INVESTMENT IN AECOM DC RETIREMENT PLANS STABLE VALUE MASTER TRUST (Details) - EBP 055 $ in Thousands	12 Months Ended
Dec. 31, 2025 USD ($)
EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment [Abstract]
Interest and dividend income	$ 7,184
Net investment income	1,000,371
Beginning of year	6,778,558
End of year	7,368,267
Master Trust \| Stable Value Master Trust
EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment [Abstract]
Interest and dividend income	9,273
Net purchases (redemptions)	(19,214)
Administrative expenses	(9)
Net investment income	(9,950)
Beginning of year	323,734
End of year	313,784
Plan interest in Master Trust \| Stable Value Master Trust
EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment [Abstract]
Interest and dividend income	9,273
Net purchases (redemptions)	(19,214)
Administrative expenses	(9)
Net investment income	(9,950)
Beginning of year	323,734
End of year	$ 313,784

Amount of decrease in net asset available for benefit from expense for generating income on investment held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

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Amount of increase (decrease) in net asset available for benefit from income (loss) on investment held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Includes, but is not limited to, realized and unrealized gain (loss) on investment.

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Amount, before investment expense, of increase (decrease) in net asset available for benefit from investment income (loss) on investment held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

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Amount of increase in net asset available for benefit from interest and dividend income on investment held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

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Amount of asset less liability available to pay benefit of participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)), including, but not limited to, aggregation of participants' individual account balances.

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