Restructuring and Other Charges, Net - Schedule of Restructuring and Other Charges, Net by Reportable Segments, Pretax (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	$ 341	$ 184	$ 696
Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	287	177	55
Corporate [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	54	7	641
Alumina [Member] | Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	$ 287	8	(27)
Aluminum Segment [Member] | Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net		$ 169	$ 82