444.1 ) TOTAL LIABILITIES AND DEFICIT $ 2,299.4 $ 1,479.9 $ 471.0 $ (1,296.9 ) $ 2,953.4
Schedule of Supplemental Statements of Condensed Consolidating Operations and Comprehensive Income (Loss)	Condensed Consolidating Statement of Operations and Comprehensive Income For the Year Ended December 31, 2018 (In Millions) Cleveland-Cliffs Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations Consolidated REVENUES FROM PRODUCT SALES AND SERVICES Product $ — $ 2,172.3 $ — $ — $ 2,172.3 Freight and venture partners' cost reimbursements — 160.1 — — 160.1 — 2,332.4 — — 2,332.4 COST OF GOODS SOLD AND OPERATING EXPENSES — (1,522.8 ) — — (1,522.8 ) SALES MARGIN — 809.6 — — 809.6 OTHER OPERATING INCOME (EXPENSE) Selling, general and administrative expenses (86.1 ) (30.4 ) (0.3 ) — (116.8 ) Miscellaneous - net (0.3 ) (23.6 ) 4.3 — (19.6 ) (86.4 ) (54.0 ) 4.0 — (136.4 ) OPERATING INCOME (LOSS) (86.4 ) 755.6 4.0 — 673.2 OTHER INCOME (EXPENSE) Interest expense, net (117.6 ) (2.1 ) 0.8 — (118.9 ) Loss on extinguishment of debt (6.8 ) — — — (6.8 ) Other non-operating income (loss) (3.5 ) 0.9 19.8 — 17.2 (127.9 ) (1.2 ) 20.6 — (108.5 ) INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES (214.3 ) 754.4 24.6 — 564.7 INCOME TAX BENEFIT 474.7 — 0.5 — 475.2 EQUITY IN INCOME OF SUBSIDIARIES 858.2 25.5 — (883.7 ) — INCOME FROM CONTINUING OPERATIONS 1,118.6 779.9 25.1 (883.7 ) 1,039.9 INCOME FROM DISCONTINUED OPERATIONS, net of tax 9.5 12.3 66.4 — 88.2 NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 1,128.1 $ 792.2 $ 91.5 $ (883.7 ) $ 1,128.1 OTHER COMPREHENSIVE LOSS (244.9 ) (24.1 ) (256.7 ) 280.8 (244.9 ) TOTAL COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 883.2 $ 768.1 $ (165.2 ) $ (602.9 ) $ 883.2 Condensed Consolidating Statement of Operations and Comprehensive Income For the Year Ended December 31, 2017 (In Millions) Cleveland-Cliffs Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations Consolidated REVENUES FROM PRODUCT SALES AND SERVICES Product $ — $ 1,644.6 $ — $ — $ 1,644.6 Freight and venture partners' cost reimbursements — 221.4 — — 221.4 — 1,866.0 — — 1,866.0 COST OF GOODS SOLD AND OPERATING EXPENSES — (1,398.4 ) — — (1,398.4 ) SALES MARGIN — 467.6 — — 467.6 OTHER OPERATING INCOME (EXPENSE) Selling, general and administrative expenses (77.2 ) (19.9 ) (5.8 ) — (102.9 ) Miscellaneous - net (2.3 ) 11.0 16.8 — 25.5 (79.5 ) (8.9 ) 11.0 — (77.4 ) OPERATING INCOME (LOSS) (79.5 ) 458.7 11.0 — 390.2 OTHER INCOME (EXPENSE) Interest expense, net (126.8 ) (1.0 ) 1.0 — (126.8 ) Loss on extinguishment of debt (165.4 ) — — — (165.4 ) Other non-operating income (expense) (4.0 ) (3.0 ) 17.2 — 10.2 (296.2 ) (4.0 ) 18.2 — (282.0 ) INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES (375.7 ) 454.7 29.2 — 108.2 INCOME TAX BENEFIT (EXPENSE) 251.4 1.3 (0.3 ) — 252.4 EQUITY IN INCOME OF SUBSIDIARIES 512.6 11.8 — (524.4 ) — INCOME FROM CONTINUING OPERATIONS 388.3 467.8 28.9 (524.4 ) 360.6 INCOME (LOSS) FROM DISCONTINUED OPERATIONS, net of tax (21.3 ) 1.7 22.1 — 2.5 NET INCOME 367.0 469.5 51.0 (524.4 ) 363.1 INCOME ATTRIBUTABLE TO NONCONTROLLING INTEREST — 3.9 — — 3.9 NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 367.0 $ 473.4 $ 51.0 $ (524.4 ) $ 367.0 OTHER COMPREHENSIVE INCOME (LOSS) (4.0 ) 12.9 (4.8 ) (8.1 ) (4.0 ) TOTAL COMPREHENSIVE INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 363.0 $ 486.3 $ 46.2 $ (532.5 ) $ 363.0 Condensed Consolidating Statement of Operations and Comprehensive Income For the Year Ended December 31, 2016 (In Millions) Cleveland-Cliffs Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations Consolidated REVENUES FROM PRODUCT SALES AND SERVICES Product $ — $ 1,379.7 $ — $ — $ 1,379.7 Freight and venture partners' cost reimbursements — 174.8 — — 174.8 — 1,554.5 — — 1,554.5 COST OF GOODS SOLD AND OPERATING EXPENSES — (1,274.4 ) — — (1,274.4 ) SALES MARGIN — 280.1 — — 280.1 OTHER OPERATING INCOME (EXPENSE) Selling, general and administrative expenses (94.3 ) (18.0 ) (3.5 ) — (115.8 ) Miscellaneous - net (5.6 ) (12.4 ) (15.6 ) — (33.6 ) (99.9 ) (30.4 ) (19.1 ) — (149.4 ) OPERATING INCOME (LOSS) (99.9 ) 249.7 (19.1 ) — 130.7 OTHER INCOME (EXPENSE) Interest expense, net (194.5 ) 0.1 0.5 — (193.9 ) Gain on extinguishment/restructuring of debt 166.3 — — — 166.3 Other non-operating income (expense) (4.1 ) (5.0 ) 16.4 — 7.3 (32.3 ) (4.9 ) 16.9 — (20.3 ) INCOME (LOSS) FROM CONTINUING OPERATIONS BEFORE INCOME TAXES (132.2 ) 244.8 (2.2 ) — 110.4 INCOME TAX BENEFIT 4.3 3.0 4.9 — 12.2 EQUITY IN INCOME OF SUBSIDIARIES 319.1 13.7 — (332.8 ) — INCOME FROM CONTINUING OPERATIONS 191.2 261.5 2.7 (332.8 ) 122.6 INCOME (LOSS) FROM DISCONTINUED OPERATIONS, net of tax (17.1 ) 2.6 91.2 — 76.7 NET INCOME (LOSS) 174.1 264.1 93.9 (332.8 ) 199.3 INCOME ATTRIBUTABLE TO NONCONTROLLING INTEREST — (25.2 ) — — (25.2 ) NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 174.1 $ 238.9 $ 93.9 $ (332.8 ) $ 174.1 OTHER COMPREHENSIVE INCOME (LOSS) (3.3 ) (20.7 ) 15.4 5.3 (3.3 ) TOTAL COMPREHENSIVE INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 170.8 $ 218.2 $ 109.3 $ (327.5 ) $ 170.8
Schedule of Supplemental Statements of Condensed Consolidating Cash Flows		Condensed Consolidating Statement of Cash Flows For the Year Ended December 31, 2018 (In Millions) Cleveland-Cliffs Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations Consolidated Net cash provided (used) by operating activities $ (120.7 ) $ 741.0 $ (141.8 ) $ — $ 478.5 INVESTING ACTIVITIES Purchase of property, plant and equipment (1.2 ) (207.3 ) (0.1 ) — (208.6 ) Deposits for property, plant and equipment — (82.3 ) (5.2 ) — (87.5 ) Intercompany investing 399.1 (7.1 ) 120.7 (512.7 ) — Other investing activities — 3.1 19.9 — 23.0 Net cash provided (used) in investing activities 397.9 (293.6 ) 135.3 (512.7 ) (273.1 ) FINANCING ACTIVITIES Repurchase of common shares (47.5 ) — — — (47.5 ) Debt issuance costs (1.5 ) — — — (1.5 ) Repurchase of debt (234.5 ) — — — (234.5 ) Distributions of partnership equity — (44.2 ) — — (44.2 ) Intercompany financing (120.7 ) (402.4 ) 10.4 512.7 — Other financing activities (2.1 ) (2.2 ) (43.2 ) — (47.5 ) Net cash used by financing activities (406.3 ) (448.8 ) (32.8 ) 512.7 (375.2 ) EFFECT OF EXCHANGE RATE CHANGES ON CASH — — (2.3 ) — (2.3 ) DECREASE IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS (129.1 ) (1.4 ) (41.6 ) — (172.1 ) LESS: DECREASE IN CASH AND CASH EQUIVALENTS CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS — — (17.0 ) — (17.0 ) NET DECREASE IN CASH AND CASH EQUIVALENTS (129.1 ) (1.4 ) (24.6 ) — (155.1 ) CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR 948.9 2.1 27.3 — 978.3 CASH AND CASH EQUIVALENTS AT END OF YEAR $ 819.8 $ 0.7 $ 2.7 $ — $ 823.2 Condensed Consolidating Statement of Cash Flows For the Year Ended December 31, 2017 (In Millions) Cleveland-Cliffs Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations Consolidated Net cash provided (used) by operating activities $ (166.8 ) $ 430.0 $ 74.9 $ — $ 338.1 INVESTING ACTIVITIES Purchase of property, plant and equipment (3.4 ) (79.8 ) (51.7 ) — (134.9 ) Deposits for property, plant and equipment — (11.7 ) (5.1 ) — (16.8 ) Intercompany investing 225.7 (7.3 ) (45.1 ) (173.3 ) — Other investing activities (7.7 ) 3.4 — — (4.3 ) Net cash provided (used) by investing activities 214.6 (95.4 ) (101.9 ) (173.3 ) (156.0 ) FINANCING ACTIVITIES Net proceeds from issuance of common shares 661.3 — — — 661.3 Proceeds from issuance of debt 1,771.5 — — — 1,771.5 Debt issuance costs (28.6 ) — — — (28.6 ) Repurchase of debt (1,720.7 ) — — — (1,720.7 ) Acquisition of noncontrolling interest (105.0 ) — — — (105.0 ) Distributions of partnership equity — (52.9 ) — — (52.9 ) Intercompany financing 45.0 (277.6 ) 59.3 173.3 — Other financing activities (5.8 ) (4.5 ) (16.4 ) — (26.7 ) Net cash provided (used) by financing activities 617.7 (335.0 ) 42.9 173.3 498.9 EFFECT OF EXCHANGE RATE CHANGES ON CASH — — 3.3 — 3.3 INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS 665.5 (0.4 ) 19.2 — 684.3 LESS: INCREASE IN CASH AND CASH EQUIVALENTS CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS — — 18.8 — 18.8 NET INCREASE IN CASH AND CASH EQUIVALENTS 665.5 (0.4 ) 0.4 — 665.5 CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR 283.4 2.5 26.9 — 312.8 CASH AND CASH EQUIVALENTS AT END OF YEAR $ 948.9 $ 2.1 $ 27.3 $ — $ 978.3 Condensed Consolidating Statement of Cash Flows For the Year Ended December 31, 2016 (In Millions) Cleveland-Cliffs Inc. Guarantor Subsidiaries Non-Guarantor Subsidiaries Eliminations Consolidated Net cash provided (used) by operating activities $ (275.7 ) $ 462.9 $ 115.8 $ — $ 303.0 INVESTING ACTIVITIES Purchase of property, plant and equipment (6.2 ) (55.1 ) (0.4 ) — (61.7 ) Deposits for property, plant and equipment — (4.9 ) (2.5 ) — (7.4 ) Intercompany investments 356.6 (3.3 ) (117.0 ) (236.3 ) — Other investing activities 0.4 10.8 — — 11.2 Net cash provided (used) by investing activities 350.8 (52.5 ) (119.9 ) (236.3 ) (57.9 ) FINANCING ACTIVITIES Net proceeds from issuance of common shares 287.4 — — — 287.4 Debt issuance costs (5.2 ) — — — (5.2 ) Borrowings under credit facilities 105.0 — — — 105.0 Repayments on credit facilities (105.0 ) — — — (105.0 ) Repayments on equipment loans (95.6 ) — — — (95.6 ) Repurchase of debt (305.4 ) — — — (305.4 ) Distributions of partnership equity — (59.9 ) — — (59.9 ) Intercompany financing 117.0 (339.9 ) (13.4 ) 236.3 — Other financing activities (0.6 ) (9.9 ) (17.2 ) — (27.7 ) Net cash used by financing activities (2.4 ) (409.7 ) (30.6 ) 236.3 (206.4 ) EFFECT OF EXCHANGE RATE CHANGES ON CASH — — (0.5 ) — (0.5 ) INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS, INCLUDING CASH CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS 72.7 0.7 (35.2 ) — 38.2 LESS: DECREASE IN CASH AND CASH EQUIVALENTS CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS — — (35.3 ) — (35.3 ) NET INCREASE IN CASH AND CASH EQUIVALENTS 72.7 0.7 0.1 — 73.5 CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR 210.7 1.8 26.8 — 239.3 CASH AND CASH EQUIVALENTS AT END OF YEAR $ 283.4 $ 2.5 $ 26.9 $ — $ 312.8

BASIS OF PRESENTATION AND SIG_4

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details) T in Millions	1 Months Ended	12 Months Ended
	Feb. 01, 2016	Dec. 31, 2018USD ($)T	Dec. 31, 2017USD ($)T	Dec. 31, 2016USD ($)	Jan. 01, 2018USD ($)
Related Party Transaction [Line Items]
Foreign Currency Transaction Gain (Loss), Realized		$ 228,100,000	$ 0	$ 0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net from product sales and services		422,600,000	119,300,000	57,800,000
Contract with Customer, Liability, Revenue Recognized		51,300,000	64,200,000
Contract with Customer, Liability, Current		21,000,000	22,400,000	16,200,000	$ 23,800,000
Deferred Revenue (Long-Term)		38,500,000	51,400,000	64,300,000
Net Income (Loss) Attributable to Noncontrolling Interest		$ 0	(3,900,000)	25,200,000
Noncontrolling Interest, Ownership Percentage by Parent		100.00%
Allowance for Doubtful Accounts Receivable		$ 0	0
Provision for Doubtful Accounts		$ 0	0
Current Fiscal Year End Date		--12-31
Inventory Valuation Reserves		$ 12,600,000	12,600,000
Trading Day Window Determining Number of Common Shares Issuable on Conversion	20
Acquisition of Noncontrolling Interest			$ (105,000,000)
Mining and Pelletizing [Member]
Related Party Transaction [Line Items]
Quantity Of Finished Goods at ports | T		0.8	1.5
Empire [Member]
Related Party Transaction [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent			100.00%
Distribution of Noncontrolling Interest			$ 132,700,000
Increase in Ownership Equity			21.00%
Stockholders' Equity, Period Increase (Decrease)			$ (12,100,000)
Acquisition of Noncontrolling Interest			$ (116,700,000)
Tilden [Member]
Related Party Transaction [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent			100.00%
Distribution of Noncontrolling Interest			$ 105,000,000
Increase in Ownership Equity			15.00%
Stockholders' Equity, Period Increase (Decrease)			$ (89,100,000)
Acquisition of Noncontrolling Interest			(15,900,000)
Investments in Ventures [Member] | Hibbing [Member]
Related Party Transaction [Line Items]
Ownership interest, equity method investment		23.00%
Other Noncurrent Liabilities [Member] | Hibbing [Member]
Related Party Transaction [Line Items]
Equity Method Investments		$ (15,400,000)	(11,000,000)
Other Noncurrent Liabilities [Member] | Empire [Member]
Related Party Transaction [Line Items]
Noncontrolling Interest Purchase, Installment Amount		44,200,000
Other Liabilities [Member] | Empire [Member]
Related Party Transaction [Line Items]
Noncontrolling Interest Purchase, Installment Amount		44,200,000
Other Current Liabilities [Member]
Related Party Transaction [Line Items]
Contract with Customer, Liability		12,800,000	12,800,000
Take or Pay Contracts [Member]
Related Party Transaction [Line Items]
Contract with Customer, Liability		$ 8,200,000	9,600,000
$316 Million 1.5% 2025 Senior Notes [Domain]
Related Party Transaction [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		1.50%
Convertible debt, principal increment		$ 1,000
$316 Million 1.5% 2025 Senior Notes [Domain] | Minimum [Member]
Related Party Transaction [Line Items]
Convertible debt, conversion price percentage		1.30
$316 Million 1.5% 2025 Senior Notes [Domain] | Maximum [Member]
Related Party Transaction [Line Items]
Convertible debt, conversion price percentage		0.98
Product [Member]
Related Party Transaction [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net from product sales and services		$ 422,600,000	$ 120,600,000	$ 55,900,000

BASIS OF PRESENTATION AND SIG_5

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule Of Subsidiaries) (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent	100.00%
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
Noncontrolling Interest, Ownership Percentage by Parent		100.00%
Empire [Member]
Related Party Transaction [Line Items]
Entity Address, State or Province	Michigan
Noncontrolling Interest, Ownership Percentage by Parent		100.00%

BASIS OF PRESENTATION AND SIG_6

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Depreciation Methods and Useful Lives) (Details)	12 Months Ended
	Dec. 31, 2018
Building [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	45 years
Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Other Machinery and Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Other Machinery and Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	45 years
Electric Power Facilities [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Electric Power Facilities [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	45 years
Land Improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Land Improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	45 years
Computer Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Computer Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	15 years

BASIS OF PRESENTATION AND SIG_7

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Revenue Reimbursement) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Freight and Reimbursement Revenue	$ 160.1	$ 221.4	$ 174.8
Mining and Pelletizing [Member]
Freight and Reimbursement Revenue	160.1	221.4	174.8
Mining and Pelletizing [Member] | Freight Revenue [Member]
Freight and Reimbursement Revenue	160.1	166.7	106.8
Mining and Pelletizing [Member] | Co-venturer [Member]
Freight and Reimbursement Revenue	0	$ 54.7	$ 68
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Freight and Reimbursement Revenue	$ 156.2

BASIS OF PRESENTATION AND SIG_8

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Transaction Gains (Losses) Resulting from Remeasurement) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Foreign Currency Transaction Gain (Loss), before Tax	$ (0.2)	$ (2.7)	$ (1.2)
Transaction Gains and Losses Resulting from Remeasurement [Member]
Foreign Currency Transaction Gain (Loss), before Tax	(0.9)	13.9	(17.8)
Intercompany loan [Member]
Foreign Currency Transaction Gain (Loss), before Tax	$ (0.7)	$ 16.6	$ (16.6)

BASIS OF PRESENTATION AND SIG_9

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES Schedule of Deferred Revenue (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred Revenue (Current)	$ 21,000,000	$ 22,400,000	$ 23,800,000	$ 16,200,000
Deferred Revenue (Long-Term)	38,500,000	51,400,000		$ 64,300,000
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | Customer Supplemental Payments [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred Revenue (Current)		1.4
Other Current Liabilities [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Increase (Decrease)	(2,800,000)	6,200,000
Other Noncurrent Liabilities [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Increase (Decrease)	$ (12,900,000)	$ (12,900,000)

NEW ACCOUNTING STANDARDS (Sched

NEW ACCOUNTING STANDARDS (Schedule of New Accounting Pronouncements and Changes in Accounting Principles) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and cash equivalents	$ 823.2	$ 978.3	$ 978.3
Accounts receivable, net	226.7	183.3	106.7
Inventories	87.9	87	138.4
Supplies and other inventories	93.2	88.8	88.8
Derivative assets	91.5	49.5	37.9
Income tax receivable, current	117.3	13.3	13.3
Loans to and accounts receivables from the Canadian Entities	0	51.6	51.6
Current assets of discontinued operations	12.4	118.5	118.5
Other current assets	27.4	11.1	11.1
TOTAL CURRENT ASSETS	1,479.6	1,581.4	1,544.6
PROPERTY, PLANT AND EQUIPMENT, NET	1,286	1,033.8	1,033.8
Deposits for property, plant and equipment	83	17.8	17.8
Income tax receivable, non-current	121.3	235.3	235.3
Non-current assets of discontinued operations	0	20.3	20.3
Other non-current assets	94.9	101.6	101.6
TOTAL OTHER ASSETS	764	375	375
TOTAL ASSETS	3,529.6	2,990.2	2,953.4	$ 1,923.9
Accounts payable	186.8	100.9	99.5
Accrued employment costs	74	52.7	52.7
State and local taxes payable	35.5	30.2	30.2
Accrued interest	38.4	31.4	31.4
Contingent claims	0	55.6	55.6
Partnership distribution payable	43.5	44.2	44.2
Current liabilities of discontinued operations	6.7	75	75
Other current liabilities	83.3	65	63.6
TOTAL CURRENT LIABILITIES	468.2	455	452.2
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES	248.7	257.7	257.7
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	172	167.7	167.7
LONG-TERM DEBT	2,092.9	2,304.2	2,304.2
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS	8.3	52.2	52.2
OTHER LIABILITIES	115.3	163.5	163.5
TOTAL LIABILITIES	3,105.4	3,400.3	3,397.5
TOTAL CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)	424.2	(410.3)	(444.3)
NONCONTROLLING INTEREST	0	0.2	0.2
TOTAL EQUITY (DEFICIT)	424.2	(410.1)	(444.1)	$ (1,330.5)	$ (1,811.6)
TOTAL LIABILITIES AND EQUITY (DEFICIT)	3,529.6	2,990.2	$ 2,953.4
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and cash equivalents	823.2
Accounts receivable, net	108.7
Inventories	141.3
Supplies and other inventories	93.2
Derivative assets	60.7
Income tax receivable, current	117.3
Current assets of discontinued operations	12.4
Other current assets	27.4
TOTAL CURRENT ASSETS	1,384.2
PROPERTY, PLANT AND EQUIPMENT, NET	1,286
Deposits for property, plant and equipment	83
Income tax receivable, non-current	121.3
Other non-current assets	94.9
TOTAL OTHER ASSETS	776.3
TOTAL ASSETS	3,446.5
Accounts payable	184.9
Accrued employment costs	74
State and local taxes payable	35.5
Accrued interest	38.4
Partnership distribution payable	43.5
Current liabilities of discontinued operations	6.7
Other current liabilities	83.7
TOTAL CURRENT LIABILITIES	466.7
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES	248.7
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	172
LONG-TERM DEBT	2,092.9
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS	8.3
OTHER LIABILITIES	115.3
TOTAL LIABILITIES	3,103.9
TOTAL CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)	342.6
TOTAL LIABILITIES AND EQUITY (DEFICIT)	3,446.5
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
Accounts receivable, net	118	76.6
Inventories	(53.4)	(51.4)
Supplies and other inventories	0	0
Derivative assets	30.8	11.6
Income tax receivable, current	0	0
Loans to and accounts receivables from the Canadian Entities		0
Current assets of discontinued operations	0	0
Other current assets	0	0
TOTAL CURRENT ASSETS	95.4	36.8
PROPERTY, PLANT AND EQUIPMENT, NET	0	0
Deposits for property, plant and equipment	0	0
Income tax receivable, non-current	0	0
Non-current assets of discontinued operations		0
Other non-current assets	0	0
TOTAL OTHER ASSETS	(12.3)	0
TOTAL ASSETS	83.1	36.8
Accounts payable	1.9	1.4
Accrued employment costs	0	0
State and local taxes payable	0	0
Accrued interest	0	0
Contingent claims		0
Partnership distribution payable	0	0
Current liabilities of discontinued operations	0	0
Other current liabilities	(0.4)	1.4
TOTAL CURRENT LIABILITIES	1.5	2.8
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES	0	0
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	0	0
LONG-TERM DEBT	0	0
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS	0	0
OTHER LIABILITIES	0	0
TOTAL LIABILITIES	1.5	2.8
TOTAL CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)	81.6	34
NONCONTROLLING INTEREST		0
TOTAL EQUITY (DEFICIT)		34
TOTAL LIABILITIES AND EQUITY (DEFICIT)	$ 83.1	$ 36.8

