Sales of Receivables - Narrative (Details) $ in Millions	Dec. 31, 2024 USD ($)
Transfers and Servicing of Financial Assets [Abstract]
Maximum amount of receivables sold	$ 400

Transfers Of Financial Assets Accounted For As Sales, Maximum Amount Of Receivables Sold

No definition available.

Name:	amtm_TransfersOfFinancialAssetsAccountedForAsSalesMaximumAmountOfReceivablesSold
Namespace Prefix:	amtm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant