Cash and Cash Equivalents, Period Increase (Decrease) [Abstract]
OPERATING ACTIVITIES
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest
Adjustments to reconcile net income to net cash provided by operating activities:
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Depreciation, depletion and amortization
Depreciation, Depletion and Amortization
Deferred income taxes
Deferred Income Tax Expense (Benefit)
Loss (gain) on extinguishment of debt
Gain on extinguishment of debt, cash flows
Gain on extinguishment of debt, cash flows
Loss on deconsolidation
Loss on Deconsolidation, net of cash deconsolidated
Loss on Deconsolidation, net of cash deconsolidated
Gain on derivatives
Unrealized Gain (Loss) on Derivatives and Commodity Contracts
Gain on foreign currency translation
Foreign Currency Transaction Gain (Loss), Realized
Other
Other Noncash Income (Expense)
Changes in operating assets and liabilities:
Increase (Decrease) in Operating Capital [Abstract]
Receivables and other assets
Increase (Decrease) in Accounts Receivable and Other Operating Assets
Inventories
Increase (Decrease) in Inventories
Payables, accrued expenses and other liabilities
Increase (Decrease) in Accounts Payable and Accrued Liabilities
Net cash provided by operating activities
Net Cash Provided by (Used in) Operating Activities
INVESTING ACTIVITIES
Net Cash Provided by (Used in) Investing Activities [Abstract]
Purchase of property, plant and equipment
Property, Plant and Equipment, Cash Additions
Property, Plant and Equipment, Cash Additions
Deposits for property, plant and equipment
Payments to Acquire Property, Plant, and Equipment
Other investing activities
Payments for (Proceeds from) Other Investing Activities
Net cash used by investing activities
Net Cash Provided by (Used in) Investing Activities
FINANCING ACTIVITIES
Net Cash Provided by (Used in) Financing Activities [Abstract]
Net proceeds from issuance of common shares
Proceeds from Issuance of Common Stock
Repurchase of common shares
Stock Repurchased During Period, Value
Proceeds from issuance of debt
Proceeds from Issuance of Senior Long-term Debt
Debt issuance costs
Payments of Debt Issuance Costs
Borrowings under credit facilities
Proceeds from Long-term Lines of Credit
Repayment under credit facilities
Repayments of Long-term Lines of Credit
Repayments on equipment loans
Repayments of equipment loans
Repayments of equipment loans
Repurchase of debt
Gain (Loss) on Repurchase of Debt Instrument
Acquisition of noncontrolling interest
Payments for Repurchase of Redeemable Noncontrolling Interest
Distributions of partnership equity
Payments of Distributions to Affiliates
Other financing activities
Proceeds from (Payments for) Other Financing Activities
Net cash provided (used) by financing activities
Net Cash Provided by (Used in) Financing Activities
EFFECT OF EXCHANGE RATE CHANGES ON CASH
Effect of Exchange Rate on Cash and Cash Equivalents
Increase (Decrease) in Cash and Cash Equivalents, Including Cash Classified Within Current Assets of Discontinued Operations
Increase/Decrease in Cash and Cash Equivalents, Including Cash Classified Within Current Assets of Discontinued Operations
Increase/Decrease in Cash and Cash Equivalents, Including Cash Classified Within Current Assets of Discontinued Operations
LESS: INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS CLASSIFIED WITHIN CURRENT ASSETS OF DISCONTINUED OPERATIONS
Increase/Decrease in Cash and Cash Equivalents in Cash Classified within Current Assets of Discontinued Operations
Increase/Decrease in Cash and Cash Equivalents in Cash Classified within Current Assets of Discontinued Operations
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS
Cash and Cash Equivalents, Period Increase (Decrease)
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR
Cash And Cash Equivalents, At Carrying Value, Including Assets Held For Sale
Cash And Cash Equivalents, At Carrying Value, Including Assets Held For Sale
CASH AND CASH EQUIVALENTS AT END OF YEAR
Income Tax Disclosure [Abstract]
Income Tax Contingency [Table]
Income Tax Contingency [Table]
Valuation Allowance by Deferred Tax Asset [Axis]
Valuation Allowance by Deferred Tax Asset [Axis]
Deferred Tax Asset [Domain]
Deferred Tax Asset [Domain]
Tax Law Change [Member]
Tax Law Change [Member]
Tax Law Change
Current year activity [Member]
Current year activity [Member]
Current year activity
valuation allowance reversal [Member]
valuation allowance reversal [Member]
Valuation allowance reversal
Repeal of AMT [Member]
Repeal of AMT [Member]
Repeal of AMT
Dissolution of entities [Member]
Dissolution of entities [Member]
Dissolution of entities
Prior year adjustment in current year [Member]
Prior year adjustment in current year [Member]
Prior year adjustment in current year
Income Statement Location [Axis]
Income Statement Location [Axis]
Income Statement Location [Domain]
Income Statement Location [Domain]
Income Tax Authority [Axis]
Income Tax Authority [Axis]
Income Tax Authority [Domain]
Income Tax Authority [Domain]
Income Tax Contingency [Line Items]
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount
Effective Income Tax Rate Reconciliation, Percent
Effective Income Tax Rate Reconciliation, Percent
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount
Impact Of Tax Law Change Percent
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent
Effective Income Tax Rate Reconciliation, Disposition of Business, Amount
Effective Income Tax Rate Reconciliation, Disposition of Business, Amount
Effective Income Tax Rate Reconciliation, Disposition of Business, Percent
Effective Income Tax Rate Reconciliation, Disposition of Business, Percent
Prior year adjustments made in current year, amount
Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Amount
Income Tax Reconciliation Tax Deduction for percentage depletion in excess of cost depletion
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Depletion, Amount
Income Tax Reconciliation Tax Deduction for percentage depletion in excess of cost depletion percent
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Depletion, Percent
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Amount
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Amount
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent
Tax Adjustments, Settlements, and Unusual Provisions
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Amount
Tax Adjustments Settlements And Unusual Provisions Percent
Effective Income Tax Rate Reconciliation, Tax Contingency, Percent
Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Percent
Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Percent
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent
Income Tax Expense (Benefit)
Income Tax Expense (Benefit)
Worthless Stock Deduction, Amount
Worthless Stock Deduction, Amount
Worthless Stock Deduction, Amount
Worthless Stock Deduction, Percent
Worthless Stock Deduction, Percent
Worthless Stock Deduction, Percent
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table]
Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table]
Awards Outstanding, Grant Date [Axis]
Awards Outstanding, Grant Date [Axis]
Awards Outstanding, Grant Date [Axis]
Awards Outstanding, Grant Date [Domain]
Awards Outstanding, Grant Date [Domain]
[Domain] for Awards Outstanding, Grant Date [Axis]
Plan Name [Axis]
Plan Name [Axis]
Plan Name [Domain]
Plan Name [Domain]
Award Date [Axis]
Award Date [Axis]
Award Date [Domain]
Award Date [Domain]
Award Type [Axis]
Award Type [Axis]
Equity Award [Domain]
Equity Award [Domain]
Performance Shares [Member]
Performance Shares [Member]
Class of Stock [Axis]
Class of Stock [Axis]
Class of Stock [Domain]
Class of Stock [Domain]
Range [Axis]
Range [Axis]
Range [Domain]
Range [Domain]
Vesting [Axis]
Vesting [Axis]
Vesting [Domain]
Vesting [Domain]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance shares granted
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Estimated Forfeitures
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Estimated Forfeitures
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Estimated Forfeitures
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Expected to Vest
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Expected to Vest
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Expected to Vest
Discontinued Operations and Disposal Groups [Abstract]
DISCONTINUED OPERATIONS
Disposal Groups, Including Discontinued Operations, Disclosure [Text Block]
Income Taxes
Income Tax Disclosure [Text Block]
Supplemental Cash Flow Information [Abstract]
Cash Flow Information
Cash Flow, Supplemental Disclosures [Text Block]
A&R 2015 Equity Plan [Member]
A&R 2015 Equity Plan [Member]
A&R 2015 Equity Plan [Member]
2015 Equity Plan [Member]
2015 Equity Plan [Member]
2015 Equity Plan [Member]
Amended 2015 Equity Plan [Domain]
Amended 2015 Equity Plan [Domain]
Amended 2015 Equity Plan [Member]
2012 Equity Plan [Member]
Two Thousand Twelve Equity Plan [Member]
Two Thousand Twelve Equity Plan [Member]
Restricted Stock Units (RSUs) [Member]
Restricted Stock Units (RSUs) [Member]
Employee Stock Option [Member]
Employee Stock Option [Member]
Stock Issued During Period, Shares, Restricted Stock Award, Gross
Stock Issued During Period, Shares, Restricted Stock Award, Gross
STOCK COMPENSATION PLANS
Disclosure of Compensation Related Costs, Share-based Payments [Text Block]
Environmental Remediation Obligations [Abstract]
Schedule of Environmental Loss Contingencies and Asset Retirement Obligations [Table Text Block]
Schedule of Environmental Loss Contingencies and Asset Retirement Obligations [Table Text Block]
Schedule of Environmental Loss Contingencies and Asset Retirement Obligations [Table Text Block]
Asset Retirement Obligations
Schedule of Change in Asset Retirement Obligation [Table Text Block]
Property, Plant and Equipment [Abstract]
Depreciation
Depreciation
Interest capitalized
Interest Costs Capitalized
Depletion
Depletion
Derivative Instruments and Hedging Activities Disclosure [Abstract]
DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES
Derivative Instruments and Hedging Activities Disclosure [Text Block]
Schedule of Derivatives in Fair Value Hedging Relationships, Statements of Financial Performance and Financial Position, Location [Table]
Schedule of Derivatives in Fair Value Hedging Relationships, Statements of Financial Performance and Financial Position, Location [Table]
Schedule of Derivatives in Fair Value Hedging Relationships, Statements of Financial Performance and Financial Position, Location [Table]
Statements of Consolidated Operations Location [Domain]
Derivative Instrument [Axis]
Derivative Instrument [Axis]
Derivative Contract [Domain]
Derivative Contract [Domain]
Interest Rate Swap [Member]
Interest Rate Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) [Line Items]
Statement of Financial Position [Abstract]
ASSETS
Assets [Abstract]
CURRENT ASSETS
Assets, Current [Abstract]
Cash and cash equivalents
Cash and Cash Equivalents, at Carrying Value
Accounts receivable, net
Accounts Receivable, Net, Current
Inventories
Inventory, Net
Supplies and other inventories
Prepaid Supplies
Derivative assets
Derivative Asset, Current
Income tax receivable, current
Income Taxes Receivable, Current
Loans to and accounts receivables from the Canadian Entities
Loans to and accounts receivables from the Canadian Entities
Loans to and accounts receivables from the Canadian Entities
Current assets of discontinued operations
Disposal Group, Including Discontinued Operation, Assets, Current
Other current assets
Other Assets, Current
TOTAL CURRENT ASSETS
Assets, Current
PROPERTY, PLANT AND EQUIPMENT, NET
Property, Plant and Equipment, Net
OTHER ASSETS
Other Assets, Noncurrent [Abstract]
Deposits for property, plant and equipment
Prepaid Expense and Other Assets
Income tax receivable, non-current
Income Taxes Receivable, Noncurrent
Deferred income taxes
Deferred Income Tax Assets, Net
Non-current assets of discontinued operations
Disposal Group, Including Discontinued Operation, Assets, Noncurrent
Other non-current assets
Other Assets, Noncurrent
TOTAL ASSETS
Assets
LIABILITIES
Liabilities [Abstract]
CURRENT LIABILITIES
Liabilities, Current [Abstract]
Accounts payable
Accounts Payable, Current
Accrued employment costs
Employee-related Liabilities, Current
State and local taxes payable
Taxes Payable, Current
Accrued interest
Interest Payable, Current
Contingent claims
Reserve for unasserted claims in CCAA
Reserve for unasserted claims in CCAA
Partnership distribution payable
Short-term Non-bank Loans and Notes Payable
Current liabilities of discontinued operations
Disposal Group, Including Discontinued Operation, Liabilities, Current
Other current liabilities
Other Liabilities, Current
TOTAL CURRENT LIABILITIES
Liabilities, Current
POSTEMPLOYMENT BENEFIT LIABILITIES
Liability, Defined Benefit Plan, Noncurrent [Abstract]
Pensions
Liability, Defined Benefit Pension Plan, Noncurrent
Other postretirement benefits
Liability, Other Postretirement Defined Benefit Plan, Noncurrent
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES
Liability, Defined Benefit Plan, Noncurrent
ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS
Mine Reclamation and Closing Liability, Noncurrent
LONG-TERM DEBT
Long-term Debt, Excluding Current Maturities
NON-CURRENT LIABILITIES OF DISCONTINUED OPERATIONS
Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent
OTHER LIABILITIES
Other Liabilities, Noncurrent
TOTAL LIABILITIES
Liabilities
COMMITMENTS AND CONTINGENCIES (SEE NOTE 19)
Commitments and Contingencies
EQUITY
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)
Stockholders' Equity Attributable to Parent [Abstract]
Common Shares - par value $0.125 per share, Authorized - 600,000,000 shares (2017 - 600,000,000 shares); Issued - 301,886,794 shares (2017 - 301,886,794) shares); Outstanding - 292,611,569 shares (2017 - 297,400,968) shares)
Common Stock, Value, Outstanding
Capital in excess of par value of shares
Additional Paid in Capital
Retained deficit