NEW ACCOUNTING STANDARDS NEW AC

NEW ACCOUNTING STANDARDS NEW ACCOUNTING STANDARDS (Schedule of Accounting Change) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Product revenues									$ 2,172.3	$ 1,644.6	$ 1,379.7
Freight and Reimbursement Revenue									160.1	221.4	174.8
Revenues	$ 696.3	$ 741.8	$ 714.3	$ 180	$ 511.8	$ 596.7	$ 471.3	$ 286.2	2,332.4	1,866	1,554.5
Cost of Goods and Services Sold									(1,522.8)	(1,398.4)	(1,274.4)
SALES MARGIN	202	261.6	284.5	61.5	116.1	157.8	144.7	49	809.6	467.6	280.1
Selling, general and administrative expenses									(116.8)	(102.9)	(115.8)
Miscellaneous - net									(19.6)	25.5	(33.6)
Operating Expenses									(136.4)	(77.4)	(149.4)
OPERATING INCOME									673.2	390.2	130.7
Interest expense, net									(118.9)	(126.8)	(193.9)
Gain (loss) on extinguishment of debt									(6.8)	(165.4)	166.3
Other non-operating income									17.2	10.2	7.3
TOTAL OTHER INCOME (EXPENSE)									(108.5)	(282)	(20.3)
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES									564.7	108.2	110.4
Income Tax Expense (Benefit)									(475.2)	(252.4)	(12.2)
Income (loss) from continuing operations					333	22.3	83.8	(78.5)	1,039.9	360.6	122.6
INCOME FROM DISCONTINUED OPERATIONS, net of tax	(14.6)	238	(64.3)	(70.9)	(23.1)	30.6	(53.7)	48.7	88.2	2.5	76.7
INCOME FROM DISCONTINUED OPERATIONS, net of tax									88.2	2.5	76.7
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$ 609.5	$ 437.8	$ 165.1	$ (84.3)	$ 309.9	$ 53.4	$ 31.8	$ (28.1)	$ 1,128.1	$ 367	$ 174.1
Continuing operations	$ 2.11	$ 0.67	$ 0.77	$ (0.05)	$ 1.12	$ 0.08	$ 0.28	$ (0.29)	$ 3.50	$ 1.27	$ 0.49
Discontinued operations	(0.05)	0.80	(0.22)	(0.24)	(0.08)	0.10	(0.18)	0.18	0.30	0.01	0.39
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Basic:	2.06	1.47	0.55	(0.29)	1.04	0.18	0.10	(0.11)	3.80	1.28	0.88
Continuing operations	2.03	0.64	0.76	(0.05)	1.11	0.08	0.28	(0.29)	3.42	1.25	0.49
Discontinued operations	(0.05)	0.77	(0.21)	(0.24)	(0.08)	0.10	(0.18)	0.18	0.29	0.01	0.38
Earnings per common share attributable to Cliffs common shareholders - diluted:	$ 1.98	$ 1.41	$ 0.55	$ (0.29)	$ 1.03	$ 0.18	$ 0.10	$ (0.11)	$ 3.71	$ 1.26	$ 0.87
Basic									297.2	288.4	197.7
Diluted									304.1	293	200.1
Cash and cash equivalents	$ 823.2				$ 978.3				$ 823.2	$ 978.3		$ 978.3
Accounts receivable, net	226.7				106.7				226.7	106.7		183.3
Inventories	87.9				138.4				87.9	138.4		87
Supplies and other inventories	93.2				88.8				93.2	88.8		88.8
Derivative assets	91.5				37.9				91.5	37.9		49.5
Income tax receivable, current	117.3				13.3				117.3	13.3		13.3
Current assets of discontinued operations	12.4				118.5				12.4	118.5		118.5
Other current assets	27.4				11.1				27.4	11.1		11.1
TOTAL CURRENT ASSETS	1,479.6				1,544.6				1,479.6	1,544.6		1,581.4
PROPERTY, PLANT AND EQUIPMENT, NET	1,286				1,033.8				1,286	1,033.8		1,033.8
Deposits for property, plant and equipment	83				17.8				83	17.8		17.8
Income tax receivable, non-current	121.3				235.3				121.3	235.3		235.3
Deferred income taxes	464.8				0				464.8	0
Other non-current assets	94.9				101.6				94.9	101.6		101.6
TOTAL OTHER ASSETS	764				375				764	375		375
TOTAL ASSETS	3,529.6				2,953.4				3,529.6	2,953.4	$ 1,923.9	2,990.2
Accounts payable	186.8				99.5				186.8	99.5		100.9
Accrued employment costs	74				52.7				74	52.7		52.7
State and local taxes payable	35.5				30.2				35.5	30.2		30.2
Accrued interest	38.4				31.4				38.4	31.4		31.4
Partnership distribution payable	43.5				44.2				43.5	44.2		44.2
Current liabilities of discontinued operations	6.7				75				6.7	75		75
Other current liabilities	83.3				63.6				83.3	63.6		65
TOTAL CURRENT LIABILITIES	468.2				452.2				468.2	452.2		455
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES	248.7				257.7				248.7	257.7		257.7
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	172				167.7				172	167.7		167.7
LONG-TERM DEBT	2,092.9				2,304.2				2,092.9	2,304.2		2,304.2
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS	8.3				52.2				8.3	52.2		52.2
OTHER LIABILITIES	115.3				163.5				115.3	163.5		163.5
TOTAL LIABILITIES	3,105.4				3,397.5				3,105.4	3,397.5		3,400.3
TOTAL CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)	424.2				(444.3)				424.2	(444.3)		(410.3)
TOTAL LIABILITIES AND EQUITY (DEFICIT)	3,529.6				$ 2,953.4				3,529.6	$ 2,953.4		2,990.2
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Product revenues									2,108.1
Freight and Reimbursement Revenue									156.2
Revenues									2,264.3
Cost of Goods and Services Sold									(1,513.2)
SALES MARGIN									751.1
Selling, general and administrative expenses									(116.8)
Miscellaneous - net									(19.6)
Operating Expenses									(136.4)
OPERATING INCOME									614.7
Interest expense, net									(118.9)
Gain (loss) on extinguishment of debt									(6.8)
Other non-operating income									17.2
TOTAL OTHER INCOME (EXPENSE)									(108.5)
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES									506.2
Income Tax Expense (Benefit)									(487.5)
Income (loss) from continuing operations									993.7
INCOME FROM DISCONTINUED OPERATIONS, net of tax									88.2
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS									$ 1,081.9
Continuing operations									$ 3.34
Discontinued operations									0.30
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Basic:									3.64
Continuing operations									3.27
Discontinued operations									0.29
Earnings per common share attributable to Cliffs common shareholders - diluted:									$ 3.56
Basic									297.2
Diluted									304.1
Cash and cash equivalents	823.2								$ 823.2
Accounts receivable, net	108.7								108.7
Inventories	141.3								141.3
Supplies and other inventories	93.2								93.2
Derivative assets	60.7								60.7
Income tax receivable, current	117.3								117.3
Current assets of discontinued operations	12.4								12.4
Other current assets	27.4								27.4
TOTAL CURRENT ASSETS	1,384.2								1,384.2
PROPERTY, PLANT AND EQUIPMENT, NET	1,286								1,286
Deposits for property, plant and equipment	83								83
Income tax receivable, non-current	121.3								121.3
Deferred income taxes	477.1								477.1
Other non-current assets	94.9								94.9
TOTAL OTHER ASSETS	776.3								776.3
TOTAL ASSETS	3,446.5								3,446.5
Accounts payable	184.9								184.9
Accrued employment costs	74								74
State and local taxes payable	35.5								35.5
Accrued interest	38.4								38.4
Partnership distribution payable	43.5								43.5
Current liabilities of discontinued operations	6.7								6.7
Other current liabilities	83.7								83.7
TOTAL CURRENT LIABILITIES	466.7								466.7
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES	248.7								248.7
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	172								172
LONG-TERM DEBT	2,092.9								2,092.9
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS	8.3								8.3
OTHER LIABILITIES	115.3								115.3
TOTAL LIABILITIES	3,103.9								3,103.9
TOTAL CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)	342.6								342.6
TOTAL LIABILITIES AND EQUITY (DEFICIT)	3,446.5								3,446.5
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Product revenues									64.2
Freight and Reimbursement Revenue									3.9
Revenues									68.1
Cost of Goods and Services Sold									(9.6)
SALES MARGIN									58.5
Selling, general and administrative expenses									0
Miscellaneous - net									0
Operating Expenses									0
OPERATING INCOME									58.5
Interest expense, net									0
Gain (loss) on extinguishment of debt									0
Other non-operating income									0
TOTAL OTHER INCOME (EXPENSE)									0
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES									58.5
Income Tax Expense (Benefit)									12.3
Income (loss) from continuing operations									46.2
INCOME FROM DISCONTINUED OPERATIONS, net of tax									0
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS									$ 46.2
Continuing operations									$ 0.16
Discontinued operations									0
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Basic:									0.16
Continuing operations									0.15
Discontinued operations									0
Earnings per common share attributable to Cliffs common shareholders - diluted:									$ 0.15
Cash and cash equivalents	0								$ 0			0
Accounts receivable, net	118								118			76.6
Inventories	(53.4)								(53.4)			(51.4)
Supplies and other inventories	0								0			0
Derivative assets	30.8								30.8			11.6
Income tax receivable, current	0								0			0
Current assets of discontinued operations	0								0			0
Other current assets	0								0			0
TOTAL CURRENT ASSETS	95.4								95.4			36.8
PROPERTY, PLANT AND EQUIPMENT, NET	0								0			0
Deposits for property, plant and equipment	0								0			0
Income tax receivable, non-current	0								0			0
Deferred income taxes	(12.3)								(12.3)
Other non-current assets	0								0			0
TOTAL OTHER ASSETS	(12.3)								(12.3)			0
TOTAL ASSETS	83.1								83.1			36.8
Accounts payable	1.9								1.9			1.4
Accrued employment costs	0								0			0
State and local taxes payable	0								0			0
Accrued interest	0								0			0
Partnership distribution payable	0								0			0
Current liabilities of discontinued operations	0								0			0
Other current liabilities	(0.4)								(0.4)			1.4
TOTAL CURRENT LIABILITIES	1.5								1.5			2.8
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES	0								0			0
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	0								0			0
LONG-TERM DEBT	0								0			0
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS	0								0			0
OTHER LIABILITIES	0								0			0
TOTAL LIABILITIES	1.5								1.5			2.8
TOTAL CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)	81.6								81.6			34
TOTAL LIABILITIES AND EQUITY (DEFICIT)	$ 83.1								$ 83.1			$ 36.8

NEW ACCOUNTING STANDARDS (Narra

NEW ACCOUNTING STANDARDS (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
TOTAL DEFICIT	$ 424.2	$ (410.1)	$ (444.1)	$ (1,330.5)	$ (1,811.6)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
TOTAL DEFICIT		$ 34

NEW ACCOUNTING STANDARDS NEW _2

NEW ACCOUNTING STANDARDS NEW ACCOUNTING STANDARDS (Schedule of Net Periodic Cost of Defined Benefit Pension and Other Postretirement Employee Benefit Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of Goods and Services Sold	$ 1,522.8	$ 1,398.4	$ 1,274.4
Selling, General and Administrative Expense	116.8	102.9	115.8
Miscellaneous - net	(19.6)	25.5	(33.6)
Operating Income (Loss)	673.2	390.2	130.7
Other non-operating income	17.2	10.2	7.3
Net income	$ 1,128.1	363.1	199.3
Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of Goods and Services Sold		1,400.7	1,278.7
Selling, General and Administrative Expense		95.1	106.3
Miscellaneous - net		27	(32)
Operating Income (Loss)		397.2	137.5
Other non-operating income		3.2	0.5
Net income		363.1	199.3
Accounting Standards Update 2017-07 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of Goods and Services Sold		2.3	4.3
Selling, General and Administrative Expense		(7.8)	(9.5)
Miscellaneous - net		(1.5)	(1.6)
Operating Income (Loss)		(7)	(6.8)
Other non-operating income		7	6.8
Net income		$ 0	$ 0

SEGMENT REPORTING (Narrative) (

SEGMENT REPORTING (Narrative) (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2018USD ($)customerunit	Dec. 31, 2017USD ($)customer	Dec. 31, 2016USD ($)customer
Segment Reporting Information [Line Items]
Number of Reporting Units | unit									2
Revenues	$ 696.3	$ 741.8	$ 714.3	$ 180	$ 511.8	$ 596.7	$ 471.3	$ 286.2	$ 2,332.4	$ 1,866	$ 1,554.5
Sales Revenue, Net [Member] | Customer Concentration Risk [Member]
Segment Reporting Information [Line Items]
Number of Customers | customer									3	3	2
Concentration Risk, Percentage									10.00%	10.00%	10.00%
Revenues									$ 2,100	$ 1,500	$ 1,100

SEGMENT REPORTING (Schedule Of

SEGMENT REPORTING (Schedule Of Segment Reporting Information, By Segment) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenues from product sales and services	$ 696.3	$ 741.8	$ 714.3	$ 180	$ 511.8	$ 596.7	$ 471.3	$ 286.2	$ 2,332.4	$ 1,866	$ 1,554.5
SALES MARGIN	$ 202	$ 261.6	$ 284.5	$ 61.5	$ 116.1	$ 157.8	$ 144.7	$ 49	809.6	467.6	280.1
Other operating expense									136.4	77.4	149.4
TOTAL OTHER INCOME (EXPENSE)									(108.5)	(282)	(20.3)
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES									564.7	108.2	110.4
Net income									1,128.1	363.1	199.3
Depreciation, depletion and amortization									(89)	(87.7)	(115.4)
EBITDA									878.1	330.4	503
Gain (loss) on extinguishment/restructuring of debt									(6.8)	(165.4)	166.3
Adjusted EBITDA									766.3	459.9	246.1
Depreciation, Depletion and Amortization excluding Depreciation, Amortization and Depletion expense for Discontinued Operations									73.8	73.4	90.3
Capital Additions									394.7	153.2	68.3
Mining and Pelletizing [Member]
Segment Reporting Information [Line Items]
Revenues from product sales and services									2,332.4	1,866	1,554.5
SALES MARGIN									809.6	467.6	280.1
Depreciation, depletion and amortization									(68.2)	(66.6)	(84)
EBITDA									852.9	534.9	342.4
Adjusted EBITDA									875.3	559.4	359.6
Capital Additions									145	136.8	62.2
Metallics [Member]
Segment Reporting Information [Line Items]
EBITDA									(3.3)	(0.4)	0
Adjusted EBITDA									(3.3)	(0.4)	0
Capital Additions									248.1	13.7	0
All Other Segments [Member]
Segment Reporting Information [Line Items]
Depreciation, depletion and amortization									(5.6)	(6.8)	(6.3)
Capital Additions									1.6	2.7	6.1
Other Segment [Member]
Segment Reporting Information [Line Items]
EBITDA									28.5	(204.1)	160.6
Adjusted EBITDA									(105.7)	(99.1)	(113.5)
EBITDA Calculation [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), net, including Discontinued Operations									(121.3)	(132)	(200.5)
Income Tax Expense (Benefit), including Discontinued Operations									460.3	252.4	12.2
Depreciation, depletion and amortization									(89)	(87.7)	(115.4)
Adjusted EBITDA Calculation [Member]
Segment Reporting Information [Line Items]
Impact of Discontinued Operations									120.6	22	108.4
Foreign Exchange Remeasurement									(0.9)	13.9	(17.8)
Impairment of other long-lived assets									$ (1.1)	$ 0	$ 0

SEGMENT REPORTING (Summary of A

SEGMENT REPORTING (Summary of Assets by Segment) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
TOTAL ASSETS	$ 3,529.6	$ 2,990.2	$ 2,953.4	$ 1,923.9
Mining and Pelletizing [Member]
Segment Reporting Information [Line Items]
TOTAL ASSETS	1,694.1		1,500.6	1,372.5
Metallics [Member]
Segment Reporting Information [Line Items]
TOTAL ASSETS	265.9		13.4	0
Total Segment Assets [Member]
Segment Reporting Information [Line Items]
TOTAL ASSETS	1,960		1,514	1,372.5
Corporate [Member]
Segment Reporting Information [Line Items]
TOTAL ASSETS	1,557.2		1,300.6	396.3
Discontinued Operations [Member]
Segment Reporting Information [Line Items]
Disposal Group, Including Discontinued Operation, Assets	$ 12.4		$ 138.8	$ 155.1

SEGMENTS REPORTING (Revenue by

SEGMENTS REPORTING (Revenue by Geographical Location) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 696.3	$ 741.8	$ 714.3	$ 180	$ 511.8	$ 596.7	$ 471.3	$ 286.2	$ 2,332.4	$ 1,866	$ 1,554.5
PROPERTY, PLANT AND EQUIPMENT, NET	1,286				1,033.8				1,286	1,033.8		$ 1,033.8
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									1,847.3	1,504.5	1,236.2
PROPERTY, PLANT AND EQUIPMENT, NET	$ 1,286				$ 1,033.8				1,286	1,033.8	961
Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									395.1	206.2	267.1
Other Countries [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									$ 90	$ 155.3	$ 51.2

SEGMENT REPORTING (Revenue from

SEGMENT REPORTING (Revenue from External Customers by Products and Services) (Details) - Sales Revenue, Net [Member] - Product Concentration Risk [Member]	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue from External Customer [Line Items]
Concentration Risk, Percentage	100.00%	100.00%	100.00%
Iron Ore Revenue [Member]
Revenue from External Customer [Line Items]
Concentration Risk, Percentage	93.00%	88.00%	89.00%
Freight and Venture Partners' Cost Reimbursements [Member]
Revenue from External Customer [Line Items]
Concentration Risk, Percentage	7.00%	12.00%	11.00%

INVENTORIES (Narrative) (Detail

INVENTORIES (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Inventory [Line Items]
Cost of Goods Sold	$ (0.2)
Increase in Inventories		6.2
Mining and Pelletizing [Member]
Inventory [Line Items]
Inventory, LIFO Reserve	$ 95.6	$ 96.2

PROPERTY, PLANT AND EQUIPMENT_2

PROPERTY, PLANT AND EQUIPMENT (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Depreciation	$ 65.6	$ 65.8	$ 84
Interest capitalized	6.5
Depletion	$ 7.4	$ 6.8	$ 3.8

INVENTORIES (Schedule Of Invent

INVENTORIES (Schedule Of Inventories) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Inventory, Net [Abstract]
Total Inventories	$ 87.9	$ 87	$ 138.4
Mining and Pelletizing [Member]
Inventory, Net [Abstract]
Finished Goods	77.8		127.1
Work-in-Process	$ 10.1		$ 11.3

PROPERTY, PLANT AND EQUIPMENT_3

PROPERTY, PLANT AND EQUIPMENT (Value Of Each Of The Major Classes Of Consolidated Depreciable Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 2,308.4		$ 2,000.7
Accumulated Depreciation and Depletion, Property, Plant and Equipment	(1,022.4)		(966.9)
Property, plant and equipment, net	1,286	$ 1,033.8	1,033.8
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	70		65.8
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	87.2		85.2
Mining Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	548.5		533.9
Processing Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	645.8		610.9
Electric Power Facilities [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	58.7		56.9
Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	23.8		23.7
Asset Retirement Obligation [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	14.8		16.9
Other Assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	25.2		25.2
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 284.8		$ 32.6

PROPERTY, PLANT AND EQUIPMENT_4

PROPERTY, PLANT AND EQUIPMENT (Book Value of Land and Mineral Rights Disclosure) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Land Rights	$ 12.4	$ 12.4
Mineral Rights [Abstract]
Mineral Properties, Gross	537.2	537.2
Mineral Properties, Accumulated Depletion	(126.5)	(119.1)
Mineral Properties, Net	$ 410.7	$ 418.1

