Restructuring and Other Charges, Net - Schedule of Restructuring and Other Charges, Net by Reportable Segments, Pretax (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	$ 30	$ 22	$ 250	$ 195
Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	0	3	205	170
Corporate [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	30	19	45	25
Alumina [Member] | Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	0	6	205	8
Aluminum Segment [Member] | Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	$ 0	$ (3)	$ 0	$ 162