Cleveland-Cliffs (CLF) 10-Q 23 Oct 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Oct. 22, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2020
Document Transition Report	false
Entity File Number	1-8944
Entity Registrant Name	CLEVELAND-CLIFFS INC.
Entity Incorporation, State or Country Code	OH
Entity Tax Identification Number	34-1464672
Entity Address, Address Line One	200 Public Square,
Entity Address, City or Town	Cleveland,
Entity Address, State or Province	OH
Entity Address, Postal Zip Code	44114-2315
City Area Code	216
Local Phone Number	694-5700
Title of 12(b) Security	Common shares, par value $0.125 per share
Trading Symbol	CLF
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		399,241,687
Entity Central Index Key	0000764065
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Amendment Flag	false

Statements Of Unaudited Condens

Statements Of Unaudited Condensed Consolidated Financial Position - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 56	$ 352.6
Accounts receivable, net	653.7	94
Inventories	1,795.1	317.4
Income tax receivable, current	9	58.6
Other current assets	115	75.3
Total current assets	2,628.8	897.9
Non-current assets:
Property, plant and equipment, net	4,550.7	1,929
Goodwill	144	2.1
Intangible assets, net	190.1	48.1
Income tax receivable, non-current	0	62.7
Deferred income taxes	519.5	459.5
Right-of-use asset, operating lease	207.7	11.7
Other non-current assets	240.1	92.8
TOTAL ASSETS	8,480.9	3,503.8
Current liabilities:
Accounts payable	710.7	193.2
Accrued liabilities	279.4	126.3
Other current liabilities	224	89.9
Total current liabilities	1,214.1	409.4
Non-current liabilities:
Long-term debt	4,309.8	2,113.8
Operating lease liability, non-current	174.1	10.5
Intangible liabilities, net	65.9	0
Pension and OPEB liabilities	1,130.6	311.5
Asset retirement obligations	182	163.2
Other non-current liabilities	280.7	137.5
TOTAL LIABILITIES	7,357.2	3,145.9
Commitments and contingencies (See Note 18)
SHAREHOLDERS' EQUITY
Common shares - par value $0.125 per share, Authorized - 600,000,000 shares (2019 - 600,000,000 shares); Issued - 428,645,866 shares (2019 - 301,886,794 shares); Outstanding - 399,229,917 shares (2019 - 270,084,005 shares)	53.6	37.7
Capital in excess of par value of shares	4,446.3	3,872.1
Retained deficit	(3,052.5)	(2,842.4)
Cost of 29,415,949 common shares in treasury (2019 - 31,802,789 shares)	(354.8)	(390.7)
Accumulated other comprehensive loss	(282)	(318.8)
Total Cliffs shareholders' equity	810.6	357.9
Noncontrolling interest	313.1	0
TOTAL EQUITY	1,123.7	357.9
TOTAL LIABILITIES AND EQUITY	$ 8,480.9	$ 3,503.8

Statements Of Condensed Consoli

Statements Of Condensed Consolidated Financial Position (Parenthetical) - $ / shares	Sep. 30, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Common shares, par value	$ 0.125
Common shares, authorized (in shares)	600,000,000	600,000,000
Common shares, issued (in shares)	428,645,866	301,886,794
Common shares, outstanding (in shares)	399,229,917	270,084,005
Common shares in treasury (in shares)	29,415,949	31,802,789

Statements Of Unaudited Conde_2

Statements Of Unaudited Condensed Consolidated Operations - USD ($) shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenues	$ 1,646	$ 555.6	$ 3,063.2	$ 1,455.8
Realization of deferred revenue	0	0	34.6	0
Operating costs:
Cost of goods sold	(1,525.4)	(400.7)	(3,088.9)	(1,007)
Selling, general and administrative expenses	(59.6)	(25.5)	(149.2)	(82.2)
Acquisition-related costs	(7.5)	0	(68.4)	0
Miscellaneous – net	(15.5)	(7.8)	(40.5)	(19)
Total operating costs	(1,608)	(434)	(3,347)	(1,108.2)
Operating income (loss)	38	121.6	(249.2)	347.6
Other income (expense):
Interest expense, net	(68.2)	(25.3)	(167.9)	(76.5)
Gain (loss) on extinguishment of debt	0	0	132.6	(18.2)
Other non-operating income	10	0.3	31.2	1.3
Total other expense	(58.2)	(25)	(4.1)	(93.4)
Income (loss) from continuing operations before income taxes	(20.2)	96.6	(253.3)	254.2
Income tax benefit (expense)	22.4	(4.8)	98.5	(23.1)
Income (loss) from continuing operations	2.2	91.8	(154.8)	231.1
Loss from discontinued operations, net of tax	(0.3)	(0.9)	0	(1.5)
Net income (loss)	1.9	90.9	(154.8)	229.6
Income attributable to noncontrolling interest	(11.9)	0	(31.2)	0
Net income (loss) attributable to Cliffs shareholders	$ (10)	$ 90.9	$ (186)	$ 229.6
Earnings (loss) per common share attributable to Cliffs shareholders - basic
Continuing operations (in dollars per share)	$ (0.02)	$ 0.34	$ (0.51)	$ 0.83
Discontinued operations (in dollars per share)	0	0	0	(0.01)
Earnings (Loss) per Common Share - Basic (in dollars per share)	(0.02)	0.34	(0.51)	0.82
Earnings (loss) per common share attributable to Cliffs shareholders - diluted
Continuing operations (in dollars per share)	(0.02)	0.33	(0.51)	0.80
Discontinued operations (in dollars per share)	0	0	0	0
Earnings (Loss) per Common Share - Diluted (in dollars per share)	$ (0.02)	$ 0.33	$ (0.51)	$ 0.80
Average number of shares (in thousands)
Basic	399,399	269,960	365,245	278,418
Diluted	399,399	276,578	365,245	287,755

Statements Of Unaudited Conde_3

Statements Of Unaudited Condensed Consolidated Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 1.9	$ 90.9	$ (154.8)	$ 229.6
Other comprehensive income:
Changes in pension and OPEB, net of tax	6.6	5.8	18.2	17.3
Changes in foreign currency translation	1.6	0	1.4	0
Changes in derivative financial instruments, net of tax	15.7	0.4	17.2	1
Total other comprehensive income	23.9	6.2	36.8	18.3
Comprehensive income (loss)	25.8	97.1	(118)	247.9
Comprehensive income attributable to noncontrolling interests	(11.9)	0	(31.2)	0
Comprehensive income (loss) attributable to Cliffs shareholders	$ 13.9	$ 97.1	$ (149.2)	$ 247.9

Statements Of Unaudited Conde_4

Statements Of Unaudited Condensed Consolidated Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
OPERATING ACTIVITIES
Net income (loss)	$ (154.8)	$ 229.6
Adjustments to reconcile net income (loss) to net cash provided (used) by operating activities:
Depreciation, depletion and amortization	183.9	63.1
Amortization of inventory step-up	74	0
Deferred income taxes	(89.9)	22.7
Loss (gain) on extinguishment of debt	(132.6)	18.2
Loss (gain) on derivatives	(19.1)	48.4
Other	(13)	49.4
Changes in operating assets and liabilities, net of business combination:
Receivables and other assets	259.8	174.1
Inventories	(4.2)	(147)
Payables, accrued expenses and other liabilities	(157.3)	(70.4)
Net cash provided (used) by operating activities	(53.2)	388.1
INVESTING ACTIVITIES
Purchase of property, plant and equipment	(378.9)	(460.7)
Acquisition of AK Steel, net of cash acquired	(869.3)	0
Other investing activities	8	11.2
Net cash used by investing activities	(1,240.2)	(449.5)
FINANCING ACTIVITIES
Repurchase of common shares	0	(252.9)
Proceeds from issuance of debt	1,762.9	720.9
Debt issuance costs	(57.5)	(6.8)
Repurchase of debt	(999.5)	(729.3)
Borrowings under credit facilities	800	0
Repayments under credit facilities	(400)	0
Dividends paid	(40.8)	(45.1)
Other financing activities	(23.3)	(53.7)
Net cash provided (used) by financing activities	994.2	(366.9)
Decrease in cash and cash equivalents, including cash classified within other current assets related to discontinued operations	(299.2)	(428.3)
Less: decrease in cash and cash equivalents from discontinued operations, classified within other current assets	(2.6)	(4.4)
Net decrease in cash and cash equivalents	(296.6)	(423.9)
Cash and cash equivalents at beginning of period	352.6	823.2
Cash and cash equivalents at end of period	56	399.3
SunCoke Middletown [Member]
FINANCING ACTIVITIES
SunCoke Middletown distributions to noncontrolling interest owners	$ (47.6)	$ 0

Statements of Unaudited Conde_5

Statements of Unaudited Condensed Consolidated Changes in Equity Statement - USD ($) $ in Millions	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	AOCI Attributable to Parent [Member]	Noncontrolling Interest [Member]
Balance, beginning of period (in shares) at Dec. 31, 2018		292,600,000
Balance, beginning of period at Dec. 31, 2018	$ 424.2	$ 37.7	$ 3,916.7	$ (3,060.2)	$ (186.1)	$ (283.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	(13.7)			(22.1)		8.4
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture		1,700,000
Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture	(10)		(56.5)		46.5
Stock Repurchased During Period, Shares		(11,500,000)
Common Share Repurchases, Value	(124.3)				(124.3)
Dividends, Common Stock	(14.5)			(14.5)
Balance, end of period (in shares) at Mar. 31, 2019		282,800,000
Balance, end of period at Mar. 31, 2019	$ 261.7	$ 37.7	3,860.2	(3,096.8)	(263.9)	(275.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.05
Balance, beginning of period (in shares) at Dec. 31, 2018		292,600,000
Balance, beginning of period at Dec. 31, 2018	$ 424.2	$ 37.7	3,916.7	(3,060.2)	(186.1)	(283.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 247.9
Stock Repurchased During Period, Shares	(24,400,000)
Balance, end of period (in shares) at Sep. 30, 2019		270,100,000
Balance, end of period at Sep. 30, 2019	$ 359.9	$ 37.7	3,867.7	(2,889)	(390.9)	(265.6)
Balance, beginning of period (in shares) at Mar. 31, 2019		282,800,000
Balance, beginning of period at Mar. 31, 2019	261.7	$ 37.7	3,860.2	(3,096.8)	(263.9)	(275.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	164.5			160.8		3.7
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture		100,000
Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture	4.6		3.4		1.2
Stock Repurchased During Period, Shares		(12,900,000)
Common Share Repurchases, Value	(128.6)				(128.6)
Dividends, Common Stock	(16.6)			(16.6)
Balance, end of period (in shares) at Jun. 30, 2019		270,000,000
Balance, end of period at Jun. 30, 2019	$ 285.6	$ 37.7	3,863.6	(2,952.6)	(391.3)	(271.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.06
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 97.1			90.9		6.2
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture		100,000
Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture	4.5		4.1		0.4
Dividends, Common Stock	(27.3)			(27.3)
Balance, end of period (in shares) at Sep. 30, 2019		270,100,000
Balance, end of period at Sep. 30, 2019	$ 359.9	$ 37.7	3,867.7	(2,889)	(390.9)	(265.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.10
Balance, beginning of period (in shares) at Dec. 31, 2019	270,084,005	270,100,000
Balance, beginning of period at Dec. 31, 2019	$ 357.9	$ 37.7	3,872.1	(2,842.4)	(390.7)	(318.8)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	(46.9)			(52.1)		1.7	3.5
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture		1,700,000
Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture	2.1		(23.6)		25.7
Stock Issued During Period, Shares, Acquisitions		126,800,000
Stock Issued During Period, Value, Acquisitions	947.4	$ 15.9	601.7
Noncontrolling Interest, Increase from Business Combination							329.8
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders	(5.5)						(5.5)
Dividends, Common Stock	(24)			(24)
Balance, end of period (in shares) at Mar. 31, 2020		398,600,000
Balance, end of period at Mar. 31, 2020	$ 1,231	$ 53.6	4,450.2	(2,918.5)	(365)	(317.1)	327.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.06
Balance, beginning of period (in shares) at Dec. 31, 2019	270,084,005	270,100,000
Balance, beginning of period at Dec. 31, 2019	$ 357.9	$ 37.7	3,872.1	(2,842.4)	(390.7)	(318.8)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ (118)
Balance, end of period (in shares) at Sep. 30, 2020	399,229,917	399,200,000
Balance, end of period at Sep. 30, 2020	$ 1,123.7	$ 53.6	4,446.3	(3,052.5)	(354.8)	(282)	313.1
Balance, beginning of period (in shares) at Mar. 31, 2020		398,600,000
Balance, beginning of period at Mar. 31, 2020	1,231	$ 53.6	4,450.2	(2,918.5)	(365)	(317.1)	327.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	(96.9)			(123.9)		11.2	15.8
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture		600,000
Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture	2.5		(6.6)		9.1
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders	(18.3)						(18.3)
Dividends, Common Stock	(0.1)			(0.1)
Balance, end of period (in shares) at Jun. 30, 2020		399,200,000
Balance, end of period at Jun. 30, 2020	1,118.2	$ 53.6	4,443.6	(3,042.5)	(355.9)	(305.9)	325.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	25.8			(10)		23.9	11.9
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture		0
Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture	3.8		2.7		1.1
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders	$ (24.1)						(24.1)
Balance, end of period (in shares) at Sep. 30, 2020	399,229,917	399,200,000
Balance, end of period at Sep. 30, 2020	$ 1,123.7	$ 53.6	$ 4,446.3	$ (3,052.5)	$ (354.8)	$ (282)	$ 313.1

BASIS OF PRESENTATION AND SIGNI

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Notes)	9 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Significant Accounting Policies [Text Block]	Business, Consolidation and Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with SEC rules and regulations and, in the opinion of management, include all adjustments (consisting of normal recurring adjustments) necessary to present fairly the financial position, results of operations, comprehensive income (loss), cash flows and changes in equity for the periods presented. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Management bases its estimates on various assumptions and historical experience, which are believed to be reasonable; however, due to the inherent nature of estimates, actual results may differ significantly due to changed conditions or assumptions. The results of operations for the three and nine months ended September 30, 2020 are not necessarily indicative of results to be expected for the year ending December 31, 2020 or any other future period. Due to the acquisition of AK Steel, certain balances have become material and are no longer being condensed in our Statements of Unaudited Condensed Consolidated Financial Position, such as balances for Right-of-use asset, operating lease and Operating lease liability, non-current . As a result, certain prior period amounts have been reclassified to conform with the current year presentation. These unaudited condensed consolidated financial statements should be read in conjunction with the financial statements and notes included in our Annual Report on Form 10-K for the year ended December 31, 2019 and in our Quarterly Reports on Form 10-Q for the quarterly periods ended March 31, 2020 and June 30, 2020. Proposed acquisition of substantially all of the operations of ArcelorMittal USA On September 28, 2020, we entered into a Transaction Agreement with ArcelorMittal S.A., pursuant to which Cliffs will acquire substantially all of the operations of ArcelorMittal USA for an aggregate purchase price of approximately $1.4 billion, consisting of (i) $505 million in cash, (ii) 78,186,671 of our common shares, par value $0.125 per share, and (iii) 583,273 shares of a new series of our Serial Preferred Stock, Class B, without par value, to be designated as the “Series B Participating Redeemable Preferred Stock” at closing. The cash portion of the purchase price is subject to customary working capital and purchase price adjustments. We expect to complete the Transaction in the fourth quarter of 2020. Completion of the Transaction is subject to various customary closing conditions, including the receipt of required regulatory approvals in identified jurisdictions, including the expiration or termination of the waiting period under the Hart-Scott-Rodino Act, and it is possible that factors outside of our control could result in the Transaction being completed at a later time or not at all. The Transaction Agreement also contains certain termination rights that may be exercised by either us or ArcelorMittal S.A. We plan to complete the Transaction as soon as reasonably practicable following the satisfaction or waiver of all applicable conditions. Acquisition of AK Steel On March 13, 2020, we consummated the Merger, pursuant to which, upon the terms and subject to the conditions set forth in the Merger Agreement, Merger Sub was merged with and into AK Steel, with AK Steel surviving the Merger as a wholly owned subsidiary of Cliffs. Refer to NOTE 3 - ACQUISITION OF AK STEEL for further information. AK Steel is a leading North American producer of flat-rolled carbon, stainless and electrical steel products, primarily for the automotive, infrastructure and manufacturing markets. The acquisition of AK Steel has transformed us into a vertically integrated producer of value-added iron ore and steel products. COVID-19 In response to the COVID-19 pandemic, we made various operational changes to adjust to the demand for our products. Although steel and iron ore production have been considered “essential” by the states in which we operate, certain of our facilities and construction activities were temporarily idled during the second quarter of 2020. Most of these temporarily idled facilities were restarted during the second quarter, and the remaining operations were restarted during the third quarter. Basis of Consolidation The unaudited condensed consolidated financial statements consolidate our accounts and the accounts of our wholly owned subsidiaries, all subsidiaries in which we have a controlling interest and two variable interest entities for which we are the primary beneficiary. All intercompany transactions and balances are eliminated upon consolidation. Reportable Segments The acquisition of AK Steel has transformed us into a vertically integrated producer of value-added iron ore and steel products and we are organized according to our differentiated products in two reportable segments - the Steel and Manufacturing segment and the Mining and Pelletizing segment. Our new Steel and Manufacturing segment includes the assets acquired through the acquisition of AK Steel and our previously reported Metallics segment, and our Mining and Pelletizing segment includes our three active operating mines and our indefinitely idled mine. Investments in Affiliates We have investments in several businesses accounted for using the equity method of accounting. We review an investment for impairment when circumstances indicate that a loss in value below its carrying amount is other than temporary. Investees and equity ownership percentages are presented below: Investee Segment Reported Within Equity Ownership Percentage Combined Metals of Chicago, LLC Steel and Manufacturing 40.0% Hibbing Taconite Company Mining and Pelletizing 23.0% Spartan Steel Coating, LLC Steel and Manufacturing 48.0% We recorded a basis difference for Spartan Steel of $32.5 million as part of our acquisition of AK Steel. The basis difference relates to the excess of the fair value over the investee's carrying amount of property, plant and equipment and will be amortized over the remaining useful lives of the underlying assets. Significant Accounting Policies A detailed description of our significant accounting policies can be found in the audited financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2019 filed with the SEC, which were updated and can be found in the unaudited condensed consolidated financial statements included in our Quarterly Reports on Form 10-Q for the quarterly periods ended March 31, 2020 and June 30, 2020 filed with the SEC. There have been no material changes in our significant accounting policies and estimates from those disclosed therein. Recent Accounting Pronouncements Issued and Adopted On March 2, 2020, the SEC issued a final rule that amended the disclosure requirements related to certain registered securities under SEC Regulation S-X, Rule 3-10, which required separate financial statements for subsidiary issuers and guarantors of registered debt securities unless certain exceptions are met. The final rule replaces the previous requirement under Rule 3-10 to provide condensed consolidating financial information in the registrant’s financial statements with a requirement to provide alternative financial disclosures (which include summarized financial information of the parent and any issuers and guarantors, as well as other qualitative disclosures) in either the registrant’s Management's Discussion and Analysis of Financial Condition and Results of Operations or its financial statements, in addition to other simplifications. The final rule is effective for filings on or after January 4, 2021, and early adoption is permitted. We elected to early adopt this disclosure update for the period ended March 31, 2020. As a result, we have excluded the footnote disclosures required under the previous Rule 3-10, and applied the final rule by including the summarized financial information and qualitative disclosures in Part I - Item 2. Management's Discussion and Analysis of Financial Condition and Results of Operations of this Quarterly Report on Form 10-Q and Exhibit 22.1 , hereto. In August 2020, the Financial Accounting Standards Board issued Accounting Standards Update No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40).

