Asset Retirement Obligations - Schedule of Estimated Timing of Cash Outflows on Asset Retirement Obligations (Details) $ in Millions	12 Months Ended
Dec. 31, 2023 USD ($)
Asset Retirement Obligation Disclosure [Abstract]
2024	$ 217
2025 - 2028	573
Thereafter	199
Total	$ 989

Asset retirement obligation revision of estimate, due after five years

No definition available.

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