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DEBT AND CREDIT FACILITIES - Schedule Of Long-Term Debt (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Jun. 19, 2020 | Apr. 24, 2020 | Apr. 17, 2020 | Mar. 16, 2020 | Mar. 13, 2020 | Dec. 31, 2019
--- | --- | --- | --- | --- | --- | --- | ---
Debt Instrument [Line Items] |  |  |  |  |  |  |
Debt Instrument, Par Value | $ 5,595 |  |  |  |  |  |
Total Debt | 5,424 |  |  |  |  |  |
Long-term Debt, Current Maturities | 34 |  |  |  |  |  |
Long-term debt | $ 5,390 |  |  |  |  |  | $ 2,114
Cleveland-Cliffs Inc. [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Imputed interest rate | 3.25% |  |  |  |  |  |
Cleveland-Cliffs Inc. [Member] | ABL Facility [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Imputed interest rate | 2.15% |  |  |  |  |  |
Debt Instrument, Par Value |  |  |  |  |  |  | 450
Line of Credit Facility, Maximum Borrowing Capacity | $ 3,500 |  |  |  |  |  |
Credit facility, amount outstanding | 1,510 |  |  |  |  |  | $ 0
Cleveland-Cliffs Inc. [Member] | EDC Revolving Credit Facility |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Line of Credit Facility, Maximum Borrowing Capacity | 40 |  |  |  |  |  |
Credit facility, amount outstanding | 18 |  |  |  |  |  |
AK Steel [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Debt Instrument, Par Value | 132 |  |  |  |  |  |
AK Steel [Member] | Industrial Revenue Bonds [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Debt Instrument, Par Value | 92 |  |  |  |  |  |
Unamortized Debt Issuance Expense | 0 |  |  |  |  |  |
Total Debt | 94 |  |  |  |  |  |
Debt Instrument, Unamortized Premium | $ 2 |  |  |  |  |  |
4.875% 2024 Senior Secured Notes | Cleveland-Cliffs Inc. [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Imputed interest rate | 5.00% |  |  |  |  |  | 5.00%
Debt Instrument, Par Value | $ 395 |  |  |  |  |  | $ 400
Unamortized Debt Issuance Expense | (3) |  |  |  |  |  | (5)
Debt Instrument, Unamortized Discount | 1 |  |  |  |  |  | 2
Total Debt | $ 391 |  |  |  |  |  | $ 393
9.875% 2025 Senior Secured Notes | Cleveland-Cliffs Inc. [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Imputed interest rate | 10.57% |  |  |  |  |  |
Debt Instrument, Par Value | $ 955 |  | $ 555 | $ 400 |  |  |
Unamortized Debt Issuance Expense | (8) |  |  |  |  |  |
Debt Instrument, Unamortized Discount | 25 |  |  |  |  |  |
Total Debt | $ 922 |  |  |  |  |  |
6.75% 2026 Senior Secured Notes | Cleveland-Cliffs Inc. [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Imputed interest rate | 6.99% |  |  |  |  |  |
Debt Instrument, Par Value | $ 845 | $ 120 |  |  |  | $ 725 |
Unamortized Debt Issuance Expense | (20) |  |  |  |  |  |
Debt Instrument, Unamortized Discount | 9 |  |  |  |  |  |
Total Debt | $ 816 |  |  |  |  |  |
7.625% 2021 AK Senior Notes | AK Steel [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Imputed interest rate | 7.33% |  |  |  |  |  |
Debt Instrument, Par Value | $ 34 |  |  |  |  |  |
Unamortized Debt Issuance Expense | 0 |  |  |  |  |  |
Debt Instrument, Unamortized Discount | 0 |  |  |  |  |  |
Total Debt | $ 34 |  |  |  |  |  |
7.50% 2023 AK Senior Notes [Member] | AK Steel [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Imputed interest rate | 6.17% |  |  |  |  |  |