DEBT AND CREDIT FACILITIES (Nar

DEBT AND CREDIT FACILITIES (Narrative) (Details) $ / shares in Units, shares in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018USD ($)	Sep. 30, 2016USD ($)	Dec. 31, 2018USD ($)$ / shares	Dec. 31, 2017USD ($)$ / shares	Dec. 31, 2016USD ($)shares	Feb. 28, 2018USD ($)	Feb. 09, 2017$ / sharesshares	Sep. 16, 2016USD ($)	Aug. 10, 2016$ / sharesshares	Mar. 30, 2015USD ($)
Line of Credit Facility [Line Items]
Debt Extinguished			$ 227,400,000	$ 1,610,700,000
Common shares, par value | $ / shares			$ 0.125	$ 0.125
Common Stock, New Shares, Issued | shares							63,250		44,400
Net proceeds from issuance of common shares			$ 0	$ 661,300,000	$ 287,400,000
Shares Issued, Price Per Share | $ / shares							$ 10.75		$ 6.75
Gain (loss) on extinguishment of debt			(6,800,000)	(165,400,000)	166,300,000
Debt redemption premiums paid		$ 17,400,000	7,100,000	110,000,000
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
Debt issuance costs			$ 1,500,000	28,600,000	$ 5,200,000
Adjustments to Additional Paid in Capital, Convertible Debt with Conversion Feature				$ 83,400,000
Common Shares Issued in Debt to Equity Exchange | shares					8,200
$400 Million 4.875% 2024 Senior Notes [Member]
Line of Credit Facility [Line Items]
Imputed interest rate			5.00%	5.00%
Debt Instrument, Interest Rate, Stated Percentage			4.875%
Debt Instrument, Par Value			$ 400,000,000	$ 400,000,000
Unamortized Debt Issuance Expense			5,700,000	7,100,000
Debt Instrument, Unamortized Discount			$ 2,200,000	$ 2,600,000
$1.075 Billion 5.75% 2025 Senior Notes [Member]
Line of Credit Facility [Line Items]
Proceeds from Issuance of Debt	$ 500,000,000
Imputed interest rate			6.01%	6.01%
Redemption Price of 35 percent or less of Outstanding			1.0575
Debt Instrument, Interest Rate, Stated Percentage			5.75%
Debt Instrument, Par Value			$ 1,073,300,000
Note Redemption Price, Percent of Principal Amount to be Redeemed			100.00%
Amount in aggregate that can be redeemed on or prior to March 1, 2020			0.35
Unamortized Debt Issuance Expense			$ 9,900,000	$ 11,300,000
Debt Instrument, Unamortized Discount			$ 14,600,000	$ 16,500,000
$316 Million 1.5% 2025 Senior Notes [Domain]
Line of Credit Facility [Line Items]
Imputed interest rate			6.26%	6.26%
Convertible debt, initial conversion price			$ 8.17
Convertible debt, common shares exchanged			$ 122.4365
Common shares, par value | $ / shares			$ 0.125
Convertible debt, principal increment			$ 1,000
Debt Instrument, Interest Rate, Stated Percentage			1.50%
Debt Instrument, Par Value			$ 316,300,000	$ 316,300,000
Note Redemption Price, Percent of Principal Amount to be Redeemed			100.00%
Unamortized Debt Issuance Expense			$ 5,500,000	6,600,000
Debt Instrument, Unamortized Discount			75,600,000	85,600,000
$316 Million 1.5% 2025 Senior Notes [Domain] | Maximum [Member]
Line of Credit Facility [Line Items]
Convertible debt, conversion price percentage			0.98
$316 Million 1.5% 2025 Senior Notes [Domain] | Minimum [Member]
Line of Credit Facility [Line Items]
Convertible debt, conversion price percentage			1.30
$1.075 Billion 5.75% 2025 Senior Notes
Line of Credit Facility [Line Items]
Debt Extinguished			1,700,000
Debt Instrument, Par Value				1,075,000,000
Gain (loss) on extinguishment of debt			100,000
$540 Million 8.25% 2020 First Lien Notes
Line of Credit Facility [Line Items]
Debt Extinguished	$ 35,600,000			$ 540,000,000
Debt Instrument, Interest Rate, Stated Percentage				8.25%
Gain (loss) on extinguishment of debt				$ (93,500,000)
$218.5 Million 8.00% 2020 1.5 Lien Notes
Line of Credit Facility [Line Items]
Debt Extinguished				$ 218,500,000
Debt Instrument, Interest Rate, Stated Percentage				8.00%	8.00%
Debt Instrument, Par Value					$ 218,500,000
Gain (loss) on extinguishment of debt				$ 45,100,000	174,300,000
Debt Instrument, Face Amount Exchanged					512,200,000
$544.2 Million 7.75% 2020 Second Lien Notes
Line of Credit Facility [Line Items]
Debt Extinguished				$ 430,100,000
Debt Instrument, Interest Rate, Stated Percentage				7.75%
Gain (loss) on extinguishment of debt				$ (104,500,000)	6,900,000
Debt Instrument, Face Amount Exchanged					$ 114,100,000
Secured Debt [Member]
Line of Credit Facility [Line Items]
Debt Extinguished			648,600,000
$500 Million 3.95% 2018 Senior Notes [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					3.95%
Gain (loss) on extinguishment of debt		19,900,000			$ 1,800,000
Debt Instrument, Face Amount Exchanged					17,600,000
$400 Million 5.90% 2020 Senior Notes
Line of Credit Facility [Line Items]
Imputed interest rate				5.98%
Debt Extinguished			$ 88,900,000	$ 136,700,000
Debt Instrument, Interest Rate, Stated Percentage			5.90%	5.90%
Debt Instrument, Par Value				$ 88,900,000
Gain (loss) on extinguishment of debt			$ (3,300,000)	(7,800,000)	28,300,000
Unamortized Debt Issuance Expense				200,000
Debt Instrument, Unamortized Discount				$ 100,000
Debt Instrument, Face Amount Exchanged					$ 65,100,000
$500 Million 4.80% 2020 Senior Notes
Line of Credit Facility [Line Items]
Imputed interest rate				4.83%
Debt Extinguished			$ 122,400,000	$ 114,400,000
Debt Instrument, Interest Rate, Stated Percentage			4.80%	4.80%	4.80%
Debt Instrument, Par Value				$ 122,400,000
Gain (loss) on extinguishment of debt			$ (3,700,000)	(1,900,000)	$ 19,500,000
Debt Redemption Expenses		2,500,000
Unamortized Debt Issuance Expense				300,000
Debt Instrument, Unamortized Discount				$ 100,000
Debt Instrument, Face Amount Exchanged					$ 44,700,000
$700 Million 4.875% 2021 Senior Notes
Line of Credit Facility [Line Items]
Imputed interest rate			4.89%	4.89%
Debt Extinguished			$ 14,400,000	$ 171,000,000
Debt Instrument, Interest Rate, Stated Percentage			4.875%	4.875%	4.875%
Debt Instrument, Par Value			$ 124,000,000	$ 138,400,000
Gain (loss) on extinguishment of debt			$ 100,000	(2,800,000)	$ 33,300,000
Basis points			25
Unamortized Debt Issuance Expense			$ 200,000	300,000
Debt Instrument, Unamortized Discount			$ 0	$ 100,000
Debt Instrument, Face Amount Exchanged					76,300,000
$800 Million 6.25% 2040 Senior Notes [Member]
Line of Credit Facility [Line Items]
Imputed interest rate			6.34%	6.34%
Debt Instrument, Par Value			$ 298,400,000	$ 298,400,000
Gain (loss) on extinguishment of debt					84,500,000
Basis points			40
Unamortized Debt Issuance Expense			$ 2,300,000	2,400,000
Debt Instrument, Unamortized Discount			3,300,000	3,400,000
Debt Instrument, Face Amount Exchanged					194,400,000
Unsecured Debt [Member]
Line of Credit Facility [Line Items]
Debt Extinguished			$ 422,200,000
Repurchase price if triggering event occurs			1.01
Note Redemption Price, Percent of Principal Amount to be Redeemed			100.00%
Unsecured Debt [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Time Period During Which Senior Notes May Be Redeemed at Company's Option, Number of Days From When Prior Notice Sent to Holders			60 days
Unsecured Debt [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Time Period During Which Senior Notes May Be Redeemed at Company's Option, Number of Days From When Prior Notice Sent to Holders			30 days
ABL Facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Par Value						$ 450,000,000				$ 550,000,000
U.S. Tranche			$ 450,000,000
Sublimit for Issuers of Letters of Credit for U.S. Tranche			273,200,000
Sublimit for U.S. Swingline Loans			120,000,000
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
LIBOR Rate Based on a One-month interest period plus 1 percent			0.01
Fixed Charge Coverage Ratio			1
Credit facility, amount outstanding			$ 0	0
Line of Credit Facility, Remaining Borrowing Capacity			268,700,000	226,700,000
Revolving credit facility, borrowing capacity			$ 323,700,000	273,200,000
ABL Facility [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Base Rate			0.005
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Credit facility, amount outstanding			$ 55,000,000	$ 46,500,000
Debt Repurchase [Member] | $500 Million 3.95% 2018 Senior Notes [Member]
Line of Credit Facility [Line Items]
Redemption Price								$ 301,000,000
Debt Instrument, Par Value		$ 283,600,000
Debt Repurchase [Member] | $500 Million 4.80% 2020 Senior Notes
Line of Credit Facility [Line Items]
Debt Instrument, Par Value					5,000,000
Gain (loss) on extinguishment of debt					600,000
Exchange of Debt for Equity [Member]
Line of Credit Facility [Line Items]
Gain (loss) on extinguishment of debt					11,300,000
Exchange of Debt for Equity [Member] | $218.5 Million 8.00% 2020 1.5 Lien Notes
Line of Credit Facility [Line Items]
Debt Instrument, Face Amount Exchanged					20,100,000
Exchange of Debt for Equity [Member] | $500 Million 3.95% 2018 Senior Notes [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Face Amount Exchanged					10,000,000
Exchange of Debt for Equity [Member] | $700 Million 4.875% 2021 Senior Notes
Line of Credit Facility [Line Items]
Debt Instrument, Face Amount Exchanged					$ 26,800,000
Equity [Member] | $316 Million 1.5% 2025 Senior Notes [Domain]
Line of Credit Facility [Line Items]
Debt Instrument, Unamortized Discount			$ 85,900,000
Prime Rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate			1.00%

DEBT AND CREDIT FACILITIES (Sch

DEBT AND CREDIT FACILITIES (Schedule Of Long-Term Debt) (Details)	3 Months Ended	12 Months Ended
	Sep. 30, 2016USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Feb. 28, 2018USD ($)	Jan. 01, 2018USD ($)	Dec. 31, 2016USD ($)	Mar. 30, 2015USD ($)
Debt Instrument [Line Items]
Debt redemption premiums paid	$ 17,400,000	$ 7,100,000	$ 110,000,000
Long-term Debt			2,304,200,000
LONG-TERM DEBT		2,092,900,000	$ 2,304,200,000		$ 2,304,200,000
$400 Million 4.875% 2024 Senior Notes [Member]
Debt Instrument [Line Items]
Face amount		$ 400,000,000
Debt Instrument, Interest Rate, Stated Percentage		4.875%
Imputed interest rate		5.00%	5.00%
Debt Instrument, Par Value		$ 400,000,000	$ 400,000,000
Unamortized Debt Issuance Expense		(5,700,000)	(7,100,000)
Debt Instrument, Unamortized Discount		(2,200,000)	(2,600,000)
Long-term Debt		392,100,000	$ 390,300,000
$218.5 Million 8.00% 2020 1.5 Lien Notes
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			8.00%			8.00%
Debt Instrument, Par Value						$ 218,500,000
$500 Million 3.95% 2018 Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						3.95%
$400 Million 5.90% 2020 Senior Notes
Debt Instrument [Line Items]
Face amount		$ 400,000,000
Debt Instrument, Interest Rate, Stated Percentage		5.90%	5.90%
Imputed interest rate			5.98%
Debt Instrument, Par Value			$ 88,900,000
Unamortized Debt Issuance Expense			(200,000)
Debt Instrument, Unamortized Discount			(100,000)
Long-term Debt			$ 88,600,000
$500 Million 4.80% 2020 Senior Notes
Debt Instrument [Line Items]
Face amount		$ 500,000,000
Debt Instrument, Interest Rate, Stated Percentage		4.80%	4.80%			4.80%
Imputed interest rate			4.83%
Debt Instrument, Par Value			$ 122,400,000
Unamortized Debt Issuance Expense			(300,000)
Debt Instrument, Unamortized Discount			(100,000)
Long-term Debt			$ 122,000,000
$700 Million 4.875% 2021 Senior Notes
Debt Instrument [Line Items]
Face amount		$ 700,000,000
Debt Instrument, Interest Rate, Stated Percentage		4.875%	4.875%			4.875%
Imputed interest rate		4.89%	4.89%
Debt Instrument, Par Value		$ 124,000,000	$ 138,400,000
Unamortized Debt Issuance Expense		(200,000)	(300,000)
Debt Instrument, Unamortized Discount		0	(100,000)
Long-term Debt		123,800,000	$ 138,000,000
$316 Million 1.5% 2025 Senior Notes [Domain]
Debt Instrument [Line Items]
Face amount		$ 316,250,000
Debt Instrument, Interest Rate, Stated Percentage		1.50%
Imputed interest rate		6.26%	6.26%
Debt Instrument, Par Value		$ 316,300,000	$ 316,300,000
Unamortized Debt Issuance Expense		(5,500,000)	(6,600,000)
Debt Instrument, Unamortized Discount		(75,600,000)	(85,600,000)
Long-term Debt		$ 235,200,000	$ 224,100,000
Note Redemption Price, Percent of Principal Amount to be Redeemed		100.00%
$1.075 Billion 5.75% 2025 Senior Notes [Member]
Debt Instrument [Line Items]
Face amount		$ 1,075,000,000
Debt Instrument, Interest Rate, Stated Percentage		5.75%
Imputed interest rate		6.01%	6.01%
Debt Instrument, Par Value		$ 1,073,300,000
Unamortized Debt Issuance Expense		(9,900,000)	$ (11,300,000)
Debt Instrument, Unamortized Discount		(14,600,000)	(16,500,000)
Long-term Debt		$ 1,048,800,000	$ 1,047,200,000
Note Redemption Price, Percent of Principal Amount to be Redeemed		100.00%
Redemption Price of 35 percent or less of Outstanding		1.0575
$800 Million 6.25% 2040 Senior Notes [Member]
Debt Instrument [Line Items]
Face amount		$ 800,000,000
Imputed interest rate		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		(3,300,000)	(3,400,000)
Long-term Debt		292,800,000	292,600,000
ABL 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		$ 200,000	$ 1,400,000

DEBT AND CREDIT FACILITIES DE_2

DEBT AND CREDIT FACILITIES DEBT AND CREDIT FACILITIES (Debt Redemption) (Details) - $400 Million 4.875% 2024 Senior Notes [Member]	12 Months Ended
	Dec. 31, 2018
Prior to January 15, 2021 - upon equity issuance
Debt Instrument, Redemption [Line Items]
Redemption Price	104.875%
Restricted Amount (percent of original aggregate principal)	35.00%
Prior to January 15, 2021, including premium
Debt Instrument, Redemption [Line Items]
Redemption Price	100.00%
Prior to January 15, 2021
Debt Instrument, Redemption [Line Items]
Redemption Price	103.00%
Restricted Amount (percent of original aggregate principal)	10.00%
Beginning on January 15, 2021
Debt Instrument, Redemption [Line Items]
Redemption Price	102.438%
Beginning on January 15, 2022
Debt Instrument, Redemption [Line Items]
Redemption Price	101.219%
Beginning on January 15, 2023
Debt Instrument, Redemption [Line Items]
Redemption Price	100.00%

DEBT AND CREDIT FACILITIES (Deb

DEBT AND CREDIT FACILITIES (Debt Extinguishment) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Sep. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Extinguishment of Debt [Line Items]
Debt Extinguished			$ 227.4	$ 1,610.7
Gain (loss) on extinguishment of debt			(6.8)	(165.4)	$ 166.3
Debt redemption premiums paid		$ 17.4	7.1	110
$540 Million 8.25% 2020 First Lien Notes
Extinguishment of Debt [Line Items]
Debt Extinguished	$ 35.6			540
Gain (loss) on extinguishment of debt				(93.5)
$218.5 Million 8.00% 2020 1.5 Lien Notes
Extinguishment of Debt [Line Items]
Debt Extinguished				218.5
Gain (loss) on extinguishment of debt				45.1	174.3
$544.2 Million 7.75% 2020 Second Lien Notes
Extinguishment of Debt [Line Items]
Debt Extinguished				430.1
Gain (loss) on extinguishment of debt				(104.5)	6.9
$1.075 Billion 5.75% 2025 Senior Notes
Extinguishment of Debt [Line Items]
Debt Extinguished			1.7
Gain (loss) on extinguishment of debt			0.1
$400 Million 5.90% 2020 Senior Notes
Extinguishment of Debt [Line Items]
Debt Extinguished			88.9	136.7
Gain (loss) on extinguishment of debt			(3.3)	(7.8)	28.3
$500 Million 4.80% 2020 Senior Notes
Extinguishment of Debt [Line Items]
Debt Extinguished			122.4	114.4
Gain (loss) on extinguishment of debt			(3.7)	(1.9)	19.5
$700 Million 4.875% 2021 Senior Notes
Extinguishment of Debt [Line Items]
Debt Extinguished			14.4	171
Gain (loss) on extinguishment of debt			$ 0.1	$ (2.8)	$ 33.3

DEBT AND CREDIT FACILITIES (D_2

DEBT AND CREDIT FACILITIES (Debt Extinguishment/Restructuring) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Extinguishment of Debt [Line Items]
Gain (loss) on extinguishment of debt		$ (6.8)	$ (165.4)	$ 166.3
$544.2 Million 7.75% 2020 Second Lien Notes
Extinguishment of Debt [Line Items]
Debt Instrument, Face Amount Exchanged				114.1
Debt Instrument, Face Amount Received in Debt Exchange of $544M 7.75% Notes				57
Debt, carrying value				77.5
Gain (loss) on extinguishment of debt			(104.5)	6.9
$500 Million 3.95% 2018 Senior Notes [Member]
Extinguishment of Debt [Line Items]
Debt Instrument, Face Amount Exchanged				17.6
Debt Instrument, Face Amount Received in Debt Exchange of $500M 3.95% Notes				11.4
Debt, carrying value				15.5
Gain (loss) on extinguishment of debt	$ 19.9			1.8
$400 Million 5.90% 2020 Senior Notes
Extinguishment of Debt [Line Items]
Debt Instrument, Face Amount Exchanged				65.1
Debt Instrument, Face Amount Received in Debt Exchange of $400M 5.90% Notes				26
Debt Instrument, Par Value			88.9
Debt, carrying value				35.4
Gain (loss) on extinguishment of debt		(3.3)	(7.8)	28.3
$500 Million 4.80% 2020 Senior Notes
Extinguishment of Debt [Line Items]
Debt Instrument, Face Amount Exchanged				44.7
Debt Instrument, Face Amount Received in Debt Exchange of $500M 4.80% Notes				17.9
Debt Instrument, Par Value			122.4
Debt, carrying value				24.4
Gain (loss) on extinguishment of debt		(3.7)	(1.9)	19.5
$700 Million 4.875% 2021 Senior Notes
Extinguishment of Debt [Line Items]
Debt Instrument, Face Amount Exchanged				76.3
Debt instrument, Face Amount Received in Debt Exchange of $700M 4.875% Notes				30.5
Debt Instrument, Par Value		124	138.4
Debt, carrying value				41.5
Gain (loss) on extinguishment of debt		0.1	(2.8)	33.3
$800 Million 6.25% 2040 Senior Notes [Member]
Extinguishment of Debt [Line Items]
Debt Instrument, Face Amount Exchanged				194.4
Debt Instrument, Face Amount Received in Debt Exchange of $800M 6.25% Notes				75.7
Debt Instrument, Par Value		$ 298.4	298.4
Debt, carrying value				103
Gain (loss) on extinguishment of debt				84.5
$218.5 Million 8.00% 2020 1.5 Lien Notes
Extinguishment of Debt [Line Items]
Debt Instrument, Face Amount Exchanged				512.2
Debt Instrument, Par Value				218.5
Debt, carrying value				297.3
Gain (loss) on extinguishment of debt			$ 45.1	$ 174.3

DEBT AND CREDIT FACILITIES (S_2

DEBT AND CREDIT FACILITIES (Schedule of Debt Maturities) (Details) $ in Millions	Dec. 31, 2018USD ($)
Debt Instrument [Line Items]
Debt Maturities 2018	$ 0
Debt Maturities 2019	0
Debt Maturities 2020	124
Debt Maturities 2021	0
Debt Maturities 2022	0
Debt Maturities 2023 and After	2,088
Long-term Debt, Maturities, Total	$ 2,212

DEBT AND CREDIT FACILITIES DE_3

DEBT AND CREDIT FACILITIES DEBT AND CREDIT FACILITIES - BORROWING CAPACITY (Details) - USD ($)	Dec. 31, 2018	Feb. 28, 2018	Dec. 31, 2017	Mar. 30, 2015
ABL Facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Par Value		$ 450,000,000		$ 550,000,000
Revolving credit facility, borrowing capacity	$ 323,700,000		$ 273,200,000
Long-term Line of Credit	0		0
Line of Credit Facility, Remaining Borrowing Capacity	268,700,000		226,700,000
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Long-term Line of Credit	$ (55,000,000)		$ (46,500,000)

FAIR VALUE OF FINANCIAL INSTR_3

FAIR VALUE OF FINANCIAL INSTRUMENTS (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 543.4	$ 616.9
Derivative Asset	91.5	37.9
Derivative Liability	3.7	2
Derivative asset, fair value	91.5	37.9
Derivative liability, fair value	3.7	2
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0.8	66.3
Derivative Asset	0	0
Derivative Liability	0	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	542.6	550.6
Derivative Asset	0.1	0
Derivative Liability	3.7	0.3
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Derivative Asset	91.4	37.9
Derivative Liability	0	1.7
Not Designated as Hedging Instrument [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value	91.4	37.9
Derivative liability, fair value	0	1.7
Valuation, Market Approach [Member] | Not Designated as Hedging Instrument [Member] | Other Current Assets [Member] | Customer Supply Agreement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value	89.3	37.9
Valuation, Market Approach [Member] | Not Designated as Hedging Instrument [Member] | Other Current Assets [Member] | Provisional Pricing Arrangements [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value	2.1	0
Valuation, Market Approach [Member] | Not Designated as Hedging Instrument [Member] | Other Current Liabilities [Member] | Provisional Pricing Arrangements [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, fair value	$ 0	$ 1.7

FAIR VALUE OF FINANCIAL INSTR_4

FAIR VALUE OF FINANCIAL INSTRUMENTS (Fair Value Of Assets And Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Assets:
Cash equivalents	$ 543.4	$ 616.9
Derivative Asset	91.5	37.9
Total Asset	634.9	654.8
Liabilities:
Derivative Liability	3.7	2
Total Liability	3.7	2
Fair Value, Inputs, Level 1 [Member]
Assets:
Cash equivalents	0.8	66.3
Derivative Asset	0	0
Total Asset	0.8	66.3
Liabilities:
Derivative Liability	0	0
Total Liability	0	0
Fair Value, Inputs, Level 2 [Member]
Assets:
Cash equivalents	542.6	550.6
Derivative Asset	0.1	0
Total Asset	542.7	550.6
Liabilities:
Derivative Liability	3.7	0.3
Total Liability	3.7	0.3
Fair Value, Inputs, Level 3 [Member]
Assets:
Cash equivalents	0	0
Derivative Asset	91.4	37.9
Total Asset	91.4	37.9
Liabilities:
Derivative Liability	0	1.7
Total Liability	$ 0	$ 1.7

FAIR VALUE OF FINANCIAL INSTR_5

FAIR VALUE OF FINANCIAL INSTRUMENTS (Schedule Of Quantitative Inputs And Assumptions For Level 3 Assets And Liabilities) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value	$ 91,500,000	$ 37,900,000
Derivative liability, fair value	3,700,000	2,000,000
Not Designated as Hedging Instrument [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value	91,400,000	37,900,000
Derivative liability, fair value	0	1,700,000
Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Valuation, Market Approach [Member] | Provisional Pricing Arrangements [Member] | Managements Estimate Of 62% Fe [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement with unobservable inputs derivative asset range	68
Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Valuation, Market Approach [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	750
Other Current Liabilities [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Valuation, Market Approach [Member] | Provisional Pricing Arrangements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, fair value	0	1,700,000
Other Current Assets [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Valuation, Market Approach [Member] | Provisional Pricing Arrangements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value	2,100,000	0
Other Current Assets [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Valuation, Market Approach [Member] | Customer Supply Agreement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value	$ 89,300,000	$ 37,900,000

