SEGMENT INFORMATION - Segment Revenue Segment Cost and Adjusted EBITDA (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Segment Reporting Information [Line Items]
External revenue	$ 2,103	$ 1,932	$ 4,082	$ 3,812
Segment Adjusted EBITDA	159	180	299	340
A&T
Segment Reporting Information [Line Items]
External revenue	466	473	900	941
Cost of metal	(209)	(202)	(401)	(407)
Production costs	(151)	(158)	(296)	(310)
Other segment expenses	(27)	(23)	(50)	(47)
Segment Adjusted EBITDA	78	90	153	177
A&T \| Segment revenue
Segment Reporting Information [Line Items]
External revenue	492	487	960	966
A&T \| Inter-segment elimination
Segment Reporting Information [Line Items]
External revenue	(26)	(14)	(60)	(25)
P&ARP
Segment Reporting Information [Line Items]
External revenue	1,232	1,076	2,416	2,090
Cost of metal	(895)	(743)	(1,753)	(1,435)
Production costs	(234)	(242)	(474)	(486)
Other segment expenses	(29)	(25)	(54)	(55)
Segment Adjusted EBITDA	74	66	135	114
P&ARP \| Segment revenue
Segment Reporting Information [Line Items]
External revenue	1,235	1,079	2,422	2,097
P&ARP \| Inter-segment elimination
Segment Reporting Information [Line Items]
External revenue	(3)	(3)	(6)	(7)
AS&I
Segment Reporting Information [Line Items]
External revenue	404	383	764	778
Cost of metal	(248)	(206)	(462)	(415)
Production costs	(114)	(124)	(221)	(252)
Other segment expenses	(24)	(23)	(47)	(48)
Segment Adjusted EBITDA	18	30	34	63
AS&I \| Segment revenue
Segment Reporting Information [Line Items]
External revenue	421	384	802	779
AS&I \| Inter-segment elimination
Segment Reporting Information [Line Items]
External revenue	(18)	(1)	(38)	(1)
H&C
Segment Reporting Information [Line Items]
External revenue	1	0	2	3
Cost of metal	2	1	3	3
Production costs	(2)	(1)	(4)	(3)
Other segment expenses	(12)	(6)	(24)	(17)
Segment Adjusted EBITDA	(12)	(6)	(23)	(14)
H&C \| Segment revenue
Segment Reporting Information [Line Items]
External revenue	1	0	2	3
H&C \| Inter-segment elimination
Segment Reporting Information [Line Items]
External revenue	$ 0	$ 0	$ 0	$ 0

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Cost Of Metal

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