Restructuring and Other Charges, Net - Additional Information (Detail) $ in Millions		1 Months Ended		3 Months Ended		9 Months Ended
		Sep. 30, 2023 USD ($) Employees	Mar. 31, 2023 USD ($) Employees	Sep. 30, 2024 USD ($) Employee	Sep. 30, 2023 USD ($) Employees	Sep. 30, 2024 USD ($) Employee Employees	Sep. 30, 2023 USD ($)	Dec. 31, 2025 Employee	Mar. 31, 2024 Employee	Dec. 31, 2023 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges				$ 30	$ 22	$ 250	$ 195
Restructuring and other charges, net				$ 30	$ 22	250	195
Kwinana Refinery [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges						205
Severance costs						$ 41
Number of employees | Employee				300		300			780
Number of employees associated with employee termination and severance costs | Employees					250	430
Number of additional employees redeployed | Employees						50
Asset impairments						$ 5
Contract termination cost						2
Cash outlays includes existing employee related liabilities and asset retirement obligations expected through 2025						225
Cash outlays to be spent in 2024						145
Cash outlays				$ 72		96
Kwinana Refinery [Member] | Forecast [Member]
Restructuring Cost and Reserve [Line Items]
Number of employees | Employee								50
Australia [Member]
Restructuring Cost and Reserve [Line Items]
Number of employees associated with employee termination and severance costs | Employees		90
Restructuring and other charges, net		$ 6
Pension Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Settlement of certain other postretirement benefits	[1]					(1)	21
Alcoa Corporation [Member]
Restructuring Cost and Reserve [Line Items]
Noncurrent portion of the reserve				8		8				$ 15
Intalco [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges			$ 101				101
Severance costs			$ 1
Number of employees associated with employee termination and severance costs | Employees			12
Asset impairments			$ 50
Contract termination cost				12		12
Cash outlays				1		14
San Ciprian Facility [Member]
Restructuring Cost and Reserve [Line Items]
Cash outlays includes existing employee related liabilities and asset retirement obligations expected through 2025						47
Cash outlays to be spent in 2024						35
Cash outlays				8		26
Restart costs						31
Commitments For Capital Improvement Costs						78
Restricted cash				86		86
Capital improvement costs						109
Wenatchee (Washington) [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges				4		16
Cost of Goods Sold [Member] | Intalco [Member]
Restructuring Cost and Reserve [Line Items]
Other costs			16
Restructuring and Other Charges [Member] | San Ciprian Facility [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net							47
2024 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net				30		250
Environmental and Asset Retirement Obligation Reserves [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges				$ 14	$ 15	15	15
Closure Cost [Member] | Intalco [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges			117
Cash outlays to be spent in 2024						45
Cash outlays expected over next three years						85
Certain Employee Obligations [Member] | San Ciprian Aluminum Smelter [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges							47
Environmental and Demolition Obligation [Member] | Intalco [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges			$ 50
Severance and Employee Termination Costs [Member] | Australia [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges					$ 7		$ 10
Water Management Costs [Member] | Kwinana Refinery [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges						129
Asset Retirement Obligations [Member] | Kwinana Refinery [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges						15
Take Or-Pay Contracts [Member] | Kwinana Refinery [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges						$ 13

[1] These amounts were reported in Restructuring and other charges, net on the accompanying Statement of Consolidated Operations and Cash Flows.