Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of unamortized debt discount (premium) and debt issuance costs.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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DEBT AND CREDIT FACILITIES - Schedule Of Long-Term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 5,115	$ 5,369
Unamortized discounts and issuance costs	(87)	(131)
Long-term Debt	5,028	5,238
ABL Facility
Debt Instrument [Line Items]
Long-term Line of Credit	$ 1,715
Cleveland-Cliffs Inc. \| 9.875% 2025 Senior Secured Notes
Debt Instrument [Line Items]
Stated interest rate	9.875%		9.875%
Debt Instrument, Interest Rate, Effective Percentage	10.57%
Long-term Debt, Gross	$ 607	607
Cleveland-Cliffs Inc. \| 6.750% 2026 Senior Secured Notes
Debt Instrument [Line Items]
Stated interest rate	6.75%
Debt Instrument, Interest Rate, Effective Percentage	6.99%
Long-term Debt, Gross	$ 845	845
Cleveland-Cliffs Inc. \| 1.500% 2025 Convertible Senior Notes
Debt Instrument [Line Items]
Stated interest rate	1.50%
Debt Instrument, Interest Rate, Effective Percentage	6.26%
Long-term Debt, Gross	$ 0	294
Cleveland-Cliffs Inc. \| 7.000% 2027 Senior Notes
Debt Instrument [Line Items]
Stated interest rate	7.00%
Debt Instrument, Interest Rate, Effective Percentage	9.24%
Long-term Debt, Gross	$ 73	73
Cleveland-Cliffs Inc. \| 5.875% 2027 Senior Notes
Debt Instrument [Line Items]
Stated interest rate	5.875%
Debt Instrument, Interest Rate, Effective Percentage	6.49%
Long-term Debt, Gross	$ 556	556
Cleveland-Cliffs Inc. \| 4.625% 2029 Senior Notes
Debt Instrument [Line Items]
Stated interest rate	4.625%
Debt Instrument, Interest Rate, Effective Percentage	4.63%
Long-term Debt, Gross	$ 500	500
Cleveland-Cliffs Inc. \| 4.875% 2031 Senior Notes
Debt Instrument [Line Items]
Stated interest rate	4.875%
Debt Instrument, Interest Rate, Effective Percentage	4.88%
Long-term Debt, Gross	$ 500	500
Cleveland-Cliffs Inc. \| 6.250% 2040 Senior Notes
Debt Instrument [Line Items]
Stated interest rate	6.25%
Debt Instrument, Interest Rate, Effective Percentage	6.34%
Long-term Debt, Gross	$ 263	$ 263
Cleveland-Cliffs Inc. \| ABL Facility
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	2.00%	1.87%
Long-term Line of Credit	$ 1,715	$ 1,609
AK Steel \| 7.000% 2027 AK Senior Notes
Debt Instrument [Line Items]
Stated interest rate	7.00%
Debt Instrument, Interest Rate, Effective Percentage	9.24%
Long-term Debt, Gross	$ 56	56
AK Steel \| Industrial Revenue Bonds
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 0	$ 66