SUPPLEMENTARY FINANCIAL STATEME

SUPPLEMENTARY FINANCIAL STATEMENT INFORMATION (Notes)	9 Months Ended
	Sep. 30, 2020
Disclosure Text Block [Abstract]
Supplementary Financial Statement Information	Revenues The following table represents our consolidated Revenues (excluding intercompany revenues) by market: (In Millions) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Steel and Manufacturing: Automotive $ 920.0 $ — $ 1,404.0 $ — Infrastructure and manufacturing 198.8 — 446.2 — Distributors and converters 142.9 — 344.1 — Total Steel and Manufacturing 1,261.7 — 2,194.3 — Mining and Pelletizing: Steel producers 1 384.3 555.6 903.5 1,455.8 Total revenues $ 1,646.0 $ 555.6 $ 3,097.8 $ 1,455.8 1 Includes Realization of deferred revenue of $34.6 million for the nine months ended September 30, 2020. The following table represents our consolidated Revenues (excluding intercompany revenues) by product line: (In Millions) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Steel and Manufacturing: Carbon steel $ 821.2 $ — $ 1,391.6 $ — Stainless and electrical steel 303.2 — 585.1 — Tubular products, components and other 137.3 — 217.6 — Total Steel and Manufacturing 1,261.7 — 2,194.3 — Mining and Pelletizing: Iron ore 1 357.1 515.0 838.1 1,357.8 Freight 27.2 40.6 65.4 98.0 Total Mining and Pelletizing 384.3 555.6 903.5 1,455.8 Total revenues $ 1,646.0 $ 555.6 $ 3,097.8 $ 1,455.8 1 Includes Realization of deferred revenue of $34.6 million for the nine months ended September 30, 2020. We sell to customers located primarily in the United States and to foreign customers, primarily in Canada, Mexico and Western Europe. Net revenues to customers located outside the United States were $265.0 million and $487.7 million for the three and nine months ended September 30, 2020, respectively, and $138.9 million and $318.3 million for the three and nine months ended September 30, 2019, respectively. Allowance for Credit Losses The following is a roll forward of our allowance for credit losses associated with Accounts receivable, net : (In Millions) 2020 2019 Allowance for credit losses as of January 1 $ — $ — Increase in allowance 5.2 — Allowance for credit losses as of September 30 $ 5.2 $ — Inventories The following table presents the detail of our Inventories in the Statements of Unaudited Condensed Consolidated Financial Position: (In Millions) September 30, December 31, Product inventories Finished and semi-finished goods $ 940.5 $ 114.1 Work-in-process 78.2 68.7 Raw materials 382.3 9.4 Total product inventories 1,401.0 192.2 Manufacturing supplies and critical spares 394.1 125.2 Inventories $ 1,795.1 $ 317.4 Deferred Revenue The table below summarizes our deferred revenue balances: (In Millions) Deferred Revenue (Current) Deferred Revenue (Long-Term) 2020 2019 2020 2019 Opening balance as of January 1 $ 22.1 $ 21.0 $ 25.7 $ 38.5 Net decrease (19.8) (2.7) (25.7) (8.5) Closing balance as of September 30 $ 2.3 $ 18.3 $ — $ 30.0 Prior to the Merger, our iron ore pellet sales agreement with Severstal, subsequently assumed by AK Steel, required supplemental payments to be paid by the customer during the period 2009 through 2013. Installment amounts received under this arrangement in excess of sales were classified as deferred revenue in the Statements of Consolidated Financial Position upon receipt of payment and the revenue was recognized over the term of the supply agreement, which had extended until 2022, in equal annual installments. As a result of the termination of that iron ore pellet sales agreement, we realized $34.6 million of deferred revenue, which was recognized within Realization of deferred revenue in the Statements of Unaudited Condensed Consolidated Operations, during the nine months ended September 30, 2020. We have certain other sales agreements that require customers to pay in advance. Payments received pursuant to these agreements prior to revenue being recognized are recorded as deferred revenue in Other current liabilities. Accrued Liabilities The following table presents the detail of our Accrued liabilities in the Statements of Unaudited Condensed Consolidated Financial Position: (In Millions) September 30, December 31, 2019 Accrued employment costs $ 146.6 $ 61.7 Accrued interest 81.8 29.0 Accrued dividends 1.0 17.8 Other 50.0 17.8 Accrued liabilities $ 279.4 $ 126.3 Cash Flow Information A reconciliation of capital additions to cash paid for capital expenditures is as follows: (In Millions) Nine Months Ended 2020 2019 Capital additions $ 333.0 $ 505.6 Less: Non-cash accruals (88.4) 26.1 Right-of-use assets - finance leases 42.5 29.3 Grants — (10.5) Cash paid for capital expenditures including deposits $ 378.9 $ 460.7 Cash payments (receipts) for income taxes and interest are as follows: (In Millions) Nine Months Ended 2020 2019 Taxes paid on income $ 3.2 $ 0.1 Income tax refunds (119.3) (117.9) Interest paid on debt obligations net of capitalized interest 1 106.0 71.9 1 Capitalized interest was $38.0 million and $16.9 million for the nine months ended September 30, 2020 and 2019, respectively. Non-Cash Investing and Financing Activities (In Millions) Nine Months Ended 2020 2019 Fair value of common shares issued for consideration for business combination $ 617.6 $ — Fair value of equity awards assumed from AK Steel acquisition 3.9 —

ACQUISITION OF AK STEEL (Notes)

ACQUISITION OF AK STEEL (Notes)	9 Months Ended
	Sep. 30, 2020
Business Combinations [Abstract]
Business Combination Disclosure [Text Block]	Overview On March 13, 2020, pursuant to the Merger Agreement, we completed the acquisition of AK Steel, in which we were the acquirer. As a result of the Merger, each share of AK Steel common stock issued and outstanding immediately prior to the effective time of the Merger (other than excluded shares) was converted into the right to receive 0.400 Cliffs common shares and, if applicable, cash in lieu of any fractional Cliffs common shares. The acquisition combined Cliffs, North America’s largest producer of iron ore pellets, with AK Steel, a leading producer of innovative flat-rolled carbon, stainless and electrical steel products, to create a vertically integrated producer of value-added iron ore and steel products. The combination is expected to create significant opportunities to generate additional value from market trends across the entire steel value chain and enable more consistent, predictable performance through normal market cycles. Together, Cliffs and AK Steel have a presence across the entire manufacturing process, from mining to pelletizing to the development and production of finished high value steel products, including Next Generation Advanced High Strength Steels for automotive and other markets. We expect the combination will generate additional cost synergies, which we have identified and already set into motion savings of approximately $150 million, primarily from consolidating corporate functions, reducing duplicative overhead costs, and procurement and energy cost savings, as well as operational and supply chain efficiencies. The combined company is well positioned to provide high-value iron ore and steel solutions to customers primarily across North America. Total net revenues for AK Steel for the most recent pre-acquisition year ended December 31, 2019 were $6,359.4 million. Following the acquisition, the operating results of AK Steel are included in our unaudited condensed consolidated financial statements and are reported as part of our Steel and Manufacturing segment. For the three months ended September 30, 2020, AK Steel generated Revenues of $1,261.7 million and a loss of $30.4 million included within Net income (loss) attributable to Cliffs shareholders , which included $14.6 million and $2.4 million related to amortization of the fair value inventory step-up and severance costs, respectively. For the period subsequent to the acquisition (March 13, 2020 through September 30, 2020), AK Steel generated Revenues of $2,194.3 million and a loss of $292.0 million included within Net income (loss) attributable to Cliffs shareholders , which included $74.0 million and $35.1 million related to amortization of the fair value inventory step-up and severance costs, respectively. Additionally, we incurred acquisition-related costs in connection with the acquisition of AK Steel, excluding severance costs, of $0.6 million and $25.6 million for the three and nine months ended September 30, 2020, respectively, which were recorded in Acquisition-related costs on the Statements of Unaudited Condensed Consolidated Operations . Refer to NOTE 7 - DEBT AND CREDIT FACILITIES for information regarding debt transactions executed in connection with the Merger. The Merger was accounted for under the acquisition method of accounting for business combinations. The acquisition date fair value of the consideration transferred totaled $1.5 billion. The following tables summarize the consideration paid for AK Steel and the estimated fair values of the assets acquired and liabilities assumed at the acquisition date. The fair value of the total purchase consideration was determined as follows: (In Millions) Fair value of Cliffs common shares issued for AK Steel outstanding common stock $ 617.6 Fair value of replacement equity awards 3.9 Fair value of AK Steel debt 913.6 Total purchase consideration $ 1,535.1 The fair value of Cliffs common shares issued for outstanding shares of AK Steel common stock and with respect to Cliffs common shares underlying converted AK Steel equity awards that vested upon completion of the Merger is calculated as follows: (In Millions, Except Per Share Amounts) Number of shares of AK Steel common stock issued and outstanding 316.9 Exchange ratio 0.400 Number of Cliffs common shares issued to AK Steel stockholders 126.8 Price per share of Cliffs common shares $ 4.87 Fair value of Cliffs common shares issued for AK Steel outstanding common stock $ 617.6 The fair value of AK Steel's debt included in the consideration is calculated as follows: (In Millions) Credit Facility $ 590.0 7.50% Senior Secured Notes due July 2023 323.6 Fair value of debt included in consideration $ 913.6 Valuation Assumption and Preliminary Purchase Price Allocation We estimated fair values at March 13, 2020 for the preliminary allocation of consideration to the net tangible and intangible assets acquired and liabilities assumed. During the measurement period, we will continue to obtain information to assist in finalizing the fair value of assets acquired and liabilities assumed, which may differ materially from these preliminary estimates. If we determine any measurement period adjustments are material, we will apply those adjustments, including any related impacts to net income, in the reporting period in which the adjustments are determined. We are in the process of conducting a valuation of the assets acquired and liabilities assumed related to the acquisition, most notably, inventories, including manufacturing supplies and critical spares, personal and real property, leases, investments, deferred taxes, asset retirement obligations, pension and OPEB liabilities and intangible assets and liabilities, and the final allocation will be made when completed, including the result of any identified goodwill. Accordingly, the provisional measurements noted below are preliminary and subject to modification in the future. The preliminary purchase price allocation to assets acquired and liabilities assumed in the Merger was: (In Millions) Initial Allocation of Consideration Measurement Period Adjustments Updated Preliminary Allocation Cash and cash equivalents $ 37.7 $ 2.0 $ 39.7 Accounts receivable 666.0 (3.1) 662.9 Inventories 1,562.8 (39.8) 1,523.0 Other current assets 67.5 (15.4) 52.1 Property, plant and equipment 2,184.4 (20.1) 2,164.3 Intangible assets 163.0 (15.0) 148.0 Right of use asset, operating leases 225.9 (16.3) 209.6 Other non-current assets 85.9 26.2 112.1 Accounts payable (636.3) (6.1) (642.4) Accrued liabilities (222.5) 0.1 (222.4) Other current liabilities (181.8) 6.6 (175.2) Long-term debt (1,179.4) — (1,179.4) Deferred income taxes (19.7) (0.2) (19.9) Operating lease liability, non-current (188.1) 12.7 (175.4) Intangible liabilities (140.0) 69.5 (70.5) Pension and OPEB liabilities (873.0) 2.1 (870.9) Asset retirement obligations (13.9) (2.0) (15.9) Other non-current liabilities (144.2) (2.3) (146.5) Net identifiable assets acquired 1,394.3 (1.1) 1,393.2 Goodwill 141.2 0.7 141.9 Total net assets acquired $ 1,535.5 $ (0.4) $ 1,535.1 During the second and third quarter of 2020, we made certain measurement period adjustments to the acquired assets and liabilities assumed due to clarification of information utilized to determine fair value during the measurement period. The Inventories measurement period adjustments of $39.8 million resulted in a favorable impact of $0.2 million and $8.0 million, respectively, to Cost of goods sold for the three and nine months ended September 30, 2020. The goodwill resulting from the acquisition of AK Steel was assigned to Precision Partners, our downstream tooling and stamping operations, and AK Tube, our tubing operations, that are reporting units included in the Steel and Manufacturing segment. Goodwill is calculated as the excess of the purchase price over the net identifiable assets recognized and primarily represents the growth opportunities in lightweighting solutions to automotive customers, as well as any synergistic benefits to be realized from the acquisition of AK Steel. None of the goodwill is expected be deductible for income tax purposes. The preliminary purchase price allocated to identifiable intangible assets and liabilities acquired was: (In Millions) Weighted Average Life (In Years) Intangible assets: Customer relationships $ 77.0 18 Developed technology 60.0 17 Trade names and trademarks 11.0 10 Total identifiable intangible assets $ 148.0 17 Intangible liabilities: Above-market supply contracts $ (70.5) 12 The above-market supply contracts relate to the long-term coke and energy supply agreements with SunCoke Energy, which includes SunCoke Middletown, a consolidated VIE. Refer to NOTE 16 - VARIABLE INTEREST ENTITIES for further information. Pro Forma Results The following table provides unaudited pro forma financial information, prepared in accordance with Topic 805, for the three and nine months ended September 30, 2020 and 2019, as if AK Steel had been acquired as of January 1, 2019: (In Millions) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Revenues $ 1,646.0 $ 1,937.6 $ 4,265.1 $ 5,958.7 Net income (loss) attributable to Cliffs shareholders (6.0) 84.2 (123.9) 213.3 The unaudited pro forma financial information has been calculated after applying our accounting policies and adjusting the historical results with pro forma adjustments, net of tax, that assume the acquisition occurred on January 1, 2019. Significant pro forma adjustments include the following: 1. The elimination of intercompany revenues between Cliffs and AK Steel of $135.6 million and $394.8 million for the three and nine months ended September 30, 2020, respectively, and $153.5 million and $410.8 million for the three and nine months ended September 30, 2019, respectively. 2. The 2020 pro forma net loss was adjusted to exclude $14.6 million and $74.0 million of non-recurring inventory acquisition accounting adjustments incurred during the three and nine months ended September 30, 2020, respectively. The 2019 pro forma net income was adjusted to include $74.0 million of non-recurring inventory acquisition accounting adjustments for the nine months ended September 30, 2019. 3. The elimination of nonrecurring transaction costs incurred by Cliffs and AK Steel in connection with the Merger of $0.7 million and $29.1 million for the three and nine months ended September 30, 2020, respectively. 4. Total other pro forma adjustments included expense of $10.0 million for the three and nine months ended September 30, 2020, primarily due to increased interest expense, offset by reduced amortization expense, depreciation expense and pension and OPEB expense. Total other pro forma adjustments for the three and nine months ended September 30, 2019 included expense of $1.1 million and $7.0 million, respectively, primarily due to reduced interest and amortization expense, offset by additional depreciation expense and pension and OPEB expense. 5. The income tax impact of pro forma transaction adjustments that affect Net income (loss) attributable to Cliffs shareholders at a statutory rate of 24.3% resulted in an income tax benefit of $5.6 million and $2.1 million for the three and nine months ended September 30, 2020, respectively, and an income tax benefit of $2.1 million and $4.5 million for the three and nine months ended September 30, 2019, respectively. The unaudited pro forma financial information does not reflect the potential realization of synergies or cost savings, nor does it reflect other costs relating to the integration of the two companies. This unaudited pro forma financial information should not be considered indicative of the results that would have actually occurred if the acquisition had been consummated on January 1, 2019, nor are they indicative of future results.

SEGMENT REPORTING (Notes)

SEGMENT REPORTING (Notes)	9 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Segment Reporting Disclosure	Our Company is a vertically integrated producer of value-added iron ore and steel products. Our operations are organized and managed in two operating segments according to our upstream and downstream operations. Our Steel and Manufacturing segment is a leading producer of flat-rolled carbon, stainless and electrical steel products, primarily for the automotive, infrastructure and manufacturing, and distributors and converters markets. Our Steel and Manufacturing segment includes subsidiaries that provide customer solutions with carbon and stainless steel tubing products, advanced-engineered solutions, tool design and build, hot- and cold-stamped steel components, and complex assemblies. Construction of our HBI production plant in Toledo, Ohio, included as part of our Steel and Manufacturing segment, is expected to be completed with production beginning in the fourth quarter of 2020. 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. All intercompany transactions were eliminated in consolidation. We evaluate performance on a segment basis, as well as a consolidated basis, based on Adjusted EBITDA, which is a non-GAAP measure. This measure is used by management, investors, lenders and other external users of our financial statements to assess our operating performance and to compare operating performance to other companies in the steel and iron ore industries. In addition, management believes Adjusted EBITDA is a useful measure to assess the earnings power of the business without the impact of capital structure and can be used to assess our ability to service debt and fund future capital expenditures in the business. Our results by segment are as follows: (In Millions, Except Sales Tons) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Sales volume (in thousands): Steel and Manufacturing (net tons) 1,117 — 1,935 — Mining and Pelletizing sales (long tons) 4,907 5,750 11,800 13,527 Less: Intercompany sales (long tons) (1,204) (346) (3,028) (384) Mining and Pelletizing consolidated sales (long tons) 3,703 5,404 8,772 13,143 Revenues: Steel and Manufacturing net sales to external customers $ 1,261.7 $ — $ 2,194.3 $ — Mining and Pelletizing net sales 1 520.3 590.6 1,238.7 1,494.8 Less: Intercompany sales (136.0) (35.0) (335.2) (39.0) Mining and Pelletizing net sales to external customers 384.3 555.6 903.5 1,455.8 Total revenues $ 1,646.0 $ 555.6 $ 3,097.8 $ 1,455.8 Adjusted EBITDA: Steel and Manufacturing $ 33.3 $ (2.1) $ (81.8) $ (4.0) Mining and Pelletizing 145.3 182.7 309.5 510.7 Corporate and eliminations (52.3) (36.5) (160.7) (93.0) Total Adjusted EBITDA $ 126.3 $ 144.1 $ 67.0 $ 413.7 1 Includes Realization of deferred revenue of $34.6 million for the nine months ended September 30, 2020. The following table provides a reconciliation of our consolidated Net income (loss) to total Adjusted EBITDA: (In Millions) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Net income (loss) $ 1.9 $ 90.9 $ (154.8) $ 229.6 Less: Interest expense, net (68.2) (25.4) (167.9) (76.8) Income tax benefit (expense) 22.4 (4.8) 98.5 (23.1) Depreciation, depletion and amortization (72.4) (22.2) (183.9) (63.1) Total EBITDA $ 120.1 $ 143.3 $ 98.5 $ 392.6 Less: EBITDA of noncontrolling interests 1 $ 16.2 $ — $ 41.3 $ — Gain (loss) on extinguishment of debt — — 132.6 (18.2) Severance costs (2.4) — (38.3) (1.7) Acquisition-related costs excluding severance costs (5.1) — (30.1) — Amortization of inventory step-up (14.6) — (74.0) — Impact of discontinued operations (0.3) (0.8) — (1.2) Total Adjusted EBITDA $ 126.3 $ 144.1 $ 67.0 $ 413.7 1 EBITDA of noncontrolling interests includes $11.9 million and $31.2 million for income and $4.3 million and $10.1 million for depreciation, depletion and amortization for the three and nine months ended September 30, 2020, respectively. The following summarizes our assets by segment: (In Millions) September 30, December 31, Assets: Steel and Manufacturing $ 6,345.7 $ 913.6 Mining and Pelletizing 1,643.3 1,643.1 Total segment assets 7,989.0 2,556.7 Corporate and Other (including discontinued operations) 491.9 947.1 Total assets $ 8,480.9 $ 3,503.8 The following table summarizes our capital additions by segment: (In Millions) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Capital additions 1 : Steel and Manufacturing $ 88.0 $ 160.5 $ 266.8 $ 398.0 Mining and Pelletizing 13.3 22.1 64.9 104.5 Corporate and Other 1.0 2.1 1.3 3.1 Total capital additions $ 102.3 $ 184.7 $ 333.0 $ 505.6 1 Refer to NOTE 2 - SUPPLEMENTARY FINANCIAL STATEMENT INFORMATION for additional information.

PROPERTY, PLANT AND EQUIPMENT (

PROPERTY, PLANT AND EQUIPMENT (Notes)	9 Months Ended
	Sep. 30, 2020
Property, Plant and Equipment [Abstract]
PROPERTY, PLANT AND EQUIPMENT	The following table indicates the carrying value of each of the major classes of our depreciable assets: (In Millions) September 30, December 31, Land, land improvements and mineral rights $ 653.2 $ 582.2 Buildings 454.4 157.8 Steel and Manufacturing equipment 2,128.0 42.0 Mining and Pelletizing equipment 1,455.2 1,413.6 Other 121.3 101.5 Construction-in-progress 1,145.9 730.3 Total property, plant and equipment 1 5,958.0 3,027.4 Allowance for depreciation and depletion (1,407.3) (1,098.4) Property, plant and equipment, net $ 4,550.7 $ 1,929.0 1 Includes right-of-use assets related to finance leases of $97.1 million and $49.0 million as of September 30, 2020 and December 31, 2019, respectively. We recorded capitalized interest into property, plant and equipment of $14.7 million and $38.0 million during the three and nine months ended September 30, 2020, respectively, and $7.0 million and $16.9 million for the three and nine months ended September 30, 2019, respectively. We recorded depreciation and depletion expense of $71.8 million and $182.5 million for the three and nine months ended September 30, 2020, respectively, and $22.0 million and $62.5 million for the three and nine months ended September 30, 2019, respectively.

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS AND LIABILITIES (Notes)	9 Months Ended
	Sep. 30, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets Disclosure [Text Block]	Goodwill The increase in the balance of Goodwill as of September 30, 2020, compared to December 31, 2019, is due to the preliminary assignment of $141.9 million to Goodwill in 2020 based on the preliminary purchase price allocation for the acquisition of AK Steel. The carrying amount of goodwill related to our Mining and Pelletizing segment was $2.1 million as of both September 30, 2020 and December 31, 2019. Intangible Assets and Liabilities The following is a summary of our intangible assets and liabilities: (In Millions) Classification 1 Gross Amount Accumulated Amortization Net Amount As of September 30, 2020 Intangible assets: Customer relationships Intangible assets, net $ 77.0 $ (2.6) $ 74.4 Developed technology Intangible assets, net 60.0 (2.1) 57.9 Trade names and trademarks Intangible assets, net 11.0 (0.7) 10.3 Mining permits Intangible assets, net 72.2 (24.7) 47.5 Total intangible assets $ 220.2 $ (30.1) $ 190.1 Intangible liabilities: Above-market supply contracts Intangible liabilities, net $ (70.5) $ 4.6 $ (65.9) As of December 31, 2019 Intangible assets: Mining permits Intangible assets, net $ 72.2 $ (24.1) $ 48.1 1 Amortization of intangible liabilities related to above-market supply contracts and intangible assets related to mining permits is recognized in Cost of goods sold . Amortization of all other intangible assets is recognized in Selling, general and administrative expenses. Amortization expense related to intangible assets was $2.5 million and $6.0 million for the three and nine months ended September 30, 2020, respectively, and $0.2 million and $0.6 million for the three and nine months ended September 30, 2019, respectively. Estimated future amortization expense related to intangible assets at September 30, 2020 is as follows: (In Millions) Years ending December 31, 2020 (remaining period of the year) $ 2.5 2021 10.0 2022 10.0 2023 10.0 2024 10.0 2025 10.0 Income from amortization related to the intangible liabilities was $1.9 million and $4.6 million for the three and nine months ended September 30, 2020, respectively. Estimated future amortization income related to the intangible liabilities at September 30, 2020 is as follows: (In Millions) Years ending December 31, 2020 (remaining period of the year) $ 2.0 2021 7.8 2022 7.8 2023 7.8 2024 7.8 2025 7.8

DEBT AND CREDIT FACILITIES (Not

DEBT AND CREDIT FACILITIES (Notes)	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
DEBT AND CREDIT FACILITIES	The following represents a summary of our long-term debt: (In Millions) September 30, 2020 Debt Instrument Issuer 1 Annual Effective Interest Rate Total Principal Amount Debt Issuance Costs Unamortized Premiums (Discounts) Total Debt Senior Secured Notes: 4.875% 2024 Senior Secured Notes Cliffs 5.00% $ 394.5 $ (3.7) $ (1.5) $ 389.3 9.875% 2025 Senior Secured Notes Cliffs 10.57% 955.2 (8.1) (25.8) 921.3 6.75% 2026 Senior Secured Notes Cliffs 6.99% 845.0 (21.4) (9.0) 814.6 Senior Unsecured Notes: 7.625% 2021 AK Senior Notes AK Steel 7.33% 33.5 — 0.1 33.6 7.50% 2023 AK Senior Notes AK Steel 6.17% 12.8 — 0.5 13.3 6.375% 2025 Senior Notes Cliffs 8.11% 64.3 (0.2) (4.6) 59.5 6.375% 2025 AK Senior Notes AK Steel 8.11% 38.4 — (2.7) 35.7 1.50% 2025 Convertible Senior Notes Cliffs 6.26% 296.3 (3.7) (53.0) 239.6 5.75% 2025 Senior Notes Cliffs 6.01% 396.2 (2.6) (4.1) 389.5 7.00% 2027 Senior Notes Cliffs 9.24% 88.0 (0.3) (9.6) 78.1 7.00% 2027 AK Senior Notes AK Steel 9.24% 56.3 — (6.0) 50.3 5.875% 2027 Senior Notes Cliffs 6.49% 555.5 (4.3) (18.6) 532.6 6.25% 2040 Senior Notes Cliffs 6.34% 262.7 (1.8) (2.8) 258.1 IRBs due 2024 to 2028 AK Steel Various 92.0 — 2.3 94.3 ABL Facility Cliffs 2 2.77% 2,000.0 — — 400.0 Total long-term debt $ 4,309.8 1 Unless otherwise noted, references in this column to "Cliffs" are to Cleveland-Cliffs Inc., and references to "AK Steel" are to AK Steel Corporation. 2 Refers to Cleveland-Cliffs Inc. as borrower under our ABL Facility. (In Millions) December 31, 2019 Debt Instrument Issuer 1 Annual Effective Interest Rate Total Principal Amount Debt Issuance Costs Unamortized Discounts Total Debt Senior Secured Notes: 4.875% 2024 Senior Notes Cliffs 5.00% $ 400.0 $ (4.6) $ (1.8) $ 393.6 Senior Unsecured Notes: 1.50% 2025 Convertible Senior Notes Cliffs 6.26% 316.3 (4.6) (65.0) 246.7 5.75% 2025 Senior Notes Cliffs 6.01% 473.3 (3.6) (5.5) 464.2 5.875% 2027 Senior Notes Cliffs 6.49% 750.0 (6.3) (27.3) 716.4 6.25% 2040 Senior Notes Cliffs 6.34% 298.4 (2.2) (3.3) 292.9 Former ABL Facility Cliffs 2 N/A 450.0 N/A N/A — Total long-term debt $ 2,113.8 1 Unless otherwise noted, references in this column to "Cliffs" are to Cleveland-Cliffs Inc. 2 Refers to Cleveland-Cliffs Inc. and certain of its subsidiaries as borrowers under our Former ABL Facility. Debt Extinguishments - 2020 On April 24, 2020, we used the net proceeds from the offering of the additional 9.875% 2025 Senior Secured Notes to repurchase $736.4 million aggregate principal amount of our outstanding senior notes of various series, which resulted in debt reduction of $181.2 million. During the second quarter of 2020, we also repurchased an additional $11.2 million aggregate principal amount of our outstanding senior notes of various series with cash on hand. On June 1, 2020, we redeemed $7.3 million aggregate principal amount of our outstanding 2020 IRBs. On March 13, 2020, in connection with the Merger, we purchased $364.2 million aggregate principal amount of 7.625% 2021 AK Senior Notes and $310.7 million aggregate principal amount of 7.50% 2023 AK Senior Notes upon early settlement of tender offers made by Cliffs. The net proceeds from the offering of 6.75% 2026 Senior Secured Notes, along with a portion of the ABL Facility borrowings, were used to fund such purchases. As the 7.625% 2021 AK Senior Notes and 7.50% 2023 AK Senior Notes were recorded at fair value just prior to being purchased, there was no gain or loss on extinguishment. Additionally, in connection with the final settlement of the tender offers, on March 27, 2020, we purchased $8.5 million aggregate principal amount of the 7.625% 2021 AK Senior Notes and $56.5 million aggregate principal amount of the 7.50% 2023 AK Senior Notes with cash on hand. The following is a summary of the debt extinguished and the respective gain on extinguishment: (In Millions) Nine Months Ended Debt Instrument Debt Extinguished Gain on Extinguishment 7.625% 2021 AK Senior Notes $ 372.7 $ 0.4 7.50% 2023 AK Senior Notes 367.2 2.8 4.875% 2024 Senior Secured Notes 5.5 0.5 6.375% 2025 Senior Notes 167.5 21.3 1.50% 2025 Convertible Senior Notes 20.0 1.3 5.75% 2025 Senior Notes 77.1 16.3 7.00% 2027 Senior Notes 247.3 28.4 5.875% 2027 Senior Notes 194.5 48.7 6.25% 2040 Senior Notes 35.7 12.9 $ 1,487.5 $ 132.6 Debt Extinguishments - 2019 The following is a summary of the debt extinguished with cash and the respective loss on extinguishment: (In Millions) Nine Months Ended Debt Instrument Debt Extinguished (Loss) on Extinguishment 4.875% 2021 Senior Notes $ 124.0 $ (5.3) 5.75% 2025 Senior Notes 600.0 (12.9) $ 724.0 $ (18.2) ABL Facility As of September 30, 2020, 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) September 30, Available borrowing base on ABL Facility 1 $ 1,715.2 Borrowings (400.0) Letter of credit obligations 2 (192.2) Borrowing capacity available $ 1,123.0 1 As of September 30, 2020, the ABL Facility has a maximum borrowing base of $2.0 billion. The available borrowing base is 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, employee severance, IRBs and environmental obligations. Debt Maturities The following represents a summary of our maturities of debt instruments based on the principal amounts outstanding at September 30, 2020: (In Millions) Maturities of Debt 2020 (remaining period of year) $ — 2021 33.5 2022 — 2023 12.8 2024 456.5 Thereafter 3,987.9 Total maturities of debt $ 4,490.7

FAIR VALUE MEASUREMENTS (Notes)

FAIR VALUE MEASUREMENTS (Notes)	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	The following represents the assets and liabilities measured at fair value: (In Millions) September 30, 2020 Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Assets: Other current assets: Commodity contracts $ — $ 15.8 $ — $ 15.8 Customer supply agreement — — 34.5 34.5 Provisional pricing arrangement — — 26.9 26.9 Other non-current assets: Commodity contracts — 1.8 — 1.8 Total $ — $ 17.6 $ 61.4 $ 79.0 Liabilities: Other current liabilities: Commodity contracts $ — $ (8.7) $ — $ (8.7) Provisional pricing arrangement — — (0.3) (0.3) Foreign exchange contracts — (0.6) — (0.6) Other non-current liabilities: Foreign exchange contracts — (0.1) — (0.1) Total $ — $ (9.4) $ (0.3) $ (9.7) (In Millions) December 31, 2019 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 - Commercial paper $ — $ 187.6 $ — $ 187.6 Other current assets: Customer supply agreement — — 44.5 44.5 Provisional pricing arrangement — — 1.3 1.3 Total $ — $ 187.6 $ 45.8 $ 233.4 Liabilities: Other current liabilities: Commodity contracts $ — $ (3.2) $ — $ (3.2) Provisional pricing arrangement — — (1.1) (1.1) Total $ — $ (3.2) $ (1.1) $ (4.3) The valuation of financial assets and liabilities classified in Level 2 is determined using a market approach based upon quoted prices for similar assets and liabilities in active markets, or other inputs that are observable. Level 2 assets include commercial paper and commodity hedge contracts. Our commodity hedge contracts primarily include those related to natural gas, electricity and zinc, and our foreign exchange contracts include Canadian dollars. The Level 3 assets consist of a freestanding derivative instrument related to a certain supply agreement and derivative assets related to certain provisional pricing arrangements with our customers. The Level 3 liabilities consist of derivative liabilities related to certain provisional pricing arrangements with our customers. The supply agreement included in our Level 3 assets contains provisions for supplemental revenue or refunds based on the hot-rolled coil steel price in the year the iron ore product is consumed in the customer’s blast furnaces. We account for these provisions as a derivative instrument at the time of sale and adjust the derivative instrument to fair value through Revenues each reporting period until the product is consumed and the amounts are settled. 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 control has transferred upon delivery. The derivative instruments are adjusted to fair value through Revenues each reporting period based upon current market data and forward-looking estimates provided by management until the final revenue rates are determined. 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 September 30, 2020 Balance Sheet Valuation Technique Unobservable Input Range or Point Estimate (Weighted Average) Customer supply agreement $ 34.5 Other current assets Market Approach Management's estimate of hot-rolled coil steel price per net ton $542 - $634 $(548) Provisional pricing arrangements $ 26.9 Other current assets Market Approach Management's $104 - $123 ($105) Atlantic Basin Pellet Premium $30 Provisional pricing arrangements $ (0.3) Other current liabilities Market Approach Management's $104 PPI Estimates 110 The following tables represent a reconciliation of the changes in fair value of financial instruments measured at fair value on a recurring basis using significant unobservable inputs (Level 3): (In Millions) Level 3 Assets Three Months Ended Nine Months Ended 2020 2019 2020 2019 Beginning balance $ 35.3 $ 118.1 $ 45.8 $ 91.4 Total gains (losses) included in earnings 29.5 (6.5) 43.3 83.1 Settlements (3.4) (38.8) (27.7) (101.7) Ending balance $ 61.4 $ 72.8 $ 61.4 $ 72.8 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 $ 27.8 $ (6.5) $ 40.4 $ 81.8 (In Millions) Level 3 Liabilities Three Months Ended Nine Months Ended 2020 2019 2020 2019 Beginning balance $ — $ — $ (1.1) $ — Total losses included in earnings (0.3) (34.4) (0.9) (39.7) Settlements — 4.2 1.7 9.5 Ending balance $ (0.3) $ (30.2) $ (0.3) $ (30.2) Total losses for the period included in earnings attributable to the change in unrealized losses on liabilities still held at the reporting date $ (0.3) $ (30.2) $ (0.3) $ (30.2) 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) September 30, 2020 December 31, 2019 Classification Carrying Value Fair Value Carrying Value Fair Value Long-term debt: Senior Notes Level 1 $ 3,815.5 $ 3,975.2 $ 2,113.8 $ 2,237.0 IRBs due 2024 to 2028 Level 1 94.3 90.2 — — ABL Facility - outstanding balance Level 2 400.0 400.0 — — Total long-term debt $ 4,309.8 $ 4,465.4 $ 2,113.8 $ 2,237.0 The fair value of long-term debt was determined using quoted market prices.

PENSIONS AND OTHER POSTRETIREME

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Notes)	9 Months Ended
	Sep. 30, 2020
Postemployment Benefits [Abstract]
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. As a result of the acquisition of AK Steel, we assumed the obligations under AK Steel's defined benefit pension plans and OPEB plans. Noncontributory pension and various healthcare and life insurance benefits are provided to a significant portion of our employees and retirees. AK Steel also contributes to multiemployer pension plans according to collective bargaining agreements that cover certain union-represented employees and defined contribution pension plans. The AK Steel pension and OPEB plans were remeasured as of March 13, 2020. The following are the components of defined benefit pension and OPEB costs (credits): Defined Benefit Pension Costs (Credits) (In Millions) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Service cost $ 5.4 $ 4.6 $ 16.0 $ 12.9 Interest cost 19.6 8.9 42.7 26.2 Expected return on plan assets (36.7) (13.7) (91.9) (41.0) Amortization: Prior service costs 0.2 0.3 0.7 0.9 Net actuarial loss 7.3 5.9 20.6 17.7 Net periodic benefit cost (credit) $ (4.2) $ 6.0 $ (11.9) $ 16.7 OPEB Costs (Credits) (In Millions) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Service cost $ 1.4 $ 0.5 $ 3.3 $ 1.3 Interest cost 4.4 2.3 10.9 7.0 Expected return on plan assets (4.5) (4.2) (13.6) (12.6) Amortization: Prior service credits (0.5) (0.5) (1.5) (1.5) Net actuarial loss 0.8 1.3 2.2 3.8 Net periodic benefit cost (credit) $ 1.6 $ (0.6) $ 1.3 $ (2.0) As a result of the CARES Act enacted on March 27, 2020, we have deferred pension contributions starting in the second quarter of 2020. Based on prior funding requirements, we made defined benefit pension contributions of $0.9 million and $4.9 million for the three and nine months ended September 30, 2020, respectively, compared to defined benefit pension contributions of $5.6 million and $12.3 million for the three and nine months ended September 30, 2019, respectively. OPEB contributions for our voluntary employee benefit association trust plans are typically made on an annual basis in the first quarter of each year, but due to plan funding requirements being met, no OPEB contributions for our voluntary employee benefit association trust plans were required or made for the three and nine months ended September 30, 2020 and 2019.

INCOME TAXES (Notes)

INCOME TAXES (Notes)	9 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Our 2020 estimated annual effective tax rate before discrete items as of September 30, 2020 is 35.5%. The estimated annual effective tax rate differs from the U.S. statutory rate of 21.0% primarily due to the deduction for percentage depletion in excess of cost depletion related to our Mining and Pelletizing segment operations, as well as non-deductible transaction costs, executive officers' compensation, global intangible low-taxed income and income of noncontrolling interests for which no tax is recognized. The 2019 estimated annual effective tax rate before discrete items as of September 30, 2019 was 9.6%. The increase in the estimated annual effective tax rate before discrete items is driven by the change in the mix of income, as well as transaction costs and other acquisition-related charges that were incurred only in 2020.    For the three and nine months ended September 30, 2020, we recorded discrete items that resulted in an income tax benefit of $5.0 million and $8.6 million, respectively. The discrete adjustments are primarily related to the release of uncertain tax positions due to favorable resolution of an international audit issue. The discrete adjustments also include interest on uncertain tax positions and the refunds received during the year of amounts sequestered by the Internal Revenue Service on previously filed AMT credit refund claims. For the three and nine months ended September 30, 2019, we recorded discrete items that resulted in an income tax benefit of $0.5 million and $1.3 million, respectively.

ASSET RETIREMENT OBLIGATIONS (N

ASSET RETIREMENT OBLIGATIONS (Notes)	9 Months Ended
	Sep. 30, 2020
Asset Retirement Obligation [Abstract]
ASSET RETIREMENT OBLIGATIONS	The following is a summary of our asset retirement obligations: (In Millions) September 30, December 31, Asset retirement obligations 1 $ 186.4 $ 165.3 Less current portion 4.4 2.1 Long-term asset retirement obligations $ 182.0 $ 163.2 1 Includes $33.7 million and $22.0 million related to our active operations as of September 30, 2020 and December 31, 2019, respectively. The accrued closure obligation is predominantly related to our indefinitely idled and closed iron ore mining operations and provides for contractual and legal obligations associated with the eventual closure of those operations. Additionally, we have included in our asset retirement obligation $16.7 million for our integrated steel facilities and other operations acquired in the Merger. The closure date for each of our active mine sites was determined based on the exhaustion date of the remaining iron ore reserves and the amortization of the related asset and accretion of the liability is recognized over the estimated mine lives. 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. As the majority of our asset retirement obligations at our steelmaking operations have indeterminate settlement dates, asset retirement obligations have been recorded at present values using estimated ranges of the economic lives of the underlying assets. The following is a roll forward of our asset retirement obligation liability: (In Millions) 2020 2019 Asset retirement obligation as of January 1 $ 165.3 $ 172.4 Increase from AK Steel acquisition 16.7 — Accretion expense 7.8 7.6 Remediation payments (3.4) (0.5) Asset retirement obligation as of September 30 $ 186.4 $ 179.5

DERIVATIVE INSTRUMENTS (Notes)

DERIVATIVE INSTRUMENTS (Notes)	9 Months Ended
	Sep. 30, 2020
Derivative Instruments and Hedging Activities Disclosure [Abstract]
DERIVATIVE INSTRUMENTS	The following table presents the fair value of our derivative instruments and the classification of each in the Statements of Unaudited Condensed Consolidated Financial Position: Derivatives designated as hedging instruments under Topic 815: Derivatives not designated as hedging instruments under Topic 815: Derivative Asset (Liability) September 30, December 31, September 30, December 31, Other current assets: Customer supply agreement $ — $ — $ 34.5 $ 44.5 Provisional pricing arrangements — — 26.9 1.3 Commodity contracts 7.9 — 7.9 — Other non-current assets: Commodity contracts 1.8 — — — Other current liabilities: Provisional pricing arrangements — — (0.3) (1.1) Commodity contracts (1.8) (3.2) (6.9) — Foreign exchange contracts (0.6) — — — Other non-current liabilities: Foreign exchange contracts (0.1) — — — Derivatives Designated as Hedging Instruments - Cash Flow Hedges Exchange rate fluctuations affect a portion of revenues and operating costs that are denominated in foreign currencies, and we use forward currency and currency option contracts to reduce our exposure to certain of these currency price fluctuations. Contracts to purchase Canadian dollars are designated as cash flow hedges for accounting purposes, and we record the gains and losses for the derivatives and premiums paid for option contracts in Accumulated other comprehensive loss until we reclassify them into Cost of goods sold when we recognize the associated underlying operating costs. We are exposed to fluctuations in market prices of raw materials and energy sources. We may use cash-settled commodity swaps and options to hedge the market risk associated with the purchase of certain of our raw materials and energy requirements. Our hedging strategy is to reduce the effect on earnings from the price volatility of these various commodity exposures, including timing differences between when we incur raw material commodity costs and when we receive sales surcharges from our customers based on those raw materials. Independent of any hedging activities, price changes in any of these commodity markets could negatively affect operating costs. The following table presents the notional amount of our outstanding hedge contracts: (In Millions) September 30, 2020 December 31, 2019 Unit of Measure Maturity Dates Notional Amount Notional Amount Commodity contracts: Natural gas MMBtu October 2020 - December 2021 29.7 20.1 Diesel Gallons — — 0.8 Zinc Pounds October 2020 - December 2021 10.9 — Electricity Megawatt hours October 2020 - December 2021 0.8 — Foreign exchange contracts: Canadian dollars CAD October 2020 - December 2021 C$ 38.8 C$ — Estimated gains before tax expected to be reclassified into Cost of goods sold within the next 12 months for our existing derivatives that qualify as cash flow hedges are presented below: (In Millions) Hedge: Estimated Gains Natural gas $ 10.8 Zinc 2.3 Electricity 1.1 Canadian dollars 0.2 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 hot-rolled coil steel price at the time the iron ore product is consumed in the customer’s blast furnaces. The supplemental pricing is characterized as a freestanding derivative instrument 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 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, Atlantic Basin Pellet Premium, Platts international indexed freight rates and changes in specified PPI. 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 sales contract and are integral to the host sales 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 instrument and accounted for separately. Subsequently, the derivative instruments are adjusted to fair value through Revenues each reporting period based upon current market data and forward-looking estimates provided by management until the final revenue rate is determined. The following summarizes the effect of our derivatives that are not designated as hedging instruments in the Statements of Unaudited Condensed Consolidated Operations: (In Millions) Derivatives Not Designated as Hedging Instruments Location of Gain (Loss) Recognized in Income on Derivatives Three Months Ended Nine Months Ended 2020 2019 2020 2019 Customer supply agreements Revenues $ 8.8 $ 7.6 $ 14.4 $ 82.2 Provisional pricing arrangements Revenues 20.4 (48.5) 28.0 (38.8) Commodity contracts Cost of goods sold 3.9 — (0.8) — Total $ 33.1 $ (40.9) $ 41.6 $ 43.4 Refer to NOTE 8 - FAIR VALUE MEASUREMENTS for additional information.