Retained Earnings (Accumulated Deficit)
Cost of 9,275,225 common shares in treasury (2017 - 4,485,826 shares)
Treasury Stock, Value
Accumulated other comprehensive loss
Accumulated Other Comprehensive Income (Loss), Net of Tax
TOTAL CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)
Stockholders' Equity Attributable to Parent
NONCONTROLLING INTEREST
Stockholders' Equity Attributable to Noncontrolling Interest
TOTAL EQUITY (DEFICIT)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest
TOTAL LIABILITIES AND EQUITY (DEFICIT)
Liabilities and Equity
Income Statement [Abstract]
Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table]
Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table]
Valuation Approach and Technique [Axis]
Valuation Approach and Technique [Axis]
Valuation Approach and Technique [Domain]
Valuation Approach and Technique [Domain]
Valuation, Market Approach [Member]
Valuation, Market Approach [Member]
Fair Value Hierarchy and NAV [Axis]
Fair Value Hierarchy and NAV [Axis]
Fair Value Hierarchy and NAV [Domain]
Fair Value Hierarchy and NAV [Domain]
Fair Value, Inputs, Level 2 [Member]
Fair Value, Inputs, Level 2 [Member]
Fair Value, Inputs, Level 3 [Member]
Fair Value, Inputs, Level 3 [Member]
Hedging Designation [Axis]
Hedging Designation [Axis]
Hedging Designation [Domain]
Hedging Designation [Domain]
Designated as Hedging Instrument [Member]
Designated as Hedging Instrument [Member]
Not Designated as Hedging Instrument [Member]
Not Designated as Hedging Instrument [Member]
Commodity Contract [Member]
Commodity Contract [Member]
Customer Supply Agreement [Member]
Customer Supply Agreement [Member]
Customer Supply Agreement [Member]
Provisional Pricing Arrangements [Member]
Provisional Pricing Arrangements [Member]
Provisional Pricing Arrangements [Member]
Balance Sheet Location [Axis]
Balance Sheet Location [Axis]
Balance Sheet Location [Domain]
Balance Sheet Location [Domain]
Other Current Assets [Member]
Other Current Assets [Member]
Other Current Liabilities [Member]
Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, Fair Value [Line Items]
Derivative asset, fair value
Derivative Asset, Fair Value, Gross Asset
Derivative liability, fair value
Derivative Liability, Fair Value, Gross Liability
Segment Reporting [Abstract]
Schedule Of Segment Reporting Information, By Segment
Schedule of Segment Reporting Information, by Segment [Table Text Block]
Summary of Assets by Segment
Reconciliation of Assets from Segment to Consolidated [Table Text Block]
Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas
Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block]
Revenue from External Customers by Products and Services
Revenue from External Customers by Products and Services [Table Text Block]
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Property, Plant and Equipment [Table]
Property, Plant and Equipment [Table]
Initial Application Period Cumulative Effect Transition [Axis]
Initial Application Period Cumulative Effect Transition [Axis]
Initial Application Period Cumulative Effect Transition [Domain]
Initial Application Period Cumulative Effect Transition [Domain]
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Adjustments for New Accounting Pronouncements [Axis]
Adjustments for New Accounting Pronouncements [Axis]
Type of Adoption [Domain]
Type of Adoption [Domain]
Accounting Standards Update 2014-09 [Member]
Accounting Standards Update 2014-09 [Member]
Segments [Axis]
Segments [Axis]
Segments [Domain]
Segments [Domain]
Asia Pacific Iron Ore [Member]
Asia Pacific Iron Ore [Member]
Asia Pacific Iron Ore [Member]
North American Coal [Member]
North American Coal [Member]
North American Coal [Member]
Property, Plant and Equipment, Type [Axis]
Property, Plant and Equipment, Type [Axis]
Property, Plant and Equipment, Type [Domain]
Property, Plant and Equipment, Type [Domain]
Building [Member]
Building [Member]
Equipment [Member]
Equipment [Member]
Other Machinery and Equipment [Member]
Other Machinery and Equipment [Member]
Electric Power Facilities [Member]
Electric Generation Equipment [Member]
Land Improvements [Member]
Land Improvements [Member]
Computer Equipment [Member]
Computer Equipment [Member]
Minimum [Member]
Minimum [Member]
Maximum [Member]
Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life
Property, Plant and Equipment, Useful Life
Statement [Table]
Statement [Table]
Disposal Group Name [Axis]
Disposal Group Name [Axis]
Disposal Groups, Including Discontinued Operations, Name [Domain]
Disposal Group Name [Domain]
Statement [Line Items]
Statement [Line Items]
Revenues from product sales and services
Disposal Group, Including Discontinued Operation, Revenue
Cost of goods sold and operating expenses
Disposal Group, Including Discontinued Operation, Costs of Goods Sold
Sales margin
Disposal Group, Including Discontinued Operation, Gross Profit (Loss)
Other operating expense
Disposal Group, Including Discontinued Operation, Operating Expense
Other expense
Disposal Group, Including Discontinued Operation, Other Expense
Gain on foreign currency translation
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax
Impairment of long-lived assets
Impairment of Long-Lived Assets to be Disposed of
INCOME FROM DISCONTINUED OPERATIONS, net of tax
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest
Postemployment Benefits [Abstract]
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table]
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table]
Trust for Benefit of Employees [Axis]
Trust for Benefit of Employees [Axis]
Trust for Benefit of Employees [Axis]
Trust for Benefit of Employees [Domain]
Trust for Benefit of Employees [Domain]
[Domain] for Trust for Benefit of Employees [Axis]
Veba Trust [Member]
Trust for Benefit of Employees [Member]
Defined Benefit Plan, Plan Assets, Category [Axis]
Defined Benefit Plan, Plan Assets, Category [Axis]
Defined Benefit Plan, Plan Assets, Category [Domain]
Defined Benefit Plan, Plan Assets, Category [Domain]
Hedge Funds [Member]
Hedge Funds [Member]
Private Equity Funds [Member]
Private Equity Funds [Member]
Structured Finance [Member]
Structured Finance [Member]
Real Estate [Member]
Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Roll Forward]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of plan assets — beginning of year
Defined Benefit Plan, Plan Assets, Amount
Actual return on plan assets:
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Purchase, Sale, and Settlement [Abstract]
Relating to assets still held at the reporting date
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held
Purchases
Defined Benefit Plan, Plan Assets, Business Combination
Sales
Defined Benefit Plan, Plan Assets, Divestiture
Fair value of plan assets — end of year
Debt Disclosure [Abstract]
Line of Credit Facility [Table]
Line of Credit Facility [Table]
Variable Rate [Axis]
Variable Rate [Axis]
Variable Rate [Domain]
Variable Rate [Domain]
Prime Rate [Member]
Prime Rate [Member]
Equity [Member]
Equity [Member]
Extinguishment of Debt [Axis]
Extinguishment of Debt [Axis]
Extinguishment of Debt, Type [Domain]
Extinguishment of Debt, Type [Domain]
Debt Repurchase [Member]
Debt Repurchase [Member]
Debt Repurchase [Member]
Exchange of Debt for Equity [Member]
Exchange of Debt for Equity [Member]
Exchange of Debt for Equity [Member]
Debt Instrument [Axis]
Debt Instrument [Axis]
Debt Instrument, Name [Domain]
Debt Instrument, Name [Domain]
$400 Million 4.875% 2024 Senior Notes [Member]
$400 Million 4.875% 2024 Senior Notes [Member]
$400 Million 4.875% 2024 Senior Notes [Member]
$1.075 Billion 5.75% 2025 Senior Notes [Member]
$500 Million 5.75% 2025 Senior Notes [Member]
$500 Million 5.75% 2025 Senior Notes [Member]
$316 Million 1.5% 2025 Senior Notes [Domain]
$316 Million 1.5% 2025 Senior Notes [Domain]
$316 Million 1.5% 2025 Senior Notes [Domain]
$1.075 Billion 5.75% 2025 Senior Notes
One Billion Seventy Five Million Five Point Seven Five Two Thousand Twenty Five Senior Note [Member]
One Billion Seventy Five Million Five Point Seven Five Two Thousand Twenty Five Senior Note [Member]
$540 Million 8.25% 2020 First Lien Notes
Five hundred forty million Eight point two five Twenty twenty First Lien Notes [Member]
Five hundred forty million Eight point two five Twenty twenty First Lien Notes [Member]
$218.5 Million 8.00% 2020 1.5 Lien Notes
Two hundred Eighteen Point Five Million Eight Point Zero Twenty Twenty One Point Five Lien Notes [Member]
Two hundred Eighteen Point Five Million Eight Point Zero Twenty Twenty One Point Five Lien Notes Member [Member]
$544.2 Million 7.75% 2020 Second Lien Notes
Five hundred Forty-four Million Seven Point Seven Five Twenty Twenty Second Lien Notes [Member]
Five hundred Forty-four Million Seven Point Seven Five Twenty Twenty Second Lien Notes [Member]
Secured Debt [Member]
Secured Debt [Member]
$500 Million 3.95% 2018 Senior Notes [Member]
Five Hundred Million Three Point Nine Five Two Thousand Eighteen Senior Note [Member]
Five Hundred Million Three Point Nine Five Two Thousand Eighteen Senior Note [Member]
$400 Million 5.90% 2020 Senior Notes
Four Hundred Million Five Point Nine Zero Two Thousand And Twenty Senior Note [Member]
Four Hundred Million Five Point Nine Zero Two Thousand And Twenty Senior Note [Member]
$500 Million 4.80% 2020 Senior Notes
Five Hundred Million Four Point Eight Zero Percent Senior Note [Member]
Five Hundred Million Four Point Eight Zero Percent Senior Note [Member]
$700 Million 4.875% 2021 Senior Notes
Seven Hundred Million Four Point Eight Seven Five Two Thousand Twenty-one Senior Note [Member]
Seven Hundred Million Four Point Eight Seven Five Two Thousand Twenty-one Senior Note [Member]
$800 Million 6.25% 2040 Senior Notes [Member]
Eight Hundred Million Six Point Two Five Percent Senior Notes Due Two Thousand Forty [Member]
Eight Hundred Million Six Point Two Five Percent Senior Notes Due Two Thousand Forty [Member]
Unsecured Debt [Member]
Unsecured Debt [Member]
ABL Facility [Member]
Revolving Credit Facility [Member]
Letter of Credit [Member]
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility [Line Items]
Proceeds from Issuance of Debt
Proceeds from Issuance of Debt
Imputed interest rate
Debt Instrument, Interest Rate, Effective Percentage
Debt Extinguished
Extinguishment of Debt, Amount
Convertible debt, initial conversion price
Convertible debt, initial conversion price
Convertible debt, initial conversion price
Convertible debt, common shares exchanged
Convertible debt, common shares exchanged
Convertible debt, common shares exchanged
Common shares, par value
Common Stock, Par or Stated Value Per Share
Convertible debt, conversion price percentage
Convertible debt, conversion price percentage
Convertible debt, conversion price percentage
Convertible debt, principal increment
Convertible debt, principal increment
Convertible debt, principal increment
Redemption Price of 35 percent or less of Outstanding
Redemption Price of 35 percent or less of Outstanding
Redemption Price of 35 percent or less of Outstanding
Debt Instrument, Interest Rate, Stated Percentage
Debt Instrument, Interest Rate, Stated Percentage
Repurchase price if triggering event occurs
Repurchase price if triggering event occurs
Repurchase price if triggering event occurs
Common Stock, New Shares, Issued
Common Stock, New Shares, Issued
Common Stock, New Shares, Issued
Shares Issued, Price Per Share
Shares Issued, Price Per Share
Redemption Price
Redemption Price
Redemption Price
Debt Instrument, Par Value
Debt Instrument, Par Value
Debt Instrument, Par Value
Gain (loss) on extinguishment of debt
Gain (Loss) on Extinguishment of Debt
Debt redemption premiums paid
Debt redemption premiums paid
Debt redemption premiums paid
Debt Redemption Expenses
Debt Redemption Expenses
Debt Redemption Expenses
Time Period During Which Senior Notes May Be Redeemed at Company's Option, Number of Days From When Prior Notice Sent to Holders
Time Period During Which Senior Notes May Be Redeemed at Company's Option, Number of Days From When Prior Notice Sent to Holders
Time Period During Which Senior Notes May Be Redeemed at Company's Option, Number of Days From When Prior Notice Sent to Holders
Note Redemption Price, Percent of Principal Amount to be Redeemed
Note Redemption Price, Percent of Principal Amount to be Redeemed
Note Redemption Price, Percent of Principal Amount to be Redeemed
Amount in aggregate that can be redeemed on or prior to March 1, 2020
Amount in aggregate that can be redeemed on or prior to March 1, 2020
Amount in aggregate that can be redeemed on or prior to March 1, 2020
Basis points
Basis points
Basis points
U.S. Tranche
U.S. Tranche
U.S. Tranche
Sublimit for Issuers of Letters of Credit for U.S. Tranche
Sublimit for Issuers of Letters of Credit for U.S. Tranche
Sublimit for Issuers of Letters of Credit for U.S. Tranche
Sublimit for U.S. Swingline Loans
Sublimit for U.S. Swingline Loans
Sublimit for U.S. Swingline Loans
Australian Tranche
Australian Tranche
Australian Tranche
Sublimit for Issuance of Letters of Credit for Australian Tranche
Sublimit for Issuance of Letters of Credit for Australian Tranche
Sublimit for Issuance of Letters of Credit for Australian Tranche
Sublimit for Australian Swingline Loans
Sublimit for Australian Swingline Loans
Sublimit for Australian Swingline Loans
Base Rate
Base Rate
Base Rate
LIBOR Rate Based on a One-month interest period plus 1 percent
LIBOR Rate Based on a One-month interest period plus 1 percent
LIBOR Rate Based on a One-month interest period plus 1 percent
Debt Instrument, Basis Spread on Variable Rate
Debt Instrument, Basis Spread on Variable Rate
Fixed Charge Coverage Ratio
Fixed Charge Coverage Ratio
Fixed Charge Coverage Ratio
Credit facility, amount outstanding
Long-term Line of Credit
Line of Credit Facility, Remaining Borrowing Capacity
Line of Credit Facility, Remaining Borrowing Capacity
Revolving credit facility, borrowing capacity
Line of Credit Facility, Maximum Borrowing Capacity
Debt issuance costs
Unamortized Debt Issuance Expense
