Contingencies, Commitments and Other Liabilities (Details) € in Millions, $ in Millions			3 Months Ended			12 Months Ended
	Mar. 31, 2023 USD ($)	Mar. 31, 2023 EUR (€)	Mar. 31, 2025 USD ($) location	Dec. 31, 2024 USD ($)	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2023 EUR (€)	Jul. 23, 2024 USD ($)	Jul. 23, 2024 EUR (€)
Loss Contingencies [Line Items]
Number of cleanup locations | location			30
Remediation reserve balance			$ 16	$ 19
Remediation reserve balance, classified as a current liability			7	10
Payments related to remediation expenses applied against the reserve (less than in second quarter)			3		$ 1
Guarantees of third party related to project financing			6
Combined fair value of guarantees			$ 6	6
Indemnification of liability (as a percent)			50.00%
Coverage limit				$ 80
Total amount committed under outstanding surety bonds			$ 45
Surety bonds, amount outstanding			$ 21
Termination notice period (in days)			30 days
Payment timing (in days)			120 days
Supplier Finance Program, Obligation, Current, Statement of Financial Position [Extensible Enumeration]			Accounts payable, trade (P)	Accounts payable, trade (P)
Supplier invoices subject to future payment			$ 264	$ 268
Letter of Credit
Loss Contingencies [Line Items]
Maximum borrowing capacity			81
Other Noncurrent Liabilities and Deferred Credits | Separation Agreement
Loss Contingencies [Line Items]
Guarantees of third party related to project financing			$ 1,121	$ 1,121
Foreign Tax Authority | Ministry of the Economy, Finance and Industry, France | Tax Years 2010 Through 2012
Loss Contingencies [Line Items]
Income tax assessment, estimate of possible loss	$ 17	€ 16
Income tax assessment, amount of penalties cancelled								$ 7	€ 7
Income tax reserve						$ 21	€ 19
Recurring Costs of Managing Hazardous Substances and Environmental Programs
Loss Contingencies [Line Items]
Percentage of cost of goods sold (as a percent)			1.00%
Income Tax and Interest | Foreign Tax Authority | Ministry of the Economy, Finance and Industry, France | Tax Years 2010 Through 2012
Loss Contingencies [Line Items]
Income tax assessment, estimate of possible loss	10	9
Income Tax Penalties | Foreign Tax Authority | Ministry of the Economy, Finance and Industry, France | Tax Years 2010 Through 2012
Loss Contingencies [Line Items]
Income tax assessment, estimate of possible loss	7	7
Additional Interest on Income Tax | Foreign Tax Authority | Ministry of the Economy, Finance and Industry, France | Tax Years 2010 Through 2012
Loss Contingencies [Line Items]
Income tax assessment, estimate of possible loss	$ 2	€ 2
Alcoa Corporation Workers Compensation Claims
Loss Contingencies [Line Items]
Letters of credit, total amount outstanding			$ 48
Arconic Corporation Environmental Obligations
Loss Contingencies [Line Items]
Letters of credit, total amount outstanding			9
Arconic Corporation Environmental Obligations | Letter of Credit
Loss Contingencies [Line Items]
Decrease in letters of credit			$ 8