DESCRIPTION OF THE PLAN (Details) - EBP 055 - USD ($)	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024
EBP, Description of Plan [Line Items]
Maximum annual participant pre-tax contribution rate, as percentage of compensation (percent)	75.00%
Participant automatic deferral rate (percent)	1.00%
Company's match (percent)	50.00%
Eligible compensation contributed by Participant that is matched (percent)	6.00%
Company's match allocation to participant's selected investment allocations (percent)	50.00%
Company's match allocation to AECOM common stock (percent)	50.00%
Participant vesting period in employer contributions	3 years
Forfeited non-vested accounts used to reduce future employer contributions and / or pay administrative expenses of the Plan	$ 1,200,000
EBP, Forfeited Nonvested Account	0	$ 0
Minimum loan amount	1,000
Participant loan limit	$ 50,000
Participant loan limit as a percentage of vested account balance (percent)	50.00%
Loan interest rate, spread on prime rate (percent)	1.00%
Minimum
EBP, Description of Plan [Line Items]
Interest rate on participant loans (percent)	4.25%
Loan repayment period (up to)	5 years
Maximum
EBP, Description of Plan [Line Items]
Interest rate on participant loans (percent)	9.50%
Loan repayment period (up to)	20 years

EBP, Employee Benefit Plan, Employer Contribution Matching Percent, Company Stock Allocation

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- Definition

EBP, Employee Benefit Plan, Employer Contribution Matching Percent, Participant Allocation

+ References

No definition available.

+ Details

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- Definition

EBP, Employer Contribution Vesting Service Period

+ References

No definition available.

+ Details

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- Definition

EBP, Forfeited Nonvested Account, Decrease From Administrative Expense And Employer Contributions

+ References

No definition available.

+ Details

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- Definition

EBP, Note Receivable from Participant, Account, Maximum Repayment Period

+ References

No definition available.

+ Details

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- Definition

EBP, Participant Contribution, Pretax, Maximum Annual Compensation To Eligible Bonus Compensation, Percentage

+ References

No definition available.

+ Details

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- Definition

EBP, Participant Loan, Basis Spread On Variable Rate

+ References

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

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- Definition

Percentage of employer matching contribution on eligible participant contribution to employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

+ Details

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- Definition

Percentage of participant compensation eligible for employer matching contribution for participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

+ Details

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- Definition

Amount of plan asset, in forfeited nonvested account, no longer allocated to participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 962
-SubTopic 325
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478873/962-325-55-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (j)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

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- Definition

Amount of maximum account balance that participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) can borrow.

+ References

+ Details

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- Definition

Percentage of maximum account balance that participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) can borrow to total participant account balance.

+ References

+ Details

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- Definition

Amount of minimum account balance that participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) can borrow.

+ References

+ Details

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- Definition

Percentage of eligible compensation contributed for participant automatically enrolled in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

+ Details

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- Definition

Interest rate on participant loan in schedule of asset held for investment of employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Employee Retirement Income Security Act of 1974
-Number 2520
-Section 103
-Subsection 10
-Paragraph b
-Subparagraph (1)(i)(D)
-Publisher DOL-EBSA

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6A-05(a)(Schedule I))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477804/962-205-S99-1

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