Unamortized Debt Issuance Expense
Debt Instrument, Unamortized Discount
Debt Instrument, Unamortized Discount
Adjustments to Additional Paid in Capital, Convertible Debt with Conversion Feature
Adjustments to Additional Paid in Capital, Convertible Debt with Conversion Feature
Common Shares Issued in Debt to Equity Exchange
Common Shares Issued in Debt to Equity Exchange
Common Shares Issued in Debt to Equity Exchange
Debt Instrument, Face Amount Exchanged
Debt Instrument, Face Amount Exchanged
Debt Instrument, Face Amount Exchanged
Property, Plant and Equipment, Additions, Including Discontinued Operations
Property, Plant and Equipment, Additions, Including Discontinued Operations
Property, Plant and Equipment, Additions, Including Discontinued Operations
Non-cash accruals
Capital Expenditure, Non-Cash Accruals
Capital Expenditure, Non-Cash Accruals
Capital leases
Capital Lease Obligations Incurred
Government grant rebate
Government grant rebate
Government grant rebate
Payments To Acquire Property Plant And Equipment Net
Payments To Acquire Property Plant And Equipment Net
Payments To Acquire Property Plant And Equipment, Net
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES
Commitments and Contingencies Disclosure [Text Block]
Health care cost trend rate assumed for next year
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year
Ultimate health care cost trend rate
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate
Statement of Stockholders' Equity [Abstract]
Common Stock, Dividends, Per Share, Declared
Common Stock, Dividends, Per Share, Declared
SEGMENT REPORTING
Segment Reporting Disclosure [Text Block]
Retirement Plan Type [Axis]
Retirement Plan Type [Axis]
Retirement Plan Type [Domain]
Retirement Plan Type [Domain]
Pension Benefits [Member]
Pension Plan [Member]
Other Benefits [Member]
Other Postretirement Benefits Plan [Member]
Estimated net periodic benefit cost
Defined Benefit Plan Expected Net Periodic Benefit Cost
Defined Benefit Plan, Expected Net Periodic Benefit Cost
Other Postretirement Benefit Plan, Defined Benefit [Member]
Investment Type [Axis]
Investment Type [Axis]
Investments [Domain]
Investments [Domain]
U S Small Mid Cap [Member]
U S Small Mid Cap [Member]
US Small / Mid Cap
International [Member]
International [Member]
International
U S Large Cap [Member]
U S Large Cap [Member]
US Large Cap
Fixed Income Investments [Member]
Fixed Income Investments [Member]
Structured Credit [Member]
Structured Credit [Member]
Structured Credit [Member]
Cash [Member]
Cash [Member]
Equity Securities [Member]
Equity Securities [Member]
Fair Value Hierarchy and NAV [Domain]
Fair Value, Inputs, Level 1 [Member]
Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Plan Assets, Amount
Schedule of Long-term Debt Instruments [Table]
Schedule of Long-term Debt Instruments [Table]
Debt Instrument [Line Items]
Debt Instrument [Line Items]
Face amount
Debt Instrument, Face Amount
Unamortized Debt Issuance Expense
Debt Instrument, Unamortized Discount
Long-term Debt
Long-term Debt
Fair Value Adjustment to Interest Rate Hedge
Fair Value Adjustment to Interest Rate Hedge
Fair Value Adjustment to Interest Rate Hedge
Unrecognized Tax Benefits
Unrecognized Tax Benefits
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations
Other Increases decreases to unrecognized tax benefits
Unrecognized Tax Benefits, Period Increase (Decrease)
Other Benefits [Axis]
Other Benefits [Axis]
Other Benefits [Axis]
Other Benefits [Domain]
Other Benefits [Domain]
[Domain] for Other Benefits [Axis]
Direct Payments [Member]
Direct Payments [Member]
Direct payments made into the other postretirement benefit plans.
Veba Trust [Member]
Veba Trust [Member]
Relating to the Voluntary Employees' Beneficiary Association (VEBA) Trust Plans.
Defined Benefit Plan, Funded Percentage
Defined Benefit Plan, Funded Percentage
Company contributions
Defined Benefit Plan, Plan Assets, Contributions by Employer
Expected company contributions, next fiscal year
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year
Value of VEBA Trust Assets as a Percentage of the Funding Obligation
Value of VEBA Trust Assets as a Percentage of the Funding Obligation
Value of VEBA Trust Assets as a Percentage of the Funding Obligation that causes the funding obligation to be suspended.
Site Contingency [Table]
Site Contingency [Table]
Environmental Remediation Site [Axis]
Environmental Remediation Site [Axis]
Environmental Remediation Site [Domain]
Environmental Remediation Site [Domain]
Loss Contingency Nature [Axis]
Loss Contingency Nature [Axis]
Loss Contingency, Nature [Domain]
Loss Contingency, Nature [Domain]
Mine Closure [Axis]
Mine Closure [Axis]
Mine Closure [Axis]
Mine Closure [Domain]
Mine Closure [Domain]
[Domain] for Mine Closure [Axis]
Site Contingency [Line Items]
Site Contingency [Line Items]
Accrual for Environmental Loss Contingencies
Accrual for Environmental Loss Contingencies
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current And Noncurrent
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current And Noncurrent
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current And Noncurrent
Accrual for Environmental Loss Contingencies, Period Increase (Decrease)
Accrual for Environmental Loss Contingencies, Period Increase (Decrease)
Schedule of Extinguishment of Debt [Table]
Schedule of Extinguishment of Debt [Table]
Extinguishment of Debt [Line Items]
Extinguishment of Debt [Line Items]
Debt Instrument, Face Amount Received in Debt Exchange of $544M 7.75% Notes
Debt Instrument, Face Amount Received in Debt Exchange of $544M 7.75% Notes
Debt Instrument, Face Amount Received in Debt Exchange of $544.2M 7.75% Notes
Debt Instrument, Face Amount Received in Debt Exchange of $500M 3.95% Notes
Debt Instrument, Face Amount Received in Debt Exchange of $500M 3.95% Notes
Debt Instrument, Face Amount Received in Debt Exchange of $500M 3.95% Notes
Debt Instrument, Face Amount Received in Debt Exchange of $400M 5.90% Notes
Debt Instrument, Face Amount Received in Debt Exchange of $400M 5.90% Notes
Debt Instrument, Face Amount Received in Debt Exchange of $400M 5.90% Notes
Debt Instrument, Face Amount Received in Debt Exchange of $500M 4.80% Notes
Debt Instrument, Face Amount Received in Debt Exchange of $500M 4.80% Notes
Debt Instrument, Face Amount Received in Debt Exchange of $500M 4.80% Notes
Debt instrument, Face Amount Received in Debt Exchange of $700M 4.875% Notes
Debt instrument, Face Amount Received in Debt Exchange of $700M 4.875% Notes
Debt instrument, Face Amount Received in Debt Exchange of $700M 4.875% Notes
Debt Instrument, Face Amount Received in Debt Exchange of $800M 6.25% Notes
Debt Instrument, Face Amount Received in Debt Exchange of $800M 6.25% Notes
Debt Instrument, Face Amount Received in Debt Exchange of $800M 6.25% Notes
Debt, carrying value
Debt, carrying value
Debt, carrying value
Depositary Shares [Member]
Depositary Shares [Member]
Depositary Shares [Member]
Common Stock [Member]
Common Stock [Member]
Equity Components [Axis]
Equity Components [Axis]
Equity Component [Domain]
Equity Component [Domain]
Capital in Excess of Par Value of Shares [Member]
Additional Paid-in Capital [Member]
Retained Earnings [Member]
Retained Earnings [Member]
Common Shares in Treasury [Member]
Treasury Stock [Member]
Accumulated Other Comprehensive Income (Loss) [Member]
AOCI Attributable to Parent [Member]
Noncontrolling Interest [Member]
Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period (in shares)
Common Stock, Shares, Outstanding
Balance, beginning of period
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract]
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract]
NET INCOME
Other Comprehensive Loss
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent
OTHER COMPREHENSIVE INCOME
Other Comprehensive Income (Loss), Net of Tax
Pension and OPEB liability, net of tax
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax
Total comprehensive income (loss)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification
Distributions to noncontrolling interest
Undistributed Earnings Losses Related to Noncontrolling Interests
Undistributed Earnings Losses Related to Noncontrolling Interests
Distributions of partnership equity
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders
Capital contributions by noncontrolling interest to subsidiary
Capital contributions by noncontrolling interest to subsidiary
Capital contributions by noncontrolling interest to subsidiary
Stock and other incentive plans (in shares)
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures
Stock and other incentive plans
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures
Stock Repurchased During Period, Shares
Stock Repurchased During Period, Shares
Common stock dividends ($0.05 per share)
Dividends, Common Stock
Shares issued for debt exchange
Shares issued for debt exchange
Shares issued for debt exchange
Debt for equity exchange (value)
Debt for equity exchange (value)
Debt for equity exchange (value)
Stock Issued During Period, Value, Conversion of Convertible Securities
Stock Issued During Period, Value, Conversion of Convertible Securities
Stock Issued During Period, Shares, Conversion of Units
Stock Issued During Period, Shares, Conversion of Units
Common stock issuance (value)
Common stock issuance (value)
Common stock issuance (value)
Acquisition of Noncontrolling Interest
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests
Preferred Stock, Shares Outstanding
Preferred Stock, Shares Outstanding
Balance, end of period (in shares)
Balance, end of period
Long-term Debt, Type [Axis]
Long-term Debt, Type [Axis]
Long-term Debt, Type [Domain]
Long-term Debt, Type [Domain]
Debt Instrument, Redemption, Period [Axis]
Debt Instrument, Redemption, Period [Axis]
Debt Instrument, Redemption, Period [Domain]
Debt Instrument, Redemption, Period [Domain]
Debt Maturities 2018
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months
Debt Maturities 2019
Long-term Debt, Maturities, Repayments of Principal in Year Two
Debt Maturities 2020
Long-term Debt, Maturities, Repayments of Principal in Year Three
Debt Maturities 2021
Long-term Debt, Maturities, Repayments of Principal in Year Four
Debt Maturities 2022
Long-term Debt, Maturities, Repayments of Principal in Year Five
Debt Maturities 2023 and After
Long-term Debt, Maturities, Repayments of Principal after Year Five
Long-term Debt, Maturities, Total
Long-term Debt, Maturities, Total
Long-term Debt, Maturities, Total
Intercompany Foreign Currency Balance by Description [Axis]
Intercompany Foreign Currency Balance by Description [Axis]
Intercompany Foreign Currency Balance, Name [Domain]
Intercompany Foreign Currency Balance, Name [Domain]
Transaction Gains and Losses Resulting from Remeasurement [Member]
Transaction Gains and Losses Resulting from Remeasurement [Member]
Transaction Gains and Losses Resulting from Remeasurement [Member]
Intercompany loan [Member]
Short-term intercompany loan [Member]
Short-term intercompany loan [Member]
Foreign Currency Transaction Gain (Loss), before Tax
Foreign Currency Transaction Gain (Loss), before Tax
Equity [Abstract]
Capital Stock [Table]
Schedule of Stock by Class [Table]
$400 Million 5.90% 2020 Senior Notes
Class of Stock [Line Items]
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount
Stock Repurchase Program, Authorized Amount
Stock Repurchase Program, Average Price
Stock Repurchase Program, Average Price
Stock Repurchase Program, Average Price
Stock Repurchase Program, Remaining Authorized Repurchase Amount
Stock Repurchase Program, Remaining Authorized Repurchase Amount
Dividends payable, per share
Dividends Payable, Amount Per Share
Dividends Payable
Dividends Payable
Trading Day Window Determining Number of Common Shares Issuable on Conversion
Trading Day Window Determining Number of Common Shares Issuable on Conversion
Trading Day Window Determining Number of Common Shares Issuable on Conversion
Common shares, issued (in shares)
Common Stock, Shares, Issued
Convertible Preferred Stock, Common Shares Issued Upon Conversion
Convertible Preferred Stock, Common Shares Issued Upon Conversion
Convertible Preferred Stock, Common Shares Issued Upon Conversion
Convertible Preferred Stock, Common Shares Issued Upon Conversion in Lieu of Dividend
Convertible Preferred Stock, Common Shares Issued Upon Conversion in Lieu of Dividend
Convertible Preferred Stock, Common Shares Issued Upon Conversion in Lieu of Dividend
Gain (loss) on extinguishment/restructuring of debt
Scenario [Axis]
Scenario [Axis]
Scenario, Unspecified [Domain]
Scenario, Unspecified [Domain]
Report Date [Axis]
Report Date [Axis]
Financial Statement Filing Date [Domain]
Financial Statement Filing Date [Domain]
Adjustments for Change in Accounting Principle [Axis]
Adjustments for Change in Accounting Principle [Axis]
Adjustments for Change in Accounting Principle [Domain]
Adjustments for Change in Accounting Principle [Domain]
Adjustments for Error Corrections [Axis]
Adjustments for Error Corrections [Axis]
Adjustments for Error Correction [Domain]
Adjustments for Error Correction [Domain]
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]
ACCUMLATED OTHER COMPREHENSIVE INCOME (LOSS)
Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]
Land Rights And Mineral Rights [Member]
Mining Properties and Mineral Rights [Member]
Office And Information Technology [Member]
Buildings [Member]
Mining Equipment [Member]
Processing Equipment [Member]
Asset Retirement Obligation [Member]
Asset Retirement Obligation [Member]
Asset Retirement Obligation [Member]
Other Assets [Member]
Other Assets [Member]
Construction in Progress [Member]
Construction in Progress [Member]
Property, plant and equipment, gross
Property, Plant and Equipment, Gross
Accumulated Depreciation and Depletion, Property, Plant and Equipment
Accumulated Depreciation and Depletion, Property, Plant and Equipment
Amount of accumulated depreciation and depletion for physical assets used in the normal conduct of business to produce goods and services.
