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CAPITAL STOCK - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions |  |  |  | 3 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 01, 2021 | Mar. 11, 2021 | Dec. 09, 2020 | Sep. 30, 2021 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | Feb. 10, 2022 | Apr. 29, 2021 | Mar. 31, 2021 | Feb. 11, 2021
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Authorized amount of stock repurchase |  |  |  |  |  |  |  | $ 1,000 |  |  |
Common share repurchases |  |  |  |  | $ 240 |  |  |  |  |  |
Redemption of debt |  |  |  |  | 1,318 |  |  |  |  |  |
1.500% 2025 Convertible Senior Notes redemption |  |  |  |  | $ (25) | $ (5) |  |  |  |  |
Common shares, issued (in shares) |  |  |  |  | 531,051,530 | 506,832,537 |  |  |  |  | 20,000,000
Common shares, sold (in shares) |  |  |  |  |  |  |  |  |  |  | 40,000,000
Common stock, shares issued, price per share (in usd per share) |  |  |  |  |  |  |  |  |  |  | $ 16.12
Redeemable preferred stock, issued (in shares) |  |  |  |  |  | 583,273 |  |  |  |  |
Redeemable preferred stock, outstanding (in shares) |  |  |  |  |  | 583,273 |  |  |  |  |
Common shares, authorized (in shares) |  |  |  |  | 1,200,000,000 | 1,200,000,000 |  |  | 1,200,000,000 | 600,000,000 |
Common Stock |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Common stock repurchases (in shares) |  |  |  |  | 12,500,000 |  |  |  |  |  |
1.500% 2025 Convertible Senior Notes redemption (in shares) |  |  |  |  | 24,000,000 |  |  |  |  |  |
Common Shares in Treasury |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Common share repurchases |  |  |  |  | $ 240 |  |  |  |  |  |
1.500% 2025 Convertible Senior Notes |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Redemption of debt | $ 294 |  |  |  | 294 |  |  |  |  |  |
Repayments of debt | 294 |  |  |  |  |  |  |  |  |  |
1.500% 2025 Convertible Senior Notes redemption | $ 499 |  |  |  | 499 |  |  |  |  |  |
9.875% 2025 Senior Secured Notes |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Redemption of debt |  | $ 322 |  |  | $ 607 |  |  |  |  |  |
ArcelorMittal |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Common shares, sold (in shares) |  |  |  |  |  |  |  |  |  |  | 40,000,000
Cleveland-Cliffs Inc. | 1.500% 2025 Convertible Senior Notes |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  |  | 1.50% |  |  |  |  |  |
Cleveland-Cliffs Inc. | 9.875% 2025 Senior Secured Notes |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  |  | 9.875% |  |  |  |  |  |
ArcelorMittal USA | Common Stock |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Acquisition (in shares) |  |  |  |  |  |  | 78,000,000 |  |  |  |
Common Stock |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
1.500% 2025 Convertible Senior Notes redemption (in shares) | 24,000,000 |  |  |  |  |  |  |  |  |  |
Common Stock | ArcelorMittal USA |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Acquisition (in shares) |  |  | 78,186,671 |  |  |  |  |  |  |  |
Series B Preferred Stock |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Stock redeemed during period (in shares) |  |  |  | 583,273 |  |  |  |  |  |  |
Stock redeemed during period |  |  |  | $ 1,300 |  |  |  |  |  |  |
Preferred stock authorized (in shares) |  |  |  |  | 4,000,000 |  |  |  |  |  |
Preferred stock issued (in shares) |  |  |  |  | 0 |  |  |  |  |  |
Preferred stock outstanding (in shares) |  |  |  |  | 0 |  |  |  |  |  |
Series B Preferred Stock | ArcelorMittal USA |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Acquisition (in shares) |  |  | 583,273 |  |  |  |  |  |  |  |
Series A Preferred Stock |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Preferred stock authorized (in shares) |  |  |  |  | 3,000,000 |  |  |  |  |  |
Preferred stock issued (in shares) |  |  |  |  | 0 |  |  |  |  |  |
Preferred stock outstanding (in shares) |  |  |  |  | 0 |  |  |  |  |  |

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