Restructuring and Other Charges, Net (2023 Actions) - Additional Information (Detail) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2022 USD ($)	Dec. 31, 2024 USD ($) Employees	Dec. 31, 2023 USD ($) Employees	Dec. 31, 2022 USD ($) Employees
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net		$ 341	$ 184	$ 696
Restructuring and other charges, net		341	$ 184	$ 696
Number of employees under defined benefit plan | Employees			530	4,400
Asset impairments		5	$ 50	$ 58
Severance and employee termination costs		44	11	1
Cash payments for restructuring		183	124	39
Restart costs		$ 5
Australia [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			$ 6
Number of employees associated with employee termination and severance costs | Employees			90
Intalco Aluminum Smelter [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			$ 101
Magnesium Smelter Facility in Addy [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	$ 29			29
Group Annuity Contract [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			21	635
Pension Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			235	1,000
Number of employees under defined benefit plan | Employees		16,000
2023 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			184
San Ciprian Facility [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			53
Commitments for capital improvement costs			78
Cash outlay in 2023			7
Cash outlays in 2024		$ 34
Restricted cash		86
San Ciprian Facility [Member] | Restructuring and Other Charges [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			53
Warrick Rolling Mill [Member] | Restructuring and Other Charges [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			1
Warrick Rolling Mill [Member] | Cost of Goods Sold [Member]
Restructuring Cost and Reserve [Line Items]
Charges for write-off remaining net book value of assets			1
Intalco [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			$ 101
Number of employees associated with employee termination and severance costs | Employees			12
Asset impairments			$ 50
Severance and employee termination costs			1
Intalco [Member] | Cost of Goods Sold [Member]
Restructuring Cost and Reserve [Line Items]
Other costs			16
Certain Employee Obligations [Member] | San Ciprian Facility [Member]
Restructuring Cost and Reserve [Line Items]
Cash payments for restructuring			31
Severance and Employee Termination Costs [Member]
Restructuring Cost and Reserve [Line Items]
Cash payments for restructuring		$ 38	6	$ 2
Severance and Employee Termination Costs [Member] | Australia [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			11
Additional Environmental Remediation And Asset Retirement Obligations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			17
Unused Carbon Credits [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			19
Additional Asset Retirement [Member] | Warrick Rolling Mill [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			1
Take Or-Pay Contracts [Member] | Intalco [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			1
Demolition Obligations At Previously Closed Sites [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			2
Closure Cost [Member] | Intalco [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			117
Environmental and Demolition Obligation [Member] | Intalco [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			$ 50