Property, plant and equipment, net
Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block]
Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block]
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]
Income Taxes Other Than Continuing Operations Disclosure Text Block [Table Text Block]
Income Taxes Other Than Continuing Operations Disclosure Text Block [Table Text Block]
Income Taxes Other Than Continuing Operations Disclosure Text Block [Table Text Block]
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]
Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block]
Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block]
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax
Other Comprehensive Income Unrealized Gain Loss On Mark To Market Adjustments Arising During Period Tax
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax
Other Comprehensive Income (Loss), Other Tax
Other Comprehensive Income (Loss), Other Tax
Other Comprehensive Income (Loss), Other Tax
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent
Income tax benefit
Discontinued Operation, Tax Effect of Discontinued Operation
Earnings Per Share [Abstract]
Earnings Per Share Computation
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]
Use of Estimates
Use of Estimates, Policy [Policy Text Block]
Basis Of Consolidation
Consolidation, Subsidiaries or Other Investments, Consolidated Entities, Policy [Policy Text Block]
Equity Method Investments
Equity Method Investments [Policy Text Block]
Noncontrolling Interests
Noncontrolling Interests [Policy Text Block]
Noncontrolling Interests [Policy Text Block]
Cash and Cash Equivalents
Cash and Cash Equivalents, Policy [Policy Text Block]
Trade and Other Accounts Receivable
Trade and Other Accounts Receivable, Policy [Policy Text Block]
Inventory
Inventory, Policy [Policy Text Block]
Inventory Supplies
Inventory Supplies, Policy [Policy Text Block]
Derivatives
Derivatives, Policy [Policy Text Block]
Property, Plant and Equipment
Property, Plant and Equipment, Policy [Policy Text Block]
Capitalized Stripping Costs
Capitalized Stripping Costs [Policy Text Block]
Capitalized Stripping Costs [Policy Text Block]
Other Intangible Assets and Liabilities
Goodwill and Intangible Assets, Policy [Policy Text Block]
Impairment or Disposal of Long-Lived Assets
Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block]
Fair Value of Financial Instruments
Fair Value of Financial Instruments, Policy [Policy Text Block]
Pension and Other Postretirement Plans
Pension and Other Postretirement Plans, Policy [Policy Text Block]
Asset Retirement Obligations
Asset Retirement Obligation [Policy Text Block]
Environmental Costs
Environmental Costs, Policy [Policy Text Block]
Revenue Recognition - Pre and Post Adoption of Topic 606 and Deferred Revenue
Revenue from Contract with Customer [Policy Text Block]
Cost of Sales
Cost of Sales, Policy [Policy Text Block]
Repairs And Maintenance
Repairs And Maintenance Policy Text Block
Repairs and Maintenance Policy
Share-based Compensation, Option and Incentive Plans
Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block]
Income Tax
Income Tax, Policy [Policy Text Block]
Discontinued Operations
Discontinued Operations, Policy [Policy Text Block]
Foreign Currency Transactions and Translations
Foreign Currency Transactions and Translations Policy [Policy Text Block]
Earnings Per Share
Earnings Per Share, Policy [Policy Text Block]
Fair Value Disclosures [Abstract]
Revenue, Initial Application Period Cumulative Effect Transition [Table]
Revenue, Initial Application Period Cumulative Effect Transition [Table]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Fair Value, Assets Measured On Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance - January 1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value
Total gains
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation Calculation [Abstract]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Abstract]
Included in earnings
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings
Settlements
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements
Ending balance - December 31
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
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance - January 1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value
Total gains
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Calculation [Abstract]
Fair Value, Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Abstract]
Included in earnings
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings
Settlements
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements
Ending balance - September 30
Total gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) on liabilities still held at the reporting date
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)
Accounting Changes and Error Corrections [Abstract]
New Accounting Pronouncements or Change in Accounting Principle [Table]
New Accounting Pronouncements or Change in Accounting Principle [Table]
Annual Period of Application Transition Effect [Axis]
Annual Period of Application Transition Effect [Domain]
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Product revenues
Revenue from Contract with Customer, Including Assessed Tax
Freight and Reimbursement Revenue
Freight and Reimbursement Revenue
Freight and Reimbursement Revenue
Revenues
Revenues
Cost of Goods and Services Sold
Cost of Goods and Services Sold
SALES MARGIN
Gross Profit
Selling, general and administrative expenses
Selling, General and Administrative Expense
Miscellaneous - net
Other Operating Income (Expense), Net
Operating Expenses
Operating Expenses
OPERATING INCOME
Operating Income (Loss)
Interest expense, net
Interest Income (Expense), Net
Other non-operating income
Other Nonoperating Income (Expense)
TOTAL OTHER INCOME (EXPENSE)
Nonoperating Income (Expense)
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest
Income (loss) from continuing operations
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest
INCOME FROM DISCONTINUED OPERATIONS, net of tax
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS
Net Income (Loss) Attributable to Parent
Continuing operations
Income (Loss) from Continuing Operations, Per Basic Share
Discontinued operations
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Basic:
Earnings Per Share, Basic
Continuing operations
Income (Loss) from Continuing Operations, Per Diluted Share
Discontinued operations
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share
Earnings per common share attributable to Cliffs common shareholders - diluted:
Earnings Per Share, Diluted
Basic
Weighted Average Number of Shares Outstanding, Basic
Diluted
Weighted Average Number of Shares Outstanding, Diluted
Supplies and other inventories
Derivative assets
TOTAL CURRENT ASSETS
TOTAL OTHER ASSETS
Total Other Assets
Sum of the carrying amounts as of the balance sheet date of all "other assets" that are expected to be realized in cash, sold or consumed after one year or beyond the normal operating cycle, if longer.
TOTAL ASSETS
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES
LONG-TERM DEBT
TOTAL CLIFFS SHAREHOLDERS' EQUITY (DEFICIT)
Title of Individual [Axis]
Title of Individual [Axis]
Title of Individual with Relationship to Entity [Domain]
Relationship to Entity [Domain]
Salaried Employees [Member]
Salaried Employees [Member]
Salaried Employees
Hourly Employees [Member]
Hourly Employees [Member]
Hourly Employees
Mining Employees [Member]
Mining Employees [Member]
Mining Employees
Supplemental Executive Retirement Plan S E R P [Member]
Supplemental Executive Retirement Plan S E R P [Member]
Supplemental Executive Retirement Plan (SERP)
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligations — beginning of year
Defined Benefit Plan, Benefit Obligation
Service cost (excluding expenses)
Defined Benefit Plan, Service Cost
Interest cost
Defined Benefit Plan, Interest Cost
Plan amendments
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)
Defined Benefit Plan, Benefit Obligation, Benefits Paid
Defined Benefit Plan, Benefit Obligation, Benefits Paid
Participant contributions
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant
Federal subsidy on benefits paid
Defined Benefit Plan, Benefit Obligation, Prescription Drug Subsidy Receipt
Benefit obligations — end of year
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Actual return on plan assets
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)
Participant contributions
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant
Employer contributions
Assets Transferred to (from) Plan
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Assets Transferred to (from) Plan
Benefits paid
Defined Benefit Plan, Plan Assets, Benefits Paid
Funded status at December 31:
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Defined Benefit Plan, Benefit Obligation
Defined Benefit Plan, Funded (Unfunded) Status of Plan
Defined Benefit Plan, Funded (Unfunded) Status of Plan
Total amount recognized
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position
Amounts recognized in Statements of Financial Position:
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Assets, Noncurrent
Assets, Noncurrent
Current liabilities
Liability, Defined Benefit Plan, Current
TOTAL POSTEMPLOYMENT BENEFIT LIABILITIES
Amounts recognized in accumulated other comprehensive income:
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Prior service cost
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax
Net actuarial loss
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax
Net amount recognized
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax
The estimated amounts that will be amortized from accumulated other comprehensive income into net periodic benefit cost:
Defined Benefit Plan, Expected Amortization, Next Fiscal Year [Abstract]
TOTAL DEFICIT
Value Of Each Of The Major Classes Of Consolidated Depreciable Assets
Property, Plant and Equipment [Table Text Block]
Book Value of Land and Mineral Rights Disclosure [Table Text Block]
Book Value of Land and Mineral Rights Disclosure [Table Text Block]
Book Value of Land and Mineral Rights Disclosure [Table Text Block]
Restatement [Axis]
Restatement [Axis]
Restatement [Domain]
Restatement [Domain]
Previously Reported [Member]
Previously Reported [Member]
TOTAL CURRENT LIABILITIES
NONCONTROLLING INTEREST
TOTAL EQUITY (DEFICIT)
Loss Contingencies [Table]
Loss Contingencies [Table]
Unrecorded Unconditional Purchase Obligation by Category of Item Purchased [Axis]
Unrecorded Unconditional Purchase Obligation by Category of Item Purchased [Axis]
Unconditional Purchase Obligation, Category of Goods or Services Acquired [Domain]
Unconditional Purchase Obligation, Category of Goods or Services Acquired [Domain]
Capital Addition Purchase Commitments [Member]
Capital Addition Purchase Commitments [Member]
Recorded Unconditional Purchase Obligation by Category of Item Purchased [Axis]
Recorded Unconditional Purchase Obligation by Category of Item Purchased [Axis]
Litigation Case [Axis]
Litigation Case [Axis]
Litigation Case [Domain]
Litigation Case [Domain]
Loss Contingencies [Line Items]
Loss Contingencies [Line Items]
Unrecorded Unconditional Purchase Obligation
Unrecorded Unconditional Purchase Obligation
Recorded Unconditional Purchase Obligation
Recorded Unconditional Purchase Obligation
Unrecorded Unconditional Purchase Obligation, Purchases
Unrecorded Unconditional Purchase Obligation, Purchases
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months
Unrecorded Unconditional Purchase Obligation, Due within Two Years
Unrecorded Unconditional Purchase Obligation, Due within Two Years
Consolidated Entities [Axis]
Consolidated Entities [Axis]
Consolidated Entities [Domain]
Consolidated Entities [Domain]
Parent [Member]
Parent [Member]
Guarantor Subsidiaries [Member]
Guarantor Subsidiaries [Member]
Non-Guarantor Subsidiaries [Member]
Non-Guarantor Subsidiaries [Member]
Consolidation Items [Axis]
Consolidation Items [Axis]
Consolidation Items [Domain]
Consolidation Items [Domain]
Reportable Legal Entities [Member]
Reportable Legal Entities [Member]
Consolidation, Eliminations [Member]
Consolidation, Eliminations [Member]
Investment in subsidiaries
Investment in subsidiaries
Investment in subsidiaries
Long-term intercompany notes
Long term intercompany notes
Long term intercompany notes
LONG-TERM INTERCOMPANY NOTES
Long term intercompany notes payable
Long term intercompany notes payable
Income Tax Description [Axis]
Income Tax Description [Axis]
Income Tax Description [Axis]
Income Tax Description [Domain]
Income Tax Description [Domain]
Income Tax Description [Domain]
Current Federal Tax Expense (Benefit)
Current Federal Tax Expense (Benefit)
Current State and Local Tax Expense (Benefit)
Current State and Local Tax Expense (Benefit)
Current Foreign Tax Expense (Benefit)
Current Foreign Tax Expense (Benefit)
Current Income Tax Expense (Benefit)
Current Income Tax Expense (Benefit)
Deferred Federal Income Tax Expense (Benefit)
Deferred Federal Income Tax Expense (Benefit)
Deferred Income Tax Expense (Benefit)
Retirement Plan Name [Axis]
Retirement Plan Name [Axis]
Retirement Plan Name [Domain]
Retirement Plan Name [Domain]
SERP [Domain]
SERP [Domain]
SERP [Domain]
Ore Mining [Domain]
Ore Mining [Domain]
Ore Mining [Domain]
Salary [Member]
Salary [Member]
Salary [Member]
Hourly [Member]
Hourly [Member]
Hourly [Member]
Discount Rate [Axis]
Discount Rate [Axis]
Discount Rate [Axis]
Discount Rate [Domain]
Discount Rate [Domain]
[Domain] for Discount Rate [Axis]
Obligation [Domain]
Obligation [Domain]
Obligation [Domain]
Service Cost [Domain]
Service Cost [Domain]
Service Cost [Domain]
Interest Cost [Domain]
Interest Cost [Domain]
Interest Cost [Domain]
Discount rate
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate
Expected return on plan assets
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets
Rate of compensation increase
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase
Basis Of Presentation And Significant Accounting Policies [Table]
Basis Of Presentation And Significant Accounting Policies [Table]
Basis Of Presentation And Significant Accounting Policies [Table]
Product and Service [Axis]
Product and Service [Axis]
Product and Service [Domain]
Product and Service [Domain]
Product [Member]
Product [Member]
Mining and Pelletizing [Member]
Mining and Pelletizing [Member]
Mining and Pelletizing [Member]
Mine Location [Axis]
Mine Location [Axis]
Mine Location [Axis]
Mine Location [Domain]
Mine Location [Domain]
[Domain] for Mine Location [Axis]
Business Acquisition [Axis]
Business Acquisition [Axis]
Business Acquisition, Acquiree [Domain]
Business Acquisition, Acquiree [Domain]
Deferred Revenue Arrangement Type [Axis]
Deferred Revenue Arrangement Type [Axis]
Deferred Revenue [Domain]
Deferred Revenue [Domain]
Take or Pay Contracts [Member]
Take or Pay Contracts [Member]
Take or Pay Contracts
Customer Supplemental Payments [Member]
Customer Supplemental Payments [Member]
Customer Supplemental Payments [Member]
Product Segment [Axis]
Product Segment [Axis]
Product Segment [Axis]
Product Segment [Domain]
Product Segment [Domain]
Product Segment [Domain]
Other Noncurrent Assets [Member]
Other Noncurrent Assets [Member]
Investments in Ventures [Member]
Investments in Ventures [Member]
Investments in Ventures [Member]
Other Noncurrent Liabilities [Member]
Other Noncurrent Liabilities [Member]
Other Liabilities [Member]
Other Liabilities [Member]
Name of Operation [Axis]
Name of Operation [Axis]
Name of Operation [Axis]
Name of Operation [Domain]
Name of Operation [Domain]
[Domain] for Name of Operation [Axis]
Empire [Member]
Empire [Member]
Empire [Member]
Tilden [Member]
Tilden [Member]
Tilden [Member]
Investee Name [Axis]
Investee Name [Axis]
Investee name.