FAIR VALUE OF FINANCIAL INSTR_6

FAIR VALUE OF FINANCIAL INSTRUMENTS (Fair Value, Assets and Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Derivative assets	$ 91.5	$ 91.5	$ 37.9	$ 49.5
Fair Value, Assets Measured On Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance - January 1	37.9	49.5	30.1
Total gains
Included in earnings		428.7	176.2
Settlements		(386.8)	(168.4)
Ending balance - December 31	91.4	91.4	37.9
Total gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) on assets still held at the reporting date	91.4		37.9
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance - January 1	(1.7)		0
Total gains
Included in earnings	(6.1)		(55.6)
Settlements	7.8		53.9
Ending balance - September 30	0	0	(1.7)
Total gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) on liabilities still held at the reporting date	0		$ (1.7)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Derivative assets	$ 30.8	$ 30.8		$ 11.6

FAIR VALUE OF FINANCIAL INSTR_7

FAIR VALUE OF FINANCIAL INSTRUMENTS (Carrying Value And Fair Value Of Financial Instruments Disclosure) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Interest Rate Swap [Member]
Long-term debt:
Fair Value Adjustment to Interest Rate Hedge	$ 0.2	$ 1.4
Reported Value Measurement [Member]
Long-term debt:
Long-term Debt, Fair Value	2,092.9	2,304.2
Reported Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Swap [Member]
Long-term debt:
Fair Value Adjustment to Interest Rate Hedge	0.2	1.4
Estimate of Fair Value Measurement [Member]
Long-term debt:
Long-term Debt, Fair Value	2,039.9	2,346.3
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Swap [Member]
Long-term debt:
Fair Value Adjustment to Interest Rate Hedge	0.2	1.4
Senior Notes [Member] | Reported Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | $400 Million 4.875% 2024 Senior Notes [Member]
Long-term debt:
Long-term Debt, Fair Value	392.1	390.3
Senior Notes [Member] | Reported Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | $400 Million 5.90% 2020 Senior Notes
Long-term debt:
Long-term Debt, Fair Value	0	88.6
Senior Notes [Member] | Reported Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | $500 Million 4.80% 2020 Senior Notes
Long-term debt:
Long-term Debt, Fair Value	0	122
Senior Notes [Member] | Reported Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | $700 Million 4.875% 2021 Senior Notes
Long-term debt:
Long-term Debt, Fair Value	123.8	138
Senior Notes [Member] | Reported Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | $316 Million 1.5% 2025 Senior Notes [Domain]
Long-term debt:
Long-term Debt, Fair Value	235.2	224.1
Senior Notes [Member] | Reported Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | $1.075 Billion 5.75% 2025 Senior Notes [Member]
Long-term debt:
Long-term Debt, Fair Value	1,048.8	1,047.2
Senior Notes [Member] | Reported Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | $800 Million 6.25% 2040 Senior Notes [Member]
Long-term debt:
Long-term Debt, Fair Value	292.8	292.6
Senior Notes [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | $400 Million 4.875% 2024 Senior Notes [Member]
Long-term debt:
Long-term Debt, Fair Value	370.2	398
Senior Notes [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | $400 Million 5.90% 2020 Senior Notes
Long-term debt:
Long-term Debt, Fair Value	0	88
Senior Notes [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | $500 Million 4.80% 2020 Senior Notes
Long-term debt:
Long-term Debt, Fair Value	0	118.8
Senior Notes [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | $700 Million 4.875% 2021 Senior Notes
Long-term debt:
Long-term Debt, Fair Value	122.3	130.8
Senior Notes [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | $316 Million 1.5% 2025 Senior Notes [Domain]
Long-term debt:
Long-term Debt, Fair Value	352.4	352.9
Senior Notes [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | $1.075 Billion 5.75% 2025 Senior Notes [Member]
Long-term debt:
Long-term Debt, Fair Value	962	1,029.3
Senior Notes [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | $800 Million 6.25% 2040 Senior Notes [Member]
Long-term debt:
Long-term Debt, Fair Value	232.8	227.1
Line of Credit [Member] | Reported Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | ABL Facility [Member]
Long-term debt:
Long-term Debt, Fair Value	0	0
Line of Credit [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | ABL Facility [Member]
Long-term debt:
Long-term Debt, Fair Value	$ 0	$ 0

PENSIONS AND OTHER POSTRETIRE_3

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Narrative) (Details) - USD ($)	Jan. 01, 2019	Oct. 12, 2018	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Term Of Agreement		4 years
401(k) contribution match			$ 0.50
Defined Benefit Plan, Accumulated Benefit Obligation			896,800,000	$ 963,000,000
Reserve for investment commitments			44,200,000
Early Termination Fees for Pension Benefits			22,100,000
Early Termination Fees for Other Postretirement Benefits			$ 3,400,000
Structured Finance [Member]
Defined Benefit Plan Disclosure [Line Items]
Redemption request notice period, days			90 days
Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Redemption request notice period, days			45 days
Withdrawal request notice period, days			65 days
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Decrease in Projected Benefit Obligation due to Market Conditions			$ 75,700,000	(46,100,000)
Increase in Projected Benefit Obligation due to new mortality tables			(21,700,000)	6,100,000
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)			(57,000,000)	54,600,000
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Contributions by Plan Participants			5,600,000	4,600,000
Decrease in Projected Benefit Obligation due to Market Conditions			19,000,000	(12,600,000)
Increase in Projected Benefit Obligation due to new mortality tables			(2,300,000)	1,900,000
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)			(29,400,000)	$ 7,400,000
Prior To Age65 [Member]
Defined Benefit Plan Disclosure [Line Items]
Annual limit on medical coverage for each participant			7,000
Subsequent Event [Member]
Defined Benefit Plan Disclosure [Line Items]
401(k) contribution match	$ 0.60
Adoption of New Projection Scale [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase in Projected Benefit Obligation due to new mortality tables			3,000,000
Adoption of New Projection Scale [Member] | Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase in Projected Benefit Obligation due to new mortality tables			800,000
Update Assumption per Capita Cost [Member] | Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase in Projected Benefit Obligation due to new mortality tables			$ 11,900,000

PENSIONS AND OTHER POSTRETIRE_4

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Annual Costs Related to Retirement Plans) (Details) - Pension Benefits [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plans	$ 12.7	$ 18	$ 16.5
Defined contribution pension plans	3.1	2.9	2.8
Other Postretirement Benefits Cost (Reversal of Cost)	(5.9)	(6.1)	(4)
Total	$ 9.9	$ 14.8	$ 15.3

PENSIONS AND OTHER POSTRETIRE_5

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Benefit Obligations, Fair Value of Plan Assets, and Net Funded Status) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets — beginning of year	$ 215.6	$ 202.4
Employer contributions	3.8	2.1
Fair value of plan assets — end of year	229.1	215.6	$ 202.4
Funded status at December 31:
Defined Benefit Plan, Plan Assets, Amount	215.6	202.4	202.4	$ 229.1		$ 215.6
Amounts recognized in Statements of Financial Position:
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES				(248.7)	$ (257.7)	(257.7)
Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligations — beginning of year	(973.1)	(931.6)
Service cost (excluding expenses)	18.7	17.1	17.6
Interest cost	30.3	30.5	30.3
Plan amendments	2.2	0
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment	(0.9)	0
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	(57)	54.6
Defined Benefit Plan, Benefit Obligation, Benefits Paid	60.7	60.7
Participant contributions	0	0
Federal subsidy on benefits paid	0	0
Benefit obligations — end of year	(905.7)	(973.1)	(931.6)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets — beginning of year	749.8	685.8
Actual return on plan assets	(29.6)	100.2
Participant contributions	0	0
Employer contributions	27.6	24.4
Assets Transferred to (from) Plan	0.1	0.1
Benefits paid	(60.7)	(60.7)
Fair value of plan assets — end of year	687.2	749.8	685.8
Funded status at December 31:
Defined Benefit Plan, Plan Assets, Amount	749.8	685.8	685.8	687.2		749.8
Defined Benefit Plan, Benefit Obligation	(973.1)	(931.6)	(931.6)	(905.7)		(973.1)
Defined Benefit Plan, Funded (Unfunded) Status of Plan				(218.5)		(223.3)
Total amount recognized				(218.5)		(223.3)
Amounts recognized in Statements of Financial Position:
Assets, Noncurrent				0		0
Current liabilities				(0.1)		(0.5)
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES				(218.4)		(222.8)
Total amount recognized				(218.5)		(223.3)
Amounts recognized in accumulated other comprehensive income:
Prior service cost				8.5		8.8
Net actuarial loss				330.1		318.7
Net amount recognized				338.6		327.5
Other Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligations — beginning of year	(265.9)	(264.6)
Service cost (excluding expenses)	2.2	1.8	1.7
Interest cost	8.3	8.3	9.1
Plan amendments	12.8	0
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment	0	0
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	(29.4)	7.4
Defined Benefit Plan, Benefit Obligation, Benefits Paid	24.4	21.4
Participant contributions	5.6	4.6
Federal subsidy on benefits paid	0.9	0.6
Benefit obligations — end of year	(241.9)	(265.9)	(264.6)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets — beginning of year	262.5	253
Actual return on plan assets	(8.2)	24.2
Participant contributions	0.5	0.3
Employer contributions	3	1.7
Assets Transferred to (from) Plan	0	0
Benefits paid	(17.6)	(16.7)
Fair value of plan assets — end of year	240.2	262.5	253
Funded status at December 31:
Defined Benefit Plan, Plan Assets, Amount	262.5	253	253	240.2		262.5
Defined Benefit Plan, Benefit Obligation	(265.9)	(264.6)	$ (264.6)	(241.9)		(265.9)
Defined Benefit Plan, Funded (Unfunded) Status of Plan				(1.7)		(3.4)
Total amount recognized				(1.7)		(3.4)
Amounts recognized in Statements of Financial Position:
Assets, Noncurrent				32.1		35.4
Current liabilities				(3.5)		(3.9)
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES				(30.3)		(34.9)
Total amount recognized				(1.7)		(3.4)
Amounts recognized in accumulated other comprehensive income:
Prior service cost				(9.9)		(25.6)
Net actuarial loss				82.1		88.3
Net amount recognized				72.2		62.7
Salaried Employees [Member] | Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligations — beginning of year	(368)
Benefit obligations — end of year	(340.8)	(368)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets — beginning of year	269.4
Fair value of plan assets — end of year	249.8	269.4
Funded status at December 31:
Defined Benefit Plan, Plan Assets, Amount	269.4	269.4		249.8		269.4
Defined Benefit Plan, Benefit Obligation	(368)	(368)		(340.8)		(368)
Defined Benefit Plan, Funded (Unfunded) Status of Plan				(91)		(98.6)
Salaried Employees [Member] | Other Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligations — beginning of year	(37.7)
Benefit obligations — end of year	(32.9)	(37.7)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Funded status at December 31:
Defined Benefit Plan, Plan Assets, Amount	0	0		0		0
Defined Benefit Plan, Benefit Obligation	(37.7)	(37.7)		(32.9)		(37.7)
Defined Benefit Plan, Funded (Unfunded) Status of Plan				(32.9)		(37.7)
Hourly Employees [Member] | Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligations — beginning of year	(590)
Benefit obligations — end of year	(548.9)	(590)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets — beginning of year	473
Fair value of plan assets — end of year	429.4	473
Funded status at December 31:
Defined Benefit Plan, Plan Assets, Amount	473	473		429.4		473
Defined Benefit Plan, Benefit Obligation	(590)	(590)		(548.9)		(590)
Defined Benefit Plan, Funded (Unfunded) Status of Plan				(119.5)		(117)
Hourly Employees [Member] | Other Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligations — beginning of year	(228.2)
Benefit obligations — end of year	(209)	(228.2)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets — beginning of year	262.5
Fair value of plan assets — end of year	240.2	262.5
Funded status at December 31:
Defined Benefit Plan, Plan Assets, Amount	262.5	262.5		240.2		262.5
Defined Benefit Plan, Benefit Obligation	(228.2)	(228.2)		(209)		(228.2)
Defined Benefit Plan, Funded (Unfunded) Status of Plan				31.2		34.3
Mining Employees [Member] | Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligations — beginning of year	(10.3)
Benefit obligations — end of year	(10.7)	(10.3)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets — beginning of year	7.4
Fair value of plan assets — end of year	8	7.4
Funded status at December 31:
Defined Benefit Plan, Plan Assets, Amount	7.4	7.4		8		7.4
Defined Benefit Plan, Benefit Obligation	(10.3)	(10.3)		(10.7)		(10.3)
Defined Benefit Plan, Funded (Unfunded) Status of Plan				(2.7)		(2.9)
Supplemental Executive Retirement Plan S E R P [Member] | Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligations — beginning of year	(4.8)
Benefit obligations — end of year	(5.3)	(4.8)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Funded status at December 31:
Defined Benefit Plan, Plan Assets, Amount	0	0		0		0
Defined Benefit Plan, Benefit Obligation	$ (4.8)	$ (4.8)		(5.3)		(4.8)
Defined Benefit Plan, Funded (Unfunded) Status of Plan				$ (5.3)		$ (4.8)

PENSIONS AND OTHER POSTRETIRE_6

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Components Of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Amortization:
Relating to assets sold during the period	$ 4	$ 4.8
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	18.7	17.1	$ 17.6
Interest cost	(30.3)	(30.5)	(30.3)
Expected return on plan assets	(60)	(54.5)	(54.7)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	0.3	0	0
Amortization:
Amortization of prior service (cost) credit	(2.2)	(2.6)	(2.2)
Net actuarial loss	21.2	22.3	21.1
Net periodic benefit cost	12.7	18	16.5
Current year actuarial (gain)/loss	31.6	9.3	37.8
Amortization of net loss	(21.2)	(22.3)	(21.1)
Current year prior service cost	2.2	0	5.7
Amortization of prior service (cost) credit	(2.2)	(2.6)	(2.2)
Total recognized in other comprehensive income	10.1	(15.6)	20.2
Total recognized in net periodic cost and other comprehensive income	22.8	2.4	36.7
Defined Benefit Plan, Benefit Obligation	(905.7)	(973.1)	(931.6)
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(218.5)	(223.3)
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2.2	1.8	1.7
Interest cost	(8.3)	(8.3)	(9.1)
Expected return on plan assets	(18.4)	(17.7)	(17.1)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	0	0	0
Amortization:
Amortization of prior service (cost) credit	3	3	3.7
Net actuarial loss	5	4.5	6
Net periodic benefit cost	(5.9)	(6.1)	(4)
Current year actuarial (gain)/loss	(2.9)	1.2	(8.1)
Amortization of net loss	(5)	(4.5)	(6)
Current year prior service cost	12.8	0	9.8
Amortization of prior service (cost) credit	3	3	3.7
Total recognized in other comprehensive income	7.9	(0.3)	(0.6)
Total recognized in net periodic cost and other comprehensive income	2	(6.4)	(4.6)
Defined Benefit Plan, Benefit Obligation	(241.9)	(265.9)	$ (264.6)
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(1.7)	(3.4)
Salaried Employees [Member] | Pension Benefits [Member]
Amortization:
Defined Benefit Plan, Benefit Obligation	(340.8)	(368)
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(91)	(98.6)
Salaried Employees [Member] | Other Benefits [Member]
Amortization:
Defined Benefit Plan, Benefit Obligation	(32.9)	(37.7)
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(32.9)	(37.7)
Hourly Employees [Member] | Pension Benefits [Member]
Amortization:
Defined Benefit Plan, Benefit Obligation	(548.9)	(590)
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(119.5)	(117)
Hourly Employees [Member] | Other Benefits [Member]
Amortization:
Defined Benefit Plan, Benefit Obligation	(209)	(228.2)
Defined Benefit Plan, Funded (Unfunded) Status of Plan	31.2	34.3
Mining Employees [Member] | Pension Benefits [Member]
Amortization:
Defined Benefit Plan, Benefit Obligation	(10.7)	(10.3)
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(2.7)	(2.9)
Supplemental Executive Retirement Plan S E R P [Member] | Pension Benefits [Member]
Amortization:
Defined Benefit Plan, Benefit Obligation	(5.3)	(4.8)
Defined Benefit Plan, Funded (Unfunded) Status of Plan	$ (5.3)	$ (4.8)

PENSIONS AND OTHER POSTRETIRE_7

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Additional Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual return on plan assets	$ (29.6)	$ 100.2
Other Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual return on plan assets	$ (8.2)	$ 24.2

PENSIONS AND OTHER POSTRETIRE_8

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Weighted-Average Assumptions Used to Determine Benefit Obligations) (Details)	Dec. 31, 2018	Dec. 31, 2017
Salary [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate of compensation increase	3.00%	3.00%
Hourly [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate of compensation increase	2.00%	2.00%
Iron Hourly [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.31%	3.60%
Salaried [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.21%	3.52%
Salaried [Member] | Other Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.27%	3.57%
Ore Mining [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.33%	3.61%
Supplemental Executive Retirement Plan S E R P [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.22%	3.50%
Hourly [Member] | Other Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.29%	3.60%

PENSIONS AND OTHER POSTRETIRE_9

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Weighted-Average Assumptions Used to Determine Net Benefit Cost) (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets	8.25%	8.25%	8.25%
Other Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets	7.00%	7.00%	7.00%
SERP [Domain] | Pension Benefits [Member] | Obligation [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.54%	3.90%	4.01%
SERP [Domain] | Pension Benefits [Member] | Service Cost [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.43%	3.69%	3.87%
SERP [Domain] | Pension Benefits [Member] | Interest Cost [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.16%	3.36%	3.30%
Ore Mining [Domain] | Pension Benefits [Member] | Obligation [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.61%	4.04%	4.28%
Ore Mining [Domain] | Pension Benefits [Member] | Service Cost [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.75%	4.27%	4.60%
Ore Mining [Domain] | Pension Benefits [Member] | Interest Cost [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.22%	3.41%	3.48%
Salary [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate of compensation increase	3.00%	3.00%	3.00%
Salary [Member] | Pension Benefits [Member] | Obligation [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.52%	3.91%	4.13%
Salary [Member] | Pension Benefits [Member] | Service Cost [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.53%	3.93%	4.14%
Salary [Member] | Pension Benefits [Member] | Interest Cost [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.08%	3.21%	3.21%
Salary [Member] | Other Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate of compensation increase	3.00%	3.00%	3.00%
Salary [Member] | Other Benefits [Member] | Obligation [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.57%	3.98%	4.22%
Salary [Member] | Other Benefits [Member] | Service Cost [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.76%	4.30%	4.63%
Salary [Member] | Other Benefits [Member] | Interest Cost [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.15%	3.28%	3.31%
Hourly [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets	2.00%	2.00%	2.00%
Hourly [Member] | Pension Benefits [Member] | Obligation [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.61%	4.02%	4.27%
Hourly [Member] | Pension Benefits [Member] | Service Cost [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.76%	4.30%	4.66%
Hourly [Member] | Pension Benefits [Member] | Interest Cost [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.21%	3.38%	3.46%
Hourly [Member] | Other Benefits [Member] | Obligation [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.60%	4.03%	4.32%
Hourly [Member] | Other Benefits [Member] | Service Cost [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.73%	4.23%	4.56%
Hourly [Member] | Other Benefits [Member] | Interest Cost [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.10%	3.24%	3.48%

PENSIONS AND OTHER POSTRETIR_10

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Assumed Health Care Cost Trend Rates) (Details)	Dec. 31, 2018	Dec. 31, 2017
Postemployment Benefits [Abstract]
Health care cost trend rate assumed for next year	6.75%	7.00%
Ultimate health care cost trend rate	5.00%	5.00%

PENSIONS AND OTHER POSTRETIR_11

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Target Allocation and Actual Asset Allocations for Pension and VEBA Plan Assets) (Details)	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	100.00%	100.00%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	100.00%
Pension Benefits [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	38.90%	43.60%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	45.00%
Pension Benefits [Member] | Fixed Income Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	26.00%	27.00%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	28.00%
Pension Benefits [Member] | Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	5.40%	5.00%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	5.00%
Pension Benefits [Member] | Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	6.20%	5.30%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	7.00%
Pension Benefits [Member] | Structured Finance [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	11.40%	9.70%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	7.50%
Pension Benefits [Member] | Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	10.30%	8.70%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	7.50%
Pension Benefits [Member] | Cash [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	1.80%	0.70%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Other Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	100.00%	100.00%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	100.00%
Other Benefits [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	8.10%	8.70%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	8.00%
Other Benefits [Member] | Fixed Income Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	77.00%	77.70%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	80.00%
Other Benefits [Member] | Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	4.70%	4.40%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	4.00%
Other Benefits [Member] | Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	1.20%	1.50%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	3.00%
Other Benefits [Member] | Structured Finance [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	3.50%	3.00%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	2.00%
Other Benefits [Member] | Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	5.40%	4.60%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	3.00%
Other Benefits [Member] | Cash [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	0.10%	0.10%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%

PENSIONS AND OTHER POSTRETIR_12

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Fair Values of Pension Plan Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	$ 229.1	$ 215.6	$ 202.4
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	687.2	749.8	685.8
Equity Securities [Member] | U S Large Cap [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	112.6	130.1
Equity Securities [Member] | U S Small Mid Cap [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	22.5	35.5
Equity Securities [Member] | International [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	132	160.9
Fixed Income Investments [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	178.5	202.4
Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	37.2	37.4	40.6
Hedge Funds [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	37.2	37.4
Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	42.6	39.8	36.1
Private Equity Funds [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	42.6	39.8
Structured Finance [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	78.8	72.9	63.8
Structured Finance [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	78.8	72.9
Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	70.5	65.5	$ 61.9
Real Estate [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	70.5	65.5
Cash [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	12.5	5.3
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	430.7	505.4
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Equity Securities [Member] | U S Large Cap [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	112.6	130.1
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Equity Securities [Member] | U S Small Mid Cap [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	22.5	35.5
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Equity Securities [Member] | International [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	132	160.9
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fixed Income Investments [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	151.1	173.6
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Hedge Funds [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Private Equity Funds [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Structured Finance [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Real Estate [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Cash [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	12.5	5.3
Fair Value, Inputs, Level 2 [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	27.4	28.8
Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member] | U S Large Cap [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member] | U S Small Mid Cap [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member] | International [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 2 [Member] | Fixed Income Investments [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	27.4	28.8
Fair Value, Inputs, Level 2 [Member] | Hedge Funds [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 2 [Member] | Private Equity Funds [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 2 [Member] | Structured Finance [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 2 [Member] | Real Estate [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 2 [Member] | Cash [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	229.1	215.6
Significant Unobservable Inputs (Level 3) [Member] | Equity Securities [Member] | U S Large Cap [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Equity Securities [Member] | U S Small Mid Cap [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Equity Securities [Member] | International [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Fixed Income Investments [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Hedge Funds [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	37.2	37.4
Significant Unobservable Inputs (Level 3) [Member] | Private Equity Funds [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	42.6	39.8
Significant Unobservable Inputs (Level 3) [Member] | Structured Finance [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	78.8	72.9
Significant Unobservable Inputs (Level 3) [Member] | Real Estate [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	70.5	65.5
Significant Unobservable Inputs (Level 3) [Member] | Cash [Member] | Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	$ 0	$ 0

