Properties, Plants, and Equipment, Net - Schedule of Properties, Plants, and Equipment, Net (Detail) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Less: accumulated depreciation, depletion, and amortization	$ 13,161	$ 13,596
Properties, plants, and equipment excluding construction work-in-progress	5,777	6,216
Construction work-in-progress	612	569
Properties, plants, and equipment, net	6,389	6,785
Land [Member]
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	233	257
Structures [Member]
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	7,628	8,096
Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	11,077	11,459
Property Plant And Equipment Other Than Construction In Progress [Member]
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	18,938	19,812
Operating Segments [Member] | Bauxite Mining and Alumina Refining [Member] | Structures [Member]
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	3,736	4,085
Operating Segments [Member] | Bauxite Mining and Alumina Refining [Member] | Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	4,218	4,352
Operating Segments [Member] | Aluminum Smelting and Casting [Member] | Structures [Member]
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	3,214	3,274
Operating Segments [Member] | Aluminum Smelting and Casting [Member] | Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	5,551	5,781
Operating Segments [Member] | Energy [Member] | Structures [Member]
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	334	380
Operating Segments [Member] | Energy [Member] | Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	855	869
Other [Member]
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, net	366	392
Other [Member] | Structures [Member]
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	344	357
Other [Member] | Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	$ 453	$ 457