Restructuring and Other Charges, Net - Additional Information (Detail) $ in Millions		1 Months Ended	3 Months Ended			6 Months Ended
		Mar. 31, 2023 USD ($) Employees	Jun. 30, 2024 USD ($)	Sep. 30, 2023 Employees	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) Employees	Jun. 30, 2023 USD ($)	Sep. 30, 2025 Employee	Sep. 30, 2024 Employee	Mar. 31, 2024 Employee	Dec. 31, 2023 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges			$ 18		$ 24	$ 220	$ 173
Restructuring and other charges, net			18		24	220	173
Kwinana Refinery [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges			8			205
Severance costs						$ 41
Number of employees | Employee										780
Number of employees associated with employee termination and severance costs | Employees				150		580
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			22			24
Kwinana Refinery [Member] | Forecast [Member]
Restructuring Cost and Reserve [Line Items]
Number of employees | Employee								50	250
Pension Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Settlement of certain other postretirement benefits	[1]		(1)		$ 21	(1)	21
Alcoa Corporation [Member]
Restructuring Cost and Reserve [Line Items]
Noncurrent portion of the reserve			22			22					$ 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
Cash outlays			9			13
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						36
Cash outlays			9			18
Restart costs						32
Commitments For Capital Improvement Costs						78
Restricted cash			86			86
Capital improvement costs						111
Wenatchee (Washington) [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges			8			12
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
2023 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net							173
2024 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net			$ 18			220
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
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.