Investee Name [Domain]
Investee Name [Domain]
Investee Name [Domain]
Reporting Unit [Axis]
Reporting Unit [Axis]
Reporting Unit [Domain]
Reporting Unit [Domain]
Asia Pacific Iron Ore [Member]
Other Segment [Member]
Other Segment [Member]
Other Segment [Member]
Equity Method Investee, Name [Axis]
Investment, Name [Axis]
Equity Method Investee, Name [Domain]
Investment, Name [Domain]
Hibbing [Member]
Hibbing [Member]
Hibbing [Member]
Related Party Transaction [Line Items]
Related Party Transaction [Line Items]
Foreign Currency Transaction Gain (Loss), Realized
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net from product sales and services
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net
Contract with Customer, Liability, Revenue Recognized
Contract with Customer, Liability, Revenue Recognized
Contract with Customer, Liability, Current
Contract with Customer, Liability, Current
Contract with Customer, Liability
Contract with Customer, Liability
Deferred Revenue (Long-Term)
Contract with Customer, Liability, Noncurrent
Ownership interest, equity method investment
Equity Method Investment, Ownership Percentage
Equity Method Investments
Equity Method Investments
Net Income (Loss) Attributable to Noncontrolling Interest
Net Income (Loss) Attributable to Noncontrolling Interest
Noncontrolling Interest, Ownership Percentage by Parent
Noncontrolling Interest, Ownership Percentage by Parent
Allowance for Doubtful Accounts Receivable
Allowance for Doubtful Accounts Receivable
Provision for Doubtful Accounts
Provision for Doubtful Accounts
Quantity Of Finished Goods at ports
Quantity Of Finished Goods
The quantity of finished goods stored at ports and customer facilities
Current Fiscal Year End Date
Current Fiscal Year End Date
Inventory Valuation Reserves
Inventory Valuation Reserves
Distribution of Noncontrolling Interest
Purchase of Noncontrolling Interest
Purchase of Noncontrolling Interest
Noncontrolling Interest Purchase, Installment Amount
Noncontrolling Interest Purchase, Installment Amount
Noncontrolling Interest Purchase, Installment Amount
Increase in Ownership Equity
Increase in Ownership Equity
Increase in Ownership Equity
Stockholders' Equity, Period Increase (Decrease)
Stockholders' Equity, Period Increase (Decrease)
Customer Supply Agreements [Member]
Customer Supply Agreements [Member]
Customer Supply Agreements [Member]
Product Revenues [Member]
Sales Revenue, Goods, Net [Member]
Cost of goods sold and operating expenses [Member]
Cost of Sales [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net
Type of Deferred Compensation [Axis]
Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Axis]
Type of Deferred Compensation, All Types [Domain]
Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Domain]
Employee Plans [Member]
Employee Plans [Member]
Employee Plans [Member]
Directors Plan [Member]
Directors Plan [Member]
Directors Plan [Member]
January 12, 2015 [Member]
January 12, 2015 [Member]
January 12, 2015 [Member]
Restricted Stock [Member]
Restricted Stock [Member]
Directors Retainer and Voluntary Shares [Member]
Directors Retainer and Voluntary Shares [Member]
Directors Retainer and Voluntary Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number
Grant Date Market Price
Share Based Compensation Arrangement By Share Based Payment Award Grant Date Price
Share Based Compensation Arrangement by Share Based Payment Award Grant Date Price
Option Indexed to Issuer's Equity, Strike Price
Option Indexed to Issuer's Equity, Strike Price
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period
Share Based Goods And Nonemployee Services Transaction Valuation Method Payout Rate
Share Based Goods And Nonemployee Services Transaction Valuation Method Payout Rate
Share Based Goods and Nonemployee Services Transaction Valuation Method, Payout Rate
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested or Expected to Vest, Outstanding, Number
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number
Common Stock, Capital Shares Reserved for Future Issuance
Common Stock, Capital Shares Reserved for Future Issuance
Fair Value
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Exercisable Options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Exercisable Options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price
Related Party Transactions [Abstract]
Schedule of Related Party Transactions, by Related Party [Table]
Schedule of Related Party Transactions, by Related Party [Table]
Arcelor Mittal [Member]
Arcelor Mittal [Member]
Arcelor Mittal [Member]
Related Party [Axis]
Related Party [Axis]
Related Party [Domain]
Related Party [Domain]
U. S. Steel Canada [Member]
U. S. Steel Canada [Member]
U. S. Steel Canada
Noncontrolling Interest, Ownership Percentage by Parent
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value
CAPITAL STOCK
Capital Stock Disclosure [Text Block]
Capital Stock Disclosure Text Block
Schedule of Segment Reporting Information, by Segment [Table]
Schedule of Segment Reporting Information, by Segment [Table]
Concentration Risk Benchmark [Axis]
Concentration Risk Benchmark [Axis]
Concentration Risk Benchmark [Domain]
Concentration Risk Benchmark [Domain]
Sales Revenue, Net [Member]
Sales Revenue, Net [Member]
Concentration Risk Type [Axis]
Concentration Risk Type [Axis]
Concentration Risk Type [Domain]
Concentration Risk Type [Domain]
Customer Concentration Risk [Member]
Customer Concentration Risk [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information [Line Items]
Number of Reporting Units
Number of Reporting Units
Number of Customers
Number of Customers
Number of Customers
Concentration Risk, Percentage
Concentration Risk, Percentage
Schedule of Defined Benefit Plans Disclosures [Table]
Schedule of Defined Benefit Plans Disclosures [Table]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Disclosure [Line Items]
Retirement And Defined Compensation Plans Disclosures [Table Text Block]
Retirement And Defined Compensation Plans Disclosures [Table Text Block]
Net Periodic Benefit Cost for Pension and Other Post Retirement Benefits
Obligations and Funded Status
Schedule of Defined Benefit Plans Disclosures [Table Text Block]
Fair Value Of Plan Assets, Benefit Obligation And Funded Status
Schedule of Net Funded Status [Table Text Block]
Components Of Net Periodic Benefit Cost
Schedule of Net Benefit Costs [Table Text Block]
Weighted-Average Assumptions Used to Determine Benefit Obligations
Schedule of Assumptions Used [Table Text Block]
Weighted-Average Assumptions Used To Determine Net Benefit Costs
Weighted-Average Assumptions Used To Determine Net Benefit Costs [Table Text Block]
Weighted-Average Assumptions Used To Determine Net Benefit Costs
Assumed Health Care Cost Trend Rates
Schedule of Health Care Cost Trend Rates [Table Text Block]
Plan Assets and Asset Allocation
Schedule of Allocation of Plan Assets [Table Text Block]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]
Effect of Fair Value Measurements Using Significant Unobservable Inputs on Changes in Plan Assets
Schedule of Effect of Significant Unobservable Inputs, Changes in Plan Assets [Table Text Block]
Schedule Of Annual Contributions
Schedule Of Annual Contributions [Table Text Block]
Schedule Of Annual Contributions
Estimated Net Periodic Benefit Cost
Schedule of Net Periodic Benefit Cost Not yet Recognized [Table Text Block]
Estimated Future Benefit Payments
Schedule of Expected Benefit Payments [Table Text Block]
SUPPLEMENTARY GUARANTOR INFORMATION
Supplemental Guarantor Information [Text Block]
Supplemental Guarantor Information [Text Block]
Deferred Compensation, Share-based Payments [Member]
Deferred Compensation, Share-based Payments [Member]
Costs and Expenses
Costs and Expenses
Earnings per common share attributable to Cliffs common shareholders - basic:
Iron Hourly [Member]
Iron Hourly [Member]
Iron Hourly [Member]
Salaried [Member]
Salaried [Member]
Salaried [Member]
Ore Mining [Member]
Ore Mining [Member]
Ore Mining [Member]
Supplemental Executive Retirement Plan S E R P [Member]
Supplemental Employee Retirement Plan [Member]
Plan Name [Axis]
Type of Compensation [Axis]
Type of Compensation [Axis]
Plan Name [Domain]
Type of Compensation [Domain]
[Domain] for Type of Compensation [Axis]
Discount rate
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate
Rate of compensation increase
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase
REVENUES FROM PRODUCT SALES AND SERVICES
Revenues [Abstract]
TOTAL REVENUES FROM PRODUCT SALES AND SERVICES
COST OF GOODS SOLD AND OPERATING EXPENSES
OTHER OPERATING INCOME (EXPENSE)
Operating Expenses [Abstract]
Other operating expense
OPERATING INCOME
OTHER INCOME (EXPENSE)
Nonoperating Income (Expense) [Abstract]
TOTAL OTHER INCOME (EXPENSE)
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES
INCOME TAX BENEFIT
INCOME FROM CONTINUING OPERATIONS
LOSS (INCOME) ATTRIBUTABLE TO NONCONTROLLING INTEREST
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS
Net Income (Loss) Available to Common Stockholders, Basic
EARNINGS PER COMMON SHARE ATTRIBUTABLE TO CLIFFS SHAREHOLDERS - BASIC
Earnings Per Share, Basic [Abstract]
EARNINGS PER COMMON SHARE ATTRIBUTABLE TO CLIFFS SHAREHOLDERS - DILUTED
Earnings Per Share, Diluted [Abstract]
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Diluted:
AVERAGE NUMBER OF SHARES (IN THOUSANDS)
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Summary Of Other Ownership Interests
Schedule of Other Ownership Interests [Table Text Block]
Summary Of Related Party Transactions Table Disclosure
Schedule of Related Party Transactions [Table Text Block]
Summary of Balance Sheet Presentation [Table Text Block]
Summary of Balance Sheet Presentation [Table Text Block]
Summary of Balance Sheet Presentation [Table Text Block]
Triggering Events [Axis]
Triggering Events [Axis]
Triggering Events [Axis]
Triggering Events [Domain]
Triggering Events [Domain]
[Domain] for Triggering Events [Axis]
Adoption of New Projection Scale [Member]
Adoption of New Projection Scale [Member]
Adoption of New Projection Scale [Member]
Update Assumption per Capita Cost [Member]
Update Assumption per Capita Cost [Member]
Update Assumption per Capita Cost [Member]
Subsequent Event Type [Axis]
Subsequent Event Type [Axis]
Subsequent Event Type [Domain]
Subsequent Event Type [Domain]
Subsequent Event [Member]
Subsequent Event [Member]
Coverage Age [Axis]
Coverage Age [Axis]
Coverage Age [Axis]
Coverage Age [Domain]
Coverage Age [Domain]
[Domain] for Coverage Age [Axis]
Prior To Age65 [Member]
Prior To Age65 [Member]
Prior to Age 65
United States [Member]
UNITED STATES
Northshore [Member]
Northshore [Member]
Northshore [Member]
Defined Benefit Plan, Plan Assets, Contributions by Plan Participants
Defined Benefit Plan, Plan Assets, Contributions by Plan Participants
Defined Benefit Plan, Plan Assets, Contributions by Plan Participants
Defined Benefit Plan, Term Of Agreement
Labor Agreement, Contract Term
Labor Agreement, Contract Term
401(k) contribution match
Defined Contribution Plan, Employer Discretionary Contribution Amount
Annual limit on medical coverage for each participant
Postretirement Benefits Medical Coverage Annual Limit
Postretirement Benefits Medical Coverage, Annual Limit
Defined Benefit Plan, Accumulated Benefit Obligation
Defined Benefit Plan, Accumulated Benefit Obligation
Decrease in Projected Benefit Obligation due to Market Conditions
Decrease in Projected Benefit Obligation due to Market Conditions
Decrease in Projected Benefit Obligation due to Market Conditions
Increase in Projected Benefit Obligation due to new mortality tables
Increase in Projected Benefit Obligation due to new mortality tables
Increase in Projected Benefit Obligation due to new mortality tables
Reserve for investment commitments
Reserve For Investment Commitments
Reserve for Investment Commitments
Redemption request notice period, days
Redemption Request Notice Period
Redemption Request Notice Period
Withdrawal request notice period, days
Deferred Compensation Arrangement with Individual, Written Notice Period Required for Withdrawals
Deferred Compensation Arrangement with Individual, Written Notice Period Required for Withdrawals
Early Termination Fees for Pension Benefits
Early Termination Fees for Pension Benefits
Early Termination Fees for Pension Benefits
Early Termination Fees for Other Postretirement Benefits
Early Termination Fees for Other Postretirement Benefits
Early Termination Fees for Other Postretirement Benefits
Schedule of Disposal Groups, Including Discontinued Operations, Income Statement, Balance Sheet and Additional Disclosures [Table Text Block]
Disposal Groups, Including Discontinued Operations [Table Text Block]
Schedule of Disposal Groups, including Discontinued Operations, Income Statement [Table Text Block]
Schedule of Disposal Groups, including Discontinued Operations, Income Statement [Table Text Block]
[Table Text Block] for Schedule of Disposal Groups, including Discontinued Operations, Income Statement [Table]