SHAREHOLDERS' EQUITY (Notes)

SHAREHOLDERS' EQUITY (Notes)	9 Months Ended
	Sep. 30, 2020
Stockholders' Equity Note [Abstract]
SHAREHOLDERS' EQUITY	Acquisition of AK Steel As more fully described in NOTE 3 - ACQUISITION OF AK STEEL, we acquired AK Steel on March 13, 2020. At the effective time of the Merger, each share of AK Steel common stock issued and outstanding prior to the effective time of the Merger was converted into, and became exchangeable for, 0.400 Cliffs common shares, par value $0.125 per share. We issued a total of 126.8 million Cliffs common shares in connection with the Merger at a fair value of $617.6 million. Following the closing of the Merger, AK Steel's common stock was de-listed from the New York Stock Exchange. Dividends The below table summarizes our recent dividend activity: Declaration Date Record Date Payment Date Dividend Declared per Common Share 1 2/18/2020 4/3/2020 4/15/2020 $ 0.06 12/2/2019 1/3/2020 1/15/2020 0.06 9/3/2019 10/4/2019 10/15/2019 0.10 5/31/2019 7/5/2019 7/15/2019 0.06 2/19/2019 4/5/2019 4/15/2019 0.05 10/18/2018 1/4/2019 1/15/2019 0.05 1 The dividend declared on September 3, 2019 included a special cash dividend of $0.04 per common share. Subsequent to the dividend paid on April 15, 2020, our Board temporarily suspended future dividends as a result of the COVID-19 pandemic in order to preserve cash during this time of economic uncertainty. Preferred Stock We have 3,000,000 shares of Serial Preferred Stock, Class A, without par value, authorized and 4,000,000 shares of Serial Preferred Stock, Class B, without par value, authorized; no preferred shares are issued or outstanding. Pursuant to the terms of the Transaction Agreement, we agreed to issue ArcelorMittal S.A. 583,273 shares of a new series of our Serial Preferred Stock, Class B, without par value, to be designated as the "Series B Participating Redeemable Preferred Stock" at closing of the pending Transaction. Share Repurchase Program

ACCUMULATED OTHER COMPREHENSIVE

ACCUMULATED OTHER COMPREHENSIVE LOSS (Notes)	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Comprehensive Income (Loss) Note [Text Block]	The following tables reflect the changes in Accumulated other comprehensive loss related to shareholders’ equity: (In Millions) Postretirement Benefit Liability, Foreign Currency Translation Derivative Financial Instruments, net of tax Accumulated Other Comprehensive Loss December 31, 2019 $ (315.7) $ — $ (3.1) $ (318.8) Other comprehensive loss before reclassifications — (0.9) (5.2) (6.1) Net loss reclassified from accumulated other comprehensive loss 5.6 — 2.2 7.8 March 31, 2020 $ (310.1) $ (0.9) $ (6.1) $ (317.1) Other comprehensive income before reclassifications 0.4 0.7 1.4 2.5 Net loss reclassified from accumulated other comprehensive loss 5.6 — 3.1 8.7 June 30, 2020 $ (304.1) $ (0.2) $ (1.6) $ (305.9) Other comprehensive income before reclassifications 0.4 1.6 12.2 14.2 Net loss reclassified from accumulated other comprehensive loss 6.2 — 3.5 9.7 September 30, 2020 $ (297.5) $ 1.4 $ 14.1 $ (282.0) (In Millions) Postretirement Benefit Liability, net of tax Derivative Financial Instruments, net of tax Accumulated Other Comprehensive Loss December 31, 2018 $ (281.1) $ (2.8) $ (283.9) Other comprehensive income before reclassifications 0.2 2.5 2.7 Net loss reclassified from accumulated other comprehensive loss 5.5 0.2 5.7 March 31, 2019 $ (275.4) $ (0.1) $ (275.5) Other comprehensive income (loss) before reclassifications 0.3 (2.3) (2.0) Net loss reclassified from accumulated other comprehensive loss 5.5 0.2 5.7 June 30, 2019 $ (269.6) $ (2.2) $ (271.8) Other comprehensive income (loss) before reclassifications 0.3 (0.5) (0.2) Net loss reclassified from accumulated other comprehensive loss 5.5 0.9 6.4 September 30, 2019 $ (263.8) $ (1.8) $ (265.6) The following table reflects the details about Accumulated other comprehensive loss components related to shareholders’ equity: (In Millions) Details about Accumulated Other Comprehensive Loss Components Amount of (Gain)/Loss Reclassified into Income, Net of Tax Affected Line Item in the Statement of Unaudited Condensed Consolidated Operations Three Months Ended Nine Months Ended 2020 2019 2020 2019 Amortization of pension and OPEB liability: Prior service credits $ (0.3) $ (0.2) $ (0.8) $ (0.6) Other non-operating income Net actuarial loss 8.1 7.2 22.8 21.5 Other non-operating income 7.8 7.0 22.0 20.9 Total before taxes (1.6) (1.5) (4.6) (4.4) Income tax benefit (expense) $ 6.2 $ 5.5 $ 17.4 $ 16.5 Net of taxes Unrealized loss on derivative financial instruments: Commodity contracts $ 4.5 $ 1.2 $ 11.2 $ 1.7 Cost of goods sold (1.0) (0.3) (2.4) (0.4) Income tax benefit (expense) $ 3.5 $ 0.9 $ 8.8 $ 1.3 Net of taxes Total reclassifications for the period, net of tax $ 9.7 $ 6.4 $ 26.2 $ 17.8

RELATED PARTIES (Notes)

RELATED PARTIES (Notes)	9 Months Ended
	Sep. 30, 2020
Related Party Transactions [Abstract]
RELATED PARTIES	We have certain co-owned joint ventures with companies from the steel and mining industries, including integrated steel companies, their subsidiaries and other downstream users of steel and iron ore products. In addition, we have certain long-term contracts, and from time to time, enter into other sales agreements with these parties, and as a result, generate Revenues from related parties. Hibbing is a co-owned joint venture with companies that are integrated steel producers or their subsidiaries. The following is a summary of the mine ownership of the co-owned iron ore mine at September 30, 2020: Mine Cleveland-Cliffs Inc. ArcelorMittal USA U.S. Steel Hibbing 23.0% 62.3% 14.7% The tables below summarize our material related party transactions: Revenues from related parties were as follows: (Dollars In Millions) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Revenue from related parties $ 294.9 $ 293.5 $ 587.5 $ 792.8 Revenues 1 $ 1,646.0 $ 555.6 $ 3,097.8 $ 1,455.8 Related party revenues as a percent of Revenues 1 17.9 % 52.8 % 19.0 % 54.5 % Purchases from related parties $ 8.2 $ — $ 20.4 $ — 1 Includes Realization of deferred revenue of $34.6 million for the nine months ended September 30, 2020. The following table presents the classification of related party assets and liabilities in the Statements of Unaudited Condensed Consolidated Financial Position: (In Millions) Balance Sheet Location September 30, December 31, Accounts receivable, net $ 91.6 $ 31.1 Other current assets 58.5 44.5 Accounts payable (1.2) — Other current liabilities (1.7) (2.0) Other current assets A supply agreement with one customer provides for supplemental revenue or refunds to the customer based on the hot-rolled coil steel price at the time the product is consumed in the customer’s blast furnaces. The supplemental pricing is characterized as a freestanding derivative. Additionally, the customer also has certain provisional pricing arrangements where 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 control has transferred upon delivery. Refer to NOTE 12 - DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES for further information.

VARIABLE INTEREST ENTITIES (Not

VARIABLE INTEREST ENTITIES (Notes)	9 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Variable Interest Entity Disclosure [Text Block]	SunCoke Middletown We purchase all the coke and electrical power generated from SunCoke Middletown’s plant under long-term supply agreements. SunCoke Middletown is a VIE because we have committed to purchase all the expected production from the facility through 2032 and we are the primary beneficiary. Therefore, we consolidate SunCoke Middletown’s financial results with our financial results, even though we have no ownership interest in SunCoke Middletown. SunCoke Middletown had income before income taxes of $11.8 million and $31.3 million for the three and nine months ended September 30, 2020, respectively, that was included in our consolidated income before income taxes. The assets of the consolidated VIE can only be used to settle the obligations of the consolidated VIE and not obligations of the Company. The creditors of SunCoke Middletown do not have recourse to the assets or general credit of the Company to satisfy liabilities of the VIE. The consolidated balance sheet as of September 30, 2020 includes the following amounts for SunCoke Middletown: (In Millions) September 30, Cash and cash equivalents $ 0.3 Inventories 22.5 Property, plant and equipment, net 305.4 Accounts payable (10.0) Other assets (liabilities), net (5.6) Noncontrolling interests (312.6)

EARNINGS PER SHARE (Notes)

EARNINGS PER SHARE (Notes)	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
EARNINGS PER SHARE	The following table summarizes the computation of basic and diluted earnings per share: (In Millions, Except Per Share Amounts) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Income (loss) from continuing operations $ 2.2 $ 91.8 $ (154.8) $ 231.1 Income from continuing operations attributable to noncontrolling interest (11.9) — (31.2) — Net income (loss) from continuing operations attributable to Cliffs shareholders (9.7) 91.8 (186.0) 231.1 Loss from discontinued operations, net of tax (0.3) (0.9) — (1.5) Net income (loss) attributable to Cliffs shareholders $ (10.0) $ 90.9 $ (186.0) $ 229.6 Weighted average number of shares: Basic 399.4 270.0 365.2 278.4 Convertible senior notes — 3.7 — 5.8 Employee stock plans — 2.9 — 3.6 Diluted 399.4 276.6 365.2 287.8 Earnings (loss) per common share attributable to Cliffs shareholders - basic: Continuing operations $ (0.02) $ 0.34 $ (0.51) $ 0.83 Discontinued operations — — — (0.01) $ (0.02) $ 0.34 $ (0.51) $ 0.82 Earnings (loss) per common share attributable to Cliffs shareholders - diluted: Continuing operations $ (0.02) $ 0.33 $ (0.51) $ 0.80 Discontinued operations — — — — $ (0.02) $ 0.33 $ (0.51) $ 0.80 The following table summarizes the shares that have been excluded from the diluted earnings per share calculation as they were anti-dilutive: (In Millions) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Shares related to employee stock plans 1.8 — 1.6 — There was no dilution during the three and nine months ended September 30, 2020 related to the common share equivalents for the convertible senior notes as our common shares average price did not rise above the conversion price.

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Notes)	9 Months Ended
	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	Purchase Commitments HBI production plant In 2017, we began to incur capital commitments related to the construction of our HBI production plant in Toledo, Ohio; however, due to the COVID-19 pandemic, we temporarily halted construction in March 2020. In June 2020, we resumed construction and now expect to complete the project and begin production in the fourth quarter of 2020. In total, to complete the project, we expect to spend approximately $1 billion on the HBI production plant, excluding capitalized interest, of which $940.2 million was paid as of September 30, 2020. As of September 30, 2020, we have contracts and purchase orders in place for $97.8 million. Contingencies We are currently the subject of, or party to, various claims and legal proceedings incidental to our operations. 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 effect on the financial position and results of operations for the period in which the ruling occurs or future periods. However, based on currently available information we do not believe that any pending claims or legal proceedings will result in a material effect in relation to our consolidated financial statements. Environmental Contingencies Although we believe our operating practices have been consistent with prevailing industry standards, hazardous materials may have been released at operating sites or third-party sites in the past, including operating sites that we no longer own. If we reasonably can, we estimate potential remediation expenditures for those sites where future remediation efforts are probable based on identified conditions, regulatory requirements or contractual obligations arising from the sale of a business or facility. For sites involving government required investigations, we typically make an estimate of potential remediation expenditures only after the investigation is complete and when we better understand the nature and scope of the remediation. In general, the material factors in these estimates include the costs associated with investigations, delineations, risk assessments, remedial work, governmental response and oversight, site monitoring, and preparation of reports to the appropriate environmental agencies. The following is a summary of our environmental obligations: (In Millions) September 30, December 31, Environmental obligations $ 40.9 $ 2.0 Less current portion 6.4 0.3 Long-term environmental obligations $ 34.5 $ 1.7 We cannot predict the ultimate costs for each site with certainty because of the evolving nature of the investigation and remediation process. Rather, to estimate the probable costs, we must make certain assumptions. The most significant of these assumptions is for the nature and scope of the work that will be necessary to investigate and remediate a particular site and the cost of that work. Other significant assumptions include the cleanup technology that will be used, whether and to what extent any other parties will participate in paying the investigation and remediation costs, reimbursement of past response costs and future oversight costs by governmental agencies, and the reaction of the governing environmental agencies to the proposed work plans. Costs for future investigation and remediation are not discounted to their present value, unless the amount and timing of the cash disbursements are readily known. To the extent that we have been able to reasonably estimate future liabilities, we do not believe that there is a reasonable possibility that we will incur a loss or losses that exceed the amounts we accrued for the environmental matters discussed below that would, either individually or in the aggregate, have a material adverse effect on our consolidated financial condition, results of operations or cash flows. However, since we recognize amounts in the consolidated financial statements in accordance with GAAP that exclude potential losses that are not probable or that may not be currently estimable, the ultimate costs of these environmental matters may be higher than the liabilities we currently have recorded in our consolidated financial statements. Except as we expressly note below, we do not currently anticipate any material effect on our consolidated financial position, results of operations or cash flows as a result of compliance with current environmental regulations. Moreover, because all domestic steel and iron ore producers operate under the same federal environmental regulations, we do not believe that we are more disadvantaged than our domestic competitors by our need to comply with these regulations. Some foreign competitors may benefit from less stringent environmental requirements in the countries where they produce, resulting in lower compliance costs for them and providing those foreign competitors with a cost advantage on their products. According to RCRA, which governs the treatment, handling and disposal of hazardous waste, the EPA and authorized state environmental agencies may conduct inspections of RCRA-regulated facilities to identify areas where there have been releases of hazardous waste or hazardous constituents into the environment and may order the facilities to take corrective action to remediate such releases. Environmental regulators may inspect our major iron ore and steelmaking facilities. While we cannot predict the future actions of these regulators, it is possible that they may identify conditions in future inspections of these facilities which they believe require corrective action. Under authority from CERCLA, the EPA and state environmental authorities have conducted site investigations at certain of our facilities and other third-party facilities, portions of which previously may have been used for disposal of materials that are currently regulated. The results of these investigations are still pending, and we could be directed to spend funds for remedial activities at the former disposal areas. Because of the uncertain status of these investigations, however, we cannot reliably predict whether or when such spending might be required or its magnitude. On April 29, 2002, AK Steel entered a mutually agreed-upon administrative order on consent with the EPA pursuant to Section 122 of CERCLA to perform a Remedial Investigation/Feasibility Study (“RI/FS”) of the Hamilton Plant site located in New Miami, Ohio. The plant ceased operations in 1990 and all of its former structures have been demolished. AK Steel submitted the investigation portion of the RI/FS and completed supplemental studies. We currently have accrued $0.7 million for the remaining cost of the RI/FS. Until the RI/FS is complete, we cannot reliably estimate the additional costs, if any, we may incur for potentially required remediation of the site or when we may incur them. On September 26, 2012, the EPA issued an order under Section 3013 of RCRA requiring a plan to be developed for investigation of four areas at the Ashland Works coke plant. The Ashland Works coke plant ceased operations in 2011 and all of its former structures have been demolished and removed. In 1981, AK Steel acquired the plant from Honeywell International Corporation (as successor to Allied Corporation), who had managed the coking operations there for approximately 60 years. In connection with the sale of the coke plant, Honeywell agreed to indemnify AK Steel against certain claims and obligations that could arise from the investigation, and we intend to pursue such indemnification from Honeywell, if necessary. We cannot reliably estimate how long it will take to complete the site investigation. On March 10, 2016, the EPA invited AK Steel to participate in settlement discussions regarding an enforcement action. Settlement discussions between the parties are ongoing, though whether the parties will reach agreement and any such agreement’s terms are uncertain. We currently have accrued $1.4 million for the projected cost of the investigation and known remediation. Until the site investigation is complete, we cannot reliably estimate the costs, if any, we may incur for potential additional required remediation of the site or when we may incur them. On May 12, 2014, the Michigan Department of Environment, Great Lakes, and Energy (“EGLE”) (previously the Michigan Department of Environmental Quality) issued to Dearborn Works an Air Permit to Install No. 182-05C (the “PTI”) to increase the emission limits for the blast furnace and other emission sources. The PTI was issued as a correction to a prior permit to install that did not include certain information during the prior permitting process. On July 10, 2014, the South Dearborn Environmental Improvement Association (“SDEIA”), Detroiters Working for Environmental Justice, Original United Citizens of Southwest Detroit and the Sierra Club filed a Claim of Appeal of the PTI in the State of Michigan, Wayne County Circuit Court, Case No. 14-008887-AA. The appellants and EGLE required the intervention of Severstal Dearborn, LLC (later merged into AK Steel Corporation) in this action as an additional appellee. The appellants allege multiple deficiencies with the PTI and the permitting process. On July 2, 2019, the Circuit Court dismissed the PTI appeal and ruled that EGLE appropriately issued the permit modification. The appellants have appealed that decision. Until the appeal is resolved, we cannot determine what the ultimate permit limits will be. Until the permit limits are determined and final, we cannot reliably estimate the costs we may incur, if any, or when we may incur them. On August 21, 2014, the SDEIA filed a Complaint under the Michigan Environmental Protection Act (“MEPA”) in the State of Michigan, Wayne County Circuit Court, Case No. 14-010875-CE. The plaintiffs allege that the air emissions from Dearborn Works are impacting the air, water and other natural resources, as well as the public trust in such resources. The plaintiffs are requesting, among other requested relief, that the court assess and determine the sufficiency of the PTI’s limitations. On October 15, 2014, the court ordered a stay of the proceedings until a final order is issued in Wayne County Circuit Court Case No. 14-008887-AA (discussed above). When the proceedings resume, we intend to vigorously contest these claims. Until the claims in this complaint are resolved, we cannot reliably estimate the costs we may incur, if any, or when we may incur them. On November 18, 2019, November 26, 2019, and March 16, 2020, EGLE issued Notices of Violations (“NOVs”) with respect to the basic oxygen furnace electrostatic precipitator at Dearborn Works alleging violations of manganese, lead and opacity limits. We are investigating these claims and will work with EGLE to attempt to resolve them. We intend to vigorously contest any claims which cannot be resolved through a settlement. Until a settlement is reached with EGLE or the claims of the NOVs are otherwise resolved, we cannot reliably estimate the costs, if any, associated with any potentially required work. In addition to the foregoing matters, we are or may be involved in proceedings with various regulatory authorities that may require us to pay fines, comply with more rigorous standards or other requirements or incur capital and operating expenses for environmental compliance. We believe that the ultimate disposition of the proceedings will not have, individually or in the aggregate, a material adverse effect on our consolidated financial condition, results of operations or cash flows. Other Contingencies In addition to the matters discussed above, there are various pending and potential claims against us and our subsidiaries involving product liability, commercial, employee benefits, and other matters arising in the ordinary course of business. Because of the considerable uncertainties which exist for any claim, it is difficult to reliably or accurately estimate what the amount of a loss would be if a claimant prevails. If material assumptions or factual understandings we rely on to evaluate exposure for these contingencies prove to be inaccurate or otherwise change, we may be required to record a liability for an adverse outcome. If, however, we have reasonably evaluated potential future liabilities for all of these contingencies, including those described more specifically above, it is our opinion, unless we otherwise noted, that the ultimate liability from these contingencies, individually and in the aggregate, should not have a material adverse effect on our consolidated financial position, results of operations or cash flows.

SUBSEQUENT EVENTS (Notes)

SUBSEQUENT EVENTS (Notes)	9 Months Ended
	Sep. 30, 2020
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	We have evaluated subsequent events through the date of financial statement issuance.

BASIS OF PRESENTATION AND SIG_2

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Accounting	Business, Consolidation and Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with SEC rules and regulations and, in the opinion of management, include all adjustments (consisting of normal recurring adjustments) necessary to present fairly the financial position, results of operations, comprehensive income (loss), cash flows and changes in equity for the periods presented. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Management bases its estimates on various assumptions and historical experience, which are believed to be reasonable; however, due to the inherent nature of estimates, actual results may differ significantly due to changed conditions or assumptions. The results of operations for the three and nine months ended September 30, 2020 are not necessarily indicative of results to be expected for the year ending December 31, 2020 or any other future period. Due to the acquisition of AK Steel, certain balances have become material and are no longer being condensed in our Statements of Unaudited Condensed Consolidated Financial Position, such as balances for Right-of-use asset, operating lease and Operating lease liability, non-current . As a result, certain prior period amounts have been reclassified to conform with the current year presentation. These unaudited condensed consolidated financial statements should be read in conjunction with the financial statements and notes included in our Annual Report on Form 10-K for the year ended December 31, 2019 and in our Quarterly Reports on Form 10-Q for the quarterly periods ended March 31, 2020 and June 30, 2020.
Basis of Consolidation	Basis of Consolidation The unaudited condensed consolidated financial statements consolidate our accounts and the accounts of our wholly owned subsidiaries, all subsidiaries in which we have a controlling interest and two variable interest entities for which we are the primary beneficiary. All intercompany transactions and balances are eliminated upon consolidation. Reportable Segments
Equity Method Investments	Investments in Affiliates We have investments in several businesses accounted for using the equity method of accounting. We review an investment for impairment when circumstances indicate that a loss in value below its carrying amount is other than temporary. Investees and equity ownership percentages are presented below: Investee Segment Reported Within Equity Ownership Percentage Combined Metals of Chicago, LLC Steel and Manufacturing 40.0% Hibbing Taconite Company Mining and Pelletizing 23.0% Spartan Steel Coating, LLC Steel and Manufacturing 48.0%
New Accounting Pronouncements	Recent Accounting Pronouncements Issued and Adopted On March 2, 2020, the SEC issued a final rule that amended the disclosure requirements related to certain registered securities under SEC Regulation S-X, Rule 3-10, which required separate financial statements for subsidiary issuers and guarantors of registered debt securities unless certain exceptions are met. The final rule replaces the previous requirement under Rule 3-10 to provide condensed consolidating financial information in the registrant’s financial statements with a requirement to provide alternative financial disclosures (which include summarized financial information of the parent and any issuers and guarantors, as well as other qualitative disclosures) in either the registrant’s Management's Discussion and Analysis of Financial Condition and Results of Operations or its financial statements, in addition to other simplifications. The final rule is effective for filings on or after January 4, 2021, and early adoption is permitted. We elected to early adopt this disclosure update for the period ended March 31, 2020. As a result, we have excluded the footnote disclosures required under the previous Rule 3-10, and applied the final rule by including the summarized financial information and qualitative disclosures in Part I - Item 2. Management's Discussion and Analysis of Financial Condition and Results of Operations of this Quarterly Report on Form 10-Q and Exhibit 22.1 , hereto. In August 2020, the Financial Accounting Standards Board issued Accounting Standards Update No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40).

BASIS OF PRESENTATION AND SIG_3

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Tables)	9 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Equity Method Investments	Investees and equity ownership percentages are presented below: Investee Segment Reported Within Equity Ownership Percentage Combined Metals of Chicago, LLC Steel and Manufacturing 40.0% Hibbing Taconite Company Mining and Pelletizing 23.0% Spartan Steel Coating, LLC Steel and Manufacturing 48.0%

SUPPLEMENTARY FINANCIAL STATE_2

SUPPLEMENTARY FINANCIAL STATEMENT INFORMATION (Tables)	9 Months Ended
	Sep. 30, 2020
Disclosure Text Block [Abstract]
Revenues from Product Sales and Services [Table Text Block]	The following table represents our consolidated Revenues (excluding intercompany revenues) by market: (In Millions) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Steel and Manufacturing: Automotive $ 920.0 $ — $ 1,404.0 $ — Infrastructure and manufacturing 198.8 — 446.2 — Distributors and converters 142.9 — 344.1 — Total Steel and Manufacturing 1,261.7 — 2,194.3 — Mining and Pelletizing: Steel producers 1 384.3 555.6 903.5 1,455.8 Total revenues $ 1,646.0 $ 555.6 $ 3,097.8 $ 1,455.8 1 Includes Realization of deferred revenue of $34.6 million for the nine months ended September 30, 2020. The following table represents our consolidated Revenues (excluding intercompany revenues) by product line: (In Millions) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Steel and Manufacturing: Carbon steel $ 821.2 $ — $ 1,391.6 $ — Stainless and electrical steel 303.2 — 585.1 — Tubular products, components and other 137.3 — 217.6 — Total Steel and Manufacturing 1,261.7 — 2,194.3 — Mining and Pelletizing: Iron ore 1 357.1 515.0 838.1 1,357.8 Freight 27.2 40.6 65.4 98.0 Total Mining and Pelletizing 384.3 555.6 903.5 1,455.8 Total revenues $ 1,646.0 $ 555.6 $ 3,097.8 $ 1,455.8 1 Includes Realization of deferred revenue of $34.6 million for the nine months ended September 30, 2020.
Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block]	The following is a roll forward of our allowance for credit losses associated with Accounts receivable, net : (In Millions) 2020 2019 Allowance for credit losses as of January 1 $ — $ — Increase in allowance 5.2 — Allowance for credit losses as of September 30 $ 5.2 $ —
Schedule of Inventory, Current [Table Text Block]	The following table presents the detail of our Inventories in the Statements of Unaudited Condensed Consolidated Financial Position: (In Millions) September 30, December 31, Product inventories Finished and semi-finished goods $ 940.5 $ 114.1 Work-in-process 78.2 68.7 Raw materials 382.3 9.4 Total product inventories 1,401.0 192.2 Manufacturing supplies and critical spares 394.1 125.2 Inventories $ 1,795.1 $ 317.4
Contract with Customer, Asset and Liability [Table Text Block]	The table below summarizes our deferred revenue balances: (In Millions) Deferred Revenue (Current) Deferred Revenue (Long-Term) 2020 2019 2020 2019 Opening balance as of January 1 $ 22.1 $ 21.0 $ 25.7 $ 38.5 Net decrease (19.8) (2.7) (25.7) (8.5) Closing balance as of September 30 $ 2.3 $ 18.3 $ — $ 30.0
Schedule of Accrued Liabilities [Table Text Block]	The following table presents the detail of our Accrued liabilities in the Statements of Unaudited Condensed Consolidated Financial Position: (In Millions) September 30, December 31, 2019 Accrued employment costs $ 146.6 $ 61.7 Accrued interest 81.8 29.0 Accrued dividends 1.0 17.8 Other 50.0 17.8 Accrued liabilities $ 279.4 $ 126.3
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]	A reconciliation of capital additions to cash paid for capital expenditures is as follows: (In Millions) Nine Months Ended 2020 2019 Capital additions $ 333.0 $ 505.6 Less: Non-cash accruals (88.4) 26.1 Right-of-use assets - finance leases 42.5 29.3 Grants — (10.5) Cash paid for capital expenditures including deposits $ 378.9 $ 460.7 Cash payments (receipts) for income taxes and interest are as follows: (In Millions) Nine Months Ended 2020 2019 Taxes paid on income $ 3.2 $ 0.1 Income tax refunds (119.3) (117.9) Interest paid on debt obligations net of capitalized interest 1 106.0 71.9 1 Capitalized interest was $38.0 million and $16.9 million for the nine months ended September 30, 2020 and 2019, respectively. Non-Cash Investing and Financing Activities (In Millions) Nine Months Ended 2020 2019 Fair value of common shares issued for consideration for business combination $ 617.6 $ — Fair value of equity awards assumed from AK Steel acquisition 3.9 —

ACQUISITION OF AK STEEL (Tables

ACQUISITION OF AK STEEL (Tables)	9 Months Ended
	Sep. 30, 2020
Business Combinations [Abstract]
Schedule of Business Acquisitions by Acquisition, by Acquisition [Table Text Block]	The fair value of the total purchase consideration was determined as follows: (In Millions) Fair value of Cliffs common shares issued for AK Steel outstanding common stock $ 617.6 Fair value of replacement equity awards 3.9 Fair value of AK Steel debt 913.6 Total purchase consideration $ 1,535.1 (In Millions) Credit Facility $ 590.0 7.50% Senior Secured Notes due July 2023 323.6 Fair value of debt included in consideration $ 913.6
Schedule of Business Acquisitions by Acquisition, Equity Interest Issued or Issuable [Table Text Block]	The fair value of the total purchase consideration was determined as follows: (In Millions) Fair value of Cliffs common shares issued for AK Steel outstanding common stock $ 617.6 Fair value of replacement equity awards 3.9 Fair value of AK Steel debt 913.6 Total purchase consideration $ 1,535.1 The fair value of Cliffs common shares issued for outstanding shares of AK Steel common stock and with respect to Cliffs common shares underlying converted AK Steel equity awards that vested upon completion of the Merger is calculated as follows: (In Millions, Except Per Share Amounts) Number of shares of AK Steel common stock issued and outstanding 316.9 Exchange ratio 0.400 Number of Cliffs common shares issued to AK Steel stockholders 126.8 Price per share of Cliffs common shares $ 4.87 Fair value of Cliffs common shares issued for AK Steel outstanding common stock $ 617.6
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block]	The preliminary purchase price allocation to assets acquired and liabilities assumed in the Merger was: (In Millions) Initial Allocation of Consideration Measurement Period Adjustments Updated Preliminary Allocation Cash and cash equivalents $ 37.7 $ 2.0 $ 39.7 Accounts receivable 666.0 (3.1) 662.9 Inventories 1,562.8 (39.8) 1,523.0 Other current assets 67.5 (15.4) 52.1 Property, plant and equipment 2,184.4 (20.1) 2,164.3 Intangible assets 163.0 (15.0) 148.0 Right of use asset, operating leases 225.9 (16.3) 209.6 Other non-current assets 85.9 26.2 112.1 Accounts payable (636.3) (6.1) (642.4) Accrued liabilities (222.5) 0.1 (222.4) Other current liabilities (181.8) 6.6 (175.2) Long-term debt (1,179.4) — (1,179.4) Deferred income taxes (19.7) (0.2) (19.9) Operating lease liability, non-current (188.1) 12.7 (175.4) Intangible liabilities (140.0) 69.5 (70.5) Pension and OPEB liabilities (873.0) 2.1 (870.9) Asset retirement obligations (13.9) (2.0) (15.9) Other non-current liabilities (144.2) (2.3) (146.5) Net identifiable assets acquired 1,394.3 (1.1) 1,393.2 Goodwill 141.2 0.7 141.9 Total net assets acquired $ 1,535.5 $ (0.4) $ 1,535.1
Finite-Lived and Indefinite-Lived Intangible Assets Acquired as Part of Business Combination [Table Text Block]	The preliminary purchase price allocated to identifiable intangible assets and liabilities acquired was: (In Millions) Weighted Average Life (In Years) Intangible assets: Customer relationships $ 77.0 18 Developed technology 60.0 17 Trade names and trademarks 11.0 10 Total identifiable intangible assets $ 148.0 17 Intangible liabilities: Above-market supply contracts $ (70.5) 12
Business Acquisition, Pro Forma Information [Table Text Block]	The following table provides unaudited pro forma financial information, prepared in accordance with Topic 805, for the three and nine months ended September 30, 2020 and 2019, as if AK Steel had been acquired as of January 1, 2019: (In Millions) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Revenues $ 1,646.0 $ 1,937.6 $ 4,265.1 $ 5,958.7 Net income (loss) attributable to Cliffs shareholders (6.0) 84.2 (123.9) 213.3

SEGMENT REPORTING (Tables)

SEGMENT REPORTING (Tables)	9 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Schedule Of Segment Reporting Information, By Segment	Our results by segment are as follows: (In Millions, Except Sales Tons) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Sales volume (in thousands): Steel and Manufacturing (net tons) 1,117 — 1,935 — Mining and Pelletizing sales (long tons) 4,907 5,750 11,800 13,527 Less: Intercompany sales (long tons) (1,204) (346) (3,028) (384) Mining and Pelletizing consolidated sales (long tons) 3,703 5,404 8,772 13,143 Revenues: Steel and Manufacturing net sales to external customers $ 1,261.7 $ — $ 2,194.3 $ — Mining and Pelletizing net sales 1 520.3 590.6 1,238.7 1,494.8 Less: Intercompany sales (136.0) (35.0) (335.2) (39.0) Mining and Pelletizing net sales to external customers 384.3 555.6 903.5 1,455.8 Total revenues $ 1,646.0 $ 555.6 $ 3,097.8 $ 1,455.8 Adjusted EBITDA: Steel and Manufacturing $ 33.3 $ (2.1) $ (81.8) $ (4.0) Mining and Pelletizing 145.3 182.7 309.5 510.7 Corporate and eliminations (52.3) (36.5) (160.7) (93.0) Total Adjusted EBITDA $ 126.3 $ 144.1 $ 67.0 $ 413.7 1 Includes Realization of deferred revenue of $34.6 million for the nine months ended September 30, 2020. The following table provides a reconciliation of our consolidated Net income (loss) to total Adjusted EBITDA: (In Millions) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Net income (loss) $ 1.9 $ 90.9 $ (154.8) $ 229.6 Less: Interest expense, net (68.2) (25.4) (167.9) (76.8) Income tax benefit (expense) 22.4 (4.8) 98.5 (23.1) Depreciation, depletion and amortization (72.4) (22.2) (183.9) (63.1) Total EBITDA $ 120.1 $ 143.3 $ 98.5 $ 392.6 Less: EBITDA of noncontrolling interests 1 $ 16.2 $ — $ 41.3 $ — Gain (loss) on extinguishment of debt — — 132.6 (18.2) Severance costs (2.4) — (38.3) (1.7) Acquisition-related costs excluding severance costs (5.1) — (30.1) — Amortization of inventory step-up (14.6) — (74.0) — Impact of discontinued operations (0.3) (0.8) — (1.2) Total Adjusted EBITDA $ 126.3 $ 144.1 $ 67.0 $ 413.7 1 EBITDA of noncontrolling interests includes $11.9 million and $31.2 million for income and $4.3 million and $10.1 million for depreciation, depletion and amortization for the three and nine months ended September 30, 2020, respectively. (In Millions) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Capital additions 1 : Steel and Manufacturing $ 88.0 $ 160.5 $ 266.8 $ 398.0 Mining and Pelletizing 13.3 22.1 64.9 104.5 Corporate and Other 1.0 2.1 1.3 3.1 Total capital additions $ 102.3 $ 184.7 $ 333.0 $ 505.6 1 Refer to NOTE 2 - SUPPLEMENTARY FINANCIAL STATEMENT INFORMATION for additional information.
Reconciliation of Assets from Segment to Consolidated	The following summarizes our assets by segment: (In Millions) September 30, December 31, Assets: Steel and Manufacturing $ 6,345.7 $ 913.6 Mining and Pelletizing 1,643.3 1,643.1 Total segment assets 7,989.0 2,556.7 Corporate and Other (including discontinued operations) 491.9 947.1 Total assets $ 8,480.9 $ 3,503.8

PROPERTY, PLANT AND EQUIPMENT_2

PROPERTY, PLANT AND EQUIPMENT (Tables)	9 Months Ended
	Sep. 30, 2020
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 depreciable assets: (In Millions) September 30, December 31, Land, land improvements and mineral rights $ 653.2 $ 582.2 Buildings 454.4 157.8 Steel and Manufacturing equipment 2,128.0 42.0 Mining and Pelletizing equipment 1,455.2 1,413.6 Other 121.3 101.5 Construction-in-progress 1,145.9 730.3 Total property, plant and equipment 1 5,958.0 3,027.4 Allowance for depreciation and depletion (1,407.3) (1,098.4) Property, plant and equipment, net $ 4,550.7 $ 1,929.0 1 Includes right-of-use assets related to finance leases of $97.1 million and $49.0 million as of September 30, 2020 and December 31, 2019, respectively.

GOODWILL AND INTANGIBLE ASSET_2

GOODWILL AND INTANGIBLE ASSETS AND LIABILITIES (Tables)	9 Months Ended
	Sep. 30, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Intangible Assets and Goodwill [Table Text Block]	The following is a summary of our intangible assets and liabilities: (In Millions) Classification 1 Gross Amount Accumulated Amortization Net Amount As of September 30, 2020 Intangible assets: Customer relationships Intangible assets, net $ 77.0 $ (2.6) $ 74.4 Developed technology Intangible assets, net 60.0 (2.1) 57.9 Trade names and trademarks Intangible assets, net 11.0 (0.7) 10.3 Mining permits Intangible assets, net 72.2 (24.7) 47.5 Total intangible assets $ 220.2 $ (30.1) $ 190.1 Intangible liabilities: Above-market supply contracts Intangible liabilities, net $ (70.5) $ 4.6 $ (65.9) As of December 31, 2019 Intangible assets: Mining permits Intangible assets, net $ 72.2 $ (24.1) $ 48.1 1 Amortization of intangible liabilities related to above-market supply contracts and intangible assets related to mining permits is recognized in Cost of goods sold . Amortization of all other intangible assets is recognized in Selling, general and administrative expenses.
Finite-lived Intangible Assets Amortization Expense [Table Text Block]	Estimated future amortization expense related to intangible assets at September 30, 2020 is as follows: (In Millions) Years ending December 31, 2020 (remaining period of the year) $ 2.5 2021 10.0 2022 10.0 2023 10.0 2024 10.0 2025 10.0
Schedule of Finite-Lived Intangible Liabilities, Future Amortization Credit [Table Text Block]	Estimated future amortization income related to the intangible liabilities at September 30, 2020 is as follows: (In Millions) Years ending December 31, 2020 (remaining period of the year) $ 2.0 2021 7.8 2022 7.8 2023 7.8 2024 7.8 2025 7.8

DEBT AND CREDIT FACILITIES (Tab

DEBT AND CREDIT FACILITIES (Tables)	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Schedule Of Long-Term Debt	The following represents a summary of our long-term debt: (In Millions) September 30, 2020 Debt Instrument Issuer 1 Annual Effective Interest Rate Total Principal Amount Debt Issuance Costs Unamortized Premiums (Discounts) Total Debt Senior Secured Notes: 4.875% 2024 Senior Secured Notes Cliffs 5.00% $ 394.5 $ (3.7) $ (1.5) $ 389.3 9.875% 2025 Senior Secured Notes Cliffs 10.57% 955.2 (8.1) (25.8) 921.3 6.75% 2026 Senior Secured Notes Cliffs 6.99% 845.0 (21.4) (9.0) 814.6 Senior Unsecured Notes: 7.625% 2021 AK Senior Notes AK Steel 7.33% 33.5 — 0.1 33.6 7.50% 2023 AK Senior Notes AK Steel 6.17% 12.8 — 0.5 13.3 6.375% 2025 Senior Notes Cliffs 8.11% 64.3 (0.2) (4.6) 59.5 6.375% 2025 AK Senior Notes AK Steel 8.11% 38.4 — (2.7) 35.7 1.50% 2025 Convertible Senior Notes Cliffs 6.26% 296.3 (3.7) (53.0) 239.6 5.75% 2025 Senior Notes Cliffs 6.01% 396.2 (2.6) (4.1) 389.5 7.00% 2027 Senior Notes Cliffs 9.24% 88.0 (0.3) (9.6) 78.1 7.00% 2027 AK Senior Notes AK Steel 9.24% 56.3 — (6.0) 50.3 5.875% 2027 Senior Notes Cliffs 6.49% 555.5 (4.3) (18.6) 532.6 6.25% 2040 Senior Notes Cliffs 6.34% 262.7 (1.8) (2.8) 258.1 IRBs due 2024 to 2028 AK Steel Various 92.0 — 2.3 94.3 ABL Facility Cliffs 2 2.77% 2,000.0 — — 400.0 Total long-term debt $ 4,309.8 1 Unless otherwise noted, references in this column to "Cliffs" are to Cleveland-Cliffs Inc., and references to "AK Steel" are to AK Steel Corporation. 2 Refers to Cleveland-Cliffs Inc. as borrower under our ABL Facility. (In Millions) December 31, 2019 Debt Instrument Issuer 1 Annual Effective Interest Rate Total Principal Amount Debt Issuance Costs Unamortized Discounts Total Debt Senior Secured Notes: 4.875% 2024 Senior Notes Cliffs 5.00% $ 400.0 $ (4.6) $ (1.8) $ 393.6 Senior Unsecured Notes: 1.50% 2025 Convertible Senior Notes Cliffs 6.26% 316.3 (4.6) (65.0) 246.7 5.75% 2025 Senior Notes Cliffs 6.01% 473.3 (3.6) (5.5) 464.2 5.875% 2027 Senior Notes Cliffs 6.49% 750.0 (6.3) (27.3) 716.4 6.25% 2040 Senior Notes Cliffs 6.34% 298.4 (2.2) (3.3) 292.9 Former ABL Facility Cliffs 2 N/A 450.0 N/A N/A — Total long-term debt $ 2,113.8 1 Unless otherwise noted, references in this column to "Cliffs" are to Cleveland-Cliffs Inc. 2 Refers to Cleveland-Cliffs Inc. and certain of its subsidiaries as borrowers under our Former ABL Facility.
Schedule of Extinguishment of Debt	The following is a summary of the debt extinguished and the respective gain on extinguishment: (In Millions) Nine Months Ended Debt Instrument Debt Extinguished Gain on Extinguishment 7.625% 2021 AK Senior Notes $ 372.7 $ 0.4 7.50% 2023 AK Senior Notes 367.2 2.8 4.875% 2024 Senior Secured Notes 5.5 0.5 6.375% 2025 Senior Notes 167.5 21.3 1.50% 2025 Convertible Senior Notes 20.0 1.3 5.75% 2025 Senior Notes 77.1 16.3 7.00% 2027 Senior Notes 247.3 28.4 5.875% 2027 Senior Notes 194.5 48.7 6.25% 2040 Senior Notes 35.7 12.9 $ 1,487.5 $ 132.6 Debt Extinguishments - 2019 The following is a summary of the debt extinguished with cash and the respective loss on extinguishment: (In Millions) Nine Months Ended Debt Instrument Debt Extinguished (Loss) on Extinguishment 4.875% 2021 Senior Notes $ 124.0 $ (5.3) 5.75% 2025 Senior Notes 600.0 (12.9) $ 724.0 $ (18.2)
Schedule of Line of Credit Facilities	The following represents a summary of our borrowing capacity under the ABL Facility: (In Millions) September 30, Available borrowing base on ABL Facility 1 $ 1,715.2 Borrowings (400.0) Letter of credit obligations 2 (192.2) Borrowing capacity available $ 1,123.0 1 As of September 30, 2020, the ABL Facility has a maximum borrowing base of $2.0 billion. The available borrowing base is 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, employee severance, IRBs and environmental obligations.
Schedule of Maturities of Long-term Debt	The following represents a summary of our maturities of debt instruments based on the principal amounts outstanding at September 30, 2020: (In Millions) Maturities of Debt 2020 (remaining period of year) $ — 2021 33.5 2022 — 2023 12.8 2024 456.5 Thereafter 3,987.9 Total maturities of debt $ 4,490.7

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value, by Balance Sheet Grouping	The following represents the assets and liabilities measured at fair value: (In Millions) September 30, 2020 Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Assets: Other current assets: Commodity contracts $ — $ 15.8 $ — $ 15.8 Customer supply agreement — — 34.5 34.5 Provisional pricing arrangement — — 26.9 26.9 Other non-current assets: Commodity contracts — 1.8 — 1.8 Total $ — $ 17.6 $ 61.4 $ 79.0 Liabilities: Other current liabilities: Commodity contracts $ — $ (8.7) $ — $ (8.7) Provisional pricing arrangement — — (0.3) (0.3) Foreign exchange contracts — (0.6) — (0.6) Other non-current liabilities: Foreign exchange contracts — (0.1) — (0.1) Total $ — $ (9.4) $ (0.3) $ (9.7) (In Millions) December 31, 2019 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 - Commercial paper $ — $ 187.6 $ — $ 187.6 Other current assets: Customer supply agreement — — 44.5 44.5 Provisional pricing arrangement — — 1.3 1.3 Total $ — $ 187.6 $ 45.8 $ 233.4 Liabilities: Other current liabilities: Commodity contracts $ — $ (3.2) $ — $ (3.2) Provisional pricing arrangement — — (1.1) (1.1) Total $ — $ (3.2) $ (1.1) $ (4.3)
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 September 30, 2020 Balance Sheet Valuation Technique Unobservable Input Range or Point Estimate (Weighted Average) Customer supply agreement $ 34.5 Other current assets Market Approach Management's estimate of hot-rolled coil steel price per net ton $542 - $634 $(548) Provisional pricing arrangements $ 26.9 Other current assets Market Approach Management's $104 - $123 ($105) Atlantic Basin Pellet Premium $30 Provisional pricing arrangements $ (0.3) Other current liabilities Market Approach Management's $104 PPI Estimates 110
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): (In Millions) Level 3 Assets Three Months Ended Nine Months Ended 2020 2019 2020 2019 Beginning balance $ 35.3 $ 118.1 $ 45.8 $ 91.4 Total gains (losses) included in earnings 29.5 (6.5) 43.3 83.1 Settlements (3.4) (38.8) (27.7) (101.7) Ending balance $ 61.4 $ 72.8 $ 61.4 $ 72.8 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 $ 27.8 $ (6.5) $ 40.4 $ 81.8
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation	(In Millions) Level 3 Liabilities Three Months Ended Nine Months Ended 2020 2019 2020 2019 Beginning balance $ — $ — $ (1.1) $ — Total losses included in earnings (0.3) (34.4) (0.9) (39.7) Settlements — 4.2 1.7 9.5 Ending balance $ (0.3) $ (30.2) $ (0.3) $ (30.2) Total losses for the period included in earnings attributable to the change in unrealized losses on liabilities still held at the reporting date $ (0.3) $ (30.2) $ (0.3) $ (30.2)
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) September 30, 2020 December 31, 2019 Classification Carrying Value Fair Value Carrying Value Fair Value Long-term debt: Senior Notes Level 1 $ 3,815.5 $ 3,975.2 $ 2,113.8 $ 2,237.0 IRBs due 2024 to 2028 Level 1 94.3 90.2 — — ABL Facility - outstanding balance Level 2 400.0 400.0 — — Total long-term debt $ 4,309.8 $ 4,465.4 $ 2,113.8 $ 2,237.0

