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BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Details) - Stelco Holdings Inc | Nov. 01, 2024 USD ($) shares | Jul. 12, 2024 USD ($) | Nov. 01, 2024 $ / shares
--- | --- | --- | ---
Business Acquisition [Line Items] |  |  |
Expected enterprise value of acquisition |  | $ 2,500,000,000 |
Subsequent Event |  |  |
Business Acquisition [Line Items] |  |  |
Shares of Cliffs common shares issued to Stelco Holdings stockholders (in shares) | shares | 0.454 |  |
Expected enterprise value of acquisition | $ 3,200,000,000 |  |
Stelco Holdings Inc | Subsequent Event |  |  |
Business Acquisition [Line Items] |  |  |
Price per share (in dollars per share) | $ / shares |  |  | $ 60.00

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