PENSIONS AND POSTRETIREMENT BEN

PENSIONS AND POSTRETIREMENT BENEFITS (Effect of Fair Value Measurements Using Significant Unobservable Inputs (Level 3) on Changes in Pension Plan Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Roll Forward]
Fair value of plan assets — beginning of year	$ 215.6	$ 202.4
Actual return on plan assets:
Relating to assets still held at the reporting date	12.5	16.1
Purchases	5.2	57.9
Sales	8.2	65.6
Fair value of plan assets — end of year	229.1	215.6
Hedge Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Roll Forward]
Fair value of plan assets — beginning of year	37.4	40.6
Actual return on plan assets:
Relating to assets still held at the reporting date	(0.2)	2.5
Purchases	0	39
Sales	0	45.1
Fair value of plan assets — end of year	37.2	37.4
Private Equity Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Roll Forward]
Fair value of plan assets — beginning of year	39.8	36.1
Actual return on plan assets:
Relating to assets still held at the reporting date	1.4	0.3
Purchases	5.2	4.5
Sales	7.8	5.6
Fair value of plan assets — end of year	42.6	39.8
Structured Finance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Roll Forward]
Fair value of plan assets — beginning of year	72.9	63.8
Actual return on plan assets:
Relating to assets still held at the reporting date	5.9	9.1
Purchases	0	0
Sales	0	0
Fair value of plan assets — end of year	78.8	72.9
Real Estate [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Roll Forward]
Fair value of plan assets — beginning of year	65.5	61.9
Actual return on plan assets:
Relating to assets still held at the reporting date	5.4	4.2
Purchases	0	14.4
Sales	0.4	14.9
Fair value of plan assets — end of year	$ 70.5	$ 65.5

PENSIONS AND OTHER POSTRETIR_13

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Fair Values of Other Benefit Plan Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 229.1	$ 215.6	$ 202.4
Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	37.2	37.4	40.6
Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	42.6	39.8	36.1
Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	70.5	65.5	61.9
Other Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	240.2	262.5	253
Other Benefits [Member] | Equity Securities [Member] | U S Large Cap [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	9.7	11.4
Other Benefits [Member] | Equity Securities [Member] | U S Small Mid Cap [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	2.4	2.8
Other Benefits [Member] | Equity Securities [Member] | International [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	7.3	8.8
Other Benefits [Member] | Fixed Income Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	184.6	204.1
Other Benefits [Member] | Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	11.4	11.4
Other Benefits [Member] | Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	3	3.9
Other Benefits [Member] | Structured Credit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	8.5	7.9
Other Benefits [Member] | Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	13.1	12
Other Benefits [Member] | Cash [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0.2	0.2
Other Benefits [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	166.4	187.3
Other Benefits [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Equity Securities [Member] | U S Large Cap [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	9.7	11.4
Other Benefits [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Equity Securities [Member] | U S Small Mid Cap [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	2.4	2.8
Other Benefits [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Equity Securities [Member] | International [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	7.3	8.8
Other Benefits [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fixed Income Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	146.8	164.1
Other Benefits [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Benefits [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Benefits [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Structured Credit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Benefits [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Benefits [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Cash [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0.2	0.2
Other Benefits [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	37.8	40
Other Benefits [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member] | U S Large Cap [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Benefits [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member] | U S Small Mid Cap [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Benefits [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member] | International [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Benefits [Member] | Fair Value, Inputs, Level 2 [Member] | Fixed Income Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	37.8	40
Other Benefits [Member] | Fair Value, Inputs, Level 2 [Member] | Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Benefits [Member] | Fair Value, Inputs, Level 2 [Member] | Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Benefits [Member] | Fair Value, Inputs, Level 2 [Member] | Structured Credit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Benefits [Member] | Fair Value, Inputs, Level 2 [Member] | Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Benefits [Member] | Fair Value, Inputs, Level 2 [Member] | Cash [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Benefits [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	36	35.2	33.5
Other Benefits [Member] | Significant Unobservable Inputs (Level 3) [Member] | Equity Securities [Member] | U S Large Cap [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Benefits [Member] | Significant Unobservable Inputs (Level 3) [Member] | Equity Securities [Member] | U S Small Mid Cap [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Benefits [Member] | Significant Unobservable Inputs (Level 3) [Member] | Equity Securities [Member] | International [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Benefits [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fixed Income Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Benefits [Member] | Significant Unobservable Inputs (Level 3) [Member] | Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	11.4	11.4	11.2
Other Benefits [Member] | Significant Unobservable Inputs (Level 3) [Member] | Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	3	3.9	4.3
Other Benefits [Member] | Significant Unobservable Inputs (Level 3) [Member] | Structured Credit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	8.5	7.9	6.9
Other Benefits [Member] | Significant Unobservable Inputs (Level 3) [Member] | Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	13.1	12	$ 11.1
Other Benefits [Member] | Significant Unobservable Inputs (Level 3) [Member] | Cash [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 0	$ 0

PENSION AND OTHER POSTRETIREMEN

PENSION AND OTHER POSTRETIREMENT BENEFITS (Effect of Fair Value Measurements Using Significant Unobservable Inputs (Level 3) on Changes in Other Benefit Plan Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	$ 215.6	$ 202.4
Actual return on plan assets:
Relating to assets still held at the reporting date	12.5	16.1
Acquired through business combinations	5.2	57.9
Sales	8.2	65.6
Fair value of plan assets — end of year	229.1	215.6
Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	37.4	40.6
Actual return on plan assets:
Relating to assets still held at the reporting date	(0.2)	2.5
Acquired through business combinations	0	39
Sales	0	45.1
Fair value of plan assets — end of year	37.2	37.4
Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	39.8	36.1
Actual return on plan assets:
Relating to assets still held at the reporting date	1.4	0.3
Acquired through business combinations	5.2	4.5
Sales	7.8	5.6
Fair value of plan assets — end of year	42.6	39.8
Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	65.5	61.9
Actual return on plan assets:
Relating to assets still held at the reporting date	5.4	4.2
Acquired through business combinations	0	14.4
Sales	0.4	14.9
Fair value of plan assets — end of year	70.5	65.5
Other Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	262.5	253
Actual return on plan assets:
Fair value of plan assets — end of year	240.2	262.5
Other Benefits [Member] | Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	11.4
Actual return on plan assets:
Fair value of plan assets — end of year	11.4	11.4
Other Benefits [Member] | Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	3.9
Actual return on plan assets:
Fair value of plan assets — end of year	3	3.9
Other Benefits [Member] | Structured Credit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	7.9
Actual return on plan assets:
Fair value of plan assets — end of year	8.5	7.9
Other Benefits [Member] | Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	12
Actual return on plan assets:
Fair value of plan assets — end of year	13.1	12
Significant Unobservable Inputs (Level 3) [Member] | Other Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	35.2	33.5
Actual return on plan assets:
Relating to assets still held at the reporting date	1.6	7.1
Acquired through business combinations	0	24
Sales	1.1	25.5
Fair value of plan assets — end of year	36	35.2
Significant Unobservable Inputs (Level 3) [Member] | Other Benefits [Member] | Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	11.4	11.2
Actual return on plan assets:
Relating to assets still held at the reporting date	0	0.8
Acquired through business combinations	0	17.1
Sales	0	17.7
Fair value of plan assets — end of year	11.4	11.4
Significant Unobservable Inputs (Level 3) [Member] | Other Benefits [Member] | Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	3.9	4.3
Actual return on plan assets:
Relating to assets still held at the reporting date	(0.1)	0.9
Acquired through business combinations	0	1.8
Sales	1.1	2.7
Fair value of plan assets — end of year	3	3.9
Significant Unobservable Inputs (Level 3) [Member] | Other Benefits [Member] | Structured Credit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	7.9	6.9
Actual return on plan assets:
Relating to assets still held at the reporting date	0.6	2
Acquired through business combinations	0	2.1
Sales	0	2.1
Fair value of plan assets — end of year	8.5	7.9
Significant Unobservable Inputs (Level 3) [Member] | Other Benefits [Member] | Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	12	11.1
Actual return on plan assets:
Relating to assets still held at the reporting date	1.1	3.4
Acquired through business combinations	0	3
Sales	0	3
Fair value of plan assets — end of year	$ 13.1	$ 12

PENSIONS AND OTHER POSTRETIR_14

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Unobservable Inputs, Level 3) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 229.1	$ 215.6	$ 202.4
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held	12.5	16.1
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold	4	4.8
Defined Benefit Plan, Plan Assets, Business Combination	5.2	57.9
Defined Benefit Plan, Plan Assets, Divestiture	(8.2)	(65.6)
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	240.2	262.5	253
Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	42.6	39.8	36.1
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held	1.4	0.3
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold	4	4.5
Defined Benefit Plan, Plan Assets, Business Combination	5.2	4.5
Defined Benefit Plan, Plan Assets, Divestiture	(7.8)	(5.6)
Private Equity Funds [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	3	3.9
Structured Finance [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	78.8	72.9	63.8
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held	5.9	9.1
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold	0	0
Defined Benefit Plan, Plan Assets, Business Combination	0	0
Defined Benefit Plan, Plan Assets, Divestiture	0	0
Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	70.5	65.5	61.9
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held	5.4	4.2
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold	0	(0.1)
Defined Benefit Plan, Plan Assets, Business Combination	0	14.4
Defined Benefit Plan, Plan Assets, Divestiture	(0.4)	(14.9)
Real Estate [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	13.1	12
Structured Credit [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	8.5	7.9
Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	37.2	37.4	40.6
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held	(0.2)	2.5
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold	0	0.4
Defined Benefit Plan, Plan Assets, Business Combination	0	39
Defined Benefit Plan, Plan Assets, Divestiture	0	(45.1)
Hedge Funds [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	11.4	11.4
Fair Value, Inputs, Level 3 [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	36	35.2	33.5
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held	1.6	7.1
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold	0.3	(3.9)
Defined Benefit Plan, Plan Assets, Business Combination	0	24
Defined Benefit Plan, Plan Assets, Divestiture	(1.1)	(25.5)
Fair Value, Inputs, Level 3 [Member] | Private Equity Funds [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	3	3.9	4.3
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held	(0.1)	0.9
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold	0.3	(0.4)
Defined Benefit Plan, Plan Assets, Business Combination	0	1.8
Defined Benefit Plan, Plan Assets, Divestiture	(1.1)	(2.7)
Fair Value, Inputs, Level 3 [Member] | Real Estate [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	13.1	12	11.1
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held	1.1	3.4
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold	0	(2.5)
Defined Benefit Plan, Plan Assets, Business Combination	0	3
Defined Benefit Plan, Plan Assets, Divestiture	0	(3)
Fair Value, Inputs, Level 3 [Member] | Structured Credit [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	8.5	7.9	6.9
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held	0.6	2
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold	0	(1)
Defined Benefit Plan, Plan Assets, Business Combination	0	2.1
Defined Benefit Plan, Plan Assets, Divestiture	0	(2.1)
Fair Value, Inputs, Level 3 [Member] | Hedge Funds [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	11.4	11.4	$ 11.2
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held	0	0.8
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold	0	0
Defined Benefit Plan, Plan Assets, Business Combination	0	17.1
Defined Benefit Plan, Plan Assets, Divestiture	$ 0	$ (17.7)

PENSIONS AND OTHER POSTRETIR_15

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Annual Contributions To The Pension Plans) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Funded Percentage	70.00%
Company contributions	$ 3.8	$ 2.1
Expected company contributions, next fiscal year	$ 3.5
Value of VEBA Trust Assets as a Percentage of the Funding Obligation	0.9
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Company contributions	$ 27.6	24.4
Expected company contributions, next fiscal year	15.9
Direct Payments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Company contributions	3.8	2.1
Expected company contributions, next fiscal year	3.5
Veba Trust [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Company contributions	0	$ 0
Expected company contributions, next fiscal year	$ 0

PENSIONS AND OTHER POSTRETIR_16

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Estimated Net Periodic Benefit Cost) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated net periodic benefit cost	$ 18.7
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated net periodic benefit cost	21.5
Other Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated net periodic benefit cost	$ (2.8)

PENSION AND OTHER POSTRETIREM_2

PENSION AND OTHER POSTRETIREMENT BENEFITS (Estimated Future Benefit Payments) (Details) $ in Millions	Dec. 31, 2018USD ($)
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2,017	$ (70.4)
2,018	(67.9)
2,019	(67.5)
2,020	(67)
2,021	(67.9)
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter	(309.7)
Gross Company Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2,017	(18)
2,018	(17.7)
2,019	(17.2)
2,020	(17)
2,021	(16.9)
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter	(82.2)
Less Medicare Subsidy [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2,017	(0.8)
2,018	(0.8)
2,019	(0.9)
2,020	(0.9)
2,021	(1)
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter	(5.4)
Net Company Payments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2,017	(17.2)
2,018	(16.9)
2,019	(16.3)
2,020	(16.1)
2,021	(15.9)
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter	$ (76.8)

PENSIONS AND OTHER POSTRETIR_17

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Other Potential Benefit Obligations) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 229.1	$ 215.6	$ 202.4
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	687.2	749.8	685.8
Defined Benefit Plan, Benefit Obligation	(905.7)	(973.1)	(931.6)
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(218.5)	(223.3)
Other Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	240.2	262.5	253
Defined Benefit Plan, Benefit Obligation	(241.9)	(265.9)	$ (264.6)
Defined Benefit Plan, Funded (Unfunded) Status of Plan	$ (1.7)	$ (3.4)

PENSIONS AND OTHER POSTRETIR_18

PENSIONS AND OTHER POSTRETIREMENT BENEFITS ( Fair Value of Recurring) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 229.1	$ 215.6	$ 202.4
Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	37.2	37.4	40.6
Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	42.6	39.8	36.1
Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	70.5	65.5	61.9
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	240.2	262.5	253
Other Postretirement Benefit Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	37.8	40
Other Postretirement Benefit Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	36	35.2	33.5
Other Postretirement Benefit Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	166.4	187.3
Other Postretirement Benefit Plan, Defined Benefit [Member] | Fixed Income Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	184.6	204.1
Other Postretirement Benefit Plan, Defined Benefit [Member] | Fixed Income Investments [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	37.8	40
Other Postretirement Benefit Plan, Defined Benefit [Member] | Fixed Income Investments [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefit Plan, Defined Benefit [Member] | Fixed Income Investments [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	146.8	164.1
Other Postretirement Benefit Plan, Defined Benefit [Member] | Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	11.4	11.4
Other Postretirement Benefit Plan, Defined Benefit [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefit Plan, Defined Benefit [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	11.4	11.4	11.2
Other Postretirement Benefit Plan, Defined Benefit [Member] | Hedge Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefit Plan, Defined Benefit [Member] | Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	3	3.9
Other Postretirement Benefit Plan, Defined Benefit [Member] | Private Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefit Plan, Defined Benefit [Member] | Private Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	3	3.9	4.3
Other Postretirement Benefit Plan, Defined Benefit [Member] | Private Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefit Plan, Defined Benefit [Member] | Structured Credit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	8.5	7.9
Other Postretirement Benefit Plan, Defined Benefit [Member] | Structured Credit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefit Plan, Defined Benefit [Member] | Structured Credit [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	8.5	7.9	6.9
Other Postretirement Benefit Plan, Defined Benefit [Member] | Structured Credit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefit Plan, Defined Benefit [Member] | Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	13.1	12
Other Postretirement Benefit Plan, Defined Benefit [Member] | Real Estate [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefit Plan, Defined Benefit [Member] | Real Estate [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	13.1	12	$ 11.1
Other Postretirement Benefit Plan, Defined Benefit [Member] | Real Estate [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefit Plan, Defined Benefit [Member] | Cash [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0.2	0.2
Other Postretirement Benefit Plan, Defined Benefit [Member] | Cash [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefit Plan, Defined Benefit [Member] | Cash [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefit Plan, Defined Benefit [Member] | Cash [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0.2	0.2
Other Postretirement Benefit Plan, Defined Benefit [Member] | U S Small Mid Cap [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	2.4	2.8
Other Postretirement Benefit Plan, Defined Benefit [Member] | U S Small Mid Cap [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefit Plan, Defined Benefit [Member] | U S Small Mid Cap [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefit Plan, Defined Benefit [Member] | U S Small Mid Cap [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	2.4	2.8
Other Postretirement Benefit Plan, Defined Benefit [Member] | International [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	7.3	8.8
Other Postretirement Benefit Plan, Defined Benefit [Member] | International [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefit Plan, Defined Benefit [Member] | International [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefit Plan, Defined Benefit [Member] | International [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	7.3	8.8
Other Postretirement Benefit Plan, Defined Benefit [Member] | U S Large Cap [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	9.7	11.4
Other Postretirement Benefit Plan, Defined Benefit [Member] | U S Large Cap [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefit Plan, Defined Benefit [Member] | U S Large Cap [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Postretirement Benefit Plan, Defined Benefit [Member] | U S Large Cap [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 9.7	$ 11.4

STOCK COMPENSATION PLANS (Narra

STOCK COMPENSATION PLANS (Narrative) (Details) - USD ($)	Apr. 25, 2018	Apr. 23, 2018	Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 09, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense					$ 15,100,000	$ 18,200,000	$ 13,600,000
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense					$ 0	$ 0	0
Performance/vesting period					3 years
Payout rate, as a percentage of the original grant					75.30%
Number of performance shares granted					1,498,386
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized					$ 17,100,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition					1 year
Option Indexed to Issuer's Equity, Strike Price						$ 13.83
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Exercisable Options					563,230
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price					$ 10.42
Common Stock, Shares Authorized					600,000,000	600,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value					$ 6.90	$ 6.79
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payout rate, as a percentage of the original grant					0.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payout rate, as a percentage of the original grant					200.00%
2015 Equity Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares that may be issued (in shares)					12,900,000
Directors Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance/vesting period	1 year	3 years
Deferred Compensation Arrangement with Individual, Fair Value of Shares Issued					$ 100,000	$ 100,000	$ 85,000
A&R 2015 Equity Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares that may be issued (in shares)					15,000,000
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance/vesting period					3 years
Restricted Stock Units (RSUs) [Member] | 2015 Equity Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted shares granted							3,406,716
Restricted Stock Units (RSUs) [Member] | A&R 2015 Equity Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted shares granted					685,599	532,358
Employee Stock Option [Member] | 2012 Equity Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance shares granted				250,000		412,710
Cliffs Natural Resource Inc. 2015 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares that may be issued (in shares)								10,000,000
January 12, 2015 [Member] | Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant Date Market Price			$ 7.70

STOCK COMPENSATION PLANS (Appro

STOCK COMPENSATION PLANS (Approved Grants) (Details) - shares	Feb. 21, 2018	Jun. 26, 2017	Feb. 21, 2017	Dec. 31, 2014	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance shares granted					1,498,386
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance shares granted	675,599	249,106	553,725		675,599	802,831	0
A&R 2015 Equity Plan [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance shares granted					675,599
A&R 2015 Equity Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Issued During Period, Shares, Restricted Stock Award, Gross					685,599	532,358
2015 Equity Plan [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance shares granted					249,106		0
2015 Equity Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Issued During Period, Shares, Restricted Stock Award, Gross							3,406,716
Amended 2015 Equity Plan [Domain] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance shares granted						553,725
Amended 2015 Equity Plan [Domain] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Issued During Period, Shares, Restricted Stock Award, Gross						553,725
2012 Equity Plan [Member] | Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance shares granted				250,000		412,710

STOCK COMPENSATION PLANS (Incen

STOCK COMPENSATION PLANS (Incentive Plan Details) (Details) - shares	Feb. 21, 2018	Jun. 26, 2017	Feb. 21, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance shares granted				1,498,386
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance shares granted	675,599	249,106	553,725	675,599	802,831	0
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Estimated Forfeitures	2,236	0	51,471
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Expected to Vest	673,363	249,106	502,254

STOCK COMPENSATION PLANS (Nonem

STOCK COMPENSATION PLANS (Nonemployee Directors) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Directors Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred Compensation Arrangement with Individual, Fair Value of Shares Issued	$ 100,000	$ 100,000	$ 85,000

STOCK COMPENSATION PLANS (Inc_2

STOCK COMPENSATION PLANS (Incentive Compensation and Other Benefit Plans for Employees and Directors) (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restricted Equity Grant Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Issued During Period Shares Director Stock Award	92,718	93,359	135,038
Deferred Equity Grant Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Issued During Period Shares Director Stock Award	17,170	17,289	29,583

STOCK COMPENSATION PLANS (Sched

STOCK COMPENSATION PLANS (Schedule of Compensation Costs) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Selling, general and administrative expenses									$ (116.8)	$ (102.9)	$ (115.8)
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES									564.7	108.2	110.4
Income Tax Expense (Benefit)									(475.2)	(252.4)	(12.2)
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$ 609.5	$ 437.8	$ 165.1	$ (84.3)	$ 309.9	$ 53.4	$ 31.8	$ (28.1)	$ 1,128.1	$ 367	$ 174.1
Earnings per common share attributable to Cliffs common shareholders - basic:	$ 2.06	$ 1.47	$ 0.55	$ (0.29)	$ 1.04	$ 0.18	$ 0.10	$ (0.11)	$ 3.80	$ 1.28	$ 0.88
Earnings per common share attributable to Cliffs common shareholders - diluted:	$ 1.98	$ 1.41	$ 0.55	$ (0.29)	$ 1.03	$ 0.18	$ 0.10	$ (0.11)	$ 3.71	$ 1.26	$ 0.87
Deferred Compensation, Share-based Payments [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Costs and Expenses									$ 1.7	$ 1.9	$ 1.8
Selling, general and administrative expenses									(13.4)	(16.3)	(11.8)
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES									15.1	18.2	13.6
Income Tax Expense (Benefit)									0	0	0
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS									$ 15.1	$ 18.2	$ 13.6
Earnings per common share attributable to Cliffs common shareholders - basic:									$ 0.05	$ 0.06	$ 0.07
Earnings per common share attributable to Cliffs common shareholders - diluted:									$ 0.05	$ 0.06	$ 0.07

STOCK COMPENSATION PLANS (Outst

STOCK COMPENSATION PLANS (Outstanding Employee Awards) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	6,792,201	7,224,665
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 6.90	$ 6.79
Number of performance shares granted	1,498,386
Fair Value	$ 9.51
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	(1,181,460)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	$ 7.38
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(749,390)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$ 10.22