PENSIONS AND OTHER POSTRETIRE_2

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Tables)	9 Months Ended
	Sep. 30, 2020
Postemployment Benefits [Abstract]
Schedule of Net Benefit Costs	The following are the components of defined benefit pension and OPEB costs (credits): Defined Benefit Pension Costs (Credits) (In Millions) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Service cost $ 5.4 $ 4.6 $ 16.0 $ 12.9 Interest cost 19.6 8.9 42.7 26.2 Expected return on plan assets (36.7) (13.7) (91.9) (41.0) Amortization: Prior service costs 0.2 0.3 0.7 0.9 Net actuarial loss 7.3 5.9 20.6 17.7 Net periodic benefit cost (credit) $ (4.2) $ 6.0 $ (11.9) $ 16.7 OPEB Costs (Credits) (In Millions) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Service cost $ 1.4 $ 0.5 $ 3.3 $ 1.3 Interest cost 4.4 2.3 10.9 7.0 Expected return on plan assets (4.5) (4.2) (13.6) (12.6) Amortization: Prior service credits (0.5) (0.5) (1.5) (1.5) Net actuarial loss 0.8 1.3 2.2 3.8 Net periodic benefit cost (credit) $ 1.6 $ (0.6) $ 1.3 $ (2.0)

ASSET RETIREMENT OBLIGATIONS (T

ASSET RETIREMENT OBLIGATIONS (Tables)	9 Months Ended
	Sep. 30, 2020
Asset Retirement Obligation [Abstract]
Summary Of Asset Retirement Obligations	The following is a summary of our asset retirement obligations: (In Millions) September 30, December 31, Asset retirement obligations 1 $ 186.4 $ 165.3 Less current portion 4.4 2.1 Long-term asset retirement obligations $ 182.0 $ 163.2 1 Includes $33.7 million and $22.0 million related to our active operations as of September 30, 2020 and December 31, 2019, respectively.
Schedule of Change in Asset Retirement Obligation	The following is a roll forward of our asset retirement obligation liability: (In Millions) 2020 2019 Asset retirement obligation as of January 1 $ 165.3 $ 172.4 Increase from AK Steel acquisition 16.7 — Accretion expense 7.8 7.6 Remediation payments (3.4) (0.5) Asset retirement obligation as of September 30 $ 186.4 $ 179.5

DERIVATIVE INSTRUMENTS (Tables)

DERIVATIVE INSTRUMENTS (Tables)	9 Months Ended
	Sep. 30, 2020
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule Of Derivative Instruments In Statement Of Financial Position, Fair Value	The following table presents the fair value of our derivative instruments and the classification of each in the Statements of Unaudited Condensed Consolidated Financial Position: Derivatives designated as hedging instruments under Topic 815: Derivatives not designated as hedging instruments under Topic 815: Derivative Asset (Liability) September 30, December 31, September 30, December 31, Other current assets: Customer supply agreement $ — $ — $ 34.5 $ 44.5 Provisional pricing arrangements — — 26.9 1.3 Commodity contracts 7.9 — 7.9 — Other non-current assets: Commodity contracts 1.8 — — — Other current liabilities: Provisional pricing arrangements — — (0.3) (1.1) Commodity contracts (1.8) (3.2) (6.9) — Foreign exchange contracts (0.6) — — — Other non-current liabilities: Foreign exchange contracts (0.1) — — —
Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block]	The following table presents the notional amount of our outstanding hedge contracts: (In Millions) September 30, 2020 December 31, 2019 Unit of Measure Maturity Dates Notional Amount Notional Amount Commodity contracts: Natural gas MMBtu October 2020 - December 2021 29.7 20.1 Diesel Gallons — — 0.8 Zinc Pounds October 2020 - December 2021 10.9 — Electricity Megawatt hours October 2020 - December 2021 0.8 — Foreign exchange contracts: Canadian dollars CAD October 2020 - December 2021 C$ 38.8 C$ —
Derivative Instruments, Gain (Loss) [Table Text Block]	Estimated gains before tax expected to be reclassified into Cost of goods sold within the next 12 months for our existing derivatives that qualify as cash flow hedges are presented below: (In Millions) Hedge: Estimated Gains Natural gas $ 10.8 Zinc 2.3 Electricity 1.1 Canadian dollars 0.2
Schedule Of Derivatives Not Designated As Hedging Instruments Statements Of Financial Performance Location Table	The following summarizes the effect of our derivatives that are not designated as hedging instruments in the Statements of Unaudited Condensed Consolidated Operations: (In Millions) Derivatives Not Designated as Hedging Instruments Location of Gain (Loss) Recognized in Income on Derivatives Three Months Ended Nine Months Ended 2020 2019 2020 2019 Customer supply agreements Revenues $ 8.8 $ 7.6 $ 14.4 $ 82.2 Provisional pricing arrangements Revenues 20.4 (48.5) 28.0 (38.8) Commodity contracts Cost of goods sold 3.9 — (0.8) — Total $ 33.1 $ (40.9) $ 41.6 $ 43.4

SHAREHOLDERS' EQUITY - Dividend

SHAREHOLDERS' EQUITY - Dividends Declared (Tables)	9 Months Ended
	Sep. 30, 2020
Stockholders' Equity Note [Abstract]
Dividends Declared [Table Text Block]	The below table summarizes our recent dividend activity: Declaration Date Record Date Payment Date Dividend Declared per Common Share 1 2/18/2020 4/3/2020 4/15/2020 $ 0.06 12/2/2019 1/3/2020 1/15/2020 0.06 9/3/2019 10/4/2019 10/15/2019 0.10 5/31/2019 7/5/2019 7/15/2019 0.06 2/19/2019 4/5/2019 4/15/2019 0.05 10/18/2018 1/4/2019 1/15/2019 0.05 1 The dividend declared on September 3, 2019 included a special cash dividend of $0.04 per common share.

ACCUMULATED OTHER COMPREHENSI_2

ACCUMULATED OTHER COMPREHENSIVE LOSS (Tables)	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	The following tables reflect the changes in Accumulated other comprehensive loss related to shareholders’ equity: (In Millions) Postretirement Benefit Liability, Foreign Currency Translation Derivative Financial Instruments, net of tax Accumulated Other Comprehensive Loss December 31, 2019 $ (315.7) $ — $ (3.1) $ (318.8) Other comprehensive loss before reclassifications — (0.9) (5.2) (6.1) Net loss reclassified from accumulated other comprehensive loss 5.6 — 2.2 7.8 March 31, 2020 $ (310.1) $ (0.9) $ (6.1) $ (317.1) Other comprehensive income before reclassifications 0.4 0.7 1.4 2.5 Net loss reclassified from accumulated other comprehensive loss 5.6 — 3.1 8.7 June 30, 2020 $ (304.1) $ (0.2) $ (1.6) $ (305.9) Other comprehensive income before reclassifications 0.4 1.6 12.2 14.2 Net loss reclassified from accumulated other comprehensive loss 6.2 — 3.5 9.7 September 30, 2020 $ (297.5) $ 1.4 $ 14.1 $ (282.0) (In Millions) Postretirement Benefit Liability, net of tax Derivative Financial Instruments, net of tax Accumulated Other Comprehensive Loss December 31, 2018 $ (281.1) $ (2.8) $ (283.9) Other comprehensive income before reclassifications 0.2 2.5 2.7 Net loss reclassified from accumulated other comprehensive loss 5.5 0.2 5.7 March 31, 2019 $ (275.4) $ (0.1) $ (275.5) Other comprehensive income (loss) before reclassifications 0.3 (2.3) (2.0) Net loss reclassified from accumulated other comprehensive loss 5.5 0.2 5.7 June 30, 2019 $ (269.6) $ (2.2) $ (271.8) Other comprehensive income (loss) before reclassifications 0.3 (0.5) (0.2) Net loss reclassified from accumulated other comprehensive loss 5.5 0.9 6.4 September 30, 2019 $ (263.8) $ (1.8) $ (265.6)
Details of Accumulated Other Comprehensive Income (Loss) Components	The following table reflects the details about Accumulated other comprehensive loss components related to shareholders’ equity: (In Millions) Details about Accumulated Other Comprehensive Loss Components Amount of (Gain)/Loss Reclassified into Income, Net of Tax Affected Line Item in the Statement of Unaudited Condensed Consolidated Operations Three Months Ended Nine Months Ended 2020 2019 2020 2019 Amortization of pension and OPEB liability: Prior service credits $ (0.3) $ (0.2) $ (0.8) $ (0.6) Other non-operating income Net actuarial loss 8.1 7.2 22.8 21.5 Other non-operating income 7.8 7.0 22.0 20.9 Total before taxes (1.6) (1.5) (4.6) (4.4) Income tax benefit (expense) $ 6.2 $ 5.5 $ 17.4 $ 16.5 Net of taxes Unrealized loss on derivative financial instruments: Commodity contracts $ 4.5 $ 1.2 $ 11.2 $ 1.7 Cost of goods sold (1.0) (0.3) (2.4) (0.4) Income tax benefit (expense) $ 3.5 $ 0.9 $ 8.8 $ 1.3 Net of taxes Total reclassifications for the period, net of tax $ 9.7 $ 6.4 $ 26.2 $ 17.8

RELATED PARTIES (Tables)

RELATED PARTIES (Tables)	9 Months Ended
	Sep. 30, 2020
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	Investees and equity ownership percentages are presented below: Investee Segment Reported Within Equity Ownership Percentage Combined Metals of Chicago, LLC Steel and Manufacturing 40.0% Hibbing Taconite Company Mining and Pelletizing 23.0% Spartan Steel Coating, LLC Steel and Manufacturing 48.0%
Summary Of Related Party Transactions Table Disclosure	The tables below summarize our material related party transactions: Revenues from related parties were as follows: (Dollars In Millions) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Revenue from related parties $ 294.9 $ 293.5 $ 587.5 $ 792.8 Revenues 1 $ 1,646.0 $ 555.6 $ 3,097.8 $ 1,455.8 Related party revenues as a percent of Revenues 1 17.9 % 52.8 % 19.0 % 54.5 % Purchases from related parties $ 8.2 $ — $ 20.4 $ — 1 Includes Realization of deferred revenue of $34.6 million for the nine months ended September 30, 2020. The following table presents the classification of related party assets and liabilities in the Statements of Unaudited Condensed Consolidated Financial Position: (In Millions) Balance Sheet Location September 30, December 31, Accounts receivable, net $ 91.6 $ 31.1 Other current assets 58.5 44.5 Accounts payable (1.2) — Other current liabilities (1.7) (2.0)
Hibbing Taconite Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	Hibbing is a co-owned joint venture with companies that are integrated steel producers or their subsidiaries. The following is a summary of the mine ownership of the co-owned iron ore mine at September 30, 2020: Mine Cleveland-Cliffs Inc. ArcelorMittal USA U.S. Steel Hibbing 23.0% 62.3% 14.7%

VARIABLE INTEREST ENTITIES (Tab

VARIABLE INTEREST ENTITIES (Tables)	9 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Variable Interest Entities [Table Text Block]	The consolidated balance sheet as of September 30, 2020 includes the following amounts for SunCoke Middletown: (In Millions) September 30, Cash and cash equivalents $ 0.3 Inventories 22.5 Property, plant and equipment, net 305.4 Accounts payable (10.0) Other assets (liabilities), net (5.6) Noncontrolling interests (312.6)

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	9 Months Ended
	Sep. 30, 2020
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) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Income (loss) from continuing operations $ 2.2 $ 91.8 $ (154.8) $ 231.1 Income from continuing operations attributable to noncontrolling interest (11.9) — (31.2) — Net income (loss) from continuing operations attributable to Cliffs shareholders (9.7) 91.8 (186.0) 231.1 Loss from discontinued operations, net of tax (0.3) (0.9) — (1.5) Net income (loss) attributable to Cliffs shareholders $ (10.0) $ 90.9 $ (186.0) $ 229.6 Weighted average number of shares: Basic 399.4 270.0 365.2 278.4 Convertible senior notes — 3.7 — 5.8 Employee stock plans — 2.9 — 3.6 Diluted 399.4 276.6 365.2 287.8 Earnings (loss) per common share attributable to Cliffs shareholders - basic: Continuing operations $ (0.02) $ 0.34 $ (0.51) $ 0.83 Discontinued operations — — — (0.01) $ (0.02) $ 0.34 $ (0.51) $ 0.82 Earnings (loss) per common share attributable to Cliffs shareholders - diluted: Continuing operations $ (0.02) $ 0.33 $ (0.51) $ 0.80 Discontinued operations — — — — $ (0.02) $ 0.33 $ (0.51) $ 0.80
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]	The following table summarizes the shares that have been excluded from the diluted earnings per share calculation as they were anti-dilutive: (In Millions) Three Months Ended Nine Months Ended 2020 2019 2020 2019 Shares related to employee stock plans 1.8 — 1.6 —

COMMITMENTS AND CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES (Tables)	9 Months Ended
	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Schedule of Environmental Obligations	The following is a summary of our environmental obligations: (In Millions) September 30, December 31, Environmental obligations $ 40.9 $ 2.0 Less current portion 6.4 0.3 Long-term environmental obligations $ 34.5 $ 1.7

BASIS OF PRESENTATION AND SIG_4

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Dec. 31, 2020	Sep. 30, 2020
Business Acquisition [Line Items]
Common shares, par value		$ 0.125
Forecast [Member] | ArcelorMittal USA [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	$ 1,400
Payments to Acquire Businesses, Gross	$ 505
Forecast [Member] | ArcelorMittal USA [Member] | Common Stock [Member]
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	78,186,671
Forecast [Member] | ArcelorMittal USA [Member] | Series B Participating Redeemable Preferred Stock [Member]
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	583,273

BASIS OF PRESENTATION AND SIG_5

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - Equity Method Investments (Details) - USD ($) $ in Millions	Sep. 30, 2020	Mar. 13, 2020
Combined Metals of Chicago, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	40.00%
Hibbing Taconite Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	23.00%
Spartan Steel Coating, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity		$ 32.5
Equity Method Investment, Ownership Percentage	48.00%

SUPPLEMENTARY FINANCIAL STATE_3

SUPPLEMENTARY FINANCIAL STATEMENT INFORMATION - Revenues (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020		Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues		$ 1,646	$ 555.6	$ 3,097.8	[1]	$ 1,455.8
Realization of deferred revenue		0	0	34.6		0
Steel and Manufacturing [Member]
Disaggregation of Revenue [Line Items]
Revenues		1,261.7	0	2,194.3		0
Steel and Manufacturing [Member] | Carbon Steel [Member]
Disaggregation of Revenue [Line Items]
Revenues		821.2	0	1,391.6		0
Steel and Manufacturing [Member] | Stainless and Electrical Steel [Member]
Disaggregation of Revenue [Line Items]
Revenues		303.2	0	585.1		0
Steel and Manufacturing [Member] | Other Product Lines [Member]
Disaggregation of Revenue [Line Items]
Revenues		137.3	0	217.6		0
Mining and Pelletizing [Member]
Disaggregation of Revenue [Line Items]
Revenues		384.3	555.6	903.5		1,455.8
Mining and Pelletizing [Member] | Iron Ore [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1]	357.1	515	838.1		1,357.8
Mining and Pelletizing [Member] | Freight [Member]
Disaggregation of Revenue [Line Items]
Revenues		27.2	40.6	65.4		98
Automotive [Member] | Steel and Manufacturing [Member]
Disaggregation of Revenue [Line Items]
Revenues		920	0	1,404		0
Infrastructure and Manufacturing [Member] | Steel and Manufacturing [Member]
Disaggregation of Revenue [Line Items]
Revenues		198.8	0	446.2		0
Distributors and Converters [Member] | Steel and Manufacturing [Member]
Disaggregation of Revenue [Line Items]
Revenues		142.9	0	344.1		0
Steel Producers [Member] | Mining and Pelletizing [Member]
Disaggregation of Revenue [Line Items]
Revenues	[1]	384.3	555.6	903.5		1,455.8
Non-US [Member]
Disaggregation of Revenue [Line Items]
Revenues		$ 265	$ 138.9	$ 487.7		$ 318.3
[1]	1 Includes Realization of deferred revenue of $34.6 million for the nine months ended September 30, 2020.

SUPPLEMENTARY FINANCIAL STATE_4

SUPPLEMENTARY FINANCIAL STATEMENT INFORMATION - Allowance for Credit Losses (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses as of beginning of period	$ 0	$ 0
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease)	5.2	0
Allowance for credit losses as of end of period	$ 5.2	$ 0

SUPPLEMENTARY FINANCIAL STATE_5

SUPPLEMENTARY FINANCIAL STATEMENT INFORMATION - Inventories (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Finished and semi-finished goods inventories	$ 940.5	$ 114.1
Work-in-process	78.2	68.7
Raw materials	382.3	9.4
Total product inventories	1,401	192.2
Manufacturing supplies and critical spares	394.1	125.2
Inventories	$ 1,795.1	$ 317.4

SUPPLEMENTARY FINANCIAL STATE_6

SUPPLEMENTARY FINANCIAL STATEMENT INFORMATION - Deferred Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Realization of deferred revenue	$ 0	$ 0	$ 34.6	$ 0
Other Current Liabilities [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Opening balance as of January 1			22.1	21
Net decrease			(19.8)	(2.7)
Closing balance as of September 30	2.3	18.3	2.3	18.3
Other Noncurrent Liabilities [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Opening balance as of January 1			25.7	38.5
Net decrease			(25.7)	(8.5)
Closing balance as of September 30	$ 0	$ 30	$ 0	$ 30

SUPPLEMENTARY FINANCIAL STATE_7

SUPPLEMENTARY FINANCIAL STATEMENT INFORMATION - Accrued Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Disclosure Text Block [Abstract]
Accrued employment costs	$ 146.6	$ 61.7
Accrued interest	81.8	29
Accrued dividends	1	17.8
Other	50	17.8
Accrued liabilities	$ 279.4	$ 126.3

SUPPLEMENTARY FINANCIAL STATE_8

SUPPLEMENTARY FINANCIAL STATEMENT INFORMATION - Cash Flow Information (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Supplemental Cash Flow Information [Abstract]
Property, Plant and Equipment, Additions		$ 102.3	$ 184.7	$ 333	$ 505.6
Non-cash accruals				(88.4)	26.1
Right-of-use assets - finance leases				42.5	29.3
Grants				0	(10.5)
Cash paid for capital expenditures including deposits				378.9	460.7
Taxes paid on income				3.2	0.1
Income tax refunds				(119.3)	(117.9)
Interest paid on debt obligations net of capitalized interest	[1]			106	71.9
Interest Costs Capitalized		$ 14.7	$ 7	$ 38	$ 16.9
[1]	1 Capitalized interest was $38.0 million and $16.9 million for the nine months ended September 30, 2020 and 2019, respectively.

SUPPLEMENTARY FINANCIAL STATE_9

SUPPLEMENTARY FINANCIAL STATEMENT INFORMATION - Non-Cash Investing and Financing Activities (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Common Stock [Member]
Other Significant Noncash Transactions [Line Items]
Other Significant Noncash Transaction, Value of Consideration Given	$ 617.6	$ 0
Share-based Payment Arrangement [Member]
Other Significant Noncash Transactions [Line Items]
Other Significant Noncash Transaction, Value of Consideration Given	$ 3.9	$ 0

ACQUISITION OF AK STEEL - Overv

ACQUISITION OF AK STEEL - Overview (Details) $ in Millions	Mar. 13, 2020USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2020USD ($)		Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)	Oct. 01, 2020USD ($)
Business Acquisition [Line Items]
Revenues		$ 1,646	$ 555.6		$ 3,097.8	[1]	$ 1,455.8
Net income (loss)		(10)	90.9		(186)		229.6
Amortization of inventory step-up					74		0
Acquisition-related costs		7.5	$ 0		68.4		$ 0
AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Acquisition, Shares Exchange Ratio	0.400
Business Acquisition, Revenue Reported by Acquired Entity for Last Annual Period								$ 6,359.4
Revenues		1,261.7		$ 2,194.3
Net income (loss)		(30.4)		(292)
Amortization of inventory step-up		14.6		74
Severance costs		2.4		$ 35.1
Acquisition-related costs		$ 0.6			$ 25.6
Business Combination, Consideration Transferred	$ 1,535.1
Forecast [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Cost synergies									$ 150
[1]	1 Includes Realization of deferred revenue of $34.6 million for the nine months ended September 30, 2020.

