SEGMENT REPORTING - Segment Assets (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
Total assets	$ 17,236	$ 17,537
Corporate
Segment Reporting Information [Line Items]
Total assets	345	507
Operating Segments
Segment Reporting Information [Line Items]
Total assets	16,891	17,030
Operating Segments | Steelmaking
Segment Reporting Information [Line Items]
Total assets	16,738	16,880
Operating Segments | Other Businesses
Segment Reporting Information [Line Items]
Total assets	658	657
Eliminations
Segment Reporting Information [Line Items]
Total assets	$ (505)	$ (507)