Restructuring and Other Charges, Net - Schedule of Restructuring and Other Charges, Net by Reportable Segments, Pretax (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	$ 5	$ 202
Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	3	197
Corporate [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	2	5
Alumina [Member] | Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	0	197
Aluminum Segment [Member] | Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	$ 3	$ 0