ACQUISITION OF AK STEEL - Consi

ACQUISITION OF AK STEEL - Consideration (Details) $ / shares in Units, $ in Millions	Mar. 13, 2020USD ($)$ / sharesshares	Sep. 30, 2020shares	Jun. 30, 2020shares	Mar. 31, 2020shares	Dec. 31, 2019shares	Sep. 30, 2019shares	Jun. 30, 2019shares	Mar. 31, 2019shares	Dec. 31, 2018shares
Business Acquisition [Line Items]
Fair value of Cliffs common shares issued for AK Steel outstanding common stock	$ 617.6
Common shares, outstanding (in shares) | shares		399,229,917			270,084,005
AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Fair value of Cliffs common shares issued for AK Steel outstanding common stock	617.6
Fair value of debt included in consideration	913.6
Business Combination, Consideration Transferred	$ 1,535.1
Common shares, outstanding (in shares) | shares	316,900,000
Business Acquisition, Shares Exchange Ratio	0.400
Shares of Cliffs common shares issued to AK Steel stockholders | shares	126,800,000
Price per share of Cliffs common shares | $ / shares	$ 4.87
Credit Facility | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Fair value of debt included in consideration	$ 590
7.50% 2023 AK Senior Notes [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Fair value of debt included in consideration	323.6
Share-based Payment Arrangement [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Fair value of Cliffs common shares issued for AK Steel outstanding common stock	3.9
Common Stock [Member]
Business Acquisition [Line Items]
Common shares, outstanding (in shares) | shares		399,200,000	399,200,000	398,600,000	270,100,000	270,100,000	270,000,000	282,800,000	292,600,000
Common Stock [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Fair value of Cliffs common shares issued for AK Steel outstanding common stock	$ 617.6

ACQUISITION OF AK STEEL - Asset

ACQUISITION OF AK STEEL - Assets and Liabilities Assumed (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Goodwill	$ 144	$ 144	$ 144		$ 2.1
AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Cash and cash equivalents	39.7	39.7	39.7	$ 37.7
Accounts receivable	662.9	662.9	662.9	666
Inventories	1,523	1,523	1,523	1,562.8
Other current assets	52.1	52.1	52.1	67.5
Property, plant and equipment	2,164.3	2,164.3	2,164.3	2,184.4
Intangible assets	148	148	148	163
Right of use asset, operating leases	209.6	209.6	209.6	225.9
Other non-current assets	112.1	112.1	112.1	85.9
Accounts payable	(642.4)	(642.4)	(642.4)	(636.3)
Accrued liabilities	(222.4)	(222.4)	(222.4)	(222.5)
Other current liabilities	(175.2)	(175.2)	(175.2)	(181.8)
Long-term debt	(1,179.4)	(1,179.4)	(1,179.4)	(1,179.4)
Deferred income taxes	(19.9)	(19.9)	(19.9)	(19.7)
Operating lease liability, non-current	(175.4)	(175.4)	(175.4)	(188.1)
Intangible liabilities	(70.5)	(70.5)	(70.5)	(140)
Pension and OPEB liabilities	(870.9)	(870.9)	(870.9)	(873)
Asset retirement obligations	(15.9)	(15.9)	(15.9)	(13.9)
Other non-current liabilities	(146.5)	(146.5)	(146.5)	(144.2)
Net identifiable assets acquired	1,393.2	1,393.2	1,393.2	1,394.3
Goodwill	141.9	141.9	141.9	141.2
Total net assets acquired	1,535.1	1,535.1	1,535.1	$ 1,535.5
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Net Identifiable Assets		(1.1)
Goodwill, Purchase Accounting Adjustments		0.7
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Consideration Transferred		(0.4)
Cash and Cash Equivalents [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Assets		2
Accounts Receivable [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Assets		(3.1)
Inventories [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Inventory		(39.8)
Other Current Assets [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Assets		(15.4)
Property, Plant and Equipment [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Property, Plant, and Equipment		(20.1)
Finite-Lived Intangible Assets [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Intangibles		(15)
Right-of-use asset, operating lease [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Assets		(16.3)
Other Noncurrent Assets [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Assets		26.2
Accounts Payable [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Liabilities		(6.1)
Accrued Liabilities [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Liabilities		0.1
Other Current Liabilities [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Liabilities		6.6
Long-term Debt [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Liabilities		0
Deferred income taxes [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Liabilities		(0.2)
Operating lease liability, non-current [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Liabilities		12.7
Intangible liabilities [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Intangibles		69.5
Pension and OPEB liabilities [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Liabilities		2.1
Asset Retirement Obligation [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Liabilities		(2)
Other Noncurrent Liabilities [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Liabilities		$ (2.3)
Cost of Sales [Member] | AK Steel Holding Corporation [Member]
Business Acquisition [Line Items]
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustments Related to Previous Period	$ 0.2		$ 8

ACQUISITION OF AK STEEL - Intan

ACQUISITION OF AK STEEL - Intangible Assets and Liabilities (Details) - AK Steel Holding Corporation [Member] $ in Millions	9 Months Ended
	Sep. 30, 2020USD ($)
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 148
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life (in years)	17 years
Intangible Liability Assumed	$ (70.5)
Assumed Finite-lived Intangible Liabilities, Weighted Average Useful Life (in years)	12 years
Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 77
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life (in years)	18 years
Technology-Based Intangible Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 60
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life (in years)	17 years
Trademarks and Trade Names [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 11
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life (in years)	10 years

ACQUISITION OF AK STEEL - Pro F

ACQUISITION OF AK STEEL - Pro Forma Information (Details) - AK Steel Holding Corporation [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Business Acquisition, Pro Forma Revenue	$ 1,646	$ 1,937.6	$ 4,265.1	$ 5,958.7
Business Acquisition, Pro Forma Net Income (Loss)	(6)	84.2	$ (123.9)	213.3
Business Acquisition, Pro Forma Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			24.30%
Business Acquisition, Pro Forma Income Tax Expense (Benefit)	(5.6)	(2.1)	$ (2.1)	(4.5)
Fair Value Adjustment to Inventory [Member]
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Business Acquisition, Pro Forma Net Income (Loss)	14.6		74	74
Acquisition-related Costs [Member]
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Business Acquisition, Pro Forma Net Income (Loss)	0.7		29.1
Other Adjustments [Member]
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Business Acquisition, Pro Forma Net Income (Loss)	(10)	(1.1)	(10)	(7)
Intersegment Eliminations [Member]
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Business Acquisition, Pro Forma Revenue	$ 135.6	$ 153.5	$ 394.8	$ 410.8

SEGMENT REPORTING - Results by

SEGMENT REPORTING - Results by Segment (Details) T in Thousands, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020USD ($)T	Sep. 30, 2019USD ($)T	Sep. 30, 2020USD ($)unitT		Sep. 30, 2019USD ($)T
Segment Reporting Information [Line Items]
Number of Reporting Units | unit				2
Revenues		$ 1,646	$ 555.6	$ 3,097.8	[1]	$ 1,455.8
Adjusted EBITDA		126.3	144.1	67		413.7
Realization of deferred revenue		$ 0	$ 0	$ 34.6		$ 0
Steel and Manufacturing [Member]
Segment Reporting Information [Line Items]
Sales Volume (Net Tons) | T		1,117	0	1,935		0
Revenues		$ 1,261.7	$ 0	$ 2,194.3		$ 0
Adjusted EBITDA		$ 33.3	$ (2.1)	$ (81.8)		$ (4)
Mining and Pelletizing [Member]
Segment Reporting Information [Line Items]
Sales Volume (Long Tons) | T		3,703	5,404	8,772		13,143
Revenues		$ 384.3	$ 555.6	$ 903.5		$ 1,455.8
Adjusted EBITDA		145.3	182.7	309.5		510.7
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Adjusted EBITDA		$ (52.3)	$ (36.5)	$ (160.7)		$ (93)
Operating Segments [Member] | Mining and Pelletizing [Member]
Segment Reporting Information [Line Items]
Sales Volume (Long Tons) | T		4,907	5,750	11,800		13,527
Revenues	[1]	$ 520.3	$ 590.6	$ 1,238.7		$ 1,494.8
Intersegment Eliminations [Member] | Mining and Pelletizing [Member]
Segment Reporting Information [Line Items]
Sales Volume (Long Tons) | T		(1,204)	(346)	(3,028)		(384)
Revenues		$ (136)	$ (35)	$ (335.2)		$ (39)
[1]	1 Includes Realization of deferred revenue of $34.6 million for the nine months ended September 30, 2020.

SEGMENT REPORTING - Net Income

SEGMENT REPORTING - Net Income (Loss) to Total Adjusted EBITDA (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2020		Sep. 30, 2019	Sep. 30, 2020		Sep. 30, 2019
Segment Reporting Information [Line Items]
Net income (loss)	$ 1.9		$ 90.9	$ (154.8)		$ 229.6
Interest expense, net	(68.2)		(25.3)	(167.9)		(76.5)
Income tax benefit (expense)	22.4		(4.8)	98.5		(23.1)
Depreciation, depletion and amortization				(183.9)		(63.1)
EBITDA	120.1		143.3	98.5		392.6
Gain (loss) on extinguishment of debt	0		0	132.6		(18.2)
Acquisition-related costs excluding severance costs	(7.5)		0	(68.4)		0
Amortization of Inventory Step-up				(74)		0
Impact of discontinued operations	(0.3)		(0.9)	0		(1.5)
Adjusted EBITDA	126.3		144.1	67		413.7
Net Income (Loss) Attributable to Noncontrolling Interest	11.9		0	31.2		0
Depreciation, Depletion and Amortization Attributable to Noncontrolling Interests	4.3			10.1
EBITDA Calculation [Member]
Segment Reporting Information [Line Items]
Interest expense, net	(68.2)		(25.4)	(167.9)		(76.8)
Income tax benefit (expense)	22.4		(4.8)	98.5		(23.1)
Depreciation, depletion and amortization	(72.4)		(22.2)	(183.9)		(63.1)
Adjusted EBITDA Calculation [Member]
Segment Reporting Information [Line Items]
EBITDA of Noncontrolling Interests	16.2	[1]	0	41.3	[1]	0
Gain (loss) on extinguishment of debt	0		0	132.6		(18.2)
Severance costs	(2.4)		0	(38.3)		(1.7)
Acquisition-related costs excluding severance costs	(5.1)		0	(30.1)		0
Amortization of Inventory Step-up	(14.6)		0	(74)		0
Impact of discontinued operations	$ (0.3)		$ (0.8)	$ 0		$ (1.2)
[1]	1 EBITDA of noncontrolling interests includes $11.9 million and $31.2 million for income and $4.3 million and $10.1 million for depreciation, depletion and amortization for the three and nine months ended September 30, 2020, respectively.

SEGMENT REPORTING - Segment Ass

SEGMENT REPORTING - Segment Assets (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Total assets	$ 8,480.9	$ 3,503.8
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Total assets	491.9	947.1
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total assets	7,989	2,556.7
Operating Segments [Member] | Steel and Manufacturing [Member]
Segment Reporting Information [Line Items]
Total assets	6,345.7	913.6
Operating Segments [Member] | Mining and Pelletizing [Member]
Segment Reporting Information [Line Items]
Total assets	$ 1,643.3	$ 1,643.1

SEGMENT REPORTING - Segment Cap

SEGMENT REPORTING - Segment Capital Additions (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Property, Plant and Equipment, Additions	$ 102.3	$ 184.7	$ 333	$ 505.6
Steel and Manufacturing [Member]
Segment Reporting Information [Line Items]
Property, Plant and Equipment, Additions	88	160.5	266.8	398
Mining and Pelletizing [Member]
Segment Reporting Information [Line Items]
Property, Plant and Equipment, Additions	13.3	22.1	64.9	104.5
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Property, Plant and Equipment, Additions	$ 1	$ 2.1	$ 1.3	$ 3.1

PROPERTY, PLANT AND EQUIPMENT_3

PROPERTY, PLANT AND EQUIPMENT (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 5,958		$ 5,958		$ 3,027.4
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	1,407.3		1,407.3		1,098.4
Property, plant and equipment, net	4,550.7		4,550.7		1,929
Finance Lease, Right-of-Use Asset	97.1		97.1		49
Interest Costs Capitalized	14.7	$ 7	38	$ 16.9
Depreciation and depletion expense	71.8	$ 22	182.5	$ 62.5
Land, Land Improvements and Mineral Rights [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	653.2		653.2		582.2
Building [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	454.4		454.4		157.8
Steel and Manufacturing Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	2,128		2,128		42
Mining and Pelletizing Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	1,455.2		1,455.2		1,413.6
Other Assets [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	121.3		121.3		101.5
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 1,145.9		$ 1,145.9		$ 730.3

GOODWILL AND INTANGIBLE ASSET_3

GOODWILL AND INTANGIBLE ASSETS AND LIABILITIES - Goodwill (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Goodwill [Line Items]
Goodwill	$ 144	$ 2.1
Steel and Manufacturing [Member]
Goodwill [Line Items]
Goodwill	141.9
Mining and Pelletizing [Member]
Goodwill [Line Items]
Goodwill	$ 2.1	$ 2.1

GOODWILL AND INTANGIBLE ASSET_4

GOODWILL AND INTANGIBLE ASSETS AND LIABILITIES - Intangible Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$ 220.2
Finite-Lived Intangible Assets, Accumulated Amortization	(30.1)
Finite-Lived Intangible Assets, Net	190.1
Finite-Lived Intangible Liabilities, Gross	(70.5)
Finite-Lived Intangible Liabilities, Accumulated Amortization	4.6
Finite-Lived Intangible Liabilities, Net	(65.9)
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	77
Finite-Lived Intangible Assets, Accumulated Amortization	(2.6)
Finite-Lived Intangible Assets, Net	74.4
Technology-Based Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	60
Finite-Lived Intangible Assets, Accumulated Amortization	(2.1)
Finite-Lived Intangible Assets, Net	57.9
Trademarks and Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	11
Finite-Lived Intangible Assets, Accumulated Amortization	(0.7)
Finite-Lived Intangible Assets, Net	10.3
Mining Permits [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	72.2	$ 72.2
Finite-Lived Intangible Assets, Accumulated Amortization	(24.7)	(24.1)
Finite-Lived Intangible Assets, Net	$ 47.5	$ 48.1

GOODWILL AND INTANGIBLE ASSET_5

GOODWILL AND INTANGIBLE ASSETS AND LIABILITIES - Amortization of Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization of Intangible Assets	$ 2.5	$ 0.2	$ 6	$ 0.6
Finite-Lived Intangible Assets, Amortization Expense, Remainder of Fiscal Year	2.5		2.5
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	10		10
Finite-Lived Intangible Assets, Amortization Expense, Year Two	10		10
Finite-Lived Intangible Assets, Amortization Expense, Year Three	10		10
Finite-Lived Intangible Assets, Amortization Expense, Year Four	10		10
Finite-Lived Intangible Assets, Amortization Expense, Year Five	$ 10		$ 10

GOODWILL AND INTANGIBLE ASSET_6

GOODWILL AND INTANGIBLE ASSETS AND LIABILITIES - Amortization of Intangible Liability (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2020USD ($)	Sep. 30, 2020USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization of Intangible Liabilities	$ 1.9	$ 4.6
Finite-Lived Intangible Liabilities, Amortization Credit, Remainder of Fiscal Year	2	2
Finite-Lived Intangible Liabilities, Amortization Credit, Next Twelve Months	7.8	7.8
Finite-Lived Intangible Liabilities, Amortization Credit, Year Two	7.8	7.8
Finite-Lived Intangible Liabilities, Amortization Credit, Year Three	7.8	7.8
Finite-Lived Intangible Liabilities, Amortization Credit, Year Four	7.8	7.8
Finite-Lived Intangible Liabilities, Amortization Credit, Year Five	$ 7.8	$ 7.8

DEBT AND CREDIT FACILITIES - Sc

DEBT AND CREDIT FACILITIES - Schedule Of Long-Term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 4,490.7
LONG-TERM DEBT	4,309.8	$ 2,113.8
Credit Facility
Debt Instrument [Line Items]
Long-term Line of Credit	$ 400
Cleveland-Cliffs Inc. [Member] | 4.875% 2024 Senior Secured Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	5.00%	5.00%
Long-term Debt, Gross	$ 394.5	$ 400
Unamortized Debt Issuance Expense	(3.7)	(4.6)
Debt Instrument, Unamortized Discount	(1.5)	(1.8)
Long-term Debt	$ 389.3	$ 393.6
Cleveland-Cliffs Inc. [Member] | 9.875% 2025 Senior Secured Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	10.57%
Long-term Debt, Gross	$ 955.2
Unamortized Debt Issuance Expense	(8.1)
Debt Instrument, Unamortized Discount	(25.8)
Long-term Debt	$ 921.3
Cleveland-Cliffs Inc. [Member] | 6.75% 2026 Senior Secured Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	6.99%
Long-term Debt, Gross	$ 845
Unamortized Debt Issuance Expense	(21.4)
Debt Instrument, Unamortized Discount	(9)
Long-term Debt	$ 814.6
Cleveland-Cliffs Inc. [Member] | 6.375% 2025 Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	8.11%
Long-term Debt, Gross	$ 64.3
Unamortized Debt Issuance Expense	(0.2)
Debt Instrument, Unamortized Discount	(4.6)
Long-term Debt	$ 59.5
Cleveland-Cliffs Inc. [Member] | 1.50% 2025 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	6.26%	6.26%
Long-term Debt, Gross	$ 296.3	$ 316.3
Unamortized Debt Issuance Expense	(3.7)	(4.6)
Debt Instrument, Unamortized Discount	(53)	(65)
Long-term Debt	$ 239.6	$ 246.7
Cleveland-Cliffs Inc. [Member] | 5.75% 2025 Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	6.01%	6.01%
Long-term Debt, Gross	$ 396.2	$ 473.3
Unamortized Debt Issuance Expense	(2.6)	(3.6)
Debt Instrument, Unamortized Discount	(4.1)	(5.5)
Long-term Debt	$ 389.5	$ 464.2
Cleveland-Cliffs Inc. [Member] | 7.00% 2027 Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	9.24%
Long-term Debt, Gross	$ 88
Unamortized Debt Issuance Expense	(0.3)
Debt Instrument, Unamortized Discount	(9.6)
Long-term Debt	$ 78.1
Cleveland-Cliffs Inc. [Member] | 5.875% 2027 Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	6.49%	6.49%
Long-term Debt, Gross	$ 555.5	$ 750
Unamortized Debt Issuance Expense	(4.3)	(6.3)
Debt Instrument, Unamortized Discount	(18.6)	(27.3)
Long-term Debt	$ 532.6	$ 716.4
Cleveland-Cliffs Inc. [Member] | 6.25% 2040 Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	6.34%	6.34%
Long-term Debt, Gross	$ 262.7	$ 298.4
Unamortized Debt Issuance Expense	(1.8)	(2.2)
Debt Instrument, Unamortized Discount	(2.8)	(3.3)
Long-term Debt	$ 258.1	292.9
Cleveland-Cliffs Inc. [Member] | Credit Facility
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	2.77%
Long-term Debt, Gross	$ 2,000	450
Long-term Line of Credit	$ 400	$ 0
AK Steel Holding Corporation [Member] | 7.625% 2021 Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	7.33%
Long-term Debt, Gross	$ 33.5
Unamortized Debt Issuance Expense	0
Debt Instrument, Unamortized Premium	0.1
Long-term Debt	$ 33.6
AK Steel Holding Corporation [Member] | 7.50% 2023 AK Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	6.17%
Long-term Debt, Gross	$ 12.8
Unamortized Debt Issuance Expense	0
Debt Instrument, Unamortized Premium	0.5
Long-term Debt	$ 13.3
AK Steel Holding Corporation [Member] | 6.375% 2025 AK Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	8.11%
Long-term Debt, Gross	$ 38.4
Unamortized Debt Issuance Expense	0
Debt Instrument, Unamortized Discount	(2.7)
Long-term Debt	$ 35.7
AK Steel Holding Corporation [Member] | 7.00% 2027 AK Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	9.24%
Long-term Debt, Gross	$ 56.3
Unamortized Debt Issuance Expense	0
Debt Instrument, Unamortized Discount	(6)
Long-term Debt	50.3
AK Steel Holding Corporation [Member] | Industrial Revenue Bonds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	92
Unamortized Debt Issuance Expense	0
Debt Instrument, Unamortized Premium	2.3
Long-term Debt	$ 94.3

DEBT AND CREDIT FACILITIES - _2

DEBT AND CREDIT FACILITIES - Schedule of Extinguishment of Debt (Details) - USD ($) $ in Millions	Jun. 01, 2020	Apr. 24, 2020	Mar. 27, 2020	Mar. 13, 2020	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount		$ 736.4						$ 1,487.5	$ 724
Reduction of Principal Long-Term Debt		$ 181.2
Gain (loss) on extinguishment of debt					$ 0		$ 0	132.6	(18.2)
Senior Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount						$ 11.2
7.625% 2021 AK Senior Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount			$ 8.5	$ 364.2				372.7
Gain (loss) on extinguishment of debt								0.4
7.50% 2023 AK Senior Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount			$ 56.5	$ 310.7				367.2
Gain (loss) on extinguishment of debt								2.8
4.875% 2024 Senior Secured Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount								5.5
Gain (loss) on extinguishment of debt								0.5
6.375% 2025 Senior Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount								167.5
Gain (loss) on extinguishment of debt								21.3
1.50% 2025 Convertible Senior Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount								20
Gain (loss) on extinguishment of debt								1.3
4.875% 2021 Senior Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount									124
Gain (loss) on extinguishment of debt									(5.3)
5.75% 2025 Senior Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount								77.1	600
Gain (loss) on extinguishment of debt								16.3	$ (12.9)
7.00% 2027 Senior Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount								247.3
Gain (loss) on extinguishment of debt								28.4
5.875% 2027 Senior Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount								194.5
Gain (loss) on extinguishment of debt								48.7
6.25% 2040 Senior Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount								35.7
Gain (loss) on extinguishment of debt								$ 12.9
AK Steel Holding Corporation [Member] | Unsecured Industrial Revenue Bonds [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount	$ 7.3

DEBT AND CREDIT FACILITIES - AB

DEBT AND CREDIT FACILITIES - ABL Facility (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020USD ($)
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 2,000
Credit Facility
Line of Credit Facility [Line Items]
Available borrowing base on ABL Facility	1,715.2	[1]
Long-term Line of Credit	(400)
Borrowing capacity available	$ 1,123
Line of Credit Facility, Covenant Compliance	As of September 30, 2020, 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.
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Long-term Line of Credit	$ (192.2)	[2]
[1]	1 As of September 30, 2020, the ABL Facility has a maximum borrowing base of $2.0 billion. The available borrowing base is determined by applying customary advance rates to eligible accounts receivable, inventory and certain mobile equipment.
[2]	2 We issued standby letters of credit with certain financial institutions in order to support business obligations including, but not limited to, workers' compensation, employee severance, IRBs and environmental obligations.