STOCK COMPENSATION PLANS (Share

STOCK COMPENSATION PLANS (Share Based Compensation Arrangement by Share-based Payment Award) (Details) - $ / shares	Feb. 21, 2018	Jun. 26, 2017	Feb. 21, 2017	Mar. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option Indexed to Issuer's Equity, Strike Price						$ 13.83
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number					6,792,201	7,224,665
Number of performance shares granted					1,498,386
Share Based Goods And Nonemployee Services Transaction Valuation Method Payout Rate					75.30%
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period					(1,181,460)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period					(749,390)
Common Stock, Capital Shares Reserved for Future Issuance					13,451,798
Fair Value					$ 9.51
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Exercisable Options					563,230
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price					$ 10.42
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number					563,230	599,870	599,870	607,489
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period					36,640	0	0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period					0	0	(7,619)
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number					4,804,248	4,776,483	5,461,783	2,338,070
Number of performance shares granted					795,487	1,196,731	3,571,337
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period					(627,567)	(1,813,315)	(271,988)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period					(140,155)	(68,716)	(175,636)
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number					1,424,723	1,848,312	1,368,469	1,496,489
Number of performance shares granted	675,599	249,106	553,725		675,599	802,831	0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period					(489,953)	0	(59,260)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period					(609,235)	(322,988)	(68,760)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested or Expected to Vest, Outstanding, Number					6,792,201
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Estimated Forfeitures	2,236	0	51,471
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Expected to Vest	673,363	249,106	502,254
Fair Value	$ 11.93	$ 10.74	$ 19.69
Directors Retainer and Voluntary Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number					0	0	0	0
Number of performance shares granted					27,300	25,476	0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period					(27,300)	(25,476)	0
January 12, 2015 [Member] | Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant Date Market Price				$ 7.70
Employee Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock, Capital Shares Reserved for Future Issuance					12,949,420
Directors Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock, Capital Shares Reserved for Future Issuance					502,378

INCOME TAXES (Narrative) (Detai

INCOME TAXES (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, Domestic	$ 3,600
Income Tax Expense (Benefit)	(475.2)	$ (252.4)	$ (12.2)
Unrecognized Tax Benefits	29	33.5	$ 30.7	$ 156.2
Undistributed Earnings of Foreign Subsidiaries	0	0
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	38.3	4,200
Deferred Tax Assets, Operating Loss Carryforwards, Foreign	$ 6,600	7,200
Document Fiscal Year Focus	2,018
Cumulative Loss Position, Period	3 years
Deferred Tax Assets, Tax Credit Carryforwards, Foreign		$ 5.8
Valuation Allowance, Deferred Tax Asset, Change in Amount	$ 695.8
Estimated Taxable Income to Fully Utilize Deferred Tax Assets	$ 109
Effective Income Tax Rate, Continuing Operations	(84.10%)	(233.30%)	(11.10%)
Deferred Tax Liabilities, Intercompany Notes	$ (465.7)	$ (465.7)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	$ 0	407.5	$ 149.1
Tax Cuts And Jobs Act, Change In Tax Rate, Deferred Tax Asset, Income Tax Expense		$ 334.1
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent	0.00%	441.70%	(36.80%)
United States [Member]
Income Tax Contingency [Line Items]
Valuation Allowance, Deferred Tax Asset, Change in Amount	$ 500
LUXEMBOURG
Income Tax Contingency [Line Items]
Valuation Allowance, Deferred Tax Asset, Change in Amount	1,200
Deferred Tax Liabilities, Intercompany Notes	161.7
Tax law change, remeasurement, amount		$ 73.4
Other Noncurrent Assets [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	24.8	27.4
Other Liabilities [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	4.2	6.1
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	$ 2.7	$ 2.1
Minimum [Member]
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent	0.00%
Maximum [Member]
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent	29.22%

INCOME TAXES (SCHEDULE OF INCOM

INCOME TAXES (SCHEDULE OF INCOME BEFORE INCOME TAXES) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Domestic	$ 565	$ 90.7	$ 124.9
Income (Loss) from Continuing Operations before Income Taxes, Foreign	(0.3)	17.5	(14.5)
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	$ 564.7	$ 108.2	$ 110.4

INCOME TAXES (Schedule of Compo

INCOME TAXES (Schedule of Components of Income Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Current Federal Tax Expense (Benefit)	$ (0.5)	$ (252.6)	$ (11.1)
Current State and Local Tax Expense (Benefit)	0	(0.1)	(0.5)
Current Foreign Tax Expense (Benefit)	0.7	0.3	(0.1)
Current Income Tax Expense (Benefit)	0.2	(252.4)	(11.7)
Deferred Federal Income Tax Expense (Benefit)	(475.4)	0	(0.5)
Deferred Income Tax Expense (Benefit)	(460.5)	0	0
Income Tax Expense (Benefit)	$ (475.2)	$ (252.4)	$ (12.2)

INCOME TAXES (Schedule of Effec

INCOME TAXES (Schedule of Effective Rate Reconciliation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount	$ 118.6	$ 37.9	$ 38.6
Effective Income Tax Rate Reconciliation, Percent	(84.10%)	(233.30%)	(11.10%)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	$ 0	$ 407.5	$ 149.1
Impact Of Tax Law Change Percent	0.00%	376.60%	135.10%
Effective Income Tax Rate Reconciliation, Disposition of Business, Amount	$ 161.7	$ 0	$ 0
Effective Income Tax Rate Reconciliation, Disposition of Business, Percent	28.60%	0.00%	0.00%
Prior year adjustments made in current year, amount	$ (1)	$ (1.1)	$ (11.8)
Income Tax Reconciliation Tax Deduction for percentage depletion in excess of cost depletion	$ (54.6)	$ (61.6)	$ (36.1)
Income Tax Reconciliation Tax Deduction for percentage depletion in excess of cost depletion percent	(9.70%)	(56.90%)	(32.70%)
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Amount	$ 0.1	$ 477.9	$ (40.6)
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent	0.00%	441.70%	(36.80%)
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	35.00%	35.00%
Tax Adjustments, Settlements, and Unusual Provisions	$ (1.3)	$ (1.4)	$ (11.3)
Tax Adjustments Settlements And Unusual Provisions Percent	(0.20%)	(1.30%)	(10.20%)
Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Percent	(0.20%)	(1.00%)	(10.70%)
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount	$ 3.1	$ 1	$ (9.8)
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent	0.60%	0.90%	(8.90%)
Income Tax Expense (Benefit)	$ (475.2)	$ (252.4)	$ (12.2)
Worthless Stock Deduction, Amount	$ 0	$ 0	$ (73.4)
Worthless Stock Deduction, Percent	0.00%	0.00%	(66.50%)
Tax Law Change [Member]
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount	$ 0	$ (407.5)	$ (149.1)
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent	0.00%	(376.60%)	(135.10%)
Current year activity [Member]
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount	$ (80.6)	$ (466.3)	$ 122.9
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent	(14.30%)	(431.00%)	111.30%
valuation allowance reversal [Member]
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount	$ (460.5)	$ 0	$ 0
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent	(81.50%)	0.00%	0.00%
Repeal of AMT [Member]
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount	$ 0	$ (235.3)	$ 0
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent	0.00%	(217.50%)	0.00%
Dissolution of entities [Member]
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount	$ (161.7)	$ 0	$ 0
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent	(28.60%)	0.00%	0.00%
Prior year adjustment in current year [Member]
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount	$ 1	$ (3.5)	$ 9.3
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent	0.20%	(3.20%)	8.40%

INCOME TAXES (Income Taxes for

INCOME TAXES (Income Taxes for Other than Continuing Operations) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax	$ 3.6	$ 0	$ 0
Other Comprehensive Income Unrealized Gain Loss On Mark To Market Adjustments Arising During Period Tax	0.7	0	0
Other Comprehensive Income (Loss), Other Tax	0	0	0.5
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent	$ 4.3	$ 0	$ 0.5

INCOME TAXES (Schedule of Defer

INCOME TAXES (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Income Tax Contingency [Line Items]
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Pensions	$ 77.5	$ 76.3
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Postretirement Benefits	25.3	25.6
Deferred Tax Assets, Deferred Income	23.3	24.2
Deferred Tax Assets, Goodwill and Intangible Assets	11.6	13
Deferred Tax Assets, Operating Loss Carryforwards	2,118.8	2,362.4
Deferred Tax Assets, Property, Plant and Equipment	13.3	0
Deferred Tax Assets, State Taxes	68.2	74.2
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Other	36.8	30.4
Deferred Tax Assets, Gross	2,374.8	2,606.1
Deferred Tax Assets, Valuation Allowance	(1,287.3)	(1,983.1)
Deferred Tax Assets, Net of Valuation Allowance	1,087.5	623
Deferred Tax Liabilities, Property, Plant and Equipment	0	(1.5)
Deferred Tax Liabilities Investment In Ventures	(141.2)	(137.5)
Deferred Tax Liabilities, Intercompany Notes	465.7	465.7
Deferred Tax Liabilities Other Assets	(15.8)	(18.3)
Deferred Tax Liabilities, Net	(622.7)	(623)
Deferred Tax Assets, Net	$ 464.8	$ 0

INCOME TAXES (Schedule of Def_2

INCOME TAXES (Schedule of Deferred Tax Assets and Liabilities by Location) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Income Tax Contingency [Line Items]
Deferred Tax Assets, Net	$ 464.8	$ 0

INCOME TAXES (Schedule of Unrec

INCOME TAXES (Schedule of Unrecognized Tax Benefits Rollforward) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	$ 29	$ 33.5	$ 30.7	$ 156.2
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions	0.1
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions		(2.8)	(61)
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions	3.6	4.5	0.2
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities	0		64.7
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities		1
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	(8.2)	0	0
Other Increases decreases to unrecognized tax benefits	$ 0	$ 0.1	$ 0

ENVIRONMENTAL AND MINE CLOSUR_3

ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018
Site Contingency [Line Items]
Accrual for Environmental Loss Contingencies	$ 2.9	$ 2.5
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current And Noncurrent	171.3	$ 174.9
Accrual for Environmental Loss Contingencies, Period Increase (Decrease)	$ (26.2)

ENVIRONMENTAL AND MINE CLOSUR_4

ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Summary Of Mine Closure Obligations) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Environmental	$ 2.5	$ 2.9
Asset Retirement Obligation	172.4	168.4	$ 187.8
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current And Noncurrent	174.9	171.3
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current	2.9	3.6
Environmental Loss Contingency And Mine Reclamation And Closing Liability Noncurrent	172	167.7
Mining and Pelletizing [Member]
Loss Contingencies [Line Items]
Asset Retirement Obligation	$ 172.4	$ 168.4

ENVIRONMENTAL AND MINE CLOSUR_5

ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Asset Retirement Obligation Disclosure) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accrual for Environmental Loss Contingencies	$ 2.5	$ 2.9
Asset Retirement Obligation	172.4	168.4	$ 187.8
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current And Noncurrent	174.9	171.3
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current	2.9	3.6
Environmental Loss Contingency And Mine Reclamation And Closing Liability Noncurrent	172	167.7
Asset Retirement Obligation, Accretion Expense	9.5	13.9
Asset Retirement Obligation, Liabilities Settled	(1)	(5.6)
Asset Retirement Obligation, Revision of Estimate	(4.5)	(27.7)
Mining and Pelletizing [Member]
Asset Retirement Obligation	$ 172.4	$ 168.4

DERIVATIVE INSTRUMENTS AND HE_3

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)galMMcf	Dec. 31, 2017USD ($)galMMcf	Dec. 31, 2016USD ($)
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 422.6	$ 119.3	$ 57.8
Derivative asset, fair value	91.5	37.9
Derivative liability, fair value	3.7	2
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative asset, fair value	91.4	37.9
Derivative liability, fair value	0	1.7
Provisional Pricing Arrangements [Member] | Product Revenues [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ (3.2)	$ (42.7)	$ 14.2
Natural Gas [Member]
Derivative [Line Items]
Natural Gas Hedges | MMcf	1,800,000	3,500,000
Energy Related Derivative [Member]
Derivative [Line Items]
Natural Gas Hedges | gal	11,000,000	0
Valuation, Market Approach [Member] | Fair Value, Inputs, Level 3 [Member] | Customer Supply Agreement [Member] | Not Designated as Hedging Instrument [Member] | Other Current Assets [Member]
Derivative [Line Items]
Derivative asset, fair value	$ 89.3	$ 37.9
Valuation, Market Approach [Member] | Fair Value, Inputs, Level 3 [Member] | Provisional Pricing Arrangements [Member] | Not Designated as Hedging Instrument [Member] | Other Current Assets [Member]
Derivative [Line Items]
Derivative asset, fair value	2.1	0
Valuation, Market Approach [Member] | Fair Value, Inputs, Level 3 [Member] | Provisional Pricing Arrangements [Member] | Not Designated as Hedging Instrument [Member] | Other Current Liabilities [Member]
Derivative [Line Items]
Derivative liability, fair value	$ 0	$ 1.7

DERIVATIVE INSTRUMENTS AND HE_4

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Schedule Of Derivative Instruments In Statement Of Financial Position, Fair Value) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative asset, fair value	$ 91.5	$ 37.9
Derivative liability, fair value	3.7	2
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value	91.4	37.9
Derivative liability, fair value	0	1.7
Valuation, Market Approach [Member] | Fair Value, Inputs, Level 2 [Member] | Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value	0.1	0
Valuation, Market Approach [Member] | Fair Value, Inputs, Level 2 [Member] | Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liability, fair value	3.7	0.3
Valuation, Market Approach [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Customer Supply Agreement [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value	89.3	37.9
Valuation, Market Approach [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value	2.1	0
Valuation, Market Approach [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liability, fair value	$ 0	$ 1.7

DERIVATIVE INSTRUMENTS AND HE_5

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Schedule Of Derivatives Not Designated As Hedging Instruments) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 422.6	$ 119.3	$ 57.8
Customer Supply Agreements [Member] | Product Revenues [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	425.8	163.3	41.7
Provisional Pricing Arrangements [Member] | Product Revenues [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(3.2)	(42.7)	14.2
Commodity Contract [Member] | Cost of goods sold and operating expenses [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 0	$ (1.3)	$ 1.9

DISCONTINUED OPERATIONS Schedul

DISCONTINUED OPERATIONS Schedule of Disposal Groups, including Discontinued Operations, Income Statement, Balance Sheet and Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
INCOME FROM DISCONTINUED OPERATIONS, net of tax	$ 88.2	$ 2.5	$ 76.7
Current assets of discontinued operations	12.4	118.5		$ 118.5
Non-current assets of discontinued operations	0	20.3		20.3
Current liabilities of discontinued operations	6.7	75		75
Non-current liabilities of discontinued operations	8.3	52.2		$ 52.2
Net cash provided (used) by operating activities	478.5	338.1	303
Net cash provided (used) by investing activities	(273.1)	(156)	(57.9)
Asia Pacific Iron Ore [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
INCOME FROM DISCONTINUED OPERATIONS, net of tax	118.3	21.2	96.6
Current assets of discontinued operations	12.4	118.5
Non-current assets of discontinued operations	0	20.3
Current liabilities of discontinued operations	3.8	71.8
Non-current liabilities of discontinued operations	8.3	52.2
North American Coal [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
INCOME FROM DISCONTINUED OPERATIONS, net of tax	(3.6)	2.6	(2.4)
Current assets of discontinued operations	0	0
Non-current assets of discontinued operations	0	0
Current liabilities of discontinued operations	2.9	3.2
Non-current liabilities of discontinued operations	0	0
Canadian Entities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
INCOME FROM DISCONTINUED OPERATIONS, net of tax	(26.5)	(21.3)	(17.5)
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net cash provided (used) by operating activities	(95.9)	79.6	99.8
Net cash provided (used) by investing activities	19.8	(8.4)	10
Discontinued Operations [Member] | Asia Pacific Iron Ore [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net cash provided (used) by operating activities	(81.3)	79.6	99.8
Net cash provided (used) by investing activities	19.8	(2.8)	(0.4)
Discontinued Operations [Member] | North American Coal [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net cash provided (used) by investing activities	0	2.1	3.6
Discontinued Operations [Member] | Canadian Entities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net cash provided (used) by operating activities	(14.6)	0	0
Net cash provided (used) by investing activities	$ 0	$ (7.7)	$ 6.8

DISCONTINUED OPERATIONS DISCONT

DISCONTINUED OPERATIONS DISCONTINUED OPERATIONS Schedule of Disposal Groups, including Discontinued Operations, Income Statement - Asia Pacific Iron Ore (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
INCOME FROM DISCONTINUED OPERATIONS, net of tax	$ 88.2	$ 2.5	$ 76.7
Asia Pacific Iron Ore [Member]
Revenues from product sales and services	129.1	464.2	554.5
Cost of goods sold and operating expenses	230.7	427.9	440.9
Sales margin	(101.6)	36.3	113.6
Other operating expense	3.3	9.9	10.4
Other expense	2.3	5.2	6.6
Gain on foreign currency translation	228.1	0	0
Impairment of long-lived assets	2.6	0	0
INCOME FROM DISCONTINUED OPERATIONS, net of tax	$ 118.3	$ 21.2	$ 96.6

DISCONTINUED OPERATIONS DISCO_2

DISCONTINUED OPERATIONS DISCONTINUED OPERATIONS Schedule of Disposal Groups, including Discontinued Operations, Assets and Liabilities - Asia Pacific Iron Ore (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Current assets of discontinued operations	$ 12.4	$ 118.5	$ 118.5
Current liabilities of discontinued operations	6.7	$ 75	75
Asia Pacific Iron Ore [Member]
Disposal Group, Including Discontinued Operation, Cash and Cash Equivalents	12.4		29.4
Disposal Group, Including Discontinued Operation, Accounts Receivable, Net	0		33.9
Disposal Group, Including Discontinued Operation, Inventory	0		45
Disposal group, including Discontinued Operations, Supplies and other inventories	0		5.1
Disposal Group, Including Discontinued Operation, Other Assets, Current	0		5.1
Current assets of discontinued operations	12.4		118.5
Disposal Group, Including Discontinued Operation, Property, Plant and Equipment	0		17.2
Disposal Group, Including Discontinued Operation, Other Assets, Noncurrent	0		3.1
Disposal Group, Including Discontinued Operation, Assets	12.4		138.8
Disposal Group, Including Discontinued Operation, Accounts Payable	3.4		28.2
Disposal Group, Including Discontinued Operation, Accrued Liabilities	0.4		28
Disposal Group, Including Discontinued Operation, Other Liabilities, Current	0		15.6
Current liabilities of discontinued operations	3.8		71.8
Disposal Group, Including Discontinued Operations, Environmental and mine closure obligations	0		28.8
Disposal Group, Including Discontinued Operation, Other Liabilities	8.3		23.4
Disposal Group, Including Discontinued Operation, Liabilities	$ 12.1		$ 124

DISCONTINUED OPERATIONS (Narrat

DISCONTINUED OPERATIONS (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018CAD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jun. 29, 2018USD ($)	Jan. 01, 2018USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Foreign Currency Translation Gains (Losses)	$ 228,100,000
Cash Contribution		$ 19
Cost Method Investments					$ 0
Loans to and accounts receivables from the Canadian Entities	0		$ 51,600,000			$ 51,600,000
Contingent claims	0		55,600,000			$ 55,600,000
Short-term loan receivable			7,700,000
INCOME FROM DISCONTINUED OPERATIONS, net of tax	88,200,000		2,500,000	$ 76,700,000
Canadian Entities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax benefit (expense)	(15,900,000)		0	0
Cost Method Investments			0
Loans to and accounts receivables from the Canadian Entities			51,600,000
Contingent Liabilities recognized in Consolidated Financials				37,200,000
INCOME FROM DISCONTINUED OPERATIONS, net of tax	(26,500,000)		(21,300,000)	(17,500,000)
North American Coal [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax benefit (expense)	1,000,000		0	0
INCOME FROM DISCONTINUED OPERATIONS, net of tax	$ (3,600,000)		2,600,000	$ (2,400,000)
Wabush Scully Mine Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
INCOME FROM DISCONTINUED OPERATIONS, net of tax			$ 31,400,000

DISCONTINUED OPERATIONS PreTax

DISCONTINUED OPERATIONS PreTax Exit Costs (Details) - Canadian Entities [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
PreTax Exit Costs [Line Items]
Investment impairment on deconsolidation	$ (67.5)	$ 3	$ (17.5)
Guarantees and contingent liabilities	41	(24.3)	0
Total loss from deconsolidation	$ (26.5)	$ (21.3)	$ (17.5)

CAPITAL STOCK (Details)

CAPITAL STOCK (Details)	1 Months Ended	3 Months Ended		12 Months Ended
	Feb. 01, 2016shares	Mar. 31, 2018USD ($)	Sep. 30, 2016USD ($)	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)shares	Nov. 26, 2018USD ($)	Oct. 18, 2018$ / shares	Feb. 09, 2017$ / sharesshares	Aug. 10, 2016$ / sharesshares
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount							$ 200,000,000
Stock Repurchased During Period, Shares | shares				5,400,000
Repurchase of common shares				$ (47,500,000)	$ 0	$ 0
Stock Repurchase Program, Average Price | $ / shares				$ 8.78
Stock Repurchase Program, Remaining Authorized Repurchase Amount				$ 152,700,000
Dividends Payable				15,000,000
Common Stock, New Shares, Issued | shares									63,250,000	44,400,000
Shares Issued, Price Per Share | $ / shares									$ 10.75	$ 6.75
Net proceeds from issuance of common shares				0	661,300,000	$ 287,400,000
Debt Extinguished				$ 227,400,000	$ 1,610,700,000
Trading Day Window Determining Number of Common Shares Issuable on Conversion	20
Common shares, issued (in shares) | shares				301,886,794	301,886,794
Common Shares Issued in Debt to Equity Exchange | shares						8,200,000
Gain (loss) on extinguishment/restructuring of debt				$ (6,800,000)	$ (165,400,000)	$ 166,300,000
Common Stock [Member]
Class of Stock [Line Items]
Dividends payable, per share | $ / shares								$ 0.05
Common shares, issued (in shares) | shares	26,500,000
Convertible Preferred Stock, Common Shares Issued Upon Conversion | shares	25,200,000
Convertible Preferred Stock, Common Shares Issued Upon Conversion in Lieu of Dividend | shares	1,300,000
Exchange of Debt for Equity [Member]
Class of Stock [Line Items]
Gain (loss) on extinguishment/restructuring of debt						11,300,000
$500 Million 3.95% 2018 Senior Notes [Member]
Class of Stock [Line Items]
Debt Instrument, Face Amount Exchanged						$ 17,600,000
Debt Instrument, Interest Rate, Stated Percentage						3.95%
Gain (loss) on extinguishment/restructuring of debt			$ 19,900,000			$ 1,800,000
$500 Million 3.95% 2018 Senior Notes [Member] | Exchange of Debt for Equity [Member]
Class of Stock [Line Items]
Debt Instrument, Face Amount Exchanged						10,000,000
$218.5 Million 8.00% 2020 1.5 Lien Notes
Class of Stock [Line Items]
Debt Extinguished					$ 218,500,000
Debt Instrument, Face Amount Exchanged						$ 512,200,000
Debt Instrument, Interest Rate, Stated Percentage					8.00%	8.00%
Gain (loss) on extinguishment/restructuring of debt					$ 45,100,000	$ 174,300,000
$218.5 Million 8.00% 2020 1.5 Lien Notes | Exchange of Debt for Equity [Member]
Class of Stock [Line Items]
Debt Instrument, Face Amount Exchanged						20,100,000
$544.2 Million 7.75% 2020 Second Lien Notes
Class of Stock [Line Items]
Debt Extinguished					$ 430,100,000
Debt Instrument, Face Amount Exchanged						114,100,000
Debt Instrument, Interest Rate, Stated Percentage					7.75%
Gain (loss) on extinguishment/restructuring of debt					$ (104,500,000)	6,900,000
$700 Million 4.875% 2021 Senior Notes
Class of Stock [Line Items]
Debt Extinguished				$ 14,400,000	$ 171,000,000
Debt Instrument, Face Amount Exchanged						$ 76,300,000
Debt Instrument, Interest Rate, Stated Percentage				4.875%	4.875%	4.875%
Gain (loss) on extinguishment/restructuring of debt				$ 100,000	$ (2,800,000)	$ 33,300,000
$700 Million 4.875% 2021 Senior Notes | Exchange of Debt for Equity [Member]
Class of Stock [Line Items]
Debt Instrument, Face Amount Exchanged						26,800,000
$1.075 Billion 5.75% 2025 Senior Notes [Member]
Class of Stock [Line Items]
Proceeds from Issuance of Debt		$ 500,000,000
Debt Instrument, Interest Rate, Stated Percentage				5.75%
Secured Debt [Member]
Class of Stock [Line Items]
Debt Extinguished				$ 648,600,000
Unsecured Debt [Member]
Class of Stock [Line Items]
Debt Extinguished				422,200,000
$540 Million 8.25% 2020 First Lien Notes
Class of Stock [Line Items]
Debt Extinguished		$ 35,600,000			$ 540,000,000
Debt Instrument, Interest Rate, Stated Percentage					8.25%
Gain (loss) on extinguishment/restructuring of debt					$ (93,500,000)
$400 Million 5.90% 2020 Senior Notes
Class of Stock [Line Items]
Debt Extinguished				$ 88,900,000	$ 136,700,000
Debt Instrument, Face Amount Exchanged						65,100,000
Debt Instrument, Interest Rate, Stated Percentage				5.90%	5.90%
Gain (loss) on extinguishment/restructuring of debt				$ (3,300,000)	$ (7,800,000)	28,300,000
$500 Million 4.80% 2020 Senior Notes
Class of Stock [Line Items]
Debt Extinguished				$ 122,400,000	$ 114,400,000
Debt Instrument, Face Amount Exchanged						$ 44,700,000
Debt Instrument, Interest Rate, Stated Percentage				4.80%	4.80%	4.80%
Gain (loss) on extinguishment/restructuring of debt				$ (3,700,000)	$ (1,900,000)	$ 19,500,000

