v3.26.1
INVESTMENT IN AECOM DC RETIREMENT PLANS VANGUARD MASTER TRUST (Details) - EBP 055 - USD ($)
$ in Thousands
Dec. 31, 2025
Dec. 31, 2024
EBP, Master Trust [Line Items]    
Investments at fair value $ 7,291,530 $ 6,704,959
Vanguard Master Trust    
EBP, Master Trust [Line Items]    
Plan's interest in Master Trust (percent) 100.00%  
Master Trust | Vanguard Master Trust    
EBP, Master Trust [Line Items]    
Investments at fair value $ 3,413,123 3,364,044
Master Trust | Vanguard Master Trust | Total Fair Value    
EBP, Master Trust [Line Items]    
Investments at fair value   630,038
Master Trust | Vanguard Master Trust | Level 1    
EBP, Master Trust [Line Items]    
Investments at fair value   630,038
Master Trust | Vanguard Master Trust | Level 2    
EBP, Master Trust [Line Items]    
Investments at fair value   0
Master Trust | Vanguard Master Trust | Collective investment trusts (measured at NAV)    
EBP, Master Trust [Line Items]    
Investments at fair value 3,413,123 2,734,006
Master Trust | Vanguard Master Trust | Collective investment trusts (measured at NAV) | Investments measured at NAV    
EBP, Master Trust [Line Items]    
Investments at fair value   2,734,006
Master Trust | Vanguard Master Trust | Mutual funds    
EBP, Master Trust [Line Items]    
Investments at fair value 0 630,038
Master Trust | Vanguard Master Trust | Mutual funds | Total Fair Value    
EBP, Master Trust [Line Items]    
Investments at fair value   630,038
Master Trust | Vanguard Master Trust | Mutual funds | Level 1    
EBP, Master Trust [Line Items]    
Investments at fair value   630,038
Master Trust | Vanguard Master Trust | Mutual funds | Level 2    
EBP, Master Trust [Line Items]    
Investments at fair value   0
Master Trust | Vanguard Master Trust | Retirement date funds    
EBP, Master Trust [Line Items]    
Investments at fair value 2,016,233 1,503,727
Unfunded Commitment 0 0
Master Trust | Vanguard Master Trust | Index funds    
EBP, Master Trust [Line Items]    
Investments at fair value 1,396,890 1,230,279
Unfunded Commitment 0 0
Plan interest in Master Trust | Vanguard Master Trust    
EBP, Master Trust [Line Items]    
Investments at fair value 3,413,123 3,364,044
Plan interest in Master Trust | Vanguard Master Trust | Total Fair Value    
EBP, Master Trust [Line Items]    
Investments at fair value   630,038
Plan interest in Master Trust | Vanguard Master Trust | Level 1    
EBP, Master Trust [Line Items]    
Investments at fair value   630,038
Plan interest in Master Trust | Vanguard Master Trust | Level 2    
EBP, Master Trust [Line Items]    
Investments at fair value   0
Plan interest in Master Trust | Vanguard Master Trust | Collective investment trusts (measured at NAV)    
EBP, Master Trust [Line Items]    
Investments at fair value 3,413,123 2,734,006
Plan interest in Master Trust | Vanguard Master Trust | Collective investment trusts (measured at NAV) | Investments measured at NAV    
EBP, Master Trust [Line Items]    
Investments at fair value   2,734,006
Plan interest in Master Trust | Vanguard Master Trust | Mutual funds    
EBP, Master Trust [Line Items]    
Investments at fair value 0 630,038
Plan interest in Master Trust | Vanguard Master Trust | Mutual funds | Total Fair Value    
EBP, Master Trust [Line Items]    
Investments at fair value   630,038
Plan interest in Master Trust | Vanguard Master Trust | Mutual funds | Level 1    
EBP, Master Trust [Line Items]    
Investments at fair value   630,038
Plan interest in Master Trust | Vanguard Master Trust | Mutual funds | Level 2    
EBP, Master Trust [Line Items]    
Investments at fair value   0
Plan interest in Master Trust | Vanguard Master Trust | Retirement date funds    
EBP, Master Trust [Line Items]    
Investments at fair value 2,016,233 1,503,727
Unfunded Commitment 0 0
Plan interest in Master Trust | Vanguard Master Trust | Index funds    
EBP, Master Trust [Line Items]    
Investments at fair value 1,396,890 1,230,279
Unfunded Commitment $ 0 $ 0