Restructuring and Other Charges, Net - Schedule of Restructuring and Other Charges, Net by Reportable Segments, Pretax (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	$ 18	$ 24	$ 220	$ 173
Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	8	20	205	167
Corporate [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	10	4	15	6
Alumina [Member] | Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	$ 8	1	$ 205	2
Aluminum Segment [Member] | Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net		$ 19		$ 165