Schedule of Disposal Groups, Including Discontinued Operations, Assets and Liabilities [Table Text Block]
Schedule of Disposal Groups, Including Discontinued Operations, Assets and Liabilities [Table Text Block]
[Table Text Block] for Schedule of Disposal Groups, Including Discontinued Operations, Assets and Liabilities [Table]
PreTax Exit Costs [Table Text Block]
PreTax Exit Costs [Table Text Block]
[Table Text Block] for PreTax Exit Costs [Table]
Subsequent Events [Abstract]
SUBSEQUENT EVENTS
Subsequent Events [Text Block]
Geographical [Axis]
Geographical [Axis]
Geographical [Domain]
Geographical [Domain]
LUXEMBOURG
LUXEMBOURG
Deferred Tax Assets, Operating Loss Carryforwards, Domestic
Deferred Tax Assets, Operating Loss Carryforwards, Domestic
Undistributed Earnings of Foreign Subsidiaries
Undistributed Earnings of Foreign Subsidiaries
Deferred Tax Assets, Operating Loss Carryforwards, State and Local
Deferred Tax Assets, Operating Loss Carryforwards, State and Local
Deferred Tax Assets, Operating Loss Carryforwards, Foreign
Deferred Tax Assets, Operating Loss Carryforwards, Foreign
Document Fiscal Year Focus
Document Fiscal Year Focus
Cumulative Loss Position, Period
Cumulative Loss Position, Period
Cumulative Loss Position, Period
Deferred Tax Assets, Tax Credit Carryforwards, Foreign
Deferred Tax Assets, Tax Credit Carryforwards, Foreign
Valuation Allowance, Deferred Tax Asset, Change in Amount
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount
Estimated Taxable Income to Fully Utilize Deferred Tax Assets
Estimated Taxable Income to Fully Utilize Deferred Tax Assets
Estimated Taxable Income to Fully Utilize Deferred Tax Assets
Effective Income Tax Rate, Continuing Operations
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued
Deferred Tax Liabilities, Intercompany Notes
Deferred Tax Liabilities, Intercompany Notes
Deferred Tax Liabilities, Intercompany Notes
Tax law change, remeasurement, amount
Tax law change, remeasurement, amount
Tax law change, remeasurement, amount
Tax Cuts And Jobs Act, Change In Tax Rate, Deferred Tax Asset, Income Tax Expense
Tax Cuts And Jobs Act, Change In Tax Rate, Deferred Tax Asset, Income Tax Expense
Tax Cuts And Jobs Act, Change In Tax Rate, Deferred Tax Asset, Income Tax Expense
Environmental
Asset Retirement Obligation
Asset Retirement Obligation
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current
Environmental Loss Contingency And Mine Reclamation And Closing Liability Current
Environmental Loss Contingency And Mine Reclamation And Closing Liability Noncurrent
Environmental Loss Contingency And Mine Reclamation And Closing Liability Noncurrent
Amount of environmental loss contingencies, such as presence of hazardous waste, relevant information from reports issued by regulators, and estimated costs to achieve compliance with regulatory requirements. As well as, the amount of a reclamation and mine closing liability that is associated with a legal obligation for the closure and reclamation of a mine including the removal of buildings, equipment, machinery and other physical remnants of mining, closure of tailings impoundments, leach pads and other mine features, and contouring, covering and revegetation of waste rock piles and other disturbed areas.
United Taconite [Member]
United Taconite [Member]
United Taconite [Member]
Entity Address, State or Province
Entity Address, State or Province
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Other Comprehensive Income Location [Axis]
Other Comprehensive Income Location [Axis]
Other Comprehensive Income Location [Domain]
Other Comprehensive Income Location [Domain]
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax
Accumulated Other Comprehensive Income (Loss), Debt Securities, Available-for-sale, Adjustment, after Tax
Accumulated Other Comprehensive Income (Loss), Debt Securities, Available-for-sale, Adjustment, after Tax
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax
Changes in foreign currency translation
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax
Document and Entity Information [Abstract]
Document and Entity Information [Abstract]
Entity Registrant Name
Entity Registrant Name
Entity Central Index Key
Entity Central Index Key
Entity Filer Category
Entity Filer Category
Document Type
Document Type
Document Period End Date
Document Period End Date
Document Fiscal Period Focus
Document Fiscal Period Focus
Amendment Flag
Amendment Flag
Entity Common Stock, Shares Outstanding
Entity Common Stock, Shares Outstanding
Trading Symbol
Trading Symbol
Entity Well-known Seasoned Issuer
Entity Well-known Seasoned Issuer
Entity Voluntary Filers
Entity Voluntary Filers
Entity Current Reporting Status
Entity Current Reporting Status
Entity Emerging Growth Company
Entity Emerging Growth Company
Entity Small Business
Entity Small Business
Entity Shell Company
Entity Shell Company
Entity Public Float
Entity Public Float
Gross Company Benefits [Member]
Gross Company Benefits [Member]
Gross Company Benefits [Member]
Less Medicare Subsidy [Member]
Medicare Part D Subsidy [Member]
Medicare Part D Subsidy
Net Company Payments [Member]
Net Company Payments [Member]
Net Company Payments [Member]
2017
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months
2018
Defined Benefit Plan, Expected Future Benefit Payment, Year Two
2019
Defined Benefit Plan, Expected Future Benefit Payment, Year Three
2020
Defined Benefit Plan, Expected Future Benefit Payment, Year Four
2021
Defined Benefit Plan, Expected Future Benefit Payment, Year Five
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter
PROPERTY, PLANT AND EQUIPMENT
Property, Plant and Equipment Disclosure [Text Block]
BUSINESS SUMMARY AND SIGNIFICANT ACCOUNTING POLICIES
Basis of Presentation and Significant Accounting Policies [Text Block]
Environmental Loss Contingency And Mine Closure Obligation Disclosure [Text Block]
Environmental Loss Contingency And Mine Closure Obligation Disclosure [Text Block]
Disclosures of environmental loss contingencies, such as presence of hazardous waste, relevant information from reports issued by regulators, and estimated costs to achieve compliance with regulatory requirements. Disclosures of accrued closure obligations for active or inactive mining operations that based upon contractual and legal obligations.
Lender Name [Axis]
Lender Name [Axis]
Line of Credit Facility, Lender [Domain]
Line of Credit Facility, Lender [Domain]
Credit Facility [Axis]
Credit Facility [Axis]
Credit Facility [Domain]
Credit Facility [Domain]
Schedule of Line of Credit Facilities [Table Text Block]
Schedule of Line of Credit Facilities [Table Text Block]
Schedule Of Long-Term Debt
Schedule of Long-term Debt Instruments [Table Text Block]
Schedule of Extinguishment of Debt [Table Text Block]
Schedule of Extinguishment of Debt [Table Text Block]
Schedule of Maturities of Long-term Debt [Table Text Block]
Schedule of Maturities of Long-term Debt [Table Text Block]
Restricted Equity Grant Shares [Member]
Restricted Equity Grant Shares [Member]
Restricted Equity Grant Shares [Member]
Deferred Equity Grant Shares [Member]
Deferred Equity Grant Shares [Member]
Deferred Equity Grant Shares [Member]
Stock Issued During Period Shares Director Stock Award
Stock Issued During Period Shares Director Stock Award
Stock Issued During Period Shares Director Stock Award
Defined Benefit Plan, Funded (Unfunded) Status of Plan
Trade Accounts Receivable [Member]
Trade Accounts Receivable [Member]
Derivative [Member]
Derivative [Member]
Related Party Transaction [Axis]
Related Party Transaction [Axis]
Related Party Transaction [Domain]
Related Party Transaction [Domain]
Due from Related Parties, Current
Due from Related Parties, Current
Short-term Notes Payable
Due to Related Parties, Current
Due to Related Parties, Current
Due to Related Parties, Noncurrent
Due to Related Parties, Noncurrent
Related Party Transaction, Due from (to) Related Party
Related Party Transaction, Due from (to) Related Party
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member]
Significant Unobservable Inputs (Level 3) [Member]
Investment Type Categorization [Domain]
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information [Text Block]
Quarterly Financial Information [Text Block]
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Pensions
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Pensions
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Postretirement Benefits
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Postretirement Benefits
Deferred Tax Assets, Deferred Income
Deferred Tax Assets, Deferred Income
Deferred Tax Assets, Goodwill and Intangible Assets
Deferred Tax Assets, Goodwill and Intangible Assets
Deferred Tax Assets, Operating Loss Carryforwards
Deferred Tax Assets, Operating Loss Carryforwards
Deferred Tax Assets, Property, Plant and Equipment
Deferred Tax Assets, Property, Plant and Equipment
Deferred Tax Assets, State Taxes
Deferred Tax Assets, State Taxes
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Other
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Other
Deferred Tax Assets, Gross
Deferred Tax Assets, Gross
Deferred Tax Assets, Valuation Allowance
Deferred Tax Assets, Valuation Allowance
Deferred Tax Assets, Net of Valuation Allowance
Deferred Tax Assets, Net of Valuation Allowance
Deferred Tax Liabilities, Property, Plant and Equipment
Deferred Tax Liabilities, Property, Plant and Equipment
Deferred Tax Liabilities Investment In Ventures
Deferred Tax Liabilities, Investments
Deferred Tax Liabilities, Intercompany Notes
Deferred Tax Liabilities Other Assets
Deferred Tax Liabilities, Other
Deferred Tax Liabilities, Net
Deferred Tax Liabilities, Net
Deferred Tax Assets, Net
Deferred Tax Assets, Net
Inventory Disclosure [Abstract]
Schedule Of Inventories
Schedule of Inventory, Current [Table Text Block]
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
NEW ACCOUNTING STANDARDS
New Accounting Pronouncements and Changes in Accounting Principles [Text Block]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Table]
Disposal Groups, Including Discontinued Operations [Table]
Wabush Scully Mine Sale [Member]
Wabush Scully Mine Sale [Member]
Wabush Scully Mine Sale [Member]
Asset group [Axis]
Asset group [Axis]
Asset group [Axis]
Asset group [Domain]
Asset group [Domain]
[Domain] for Asset group [Axis]
Canadian Entities [Member]
Canadian Entities [Member]
Canadian Entities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Foreign Currency Translation Gains (Losses)
Disposal Group, Including Discontinued Operation, Foreign Currency Translation Gains (Losses)
Income tax benefit (expense)
Cash Contribution
Cash Contribution
Cash Contribution
Cost Method Investments
Cost Method Investments
Contingent Liabilities recognized in Consolidated Financials
Contingent Liabilities recognized in Consolidated Financials
Contingent Liabilities recognized in Consolidated Financials
Short-term loan receivable
Short-term loan receivable
Short-term loan receivable
Asset Retirement Obligation, Accretion Expense
Asset Retirement Obligation, Accretion Expense
Asset Retirement Obligation, Liabilities Settled
Asset Retirement Obligation, Liabilities Settled
Asset Retirement Obligation, Revision of Estimate
Asset Retirement Obligation, Revision of Estimate
Asset Retirement Obligation [Roll Forward]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Pension and Other Postretirement Benefits Disclosure [Text Block]
Inventory, Current [Table]
Inventory, Current [Table]
Inventory [Line Items]
Inventory [Line Items]
Inventory, Net [Abstract]
Inventory, Net [Abstract]
Finished Goods
Inventory, Finished Goods, Net of Reserves
Work-in-Process
Inventory, Work in Process, Net of Reserves
Total Inventories
PreTax Exit Costs [Table]
PreTax Exit Costs [Table]
PreTax Exit Costs [Table]
PreTax Exit Costs [Line Items]
PreTax Exit Costs [Line Items]
[Line Items] for PreTax Exit Costs [Table]
Investment impairment on deconsolidation
Investment Impairment of Deconsolidation
Investment Impairment of Deconsolidation
Guarantees and contingent liabilities
Contingent Liabilities of Deconsolidated Entities
Contingent Liabilities of Deconsolidated Entities
Total loss from deconsolidation
Deconsolidation, Gain (Loss), Amount
Inventory, LIFO Reserve
Inventory, LIFO Reserve
Cost of Goods Sold
Effect of inventory reduction
Effect of inventory reduction
Increase in Inventories
LIFO Inventory Related Text
Defined benefit pension plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Defined contribution pension plans
Defined Contribution Plan, Cost
Other Postretirement Benefits Cost (Reversal of Cost)
Other Postretirement Benefits Cost (Reversal of Cost)
Total
Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Weighted-average asset allocation
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage
Region Reporting Information, by Region [Axis]
Region Reporting Information By Region [Axis]
Disclosure of profit or loss, total assets for each reportable region, and a description of the types of products and services for each reportable region.