Debt Instrument, Par Value | $ 13 |  |  |  |  |  |
Unamortized Debt Issuance Expense | 0 |  |  |  |  |  |
Debt Instrument, Unamortized Discount | 0 |  |  |  |  |  |
Total Debt | $ 13 |  |  |  |  |  |
6.375% 2025 Senior Notes | Cleveland-Cliffs Inc. [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Imputed interest rate | 8.11% |  |  |  |  |  |
Debt Instrument, Par Value | $ 64 |  |  |  | $ 232 |  |
Unamortized Debt Issuance Expense | 0 |  |  |  |  |  |
Debt Instrument, Unamortized Discount | 4 |  |  |  |  |  |
Total Debt | $ 60 |  |  |  |  |  |
6.375% 2025 AK Senior Notes | AK Steel [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Imputed interest rate | 8.11% |  |  |  |  |  |
Debt Instrument, Par Value | $ 29 |  |  |  |  |  |
Unamortized Debt Issuance Expense | 0 |  |  |  |  |  |
Debt Instrument, Unamortized Discount | 2 |  |  |  |  |  |
Total Debt | $ 27 |  |  |  |  |  |
1.50% 2025 Convertible Senior Notes | Cleveland-Cliffs Inc. [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Imputed interest rate | 6.26% |  |  |  |  |  | 6.26%
Debt Instrument, Par Value | $ 296 |  |  |  |  |  | $ 316
Unamortized Debt Issuance Expense | (4) |  |  |  |  |  | (4)
Debt Instrument, Unamortized Discount | 49 |  |  |  |  |  | 65
Total Debt | $ 243 |  |  |  |  |  | $ 247
5.75% 2025 Senior Notes | Cleveland-Cliffs Inc. [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Imputed interest rate | 6.01% |  |  |  |  |  | 6.01%
Debt Instrument, Par Value | $ 396 |  |  |  |  |  | $ 473
Unamortized Debt Issuance Expense | (3) |  |  |  |  |  | (3)
Debt Instrument, Unamortized Discount | 4 |  |  |  |  |  | 6
Total Debt | $ 389 |  |  |  |  |  | $ 464
7.00% 2027 Senior Notes | Cleveland-Cliffs Inc. [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Imputed interest rate | 9.24% |  |  |  |  |  |
Debt Instrument, Par Value | $ 73 |  |  |  | $ 335 |  |
Unamortized Debt Issuance Expense | 0 |  |  |  |  |  |
Debt Instrument, Unamortized Discount | 8 |  |  |  |  |  |
Total Debt | $ 65 |  |  |  |  |  |
7.00% 2027 AK Senior Notes | AK Steel [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Imputed interest rate | 9.24% |  |  |  |  |  |
Debt Instrument, Par Value | $ 56 |  |  |  |  |  |
Unamortized Debt Issuance Expense | 0 |  |  |  |  |  |
Debt Instrument, Unamortized Discount | 6 |  |  |  |  |  |
Total Debt | $ 50 |  |  |  |  |  |
5.875% 2027 Senior Notes | Cleveland-Cliffs Inc. [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Imputed interest rate | 6.49% |  |  |  |  |  | 6.49%
Debt Instrument, Par Value | $ 556 |  |  |  |  |  | $ 750
Unamortized Debt Issuance Expense | (4) |  |  |  |  |  | (6)
Debt Instrument, Unamortized Discount | 18 |  |  |  |  |  | 27
Total Debt | $ 534 |  |  |  |  |  | $ 717
6.25% 2040 Senior Notes | Cleveland-Cliffs Inc. [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Imputed interest rate | 6.34% |  |  |  |  |  | 6.34%
Debt Instrument, Par Value | $ 263 |  |  |  |  |  | $ 298
Unamortized Debt Issuance Expense | (2) |  |  |  |  |  | (2)
Debt Instrument, Unamortized Discount | 3 |  |  |  |  |  | 3
Total Debt | $ 258 |  |  |  |  |  | $ 293

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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 + Details
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