SEGMENT INFORMATION - Segment Revenue Segment Cost and Adjusted EBITDA (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2025	Mar. 31, 2024
Segment Reporting Information [Line Items]
External revenue	$ 1,979	$ 1,880
Segment Adjusted EBITDA	140	160
A&T
Segment Reporting Information [Line Items]
External revenue	435	469
Cost of metal	(192)	(206)
Production costs	(146)	(152)
Other segment expenses	(22)	(24)
Segment Adjusted EBITDA	75	87
A&T \| Segment revenue
Segment Reporting Information [Line Items]
External revenue	468	479
A&T \| Inter-segment elimination
Segment Reporting Information [Line Items]
External revenue	(33)	(10)
P&ARP
Segment Reporting Information [Line Items]
External revenue	1,184	1,014
Cost of metal	(859)	(691)
Production costs	(239)	(245)
Other segment expenses	(26)	(30)
Segment Adjusted EBITDA	60	48
P&ARP \| Segment revenue
Segment Reporting Information [Line Items]
External revenue	1,187	1,018
P&ARP \| Inter-segment elimination
Segment Reporting Information [Line Items]
External revenue	(3)	(4)
AS&I
Segment Reporting Information [Line Items]
External revenue	360	395
Cost of metal	(214)	(210)
Production costs	(107)	(128)
Other segment expenses	(23)	(25)
Segment Adjusted EBITDA	16	32
AS&I \| Segment revenue
Segment Reporting Information [Line Items]
External revenue	381	396
AS&I \| Inter-segment elimination
Segment Reporting Information [Line Items]
External revenue	(21)	(1)
H&C
Segment Reporting Information [Line Items]
External revenue	0	2
Cost of metal	2	2
Production costs	(2)	(2)
Other segment expenses	(11)	(9)
Segment Adjusted EBITDA	(11)	(7)
H&C \| Segment revenue
Segment Reporting Information [Line Items]
External revenue	0	2
H&C \| Inter-segment elimination
Segment Reporting Information [Line Items]
External revenue	$ 0	$ 0

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Cost Of Metal

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