Reporting Region [Domain]
Reporting Region [Domain]
Reporting Region [Domain]
Preferred Class A [Member]
Preferred Class A [Member]
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Noncontrolling Interest
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Noncontrolling Interest
Income (Loss) from Continuing Operations Attributable to Parent
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent
INCOME FROM DISCONTINUED OPERATIONS, net of tax
Net income attributable to Cliffs shareholders
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount
Income Taxes Paid
Income Taxes Paid
Proceeds from Income Tax Refunds
Proceeds from Income Tax Refunds
Interest Paid, Including Capitalized Interest, Operating and Investing Activities
Interest Paid, Excluding Capitalized Interest, Operating Activities
Fair Value, by Balance Sheet Grouping [Table]
Fair Value, by Balance Sheet Grouping [Table]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets:
Assets, Fair Value Disclosure [Abstract]
Cash equivalents
Cash and Cash Equivalents, Fair Value Disclosure
Derivative Asset
Derivative Asset
Total Asset
Total Asset
Total Asset
Liabilities:
Liabilities, Fair Value Disclosure [Abstract]
Derivative Liability
Derivative Liability
Total Liability
Total Liability
Total Liability
Reclassification out of Accumulated Other Comprehensive Income [Table]
Reclassification out of Accumulated Other Comprehensive Income [Table]
T-Lock Amortization [Member]
T-Lock Amortization [Member]
T-Lock Amortization [Member]
Australian Hedge Contracts [Member]
Commodity [Member]
Foreign Currency Translation Adjustment [Member]
Foreign Currency Translation Adjustment [Member]
Foreign Currency Translation Adjustment [Member]
Realized Gain Loss On Derivatives [Member]
Realized Gain Loss On Derivatives [Member]
Gains and losses realized and included in earnings.
Reclassification out of Accumulated Other Comprehensive Income [Axis]
Reclassification out of Accumulated Other Comprehensive Income [Axis]
Reclassification out of Accumulated Other Comprehensive Income [Domain]
Reclassification out of Accumulated Other Comprehensive Income [Domain]
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of prior service (cost) credit
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)
Defined Benefit Plan, Amortization of Gain (Loss)
Defined Benefit Plan, Amortization of Gain (Loss)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax
TaxOnDerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoEarnings
TaxOnDerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoEarnings
Tax On Derivative Instruments Gain Loss Reclassified From Accumulated OCI Into Earnings
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax
Other Comprehensive Income (Loss), Foreign Currency Translation, Dissolution of Entity
Other Comprehensive Income (Loss), Foreign Currency Translation, Dissolution of Entity
Other Comprehensive Income (Loss), Foreign Currency Translation, Dissolution of Entity
Derivative, Gain (Loss) on Derivative, Net
Derivative, Gain (Loss) on Derivative, Net
RELATED PARTIES
Related Party Transactions Disclosure [Text Block]
Revenue from External Customers by Products and Services [Table]
Revenue from External Customers by Products and Services [Table]
Revenue Type [Axis]
Revenue Type [Axis]
Revenue Type [Axis]
Revenue Type [Domain]
Revenue Type [Domain]
[Domain] for Revenue Type [Axis]
Iron Ore Revenue [Member]
Iron Ore Revenue [Member]
Iron Ore Revenue [Member]
Freight and Venture Partners' Cost Reimbursements [Member]
Freight and Venture Partners' Cost Reimbursements [Member]
Freight and Venture Partners' Cost Reimbursements [Member]
Product Concentration Risk [Member]
Product Concentration Risk [Member]
Revenue from External Customer [Line Items]
Revenue from External Customer [Line Items]
EARNINGS PER SHARE
Earnings Per Share [Text Block]
Statement of Comprehensive Income [Abstract]
OTHER COMPREHENSIVE INCOME (LOSS)
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Changes in pension and other post-retirement benefits, net of tax
Changes in derivative financial instruments, net of tax
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax
OTHER COMPREHENSIVE LOSS
OTHER COMPREHENSIVE LOSS (INCOME) ATTRIBUTABLE TO THE NONCONTROLLING INTEREST
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest
TOTAL COMPREHENSIVE INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS
Comprehensive Income (Loss), Net of Tax, Attributable to Parent
Schedule of Supplemental Condensed Consolidating Financial Position
Condensed Balance Sheet [Table Text Block]
Schedule of Supplemental Statements of Condensed Consolidating Operations and Comprehensive Income (Loss)
Condensed Statement of Operations and Comprehensive Income (Loss) [Table Text Block]
Condensed Statement of Operations and Comprehensive Income (Loss)
Schedule of Supplemental Statements of Condensed Consolidating Cash Flows
Condensed Cash Flow Statement [Table Text Block]
Relationship to Entity [Domain]
Service cost
Interest cost
Expected return on plan assets
Defined Benefit Plan, Expected Return (Loss) on Plan Assets
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment
Amortization:
Disclosure Pensions And Other Postretirement Benefits Components Of Net Periodic Benefit Cost [Abstract]
Disclosure - Pensions And Other Postretirement Benefits (Components Of Net Periodic Benefit Cost) [Abstract]
Net actuarial loss
Net periodic benefit cost
Relating to assets sold during the period
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold
Current year actuarial (gain)/loss
Defined Benefit Plan, Net Periodic Benefit Costs, Actuarial Gain (Loss)
Defined Benefit Plan, Net Periodic Benefit Costs, Actuarial Gain (Loss)
Amortization of net loss
Current year prior service cost
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax
Total recognized in other comprehensive income
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax
Total recognized in net periodic cost and other comprehensive income
Defined Benefit Plan, Amount Recognized in Net Periodic Benefit Cost (Credit) and Other Comprehensive (Income) Loss, before Tax
Schedule of Quarterly Financial Information [Table Text Block]
Quarterly Financial Information [Table Text Block]
Actual return on plan assets
Accounting Standards Update 2017-07 [Member]
Accounting Standards Update 2017-07 [Member]
Cost of Goods and Services Sold
Selling, General and Administrative Expense
Operating Income (Loss)
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold
Defined Benefit Plan, Plan Assets, Business Combination
Defined Benefit Plan, Plan Assets, Divestiture
Approved Grants Equity Plans [Table Text Block]
Approved Grants Equity Plans [Table Text Block]
Approved Grants Equity Plans [Table Text Block]
Stock Incentive Plans Disclosure [Table Text Block]
Stock Incentive Plans Disclosure [Table Text Block]
Stock Incentive Plans Disclosure [Table Text Block]
Incentive Compensation and Other Benefit Plans for Employees and Directors [Table Text Block]
Incentive Compensation and Other Benefit Plans for Employees and Directors [Table Text Block]
Incentive Compensation and Other Benefit Plans for Employees and Directors [Table Text Block]
Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block]
Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block]
Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]
Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]
Employee Stock Awards Outstanding [Table Text Block]
Employee Stock Awards Outstanding [Table Text Block]
Employee Stock Awards Outstanding [Table Text Block]
Comprehensive Income (Loss) Note [Text Block]
Comprehensive Income (Loss) Note [Text Block]
Senior Notes [Member]
Senior Notes [Member]
Line of Credit [Member]
Line of Credit [Member]
Measurement Basis [Axis]
Measurement Basis [Axis]
Fair Value Measurement [Domain]
Fair Value Measurement [Domain]
Portion at Fair Value Measurement [Member]
Portion at Fair Value Measurement [Member]
Reported Value Measurement [Member]
Reported Value Measurement [Member]
Estimate of Fair Value Measurement [Member]
Estimate of Fair Value Measurement [Member]
Receivable Type [Axis]
Receivable Type [Axis]
Receivable Type [Domain]
Receivable [Domain]
Long-term debt:
Long Term Debt Noncurrent Fair Value [Abstract]
Long Term Debt Noncurrent Fair Value [Abstract]
Long-term Debt, Fair Value
Long-term Debt, Fair Value
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized
Deferred Compensation Arrangement with Individual, Fair Value of Shares Issued
Deferred Compensation Arrangement with Individual, Fair Value of Shares Issued
Income (Loss) from Continuing Operations before Income Taxes, Domestic
Income (Loss) from Continuing Operations before Income Taxes, Domestic
Income (Loss) from Continuing Operations before Income Taxes, Foreign
Income (Loss) from Continuing Operations before Income Taxes, Foreign
Derivative Instruments [Table]
Derivative [Table]
Natural Gas [Member]
Natural Gas [Member]
Energy Related Derivative [Member]
Energy Related Derivative [Member]
Derivative [Line Items]
Derivative [Line Items]
Natural Gas Hedges
Investment Contract Volume
Schedule of Revenues from External Customers and Long-Lived Assets [Table]
Schedule of Revenues from External Customers and Long-Lived Assets [Table]
Canada [Member]
CANADA
Other Countries [Member]
Other Countries [Member]
Other Countries [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from External Customers and Long-Lived Assets [Line Items]
Disposal Group, Including Discontinued Operation, Cash and Cash Equivalents
Disposal Group, Including Discontinued Operation, Cash and Cash Equivalents
Disposal Group, Including Discontinued Operation, Accounts Receivable, Net
Disposal Group, Including Discontinued Operation, Accounts, Notes and Loans Receivable, Net
Disposal Group, Including Discontinued Operation, Inventory
Disposal Group, Including Discontinued Operation, Inventory
Disposal group, including Discontinued Operations, Supplies and other inventories
Disposal group, including Discontinued Operations, Prepaid Supplies
Disposal group, including Discontinued Operations, Prepaid Supplies
Disposal Group, Including Discontinued Operation, Other Assets, Current
Disposal Group, Including Discontinued Operation, Other Assets, Current
Disposal Group, Including Discontinued Operation, Property, Plant and Equipment
Disposal Group, Including Discontinued Operation, Property, Plant and Equipment
Disposal Group, Including Discontinued Operation, Other Assets, Noncurrent
Disposal Group, Including Discontinued Operation, Other Assets, Noncurrent
Disposal Group, Including Discontinued Operation, Assets
Disposal Group, Including Discontinued Operation, Assets
Disposal Group, Including Discontinued Operation, Accounts Payable
Disposal Group, Including Discontinued Operation, Accounts Payable
Disposal Group, Including Discontinued Operation, Accrued Liabilities
Disposal Group, Including Discontinued Operation, Accrued Liabilities
Disposal Group, Including Discontinued Operation, Other Liabilities, Current
Disposal Group, Including Discontinued Operation, Other Liabilities, Current
Disposal Group, Including Discontinued Operations, Environmental and mine closure obligations
Disposal Group, Including Discontinued Operations, Mine Reclamation, Noncurrent
Disposal Group, Including Discontinued Operations, Mine Reclamation, Noncurrent
Disposal Group, Including Discontinued Operation, Other Liabilities
Disposal Group, Including Discontinued Operation, Other Liabilities
Disposal Group, Including Discontinued Operation, Liabilities
Disposal Group, Including Discontinued Operation, Liabilities
FAIR VALUE OF FINANCIAL INSTRUMENTS
Fair Value Disclosures [Text Block]
Fair Value Measurements, Recurring and Nonrecurring [Table]
Fair Value Measurements, Recurring and Nonrecurring [Table]
Measurement Frequency [Axis]
Measurement Frequency [Axis]
Fair Value, Measurement Frequency [Domain]
Fair Value, Measurement Frequency [Domain]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Metallics [Member]
Metallics [Member]
Metallics [Member]
Total Segment Assets [Member]
Operating Segments [Member]
Corporate [Member]
Corporate Segment [Member]
Discontinued Operations [Member]
Discontinued Operations [Member]
Supplemental Cash Flow Disclosures
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]
Deferred Revenue (Current)
Increase (Decrease)
Contract With Customer, Liability, Period Increase (Decrease)
Contract With Customer, Liability, Period Increase (Decrease)
Fair Value, by Balance Sheet Grouping [Table Text Block]
Fair Value, by Balance Sheet Grouping [Table Text Block]
Fair Value, Recurring and Nonrecurring, Valuation Techniques
Fair Value Measurement Inputs and Valuation Techniques [Table Text Block]
Fair Value, Assets Measured On Recurring Basis, Unobservable Input Reconciliation
Fair Value, Assets and Liabilities Measured on a Recurring Basis, Unobservable Input Reconciliation [Text Block]
Tabular disclosure of the fair value measurement of assets and liabilities using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes during the period attributable to the following: (1) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets) and gains or losses recognized in other comprehensive income (loss), and a description of where those gains or losses included in earnings (or changes in net assets) are reported in the statement of income (or activities); (2) purchases, sales, issues, and settlements (each type disclosed separately); and (3) transfers in and transfers out of Level 3 (for example, transfers due to changes in the observability of significant inputs), by class of asset.
Schedule Of Carrying Value And Fair Value Of Financial Instruments
Schedule of Carrying Values and Estimated Fair Values of Debt Instruments [Table Text Block]
Other operating expense
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES AND EQUITY LOSS FROM VENTURES
INCOME TAX BENEFIT (EXPENSE)
EQUITY IN INCOME OF SUBSIDIARIES
Equity in income (loss) of subsidiaries
Equity in income (loss) of subsidiaries
INCOME ATTRIBUTABLE TO NONCONTROLLING INTEREST
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS
OTHER COMPREHENSIVE INCOME (LOSS)
Schedule Of Subsidiaries
Schedule Of Consolidation Subsidiaries Or Other Investments Consolidated Entities [Table Text Block]
Disclosure of subsidiaries or other investments that are consolidated.
Depreciation Disclosure [Table Text Block]
Depreciation Disclosure [Table Text Block]
Describes the methodology and periods of time over which an entity anticipates to receive utility from its property, plant and equipment (that is, the periods of time over which an entity allocates the initial cost of its property, plant and equipment and the estimated useful life of the asset in a systematic and rational manner.)
Estimated Useful Lives Of Intangible Assets Subject To Periodic Amortization On Straight Line Basis Table [Text Block]
Estimated Useful Lives Of Intangible Assets Subject To Periodic Amortization On Straight Line Basis Table [Text Block]
Estimated Useful Lives of Intangible Assets Subject to Periodic Amortization on a Straight-Line Basis [Table Text Block]
Contract with Customer, Asset and Liability [Table Text Block]
Contract with Customer, Asset and Liability [Table Text Block]
Reimbursements Revenue Disclosure [Table Text Block]
Reimbursements Revenue Disclosure [Table Text Block]
Reimbursements Revenue Disclosure
Foreign Currency Transaction [Table Text Block]
Foreign Currency Transaction [Table Text Block]
Foreign Currency Transaction [Table Text Block]
Weighted average number of shares:
Weighted Average Number of Shares Outstanding, Diluted [Abstract]
$316.5 million 1.50% 2025 Convertible Senior Notes
Incremental Common Shares Attributable to Convertible Shares
Incremental Common Shares Attributable to Convertible Shares
Employee stock plans
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements
Diluted
Earnings per common share attributable to Cliffs common shareholders - basic:
Continuing operations
Discontinued operations
Earnings per common share attributable to Cliffs common shareholders - diluted:
Discontinued operations
Net cash provided (used) by operating activities
Deposits for property, plant and equipment
Intercompany investing
Intercompany investments
Intercompany investments
Payments for Repurchase of Common Stock
Payments for Repurchase of Common Stock
Intercompany financing
Intercompany financing
Intercompany financing
DEBT AND CREDIT FACILITIES
Debt Disclosure [Text Block]
Adjusted EBITA Calculation [Axis]
Adjusted EBITA Calculation [Axis]
Adjusted EBITA Calculation [Axis]
Adjusted EBITA Calculation [Domain]
Adjusted EBITA Calculation [Domain]
[Domain] for Adjusted EBITA Calculation [Axis]
Adjusted EBITDA Calculation [Member]
Adjusted EBITDA Calculation [Member]
Adjusted EBITDA Calculation [Member]
Investment, Name [Axis]
Investment, Name [Domain]
EBITDA Calculation [Axis]
EBITDA Calculation [Axis]
EBITDA Calculation [Axis]
EBITDA Calculation [Domain]
EBITDA Calculation [Domain]
[Domain] for EBITDA Calculation [Axis]
EBITDA Calculation [Member]
EBITDA Calculation [Member]
EBITDA Calculation [Member]
All Other Segments [Member]
Other Segments [Member]
Revenues from product sales and services
Other operating expense
Interest Income (Expense), net, including Discontinued Operations
Interest Income (Expense), net, including Discontinued Operations
Interest Income (Expense), net, including Discontinued Operations
Income Tax Expense (Benefit), including Discontinued Operations
Income Tax Expense (Benefit), including Discontinued Operations
Income Tax Expense (Benefit), including Discontinued Operations
Depreciation, depletion and amortization
EBITDA
EBITDA
Earnings before Interest, Taxes, and Depreciation, Depletion and Amortization
Impact of Discontinued Operations
Impact of Discontinued Operations
Impact of Discontinued Operations
Foreign Exchange Remeasurement
Foreign Exchange Remeasurement
Foreign Exchange Remeasurement
Impairment of other long-lived assets
Asset Impairment Charges
Adjusted EBITDA
Adjusted EBITDA
Adjusted Earnings Before Interest, Taxes and Depreciation, Depletion and Amortization
Depreciation, Depletion and Amortization excluding Depreciation, Amortization and Depletion expense for Discontinued Operations
Depreciation, Depletion and Amortization excluding Depreciation, Amortization and Depletion expense for Discontinued Operations
Depreciation, Depletion and Amortization excluding Depreciation, Amortization and Depletion expense for Discontinued Operations
Capital Additions
Property, Plant and Equipment, Additions
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Table]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Table]
SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis]
SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis]
SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain]
SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain]
SEC Schedule, 12-09, Valuation Allowance, Deferred Tax Asset [Member]
SEC Schedule, 12-09, Valuation Allowance, Deferred Tax Asset [Member]
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount
Valuation Allowances and Reserves, Charged to Cost and Expense
SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Cost and Expense
Valuation Allowances and Reserves, Charged to Other Accounts
SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Other Account
SEC Schedule, 12-09, Valuation Allowances and Reserves, Business Acquired
SEC Schedule, 12-09, Valuation Allowances and Reserves, Business Acquired
SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction
SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction
BORROWING CAPACITY [Abstract]
BORROWING CAPACITY [Abstract]
Long-term Line of Credit
Schedule II - Valuation and Qualifying Accounts [Abstract]
Schedule II - Valuation and Qualifying Accounts [Abstract]
SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block]
SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block]
Disposal Group Classification [Axis]
Disposal Group Classification [Axis]
Disposal Group Classification [Domain]
Disposal Group Classification [Domain]
Non-current liabilities of discontinued operations
Net cash provided (used) by investing activities
Dividends Payable [Table]
Dividends Payable [Table]
Dividends Payable [Line Items]
Dividends Payable [Line Items]
Capital Expenditure, Discontinued Operations
Capital Expenditure, Discontinued Operations
Interest Paid, Capitalized, Investing Activities
Interest Paid, Capitalized, Investing Activities
Schedule of Error Corrections and Prior Period Adjustment Restatement [Table]
Schedule of Error Corrections and Prior Period Adjustment Restatement [Table]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles
Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block]
Product revenues from related parties
Revenue from Related Parties
Related party product revenue as a percent of total product revenue
Percentage Of Related Party Revenue
Related party product revenue as a percentage of total product revenue.
Accumulated Other Comprehensive Income Components [Axis]
Accumulated Other Comprehensive Income Components [Axis]
Accumulated Other Comprehensive Income Components [Axis]
Accumulated Other Comprehensive Income Components [Domain]
Accumulated Other Comprehensive Income Components [Domain]
[Domain] for Accumulated Other Comprehensive Income Components [Axis]
Postretirement Benefit Liability [Member]
Postretirement Benefit Liability [Member]
Postretirement Benefit Liability [Member]
Unrealized Gain Loss On Derivatives [Member]
Unrealized Gain Loss On Derivatives [Member]
Unrealized Gain (Loss) on Derivatives
Accumulated Other Comprehensive Income (Loss), Before Taxes
Accumulated Other Comprehensive Income (Loss), Before Taxes
Accumulated Other Comprehensive Income (Loss), Before Taxes
Accumulated Other Comprehensive Income (Loss), Tax
Accumulated Other Comprehensive Income (Loss), Tax
Accumulated Other Comprehensive Income (Loss), Tax
Accumulated other comprehensive loss
Fair value of plan assets
Employee Stock Ownership Plan (ESOP) Name [Axis]
Employee Stock Ownership Plan (ESOP) Name [Axis]
Employee Stock Ownership Plan (ESOP), Plan [Domain]
Employee Stock Ownership Plan (ESOP), Plan [Domain]
Cliffs Natural Resource Inc. 2015 Employee Stock Purchase Plan [Member]
Cliffs Natural Resource Inc. 2015 Employee Stock Purchase Plan [Member]
Cliffs Natural Resource Inc. 2015 Employee Stock Purchase Plan [Member]
Allocated Share-based Compensation Expense
Allocated Share-based Compensation Expense
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense
Performance/vesting period
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period
Payout rate, as a percentage of the original grant
Number of restricted shares granted
Maximum number of shares that may be issued (in shares)
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition
Common Stock, Shares Authorized
Common Stock, Shares Authorized
Debt Instrument Redemption [Table]
Debt Instrument Redemption [Table]
Prior to January 15, 2021 - upon equity issuance
Debt Instrument, Redemption, Period One, Upon Equity Issuance [Member]
Debt Instrument, Redemption, Period One, Upon Equity Issuance [Member]
Prior to January 15, 2021, including premium
Debt Instrument, Redemption, Period One, Including Premium [Member]
Debt Instrument, Redemption, Period One, Including Premium [Member]
Prior to January 15, 2021
Debt Instrument, Redemption, Period One [Member]
Beginning on January 15, 2021
Debt Instrument, Redemption, Period Two [Member]
Beginning on January 15, 2022
Debt Instrument, Redemption, Period Three [Member]
Beginning on January 15, 2023
Debt Instrument, Redemption, Period Four [Member]
Debt Instrument, Redemption [Line Items]
Debt Instrument, Redemption [Line Items]
Redemption Price
Debt Instrument, Redemption Price, Percentage
Restricted Amount (percent of original aggregate principal)
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed
Schedule Of Derivative Instruments In Statement Of Financial Position, Fair Value
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]
Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block]
Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block]
Schedule Of Derivatives Not Designated As Hedging Instruments Statements Of Financial Performance Location Table
Derivatives Not Designated as Hedging Instruments [Table Text Block]
Acquired through business combinations
Joint Venture Partners [Member]
Number Of Mines
Number Of Mines
Number of mines
Due to Related Parties, Current
Noncontrolling Interest Purchase, Number Of Installment Payments
Noncontrolling Interest Purchase, Number Of Installment Payments
Noncontrolling Interest Purchase, Number Of Installment Payments
Preferred Class B [Member]
Preferred Class B [Member]
Preferred stock, par value
Preferred Stock, Par or Stated Value Per Share
Preferred stock, shares authorized (in shares)
Preferred Stock, Shares Authorized
Preferred stock, issued and outstanding (in shares)
Preferred Shares, Issued and Outstanding, Shares
Preferred Shares, Issued and Outstanding, Shares
Common shares, authorized (in shares)
Common shares, outstanding (in shares)
Common shares in treasury
Treasury Stock, Shares
Fair Value Of Assets And Liabilities Measure On Unobservable Input [Axis]
Fair Value Of Assets And Liabilities Measure On Unobservable Input [Axis]
Fair Value Of Assets And Liabilities Measure On Unobservable Input [Axis]
Fair Value Of Assets And Liabilities Measure On Unobservable Input [Domain]
Fair Value Of Assets And Liabilities Measure On Unobservable Input [Domain]
Fair Value Of Assets And Liabilities Measure On Unobservable Input [Domain]
Customer's Hot-Rolled Steel Estimate [Member]
Hot-Rolled Steel Estimate [Member]
Hot-Rolled Steel Estimate [Member]
Managements Estimate Of 62% Fe [Member]
Managements Estimate Of Sixty Two Percent [Member]
Managements Estimate Of Sixty Two Percent [Member]
Fair value measurement with unobservable inputs derivative asset range
Fair Value Measurement With Unobservable Inputs Derivative Asset Range
Fair value measurement with unobservable inputs derivative asset range
Inventories
Inventory Disclosure [Text Block]
Reimbursement Revenue, by Type [Axis]
Reimbursement Revenue, by Type [Axis]
Reimbursement Revenue, by Type [Axis]
Reimbursement Revenue, by Type [Domain]
Reimbursement Revenue, by Type [Domain]
[Domain] for Reimbursement Revenue, by Type [Axis]
Freight Revenue [Member]
Freight Revenue [Member]
Freight Revenue [Member]
Co-venturer [Member]
Co-venturer [Member]
Land Rights
Land
Mineral Rights [Abstract]
Mineral Properties, Net [Abstract]
Mineral Properties, Gross
Mineral Properties, Gross
Mineral Properties, Accumulated Depletion
Mineral Properties, Accumulated Depletion
Mineral Properties, Net
Mineral Properties, Net