SEGMENT REPORTING - Segment Capital Additions (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Capital additions	$ 162	$ 158
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Capital additions	18	1
Steelmaking
Segment Reporting Information [Line Items]
Capital additions	133	154
Other Businesses
Segment Reporting Information [Line Items]
Capital additions	$ 11	$ 3