ACCUMULATED OTHER COMPREHENSI_2

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) Accumulated Other Comprehensive Income (Loss) and Related Tax Effects (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss), Before Taxes	$ (411.6)	$ (162.4)	$ (144.7)
Accumulated Other Comprehensive Income (Loss), Tax	127.7	123.4	123.4
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	(2.8)	(0.5)	0	$ 2.6
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	0	225.4	239.3	220.7
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax	(281.1)	(263.9)	(260.6)	(241.4)
Accumulated other comprehensive loss	283.9	39	21.3	$ 18
Postretirement Benefit Liability [Member]
Accumulated Other Comprehensive Income (Loss), Before Taxes	(408.1)	(387.3)	(384)
Accumulated Other Comprehensive Income (Loss), Tax	127	123.4	123.4
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss), Before Taxes		225.4	239.3
Accumulated Other Comprehensive Income (Loss), Tax		0	$ 0
Unrealized Gain Loss On Derivatives [Member]
Accumulated Other Comprehensive Income (Loss), Before Taxes	(3.5)	(0.5)
Accumulated Other Comprehensive Income (Loss), Tax	$ 0.7	$ 0

ACCUMULATED OTHER COMPREHENSI_3

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax	$ (281.1)	$ (263.9)	$ (260.6)	$ (241.4)
Accumulated Other Comprehensive Income (Loss), Debt Securities, Available-for-sale, Adjustment, after Tax			0	0.1
Accumulated other comprehensive loss	(283.9)	(39)	(21.3)	(18)
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	0	225.4	239.3	220.7
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	(2.8)	(0.5)	0	$ 2.6
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	17.2	(11.5)	19.8
Changes in foreign currency translation	(225.4)	(13.9)	18.6
OTHER COMPREHENSIVE INCOME	(244.9)	(2.9)	(3.8)
Accumulated Other Comprehensive Income (Loss) [Member]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(40.8)	(44.2)	(29.8)
Gain on foreign currency translation	(204.1)	26.5	26.5
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(0.6)	(0.5)	(3.3)
Gain on foreign currency translation	(1.7)	0	0.7
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	2.7	(13.9)	18.4
Gain on foreign currency translation	(228.1)	0	0.2
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(42.9)	(29.8)	(44.8)
Gain on foreign currency translation	$ 25.7	$ 26.5	25.6
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			(0.1)
Gain on foreign currency translation			$ 0

ACCUMULATED OTHER COMPREHENSI_4

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) Details of Accumulated Other Comprehensive Income (Loss) Components (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Accumulated other comprehensive loss	$ (283.9)	$ (39)	$ (21.3)	$ (18)
Other Comprehensive Income (Loss), Foreign Currency Translation, Dissolution of Entity	0	0	0.2
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	(1.7)	0	1.2
Gain on foreign currency translation	(204.1)	26.5	26.5
Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(40.8)	(44.2)	(29.8)
Gain on foreign currency translation	(204.1)	26.5	26.5
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(0.6)	(0.5)	(3.3)
Gain on foreign currency translation	(1.7)	0	0.7
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	2.7	(13.9)	18.4
Gain on foreign currency translation	(228.1)	0	0.2
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(42.9)	(29.8)	(44.8)
Gain on foreign currency translation	25.7	26.5	25.6
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of prior service (cost) credit	0.8	0.4	1.5
Defined Benefit Plan, Amortization of Gain (Loss)	26.2	26.9	27.1
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment	0.3	0	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax	25.7	26.5	25.6
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			(0.1)
Gain on foreign currency translation			0
Foreign Currency Translation Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	(228.1)	0	0.2
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax	(228.1)	0	0
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]
TaxOnDerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoEarnings	0	0	(0.5)
Derivative, Gain (Loss) on Derivative, Net	(1.7)	0	0.7
T-Lock Amortization [Member] | 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	0	1.2
Australian Hedge Contracts [Member] | 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	$ (1.7)	$ 0	$ 0

CASH FLOW INFORMATION (Narrativ

CASH FLOW INFORMATION (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Oct. 18, 2018
Dividends Payable [Line Items]
Capital Expenditure, Discontinued Operations	$ 0.1	$ 2.8	$ 0.2
Interest Paid, Capitalized, Investing Activities	6.5
Dividends Payable	$ 15
Common Stock [Member]
Dividends Payable [Line Items]
Dividends payable, per share				$ 0.05

CASH FLOW INFORMATION (Reconcil

CASH FLOW INFORMATION (Reconciliation Of Capital Additions To Cash Paid For Capital Expenditures) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Information [Abstract]
Property, Plant and Equipment, Additions, Including Discontinued Operations	$ 394.8	$ 156	$ 68.5
Non-cash accruals	(93.6)	2.2	0.6
Capital leases	(7.6)	(6.5)	0
Government grant rebate	(2.5)	0	0
Payments To Acquire Property Plant And Equipment Net	$ 296.1	$ 151.7	$ 69.1

CASH FLOW INFORMATION (Cash Pai

CASH FLOW INFORMATION (Cash Paid for Income Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Information [Abstract]
Income Taxes Paid	$ 2.9	$ 1.7	$ 5.9
Proceeds from Income Tax Refunds	(11.3)	(7.8)	(5.3)
Interest Paid, Including Capitalized Interest, Operating and Investing Activities	$ 105.7	$ 139	$ 184

RELATED PARTIES (Narrative) (De

RELATED PARTIES (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)Facility	Dec. 31, 2017USD ($)installment
Segment Reporting Information [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent	100.00%
Due to Related Parties, Current	$ 1.8	$ 12.3
Acquisition of Noncontrolling Interest		$ (105)
Mining and Pelletizing [Member]
Segment Reporting Information [Line Items]
Number Of Mines | Facility	4
Joint Venture Partners [Member] | Mining and Pelletizing [Member]
Segment Reporting Information [Line Items]
Number Of Mines | Facility	1
Empire [Member]
Segment Reporting Information [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent		100.00%
Increase in Ownership Equity		21.00%
Distribution of Noncontrolling Interest		$ 132.7
Noncontrolling Interest Purchase, Number Of Installment Payments | installment		3
Stockholders' Equity, Period Increase (Decrease)		$ (12.1)
Acquisition of Noncontrolling Interest		$ (116.7)
Other Liabilities [Member] | Empire [Member]
Segment Reporting Information [Line Items]
Noncontrolling Interest Purchase, Installment Amount	$ 44.2
Other Noncurrent Liabilities [Member] | Empire [Member]
Segment Reporting Information [Line Items]
Noncontrolling Interest Purchase, Installment Amount	$ 44.2

RELATED PARTIES (Summary Of Oth

RELATED PARTIES (Summary Of Other Ownership Interests) (Details)	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent	100.00%
Hibbing [Member] | Arcelor Mittal [Member]
Related Party Transaction [Line Items]
Ownership interest, equity method investment	62.30%
Hibbing [Member] | U. S. Steel Canada [Member]
Related Party Transaction [Line Items]
Ownership interest, equity method investment	14.70%
Empire [Member]
Related Party Transaction [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent		100.00%
Tilden [Member]
Related Party Transaction [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent		100.00%
Investments in Ventures [Member] | Hibbing [Member]
Related Party Transaction [Line Items]
Ownership interest, equity method investment	23.00%

RELATED PARTIES (Summary Of Rel

RELATED PARTIES (Summary Of Related Party Transactions Table Disclosure) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Product revenues from related parties	$ 1,234.5	$ 806.7	$ 830.1
Product revenues	$ 2,172.3	$ 1,644.6	$ 1,379.7
Related party product revenue as a percent of total product revenue	56.80%	49.10%	60.20%

RELATED PARTIES (Summary of Bal

RELATED PARTIES (Summary of Balance Sheet Presentation) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Short-term Notes Payable	$ (43.5)	$ (44.2)	$ (44.2)
Due to Related Parties, Current	(1.8)		(12.3)
Due to Related Parties, Noncurrent	0		(41.4)
Related Party Transaction, Due from (to) Related Party	220		8.1
Trade Accounts Receivable [Member]
Related Party Transaction [Line Items]
Due from Related Parties, Current	176		68.1
Derivative [Member]
Related Party Transaction [Line Items]
Due from Related Parties, Current	$ 89.3		$ 37.9

EARNINGS PER SHARE (Earnings Pe

EARNINGS PER SHARE (Earnings Per Share Computation) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
INCOME FROM CONTINUING OPERATIONS					$ 333,000,000	$ 22,300,000	$ 83,800,000	$ (78,500,000)	$ 1,039,900,000	$ 360,600,000	$ 122,600,000
Net Income (Loss) Attributable to Noncontrolling Interest									0	(3,900,000)	25,200,000
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Noncontrolling Interest					0	500,000	1,700,000	1,700,000
Income (Loss) from Continuing Operations Attributable to Parent	$ 624,100,000	$ 199,800,000	$ 229,400,000	$ (13,400,000)	333,000,000	22,800,000	85,500,000	(76,800,000)	1,039,900,000	364,500,000	97,400,000
INCOME FROM DISCONTINUED OPERATIONS, net of tax									88,200,000	2,500,000	76,700,000
INCOME FROM DISCONTINUED OPERATIONS, net of tax	(14,600,000)	238,000,000	(64,300,000)	(70,900,000)	(23,100,000)	30,600,000	(53,700,000)	48,700,000	88,200,000	2,500,000	76,700,000
Net income attributable to Cliffs shareholders	$ 609,500,000	$ 437,800,000	$ 165,100,000	$ (84,300,000)	$ 309,900,000	$ 53,400,000	$ 31,800,000	$ (28,100,000)	$ 1,128,100,000	$ 367,000,000	$ 174,100,000
Weighted average number of shares:
Basic									297,200,000	288,400,000	197,700,000
$316.5 million 1.50% 2025 Convertible Senior Notes									3,400,000	0	0
Employee stock plans									3,500,000	4,600,000	2,400,000
Diluted									304,100,000	293,000,000	200,100,000
Earnings per common share attributable to Cliffs common shareholders - basic:
Continuing operations	$ 2.11	$ 0.67	$ 0.77	$ (0.05)	$ 1.12	$ 0.08	$ 0.28	$ (0.29)	$ 3.50	$ 1.27	$ 0.49
Discontinued operations	(0.05)	0.80	(0.22)	(0.24)	(0.08)	0.10	(0.18)	0.18	0.30	0.01	0.39
Earnings per common share attributable to Cliffs common shareholders - basic:	2.06	1.47	0.55	(0.29)	1.04	0.18	0.10	(0.11)	3.80	1.28	0.88
Earnings per common share attributable to Cliffs common shareholders - diluted:
Continuing operations	2.03	0.64	0.76	(0.05)	1.11	0.08	0.28	(0.29)	3.42	1.25	0.49
Discontinued operations	(0.05)	0.77	(0.21)	(0.24)	(0.08)	0.10	(0.18)	0.18	0.29	0.01	0.38
Earnings per common share attributable to Cliffs common shareholders - diluted:	$ 1.98	$ 1.41	$ 0.55	$ (0.29)	$ 1.03	$ 0.18	$ 0.10	$ (0.11)	$ 3.71	$ 1.26	$ 0.87
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount				3,800,000				4,600,000		0
$316 Million 1.5% 2025 Senior Notes [Domain]
Debt Instrument [Line Items]
Face amount	$ 316,250,000								$ 316,250,000
Debt Instrument, Interest Rate, Stated Percentage	1.50%								1.50%

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies	$ 2.5	$ 2.9
Capital Addition Purchase Commitments [Member]
Loss Contingencies [Line Items]
Unrecorded Unconditional Purchase Obligation	830
Unrecorded Unconditional Purchase Obligation, Purchases	180
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	425
Unrecorded Unconditional Purchase Obligation, Due within Two Years	$ 225

QUARTERLY RESULTS OF OPERATIO_3

QUARTERLY RESULTS OF OPERATIONS (Schedule of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues	$ 696.3	$ 741.8	$ 714.3	$ 180	$ 511.8	$ 596.7	$ 471.3	$ 286.2	$ 2,332.4	$ 1,866	$ 1,554.5
SALES MARGIN	202	261.6	284.5	61.5	116.1	157.8	144.7	49	809.6	467.6	280.1
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest					333	22.3	83.8	(78.5)	1,039.9	360.6	122.6
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Noncontrolling Interest					0	0.5	1.7	1.7
Income (Loss) from Continuing Operations Attributable to Parent	624.1	199.8	229.4	(13.4)	333	22.8	85.5	(76.8)	1,039.9	364.5	97.4
INCOME FROM DISCONTINUED OPERATIONS, net of tax	(14.6)	238	(64.3)	(70.9)	(23.1)	30.6	(53.7)	48.7	88.2	2.5	76.7
Net income attributable to Cliffs shareholders	$ 609.5	$ 437.8	$ 165.1	$ (84.3)	$ 309.9	$ 53.4	$ 31.8	$ (28.1)	$ 1,128.1	$ 367	$ 174.1
Continuing operations	$ 2.11	$ 0.67	$ 0.77	$ (0.05)	$ 1.12	$ 0.08	$ 0.28	$ (0.29)	$ 3.50	$ 1.27	$ 0.49
Discontinued operations	(0.05)	0.80	(0.22)	(0.24)	(0.08)	0.10	(0.18)	0.18	0.30	0.01	0.39
Earnings per common share attributable to Cliffs common shareholders - basic:	2.06	1.47	0.55	(0.29)	1.04	0.18	0.10	(0.11)	3.80	1.28	0.88
Continuing operations	2.03	0.64	0.76	(0.05)	1.11	0.08	0.28	(0.29)	3.42	1.25	0.49
Discontinued operations	(0.05)	0.77	(0.21)	(0.24)	(0.08)	0.10	(0.18)	0.18	0.29	0.01	0.38
Earnings per common share attributable to Cliffs common shareholders - diluted:	$ 1.98	$ 1.41	$ 0.55	$ (0.29)	$ 1.03	$ 0.18	$ 0.10	$ (0.11)	$ 3.71	$ 1.26	$ 0.87
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount				3,800,000				4,600,000		0

SUPPLEMENTARY GUARANTOR INFOR_3

SUPPLEMENTARY GUARANTOR INFORMATION (Supplementary Statements of Condensed Consolidating Financial Position) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CURRENT ASSETS
Cash and cash equivalents	$ 823.2	$ 978.3	$ 978.3
Accounts receivable, net	226.7	183.3	106.7
Inventories	87.9	87	138.4
Supplies and other inventories	93.2	88.8	88.8
Derivative assets	91.5	49.5	37.9
Income tax receivable, current	117.3	13.3	13.3
Loans to and accounts receivables from the Canadian Entities	0	51.6	51.6
Current assets of discontinued operations	12.4	118.5	118.5
Other current assets	27.4	11.1	11.1
TOTAL CURRENT ASSETS	1,479.6	1,581.4	1,544.6
OTHER ASSETS
PROPERTY, PLANT AND EQUIPMENT, NET	1,286	1,033.8	1,033.8
Deposits for property, plant and equipment	83	17.8	17.8
Income tax receivable, non-current	121.3	235.3	235.3
Deferred income taxes	464.8		0
Investment in subsidiaries	0		0
Long-term intercompany notes	0		0
Non-current assets of discontinued operations	0	20.3	20.3
Other non-current assets	94.9	101.6	101.6
TOTAL OTHER ASSETS	764	375	375
TOTAL ASSETS	3,529.6	2,990.2	2,953.4	$ 1,923.9
CURRENT LIABILITIES
Accounts payable	186.8	100.9	99.5
Accrued employment costs	74	52.7	52.7
State and local taxes payable	35.5	30.2	30.2
Accrued interest	38.4	31.4	31.4
Contingent claims	0	55.6	55.6
Partnership distribution payable	43.5	44.2	44.2
Current liabilities of discontinued operations	6.7	75	75
Other current liabilities	83.3	65	63.6
TOTAL CURRENT LIABILITIES	468.2	455	452.2
POSTEMPLOYMENT BENEFIT LIABILITIES
Pensions	218.4		222.8
Other postretirement benefits	30.3		34.9
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES	248.7	257.7	257.7
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	172	167.7	167.7
LONG-TERM DEBT	2,092.9	2,304.2	2,304.2
LONG-TERM INTERCOMPANY NOTES	0		0
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS	8.3	52.2	52.2
OTHER LIABILITIES	115.3	163.5	163.5
TOTAL LIABILITIES	3,105.4	3,400.3	3,397.5
CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)
TOTAL CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)	424.2	(410.3)	(444.3)
NONCONTROLLING INTEREST	0	0.2	0.2
TOTAL EQUITY (DEFICIT)	424.2	(410.1)	(444.1)	$ (1,330.5)	$ (1,811.6)
TOTAL LIABILITIES AND EQUITY (DEFICIT)	3,529.6	$ 2,990.2	2,953.4
Consolidation, Eliminations [Member]
CURRENT ASSETS
Cash and cash equivalents	0		0
Accounts receivable, net	(4.1)		(0.7)
Inventories	0		0
Supplies and other inventories	0		0
Derivative assets	0		0
Income tax receivable, current	0		0
Loans to and accounts receivables from the Canadian Entities			0
Current assets of discontinued operations	0		0
Other current assets	0		0
TOTAL CURRENT ASSETS	(4.1)		(0.7)
OTHER ASSETS
PROPERTY, PLANT AND EQUIPMENT, NET	0		0
Deposits for property, plant and equipment	0		0
Income tax receivable, non-current	0		0
Deferred income taxes	0
Investment in subsidiaries	(1,313.1)		(1,054.2)
Long-term intercompany notes	(121.3)		(242)
Non-current assets of discontinued operations			0
Other non-current assets	0		0
TOTAL OTHER ASSETS	(1,434.4)		(1,296.2)
TOTAL ASSETS	(1,438.5)		(1,296.9)
CURRENT LIABILITIES
Accounts payable	(4.1)		(0.7)
Accrued employment costs	0		0
State and local taxes payable	0		0
Accrued interest	0		0
Contingent claims			0
Partnership distribution payable	0		0
Current liabilities of discontinued operations	0		0
Other current liabilities	0		0
TOTAL CURRENT LIABILITIES	(4.1)		(0.7)
POSTEMPLOYMENT BENEFIT LIABILITIES
Pensions	0		0
Other postretirement benefits	0		0
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES	0		0
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	0		0
LONG-TERM DEBT	0		0
LONG-TERM INTERCOMPANY NOTES	(121.3)		(242)
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS	0		0
OTHER LIABILITIES	0		0
TOTAL LIABILITIES	(125.4)		(242.7)
CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)
TOTAL CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)			(1,054.2)
NONCONTROLLING INTEREST			0
TOTAL EQUITY (DEFICIT)	(1,313.1)		(1,054.2)
TOTAL LIABILITIES AND EQUITY (DEFICIT)	(1,438.5)		(1,296.9)
Parent [Member] | Reportable Legal Entities [Member]
CURRENT ASSETS
Cash and cash equivalents	819.8		948.9
Accounts receivable, net	9.2		4.5
Inventories	0		0
Supplies and other inventories	0		0
Derivative assets	0.1		0
Income tax receivable, current	117.3		11.4
Loans to and accounts receivables from the Canadian Entities			44.7
Current assets of discontinued operations	0		0
Other current assets	10		5
TOTAL CURRENT ASSETS	956.4		1,014.5
OTHER ASSETS
PROPERTY, PLANT AND EQUIPMENT, NET	13.3		17.5
Deposits for property, plant and equipment	0		0
Income tax receivable, non-current	117.2		235.3
Deferred income taxes	463.6
Investment in subsidiaries	1,262.3		1,024.3
Long-term intercompany notes	0		0
Non-current assets of discontinued operations			0
Other non-current assets	8		7.8
TOTAL OTHER ASSETS	1,851.1		1,267.4
TOTAL ASSETS	2,820.8		2,299.4
CURRENT LIABILITIES
Accounts payable	5.3		7.1
Accrued employment costs	28.5		13.7
State and local taxes payable	0		0
Accrued interest	38.4		31.4
Contingent claims			55.6
Partnership distribution payable	0		0
Current liabilities of discontinued operations	0		0
Other current liabilities	30.6		7.4
TOTAL CURRENT LIABILITIES	102.8		115.2
POSTEMPLOYMENT BENEFIT LIABILITIES
Pensions	58.3		59.2
Other postretirement benefits	6		7.2
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES	64.3		66.4
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	0		0
LONG-TERM DEBT	2,092.9		2,304.2
LONG-TERM INTERCOMPANY NOTES	121.3		242
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS	0		0
OTHER LIABILITIES	15.3		15.7
TOTAL LIABILITIES	2,396.6		2,743.5
CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)
TOTAL CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)			(444.1)
NONCONTROLLING INTEREST			0
TOTAL EQUITY (DEFICIT)	424.2		(444.1)
TOTAL LIABILITIES AND EQUITY (DEFICIT)	2,820.8		2,299.4
Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
CURRENT ASSETS
Cash and cash equivalents	0.7		2.1
Accounts receivable, net	221.3		102.9
Inventories	87.9		138.4
Supplies and other inventories	93.2		88.8
Derivative assets	91.4		37.9
Income tax receivable, current	0		1.9
Loans to and accounts receivables from the Canadian Entities			6.9
Current assets of discontinued operations	0		0
Other current assets	16.9		5.6
TOTAL CURRENT ASSETS	511.4		384.5
OTHER ASSETS
PROPERTY, PLANT AND EQUIPMENT, NET	1,221.9		965.5
Deposits for property, plant and equipment	68.4		8.2
Income tax receivable, non-current	4.1		0
Deferred income taxes	0
Investment in subsidiaries	50.8		29.9
Long-term intercompany notes	0		0
Non-current assets of discontinued operations			0
Other non-current assets	85.4		91.8
TOTAL OTHER ASSETS	208.7		129.9
TOTAL ASSETS	1,942		1,479.9
CURRENT LIABILITIES
Accounts payable	181.4		92.3
Accrued employment costs	45.4		38.9
State and local taxes payable	35.4		30
Accrued interest	0		0
Contingent claims			0
Partnership distribution payable	43.5		44.2
Current liabilities of discontinued operations	0		0
Other current liabilities	51.3		54.5
TOTAL CURRENT LIABILITIES	357		259.9
POSTEMPLOYMENT BENEFIT LIABILITIES
Pensions	390.5		403.6
Other postretirement benefits	23.9		27
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES	414.4		430.6
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	152.1		140.6
LONG-TERM DEBT	0		0
LONG-TERM INTERCOMPANY NOTES	0		0
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS	0		0
OTHER LIABILITIES	99.5		147.2
TOTAL LIABILITIES	1,023		978.3
CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)
TOTAL CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)			501.6
NONCONTROLLING INTEREST			0
TOTAL EQUITY (DEFICIT)	919		501.6
TOTAL LIABILITIES AND EQUITY (DEFICIT)	1,942		1,479.9
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
CURRENT ASSETS
Cash and cash equivalents	2.7		27.3
Accounts receivable, net	0.3		0
Inventories	0		0
Supplies and other inventories	0		0
Derivative assets	0		0
Income tax receivable, current	0		0
Loans to and accounts receivables from the Canadian Entities			0
Current assets of discontinued operations	12.4		118.5
Other current assets	0.5		0.5
TOTAL CURRENT ASSETS	15.9		146.3
OTHER ASSETS
PROPERTY, PLANT AND EQUIPMENT, NET	50.8		50.8
Deposits for property, plant and equipment	14.6		9.6
Income tax receivable, non-current	0		0
Deferred income taxes	1.2
Investment in subsidiaries	0		0
Long-term intercompany notes	121.3		242
Non-current assets of discontinued operations			20.3
Other non-current assets	1.5		2
TOTAL OTHER ASSETS	138.6		273.9
TOTAL ASSETS	205.3		471
CURRENT LIABILITIES
Accounts payable	4.2		0.8
Accrued employment costs	0.1		0.1
State and local taxes payable	0.1		0.2
Accrued interest	0		0
Contingent claims			0
Partnership distribution payable	0		0
Current liabilities of discontinued operations	6.7		75
Other current liabilities	1.4		1.7
TOTAL CURRENT LIABILITIES	12.5		77.8
POSTEMPLOYMENT BENEFIT LIABILITIES
Pensions	(230.4)		(240)
Other postretirement benefits	0.4		0.7
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES	(230)		(239.3)
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS	19.9		27.1
LONG-TERM DEBT	0		0
LONG-TERM INTERCOMPANY NOTES	0		0
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS	8.3		52.2
OTHER LIABILITIES	0.5		0.6
TOTAL LIABILITIES	(188.8)		(81.6)
CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)
TOTAL CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)			552.4
NONCONTROLLING INTEREST			0.2
TOTAL EQUITY (DEFICIT)	394.1		552.6
TOTAL LIABILITIES AND EQUITY (DEFICIT)	$ 205.3		$ 471

