INVESTMENT IN AECOM DC RETIREMENT PLANS VANGUARD 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]
Net appreciation in fair value of investments and Investment gain from self-directed brokerage accounts	$ (48,300)
Interest and dividends	7,184
Net investment income	1,000,371
Beginning of year	6,778,558
End of year	7,368,267
Master Trust \| Vanguard Master Trust
EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment [Abstract]
Net appreciation in fair value of investments and Investment gain from self-directed brokerage accounts	532,759
Interest and dividends	4
Total investment income	532,763
Net purchases (redemptions)	(482,636)
Administrative expenses	(1,048)
Net investment income	49,079
Beginning of year	3,364,044
End of year	3,413,123
Plan interest in Master Trust \| Vanguard Master Trust
EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment [Abstract]
Net appreciation in fair value of investments and Investment gain from self-directed brokerage accounts	532,759
Interest and dividends	4
Total investment income	532,763
Net purchases (redemptions)	(482,636)
Administrative expenses	(1,048)
Net investment income	49,079
Beginning of year	3,364,044
End of year	$ 3,413,123

EBP, Change in Net Asset Available for Benefit, Decrease From Net Purchases (Redemptions)

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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 realized and unrealized gain (loss) on investment held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

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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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