DEBT AND CREDIT FACILITIES - _3

DEBT AND CREDIT FACILITIES - Schedule of Debt Maturities (Details) $ in Millions	Sep. 30, 2020USD ($)
Debt Disclosure [Abstract]
Debt Maturities 2020	$ 0
Debt Maturities 2021	33.5
Debt Maturities 2022	0
Debt Maturities 2023	12.8
Debt Maturities 2024	456.5
2025 and thereafter	3,987.9
Total maturities of debt	$ 4,490.7

FAIR VALUE MEASUREMENTS - Fair

FAIR VALUE MEASUREMENTS - Fair Value of Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	$ 79	$ 233.4
Liabilities, Fair Value Disclosure	(9.7)	(4.3)
Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	0	0
Liabilities, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	17.6	187.6
Liabilities, Fair Value Disclosure	(9.4)	(3.2)
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	61.4	45.8
Liabilities, Fair Value Disclosure	(0.3)	(1.1)
Cash and Cash Equivalents [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents		187.6
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents		0
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents		187.6
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents		0
Commodity Contract [Member] | Other Current Assets [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	15.8
Commodity Contract [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	0
Commodity Contract [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	15.8
Commodity Contract [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	0
Commodity Contract [Member] | Other Noncurrent Assets [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	1.8
Commodity Contract [Member] | Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	0
Commodity Contract [Member] | Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	1.8
Commodity Contract [Member] | Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	0
Commodity Contract [Member] | Other Current Liabilities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	(8.7)	(3.2)
Commodity Contract [Member] | Other Current Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	0	0
Commodity Contract [Member] | Other Current Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	(8.7)	(3.2)
Commodity Contract [Member] | Other Current Liabilities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	0	0
Customer Supply Agreement [Member] | Other Current Assets [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	34.5	44.5
Customer Supply Agreement [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	0	0
Customer Supply Agreement [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	0	0
Customer Supply Agreement [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	34.5	44.5
Provisional Pricing Arrangements [Member] | Other Current Assets [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	26.9	1.3
Provisional Pricing Arrangements [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	0	0
Provisional Pricing Arrangements [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	0	0
Provisional Pricing Arrangements [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	26.9	1.3
Provisional Pricing Arrangements [Member] | Other Current Liabilities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	(0.3)	(1.1)
Provisional Pricing Arrangements [Member] | Other Current Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	0	0
Provisional Pricing Arrangements [Member] | Other Current Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	0	0
Provisional Pricing Arrangements [Member] | Other Current Liabilities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	(0.3)	$ (1.1)
Foreign Exchange Contract [Member] | Other Current Liabilities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	(0.6)
Foreign Exchange Contract [Member] | Other Current Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	0
Foreign Exchange Contract [Member] | Other Current Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	(0.6)
Foreign Exchange Contract [Member] | Other Current Liabilities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	0
Foreign Exchange Contract [Member] | Other Noncurrent Liabilities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	(0.1)
Foreign Exchange Contract [Member] | Other Noncurrent Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	0
Foreign Exchange Contract [Member] | Other Noncurrent Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	(0.1)
Foreign Exchange Contract [Member] | Other Noncurrent Liabilities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	$ 0

FAIR VALUE MEASUREMENTS - Quant

FAIR VALUE MEASUREMENTS - Quantitative Inputs And Assumptions For Level 3 Assets And Liabilities (Details) $ in Millions	Sep. 30, 2020USD ($)	Dec. 31, 2019USD ($)
Other Current Assets [Member] | Customer Supply Agreement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	$ 34.5	$ 44.5
Other Current Assets [Member] | Provisional Pricing Arrangements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	26.9	1.3
Other Current Assets [Member] | Not Designated as Hedging Instrument [Member] | Customer Supply Agreement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	34.5	44.5
Other Current Assets [Member] | Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	26.9	1.3
Other Current Assets [Member] | Fair Value, Inputs, Level 3 [Member] | Customer Supply Agreement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	34.5	44.5
Other Current Assets [Member] | Fair Value, Inputs, Level 3 [Member] | Provisional Pricing Arrangements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	$ 26.9	1.3
Other Current Assets [Member] | Customer's Hot-Rolled Steel Estimate [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Valuation, Market Approach [Member] | Customer Supply Agreement [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement With Unobservable Inputs Range	542
Other Current Assets [Member] | Customer's Hot-Rolled Steel Estimate [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Valuation, Market Approach [Member] | Customer Supply Agreement [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement With Unobservable Inputs Range	634
Other Current Assets [Member] | Customer's Hot-Rolled Steel Estimate [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Valuation, Market Approach [Member] | Customer Supply Agreement [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement With Unobservable Inputs Range	548
Other Current Assets [Member] | Platts 62% Price | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Valuation, Market Approach [Member] | Provisional Pricing Arrangements [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement With Unobservable Inputs Range	104
Other Current Assets [Member] | Platts 62% Price | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Valuation, Market Approach [Member] | Provisional Pricing Arrangements [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement With Unobservable Inputs Range	123
Other Current Assets [Member] | Platts 62% Price | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Valuation, Market Approach [Member] | Provisional Pricing Arrangements [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement With Unobservable Inputs Range	105
Other Current Assets [Member] | Atlantic Basin Pellet Premium [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Valuation, Market Approach [Member] | Provisional Pricing Arrangements [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement With Unobservable Inputs Range	30
Other Current Liabilities [Member] | Provisional Pricing Arrangements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability	$ (0.3)	(1.1)
Other Current Liabilities [Member] | Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability	(0.3)	(1.1)
Other Current Liabilities [Member] | Fair Value, Inputs, Level 3 [Member] | Provisional Pricing Arrangements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability	$ (0.3)	$ (1.1)
Other Current Liabilities [Member] | Platts 62% Price | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Valuation, Market Approach [Member] | Provisional Pricing Arrangements [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement With Unobservable Inputs Range	104
Other Current Liabilities [Member] | Producer Price Indices | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Valuation, Market Approach [Member] | Provisional Pricing Arrangements [Member] | Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement With Unobservable Inputs Range	110

FAIR VALUE MEASUREMENTS - Fai_2

FAIR VALUE MEASUREMENTS - Fair Value, Assets and Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Fair Value, Assets Measured On Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 35.3	$ 118.1	$ 45.8	$ 91.4
Included in earnings	29.5	(6.5)	43.3	83.1
Settlements	(3.4)	(38.8)	(27.7)	(101.7)
Ending balance	61.4	72.8	61.4	72.8
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	27.8	(6.5)	40.4	81.8
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	0	0	(1.1)	0
Included in earnings	(0.3)	(34.4)	(0.9)	(39.7)
Settlements	0	4.2	1.7	9.5
Ending balance	(0.3)	(30.2)	(0.3)	(30.2)
Total losses for the period included in earnings attributable to the change in unrealized losses on liabilities still held at the reporting date	$ (0.3)	$ (30.2)	$ (0.3)	$ (30.2)

FAIR VALUE MEASUREMENTS - Carry

FAIR VALUE MEASUREMENTS - Carrying Value And Fair Value Of Financial Instruments Disclosure (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	$ 4,309.8	$ 2,113.8
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	4,465.4	2,237
Senior Notes [Member] | Carrying Value [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	3,815.5	2,113.8
Senior Notes [Member] | Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	3,975.2	2,237
Industrial Revenue Bonds [Member] | Carrying Value [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	94.3	0
Industrial Revenue Bonds [Member] | Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	90.2	0
Line of Credit [Member] | Carrying Value [Member] | Fair Value, Inputs, Level 2 [Member] | Credit Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	400	0
Line of Credit [Member] | Fair Value [Member] | Fair Value, Inputs, Level 2 [Member] | Credit Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total long-term debt, fair value	$ 400	$ 0

PENSIONS AND OTHER POSTRETIRE_3

PENSIONS AND OTHER POSTRETIREMENT BENEFITS - Pension and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 5.4	$ 4.6	$ 16	$ 12.9
Interest cost	19.6	8.9	42.7	26.2
Expected return on plan assets	(36.7)	(13.7)	(91.9)	(41)
Prior service cost (credits)	0.2	0.3	0.7	0.9
Net actuarial loss	7.3	5.9	20.6	17.7
Net periodic benefit cost (credit)	(4.2)	6	(11.9)	16.7
Defined Benefit Pension Contributions	0.9	5.6	4.9	12.3
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	1.4	0.5	3.3	1.3
Interest cost	4.4	2.3	10.9	7
Expected return on plan assets	(4.5)	(4.2)	(13.6)	(12.6)
Prior service cost (credits)	(0.5)	(0.5)	(1.5)	(1.5)
Net actuarial loss	0.8	1.3	2.2	3.8
Net periodic benefit cost (credit)	1.6	(0.6)	$ 1.3	(2)
OPEB Contributions	$ 0	$ 0		$ 0

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, Percent			35.50%	9.60%
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%
Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount of Expense (Benefit)	$ (5)	$ (0.5)	$ (8.6)	$ (1.3)

ASSET RETIREMENT OBLIGATIONS -

ASSET RETIREMENT OBLIGATIONS - Summary Of Asset Retirement Obligations (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Environmental Exit Cost [Line Items]
Asset Retirement Obligation	$ 186.4	$ 179.5	$ 165.3	$ 172.4
Asset Retirement Obligation, Current	4.4		2.1
Long-term asset retirement obligations	182		163.2
Increase from AK Steel acquisition	16.7	$ 0
Operating Segments [Member]
Environmental Exit Cost [Line Items]
Asset Retirement Obligation	$ 33.7		$ 22

ASSET RETIREMENT OBLIGATIONS _2

ASSET RETIREMENT OBLIGATIONS - Asset Retirement Obligation Disclosure (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Asset Retirement Obligation [Roll Forward]
Asset retirement obligation at beginning of period	$ 165.3	$ 172.4
Increase from AK Steel acquisition	16.7	0
Accretion expense	7.8	7.6
Remediation payments	(3.4)	(0.5)
Asset retirement obligation at end of period	$ 186.4	$ 179.5

DERIVATIVE INSTRUMENTS - Schedu

DERIVATIVE INSTRUMENTS - Schedule Of Derivative Instruments In Statement Of Financial Position, Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Customer Supply Agreement [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	$ 34.5	$ 44.5
Provisional Pricing Arrangements [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	26.9	1.3
Provisional Pricing Arrangements [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	(0.3)	(1.1)
Commodity Contract [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	15.8
Commodity Contract [Member] | Other Noncurrent Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	1.8
Commodity Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	(8.7)	(3.2)
Foreign Exchange Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	(0.6)
Foreign Exchange Contract [Member] | Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	(0.1)
Designated as Hedging Instrument [Member] | Customer Supply Agreement [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	0	0
Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	0	0
Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	0	0
Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	7.9	0
Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Noncurrent Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	1.8	0
Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	(1.8)	(3.2)
Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	(0.6)	0
Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	(0.1)	0
Not Designated as Hedging Instrument [Member] | Customer Supply Agreement [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	34.5	44.5
Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	26.9	1.3
Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	(0.3)	(1.1)
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	7.9	0
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Noncurrent Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	0	0
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	(6.9)	0
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	0	0
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	$ 0	$ 0

DERIVATIVE INSTRUMENTS - Sche_2

DERIVATIVE INSTRUMENTS - Schedule of Notional Amounts of Outstanding Derivatives (Details) - Designated as Hedging Instrument [Member] lb in Millions, gal in Millions, MWh in Millions, MMBTU in Millions, $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020CAD ($)lbgalMMBTUMWh	Dec. 31, 2019CAD ($)MMBTUlbgalMWh
Natural Gas [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU	29.7	20.1
Diesel [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | gal	0	0.8
Zinc [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | lb	10.9	0
Electricity [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh	0.8	0
Canada, Dollars | Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount | $	$ 38.8	$ 0

DERIVATIVE INSTRUMENTS - Estima

DERIVATIVE INSTRUMENTS - Estimated Losses in Future Periods (Details) - Designated as Hedging Instrument [Member] $ in Millions	9 Months Ended
	Sep. 30, 2020USD ($)
Natural Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred	$ 10.8
Zinc [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred	2.3
Electricity [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred	1.1
Foreign Exchange Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred	$ 0.2

DERIVATIVE INSTRUMENTS - Sche_3

DERIVATIVE INSTRUMENTS - Schedule Of Derivatives Not Designated As Hedging Instruments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 33.1	$ (40.9)	$ 41.6	$ 43.4
Customer Supply Agreement [Member] | Sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	8.8	7.6	14.4	82.2
Provisional Pricing Arrangements [Member] | Sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	20.4	(48.5)	28	(38.8)
Commodity Contract [Member] | Cost of Sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 3.9	$ 0	$ (0.8)	$ 0

SHAREHOLDERS' EQUITY - Narrativ

SHAREHOLDERS' EQUITY - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	Mar. 13, 2020	Dec. 31, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Apr. 24, 2019	Nov. 26, 2018
Class of Stock [Line Items]
Common shares, par value						$ 0.125
Fair value of Cliffs common shares issued for AK Steel outstanding common stock	$ 617.6
Stock Repurchase Program, Authorized Amount								$ 100	$ 200
Stock Repurchased During Period, Shares							24,400,000
Payments for Repurchase of common shares						$ 0	$ 252.9
Forecast [Member] | ArcelorMittal USA [Member] | Series B Participating Redeemable Preferred Stock [Member]
Class of Stock [Line Items]
Shares of Cliffs common shares issued to AK Steel stockholders		583,273
Preferred Class A [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized						3,000,000
Preferred Stock, Shares Outstanding						0
Preferred Stock, Shares Issued						0
Preferred Class B [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized						4,000,000
Preferred Stock, Shares Outstanding						0
Preferred Stock, Shares Issued						0
Common Stock [Member]
Class of Stock [Line Items]
Stock Issued During Period, Shares, Acquisitions	126,800,000		126,800,000
Stock Repurchased During Period, Shares				12,900,000	11,500,000

SHAREHOLDERS' EQUITY - Divide_2

SHAREHOLDERS' EQUITY - Dividends Declared (Details) - $ / shares	3 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019		Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019
Dividends, Common Stock [Abstract]
Common Stock, Dividends, Per Share, Cash Paid	$ 0.06	$ 0.06	$ 0.10	[1]	$ 0.06	$ 0.05	$ 0.05
Common Stock, Special Dividends Per Share, Cash Paid			$ 0.04
[1]	1 The dividend declared on September 3, 2019 included a special cash dividend of $0.04 per common share.

ACCUMULATED OTHER COMPREHENSI_3

ACCUMULATED OTHER COMPREHENSIVE LOSS - Changes in AOCI (loss) related to shareholders' equity (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax, Beginning Balance	$ (304.1)	$ (310.1)	$ (315.7)	$ (269.6)	$ (275.4)	$ (281.1)	$ (315.7)	$ (281.1)
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax, Beginning Balance	(0.2)	(0.9)	0				0
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax, Beginning Balance	(1.6)	(6.1)	(3.1)	(2.2)	(0.1)	(2.8)	(3.1)	(2.8)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance	(305.9)	(317.1)	(318.8)	(271.8)	(275.5)	(283.9)	(318.8)	(283.9)
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax, Ending Balance	(297.5)	(304.1)	(310.1)	(263.8)	(269.6)	(275.4)	(297.5)	(263.8)
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax, Ending Balance	1.4	(0.2)	(0.9)				1.4
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax, Ending Balance	14.1	(1.6)	(6.1)	(1.8)	(2.2)	(0.1)	14.1	(1.8)
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance	(282)	(305.9)	(317.1)	(265.6)	(271.8)	(275.5)	$ (282)	$ (265.6)
Changes in Pension and Other Post-Retirement Benefits, net of tax [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	0.4	0.4	0	0.3	0.3	0.2
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	6.2	5.6	5.6	5.5	5.5	5.5
Unrealized Net Gain (Loss) on Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	1.6	0.7	(0.9)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0	0
Net Unrealized Gain (Loss) on Derivative Financial Instruments, net of tax [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	12.2	1.4	(5.2)	(0.5)	(2.3)	2.5
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	3.5	3.1	2.2	0.9	0.2	0.2
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	14.2	2.5	(6.1)	(0.2)	(2)	2.7
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 9.7	$ 8.7	$ 7.8	$ 6.4	$ 5.7	$ 5.7

ACCUMULATED OTHER COMPREHENSI_4

ACCUMULATED OTHER COMPREHENSIVE LOSS - Accumulated Other Comprehensive Income (Loss) Components (Details) - Reclassification out of Accumulated Other Comprehensive Income [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax	$ (0.3)	$ (0.2)	$ (0.8)	$ (0.6)
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Gain (Loss) Recognized in Net Periodic Benefit Cost, before Tax	8.1	7.2	22.8	21.5
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	7.8	7	22	20.9
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax	(1.6)	(1.5)	(4.6)	(4.4)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	6.2	5.5	17.4	16.5
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax	4.5	1.2	11.2	1.7
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Tax	(1)	(0.3)	(2.4)	(0.4)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	3.5	0.9	8.8	1.3
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 9.7	$ 6.4	$ 26.2	$ 17.8

RELATED PARTIES - Summary Of Ow

RELATED PARTIES - Summary Of Ownership Interests (Details) - Hibbing Taconite Company [Member]	Sep. 30, 2020
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage	23.00%
Arcelor Mittal [Member]
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage	62.30%
U. S. Steel [Member]
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage	14.70%

RELATED PARTIES - Summary Of Re

RELATED PARTIES - Summary Of Related Party Transactions Table Disclosure (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020		Sep. 30, 2019	Dec. 31, 2019
Related Party Transaction [Line Items]
Product revenues from related parties	$ 294.9	$ 293.5	$ 587.5		$ 792.8
Revenues	$ 1,646	$ 555.6	$ 3,097.8	[1]	$ 1,455.8
Related party product revenue as a percent of total product revenue	17.90%	52.80%	19.00%	[1]	54.50%
Purchases from related parties	$ 8.2	$ 0	$ 20.4		$ 0
Realization of deferred revenue	0	$ 0	34.6		$ 0
Trade Accounts Receivable [Member]
Related Party Transaction [Line Items]
Due from Related Parties, Current	91.6		91.6			$ 31.1
Other Current Assets [Member]
Related Party Transaction [Line Items]
Due from Related Parties, Current	58.5		58.5			44.5
Accounts Payable [Member]
Related Party Transaction [Line Items]
Due to Related Parties, Current	(1.2)		(1.2)			0
Other Current Liabilities [Member]
Related Party Transaction [Line Items]
Due to Related Parties, Current	$ (1.7)		$ (1.7)			$ (2)
[1]	1 Includes Realization of deferred revenue of $34.6 million for the nine months ended September 30, 2020.

VARIABLE INTEREST ENTITIES (Det

VARIABLE INTEREST ENTITIES (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Variable Interest Entity [Line Items]
Net Income (Loss) Attributable to Noncontrolling Interest	$ 11.9	$ 0	$ 31.2	$ 0
Cash and cash equivalents	56		56		$ 352.6
Inventories	1,795.1		1,795.1		317.4
Property, plant and equipment, net	4,550.7		4,550.7		1,929
Accounts payable	(710.7)		(710.7)		(193.2)
Noncontrolling interest	(313.1)		(313.1)		$ 0
SunCoke Middletown [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Net Income (Loss) Attributable to Noncontrolling Interest	11.8		31.3
Cash and cash equivalents	0.3		0.3
Inventories	22.5		22.5
Property, plant and equipment, net	305.4		305.4
Accounts payable	(10)		(10)
Other Assets (Liabilities), Net	(5.6)		(5.6)
Noncontrolling interest	$ (312.6)		$ (312.6)

EARNINGS PER SHARE - Earnings P

EARNINGS PER SHARE - Earnings Per Share Computation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Income (loss) from continuing operations	$ 2.2	$ 91.8	$ (154.8)	$ 231.1
Income attributable to noncontrolling interest	(11.9)	0	(31.2)	0
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	(9.7)	91.8	(186)	231.1
Loss from discontinued operations, net of tax	(0.3)	(0.9)	0	(1.5)
Net income (loss) attributable to Cliffs shareholders	$ (10)	$ 90.9	$ (186)	$ 229.6
Weighted average number of shares:
Basic	399,399	269,960	365,245	278,418
Convertible Senior Notes	0	3,700	0	5,800
Employee stock plans	0	2,900	0	3,600
Diluted	399,399	276,578	365,245	287,755
Earnings (loss) per common share attributable to Cliffs shareholders - basic:
Continuing operations (in dollars per share)	$ (0.02)	$ 0.34	$ (0.51)	$ 0.83
Discontinued operations (in dollars per share)	0	0	0	(0.01)
Earnings (Loss) per Common Share - Basic (in dollars per share)	(0.02)	0.34	(0.51)	0.82
Earnings (loss) per common share attributable to Cliffs shareholders - diluted:
Continuing operations (in dollars per share)	(0.02)	0.33	(0.51)	0.80
Discontinued operations (in dollars per share)	0	0	0	0
Earnings (Loss) per Common Share - Diluted (in dollars per share)	$ (0.02)	$ 0.33	$ (0.51)	$ 0.80

EARNINGS PER SHARE - Antidiluti

EARNINGS PER SHARE - Antidilutive Securities (Details) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Convertible Debt Securities [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0		0
Share-based Payment Arrangement [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1.8	0	1.6	0

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Purchase Commitments (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020USD ($)
Unrecorded Unconditional Purchase Obligation [Line Items]
Estimated Project Capital Expenditures	$ 1,000
Total Project Expenditures, Excluding Capitalized Interest	940.2
Capital Addition Purchase Commitments [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Capital Additions, Purchase Commitments	$ 97.8

COMMITMENTS AND CONTINGENCIES_3

COMMITMENTS AND CONTINGENCIES - Contingencies (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Loss Contingencies [Line Items]
Environmental obligations	$ 40.9	$ 2
Less current portion	6.4	0.3
Long-term environmental obligations	34.5	$ 1.7
Hamilton Plant [Member]
Loss Contingencies [Line Items]
Environmental obligations	0.7
Ashland Works Coke Plant [Member]
Loss Contingencies [Line Items]
Environmental obligations	$ 1.4