SUPPLEMENTARY GUARANTOR INFOR_4

SUPPLEMENTARY GUARANTOR INFORMATION (Supplementary Statements of Condensed Consolidating Operations and Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
REVENUES FROM PRODUCT SALES AND SERVICES
Product revenues									$ 2,172.3	$ 1,644.6	$ 1,379.7
Freight and Reimbursement Revenue									160.1	221.4	174.8
TOTAL REVENUES FROM PRODUCT SALES AND SERVICES	$ 696.3	$ 741.8	$ 714.3	$ 180	$ 511.8	$ 596.7	$ 471.3	$ 286.2	2,332.4	1,866	1,554.5
COST OF GOODS SOLD AND OPERATING EXPENSES									(1,522.8)	(1,398.4)	(1,274.4)
SALES MARGIN	202	261.6	284.5	61.5	116.1	157.8	144.7	49	809.6	467.6	280.1
OTHER OPERATING INCOME (EXPENSE)
Selling, general and administrative expenses									(116.8)	(102.9)	(115.8)
Miscellaneous - net									(19.6)	25.5	(33.6)
Other operating expense									(136.4)	(77.4)	(149.4)
OPERATING INCOME									673.2	390.2	130.7
OTHER INCOME (EXPENSE)
Interest expense, net									(118.9)	(126.8)	(193.9)
Gain (loss) on extinguishment/restructuring of debt									(6.8)	(165.4)	166.3
Other non-operating income									17.2	10.2	7.3
TOTAL OTHER INCOME (EXPENSE)									(108.5)	(282)	(20.3)
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES AND EQUITY LOSS FROM VENTURES									564.7	108.2	110.4
INCOME TAX BENEFIT (EXPENSE)									475.2	252.4	12.2
EQUITY IN INCOME OF SUBSIDIARIES									0	0	0
INCOME FROM CONTINUING OPERATIONS					333	22.3	83.8	(78.5)	1,039.9	360.6	122.6
INCOME FROM DISCONTINUED OPERATIONS, net of tax									88.2	2.5	76.7
NET INCOME									1,128.1	363.1	199.3
INCOME ATTRIBUTABLE TO NONCONTROLLING INTEREST									0	3.9	(25.2)
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$ 609.5	$ 437.8	$ 165.1	$ (84.3)	$ 309.9	$ 53.4	$ 31.8	$ (28.1)	1,128.1	367	174.1
OTHER COMPREHENSIVE INCOME (LOSS)									(244.9)	(4)	(3.3)
TOTAL COMPREHENSIVE INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS									883.2	363	170.8
Consolidation, Eliminations [Member]
REVENUES FROM PRODUCT SALES AND SERVICES
Product revenues									0	0	0
Freight and Reimbursement Revenue									0	0	0
TOTAL REVENUES FROM PRODUCT SALES AND SERVICES									0	0	0
COST OF GOODS SOLD AND OPERATING EXPENSES									0	0	0
SALES MARGIN									0	0	0
OTHER OPERATING INCOME (EXPENSE)
Selling, general and administrative expenses									0	0	0
Miscellaneous - net									0	0	0
Other operating expense									0	0	0
OPERATING INCOME									0	0	0
OTHER INCOME (EXPENSE)
Interest expense, net									0	0	0
Gain (loss) on extinguishment/restructuring of debt									0	0	0
Other non-operating income									0	0	0
TOTAL OTHER INCOME (EXPENSE)									0	0	0
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES AND EQUITY LOSS FROM VENTURES									0	0	0
INCOME TAX BENEFIT (EXPENSE)									0	0	0
EQUITY IN INCOME OF SUBSIDIARIES									(883.7)	(524.4)	(332.8)
INCOME FROM CONTINUING OPERATIONS									(883.7)	(524.4)	(332.8)
INCOME FROM DISCONTINUED OPERATIONS, net of tax									0	0	0
NET INCOME										(524.4)	(332.8)
INCOME ATTRIBUTABLE TO NONCONTROLLING INTEREST										0	0
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS									(883.7)	(524.4)	(332.8)
OTHER COMPREHENSIVE INCOME (LOSS)									280.8	(8.1)	5.3
TOTAL COMPREHENSIVE INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS									(602.9)	(532.5)	(327.5)
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
REVENUES FROM PRODUCT SALES AND SERVICES
Product revenues									0	0	0
Freight and Reimbursement Revenue									0	0	0
TOTAL REVENUES FROM PRODUCT SALES AND SERVICES									0	0	0
COST OF GOODS SOLD AND OPERATING EXPENSES									0	0	0
SALES MARGIN									0	0	0
OTHER OPERATING INCOME (EXPENSE)
Selling, general and administrative expenses									(0.3)	(5.8)	(3.5)
Miscellaneous - net									4.3	16.8	(15.6)
Other operating expense									4	11	(19.1)
OPERATING INCOME									4	11	(19.1)
OTHER INCOME (EXPENSE)
Interest expense, net									0.8	1	0.5
Gain (loss) on extinguishment/restructuring of debt									0	0	0
Other non-operating income									19.8	17.2	16.4
TOTAL OTHER INCOME (EXPENSE)									20.6	18.2	16.9
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES AND EQUITY LOSS FROM VENTURES									24.6	29.2	(2.2)
INCOME TAX BENEFIT (EXPENSE)									0.5	(0.3)	4.9
EQUITY IN INCOME OF SUBSIDIARIES									0	0	0
INCOME FROM CONTINUING OPERATIONS									25.1	28.9	2.7
INCOME FROM DISCONTINUED OPERATIONS, net of tax									66.4	22.1	91.2
NET INCOME										51	93.9
INCOME ATTRIBUTABLE TO NONCONTROLLING INTEREST										0	0
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS									91.5	51	93.9
OTHER COMPREHENSIVE INCOME (LOSS)									(256.7)	(4.8)	15.4
TOTAL COMPREHENSIVE INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS									(165.2)	46.2	109.3
Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
REVENUES FROM PRODUCT SALES AND SERVICES
Product revenues									2,172.3	1,644.6	1,379.7
Freight and Reimbursement Revenue									160.1	221.4	174.8
TOTAL REVENUES FROM PRODUCT SALES AND SERVICES									2,332.4	1,866	1,554.5
COST OF GOODS SOLD AND OPERATING EXPENSES									(1,522.8)	(1,398.4)	(1,274.4)
SALES MARGIN									809.6	467.6	280.1
OTHER OPERATING INCOME (EXPENSE)
Selling, general and administrative expenses									(30.4)	(19.9)	(18)
Miscellaneous - net									(23.6)	11	(12.4)
Other operating expense									(54)	(8.9)	(30.4)
OPERATING INCOME									755.6	458.7	249.7
OTHER INCOME (EXPENSE)
Interest expense, net									(2.1)	(1)	0.1
Gain (loss) on extinguishment/restructuring of debt									0	0	0
Other non-operating income									0.9	(3)	(5)
TOTAL OTHER INCOME (EXPENSE)									(1.2)	(4)	(4.9)
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES AND EQUITY LOSS FROM VENTURES									754.4	454.7	244.8
INCOME TAX BENEFIT (EXPENSE)									0	1.3	3
EQUITY IN INCOME OF SUBSIDIARIES									25.5	11.8	13.7
INCOME FROM CONTINUING OPERATIONS									779.9	467.8	261.5
INCOME FROM DISCONTINUED OPERATIONS, net of tax									12.3	1.7	2.6
NET INCOME										469.5	264.1
INCOME ATTRIBUTABLE TO NONCONTROLLING INTEREST										3.9	(25.2)
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS									792.2	473.4	238.9
OTHER COMPREHENSIVE INCOME (LOSS)									(24.1)	12.9	(20.7)
TOTAL COMPREHENSIVE INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS									768.1	486.3	218.2
Parent [Member] | Reportable Legal Entities [Member]
REVENUES FROM PRODUCT SALES AND SERVICES
Product revenues									0	0	0
Freight and Reimbursement Revenue									0	0	0
TOTAL REVENUES FROM PRODUCT SALES AND SERVICES									0	0	0
COST OF GOODS SOLD AND OPERATING EXPENSES									0	0	0
SALES MARGIN									0	0	0
OTHER OPERATING INCOME (EXPENSE)
Selling, general and administrative expenses									(86.1)	(77.2)	(94.3)
Miscellaneous - net									(0.3)	(2.3)	(5.6)
Other operating expense									(86.4)	(79.5)	(99.9)
OPERATING INCOME									(86.4)	(79.5)	(99.9)
OTHER INCOME (EXPENSE)
Interest expense, net									(117.6)	(126.8)	(194.5)
Gain (loss) on extinguishment/restructuring of debt									(6.8)	(165.4)	166.3
Other non-operating income									(3.5)	(4)	(4.1)
TOTAL OTHER INCOME (EXPENSE)									(127.9)	(296.2)	(32.3)
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES AND EQUITY LOSS FROM VENTURES									(214.3)	(375.7)	(132.2)
INCOME TAX BENEFIT (EXPENSE)									474.7	251.4	4.3
EQUITY IN INCOME OF SUBSIDIARIES									858.2	512.6	319.1
INCOME FROM CONTINUING OPERATIONS									1,118.6	388.3	191.2
INCOME FROM DISCONTINUED OPERATIONS, net of tax									9.5	(21.3)	(17.1)
NET INCOME										367	174.1
INCOME ATTRIBUTABLE TO NONCONTROLLING INTEREST										0	0
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS									1,128.1	367	174.1
OTHER COMPREHENSIVE INCOME (LOSS)									(244.9)	(4)	(3.3)
TOTAL COMPREHENSIVE INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS									$ 883.2	$ 363	$ 170.8

SUPPLEMENTARY GUARANTOR INFOR_5

SUPPLEMENTARY GUARANTOR INFORMATION (Supplementary Statements of Condensed Consolidating Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net cash provided (used) by operating activities	$ 478.5	$ 338.1	$ 303
INVESTING ACTIVITIES
Purchase of property, plant and equipment	(208.6)	(134.9)	(61.7)
Deposits for property, plant and equipment	(87.5)	(16.8)	(7.4)
Intercompany investing	0	0	0
Other investing activities	23	(4.3)	11.2
Net cash used by investing activities	(273.1)	(156)	(57.9)
Payments for Repurchase of Common Stock	(47.5)
FINANCING ACTIVITIES
Net proceeds from issuance of common shares	0	661.3	287.4
Proceeds from issuance of debt	0	1,771.5	0
Debt issuance costs	(1.5)	(28.6)	(5.2)
Borrowings under credit facilities	0	0	105
Repayment under credit facilities	0	0	(105)
Repayments on equipment loans	0	0	(95.6)
Repurchase of debt	(234.5)	(1,720.7)	(305.4)
Acquisition of noncontrolling interest	0	(105)	0
Distributions of partnership equity	(44.2)	(52.9)	(59.9)
Intercompany financing	0	0	0
Other financing activities	(47.5)	(26.7)	(27.7)
Net cash provided (used) by financing activities	(375.2)	498.9	(206.4)
EFFECT OF EXCHANGE RATE CHANGES ON CASH	(2.3)	3.3	(0.5)
Increase (Decrease) in Cash and Cash Equivalents, Including Cash Classified Within Current Assets of Discontinued Operations	(172.1)	684.3	38.2
LESS: INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS	(17)	18.8	(35.3)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(155.1)	665.5	73.5
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	978.3	312.8	239.3
CASH AND CASH EQUIVALENTS AT END OF YEAR	823.2	978.3	312.8
Consolidation, Eliminations [Member]
Net cash provided (used) by operating activities	0	0	0
INVESTING ACTIVITIES
Purchase of property, plant and equipment	0	0	0
Deposits for property, plant and equipment	0	0	0
Intercompany investing	(512.7)	(173.3)	(236.3)
Other investing activities	0	0	0
Net cash used by investing activities	(512.7)	(173.3)	(236.3)
Payments for Repurchase of Common Stock	0
FINANCING ACTIVITIES
Net proceeds from issuance of common shares		0	0
Proceeds from issuance of debt		0
Debt issuance costs	0	0	0
Borrowings under credit facilities			0
Repayment under credit facilities			0
Repayments on equipment loans			0
Repurchase of debt	0	0	0
Acquisition of noncontrolling interest		0
Distributions of partnership equity	0	0	0
Intercompany financing	512.7	173.3	236.3
Other financing activities	0	0	0
Net cash provided (used) by financing activities	512.7	173.3	236.3
EFFECT OF EXCHANGE RATE CHANGES ON CASH	0	0	0
Increase (Decrease) in Cash and Cash Equivalents, Including Cash Classified Within Current Assets of Discontinued Operations	0	0	0
LESS: INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS	0	0	0
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	0	0	0
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	0	0	0
CASH AND CASH EQUIVALENTS AT END OF YEAR	0	0	0
Parent [Member] | Reportable Legal Entities [Member]
Net cash provided (used) by operating activities	(120.7)	(166.8)	(275.7)
INVESTING ACTIVITIES
Purchase of property, plant and equipment	(1.2)	(3.4)	(6.2)
Deposits for property, plant and equipment	0	0	0
Intercompany investing	399.1	225.7	356.6
Other investing activities	0	(7.7)	0.4
Net cash used by investing activities	397.9	214.6	350.8
Payments for Repurchase of Common Stock	(47.5)
FINANCING ACTIVITIES
Net proceeds from issuance of common shares		661.3	287.4
Proceeds from issuance of debt		1,771.5
Debt issuance costs	(1.5)	(28.6)	(5.2)
Borrowings under credit facilities			105
Repayment under credit facilities			(105)
Repayments on equipment loans			(95.6)
Repurchase of debt	(234.5)	(1,720.7)	(305.4)
Acquisition of noncontrolling interest		(105)
Distributions of partnership equity	0	0	0
Intercompany financing	(120.7)	45	117
Other financing activities	(2.1)	(5.8)	(0.6)
Net cash provided (used) by financing activities	(406.3)	617.7	(2.4)
EFFECT OF EXCHANGE RATE CHANGES ON CASH	0	0	0
Increase (Decrease) in Cash and Cash Equivalents, Including Cash Classified Within Current Assets of Discontinued Operations	(129.1)	665.5	72.7
LESS: INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS	0	0	0
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(129.1)	665.5	72.7
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	948.9	283.4	210.7
CASH AND CASH EQUIVALENTS AT END OF YEAR	819.8	948.9	283.4
Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Net cash provided (used) by operating activities	741	430	462.9
INVESTING ACTIVITIES
Purchase of property, plant and equipment	(207.3)	(79.8)	(55.1)
Deposits for property, plant and equipment	(82.3)	(11.7)	(4.9)
Intercompany investing	(7.1)	(7.3)	(3.3)
Other investing activities	3.1	3.4	10.8
Net cash used by investing activities	(293.6)	(95.4)	(52.5)
Payments for Repurchase of Common Stock	0
FINANCING ACTIVITIES
Net proceeds from issuance of common shares		0	0
Proceeds from issuance of debt		0
Debt issuance costs	0	0	0
Borrowings under credit facilities			0
Repayment under credit facilities			0
Repayments on equipment loans			0
Repurchase of debt	0	0	0
Acquisition of noncontrolling interest		0
Distributions of partnership equity	(44.2)	(52.9)	(59.9)
Intercompany financing	(402.4)	(277.6)	(339.9)
Other financing activities	(2.2)	(4.5)	(9.9)
Net cash provided (used) by financing activities	(448.8)	(335)	(409.7)
EFFECT OF EXCHANGE RATE CHANGES ON CASH	0	0	0
Increase (Decrease) in Cash and Cash Equivalents, Including Cash Classified Within Current Assets of Discontinued Operations	(1.4)	(0.4)	0.7
LESS: INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS	0	0	0
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(1.4)	(0.4)	0.7
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	2.1	2.5	1.8
CASH AND CASH EQUIVALENTS AT END OF YEAR	0.7	2.1	2.5
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Net cash provided (used) by operating activities	(141.8)	74.9	115.8
INVESTING ACTIVITIES
Purchase of property, plant and equipment	(0.1)	(51.7)	(0.4)
Deposits for property, plant and equipment	(5.2)	(5.1)	(2.5)
Intercompany investing	120.7	(45.1)	(117)
Other investing activities	19.9	0	0
Net cash used by investing activities	135.3	(101.9)	(119.9)
Payments for Repurchase of Common Stock	0
FINANCING ACTIVITIES
Net proceeds from issuance of common shares		0	0
Proceeds from issuance of debt		0
Debt issuance costs	0	0	0
Borrowings under credit facilities			0
Repayment under credit facilities			0
Repayments on equipment loans			0
Repurchase of debt	0	0	0
Acquisition of noncontrolling interest		0
Distributions of partnership equity	0	0	0
Intercompany financing	10.4	59.3	(13.4)
Other financing activities	(43.2)	(16.4)	(17.2)
Net cash provided (used) by financing activities	(32.8)	42.9	(30.6)
EFFECT OF EXCHANGE RATE CHANGES ON CASH	(2.3)	3.3	(0.5)
Increase (Decrease) in Cash and Cash Equivalents, Including Cash Classified Within Current Assets of Discontinued Operations	(41.6)	19.2	(35.2)
LESS: INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS	(17)	18.8	(35.3)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(24.6)	0.4	0.1
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	27.3	26.9	26.8
CASH AND CASH EQUIVALENTS AT END OF YEAR	$ 2.7	$ 27.3	$ 26.9

SUPPLEMENTARY GUARANTOR INFOR_6

SUPPLEMENTARY GUARANTOR INFORMATION (Narrative) (Details) $ in Millions	Dec. 31, 2018USD ($)
Noncontrolling Interest, Ownership Percentage by Parent	100.00%
$1.075 Billion 5.75% 2025 Senior Notes [Member]
Debt Instrument, Par Value	$ 1,073.3
Debt Instrument, Interest Rate, Stated Percentage	5.75%

Schedule II - Valuation and Q_2

Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
SEC Schedule, 12-09, Valuation Allowance, Deferred Tax Asset [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount	$ 1,287.3	$ 1,983.1	$ 3,095.1	$ 3,099.8
Valuation Allowances and Reserves, Charged to Cost and Expense	(691.3)	(1,120)	(7.6)
Valuation Allowances and Reserves, Charged to Other Accounts	(4.5)	(9.8)	5.1
SEC Schedule, 12-09, Valuation Allowances and Reserves, Business Acquired	0	17.8	0
SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction	$ 0	$ 0	2.2
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount			0	$ 7.1
Valuation Allowances and Reserves, Charged to Cost and Expense			0
Valuation Allowances and Reserves, Charged to Other Accounts			(7.1)
SEC Schedule, 12-09, Valuation Allowances and Reserves, Business Acquired			0
SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction			$ 0

Uncategorized Items - clf-20181

Label	Element	Value
Capital Addition Purchase Commitments [Member]
Recorded Unconditional Purchase Obligation	us-gaap_RecordedUnconditionalPurchaseObligation	$ 580,000,000
Common Stock [Member]
Common Stock, New Shares, Issued	clf_CommonStockNewSharesIssued	44,400,000
Common Stock, New Shares, Issued	clf_CommonStockNewSharesIssued	63,300,000