Asset Retirement Obligations - Schedule of Estimated Timing of Cash Outflows on Asset Retirement Obligations (Details) $ in Millions	12 Months Ended
Dec. 31, 2024 USD ($)
Asset Retirement Obligation Disclosure [Abstract]
2025	$ 204
2026 - 2029	522
Thereafter	169
Total	$ 895

Asset retirement obligation revision of estimate, due after five years

No definition available.

Name:	aa_AssetRetirementObligationRevisionOfEstimateDueAfterFiveYears
Namespace Prefix:	aa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration