Accumulated Amortization Finite-Lived Intangible Assets, Accumulated Amortization Statistical Measurement [Domain] Statistical Measurement [Domain] Other current assets Other Current Assets [Member] Debt Instrument, Redemption, Period Four Debt Instrument, Redemption, Period Four [Member] Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Expected return on plan assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Int’l Foreign Plan [Member] Award Timing Predetermined Award Timing Predetermined [Flag] 2026 (six months remaining) Lessee, Operating Lease, Liability, to be Paid, Remainder of Fiscal Year Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Entity File Number Entity File Number Additional Paid-In Capital Additional Paid-in Capital [Member] Other non-current assets Other Noncurrent Assets [Member] Interest Rate Swap Interest Rate Swap [Member] Term extension Debt Instrument, Term Extension Debt Instrument, Term Extension Tax benefit related to income tax credits and incentives Effective Income Tax Rate Reconciliation, Tax Credit, Amount Investment Gains/(Losses) Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss) Equity in earnings of joint ventures Total Equity in earnings of joint ventures Income (Loss) from Equity Method Investments Tabular List, Table Tabular List [Table Text Block] Leases [Abstract] Leases [Abstract] Other Financial Information Additional Financial Information Disclosure [Text Block] New Accounting Pronouncements and Changes in Accounting New Accounting Pronouncements, Policy [Policy Text Block] Accounts payable Increase (Decrease) in Accounts Payable SOFR Secured Overnight Financing Rate (SOFR) [Member] Schedule of Balance Sheet of Assets and Liabilities Held for Sale and Income Statement and Cash Flow Information of Discontinued Operations Disposal Groups, Including Discontinued Operations [Table Text Block] Contract assets Contract with Customer, Asset, after Allowance for Credit Loss, Current Type of Restructuring [Domain] Type of Restructuring [Domain] Gross book-tax differences from non-U.S. subsidiaries Undistributed Earnings of Foreign Subsidiaries Backlog and Customer relationships Backlog And Customer Relationships [Member] Backlog and Customer relationship that exists between an entity and its customer, for example, but not limited to, tenant relationships. Goodwill [Line Items] Goodwill [Line Items] Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Basic earnings per share (in dollar per share) Earnings Per Share, Basic Adjustment to Compensation: Adjustment to Compensation [Axis] Income attributable to noncontrolling interests from continuing operations Income (Loss) Attributable To Non-Controlling Interests, Continuing Operations Income (Loss) Attributable To Non-Controlling Interests, Continuing Operations Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Net income attributable to noncontrolling interests from discontinued operations Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Noncontrolling Interest Revenue Recognition Revenue from Contract with Customer [Text Block] Non-cash net fair value (gains) losses Non-Cash Gain (Loss) In Net Fair Value Non-Cash Gain (Loss) In Net Fair Value Commitment period (in years) Long-Term Purchase Commitment, Period Other comprehensive (loss) income, net of tax Other comprehensive loss Other Comprehensive Income (Loss), Net of Tax Gain (loss) recorded representing increase in fair value Fair Value, Option, Changes in Fair Value, Gain (Loss) Other joint ventures Corporate Joint Venture [Member] Schedule of Financial Information Concerning the Company's Reportable Segments Schedule of Segment Reporting Information, by Segment [Table Text Block] Diluted discontinued operations per share (in dollar per share) Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share Short-term debt Short-Term Debt Interest Rate Cap Interest Rate Cap [Member] Debt Instrument, Redemption, Period [Axis] Debt Instrument, Redemption, Period [Axis] Transaction price, allocated Revenue, Remaining Performance Obligation, Amount 2033 Senior Notes 2033 Senior Notes [Member] 2033 Senior Notes Adjustment to Compensation, Amount Adjustment to Compensation Amount Additional fees on changed work scope Construction Contractor, Contract Cost, Subject to Uncertainty, Amount Revenue, remaining performance obligation (as percent) Revenue, Remaining Performance Obligation, Percentage Non-cash stock compensation Share-Based Payment Arrangement, Noncash Expense 2029 Finance Lease, Liability, to be Paid, Year Three February 2023 February 2023 [Member] Represents February 2023 effective date. Employee Stock Option Share-Based Payment Arrangement, Option [Member] Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Category of Item Purchased [Axis] Category of Item Purchased [Axis] Equity in losses of joint ventures Disposal Group, Including Discontinued Operations, Income (Loss) From Equity Method Investments Amount of income (loss) for proportionate share of equity method investee's income (loss), attributable to disposal group, including, but not limited to, discontinued operation. Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Consolidated Joint Ventures Variable Interest Entity, Primary Beneficiary [Member] Dividends declared Dividends, Common Stock, Cash TOTAL AECOM STOCKHOLDERS’ EQUITY Total AECOM deficit Equity, Attributable to Parent Other comprehensive (loss) income, net of tax: Other Comprehensive Income (Loss), Net of Tax [Abstract] Insider Trading Policies and Procedures [Line Items] Compensation expense related to share-based payments Share-Based Payment Arrangement, Expense Common stock, shares authorized (in shares) Common Stock, Shares Authorized Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Hedging Designation [Domain] Hedging Designation [Domain] Surety Bond Surety Bond [Member] CURRENT ASSETS: Assets, Current [Abstract] TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY Total liabilities and owners’ equity Liabilities and Equity Pension Related Adjustments Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Amortization of Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Amortization of Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD CASH AND CASH EQUIVALENTS AT END OF PERIOD Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Including Discontinued Operation LIABILITIES AND STOCKHOLDERS’ EQUITY Liabilities and Equity [Abstract] Cover [Abstract] Cover [Abstract] Maximum Maximum Maximum [Member] Amortization Period (in years) Finite-Lived Intangible Asset, Useful Life Net income attributable to noncontrolling interests Net Income (Loss) Attributable to Noncontrolling Interest INTANGIBLE ASSETS—NET Intangible Assets, Net Finite-Lived Intangible Assets, Net Schedule of Operating Lease, Liability, to be Paid, Maturity Lessee, Operating Lease, Liability, to be Paid, Maturity [Table Text Block] Income Tax Contingency [Line Items] Income Tax Contingency [Line Items] Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Debt Instrument [Line Items] Debt Debt Instrument [Line Items] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Schedule of Restricted Stock Units and PEP Units Activity Share-Based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block] Net income from continuing operations Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Percentage of claim recoveries due to purchaser Percentage Of Claim Recoveries And Costs Due To Purchaser Percentage of claim recoveries and costs due to purchaser. Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Pay vs Performance Disclosure [Line Items] Schedule of Notional Principle, Fixed Rates and Expiration Dates of Outstanding Interest Rate Swap Agreements Schedule of Notional Amounts and Fixed Rates and Expiration Dates of Outstanding Derivative Positions [Table Text Block] Tabular disclosure of the notional amounts, fixed rates and related expiration dates of outstanding derivative positions. Total lease liabilities Operating Lease, Liability Retirement Benefits [Abstract] Retirement Benefits [Abstract] Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Debt Instrument, Redemption, Period One Debt Instrument, Redemption, Period One [Member] Liabilities: Liabilities [Abstract] Percentage of claim recoveries due to seller Percentage Of Claim Recoveries And Costs Due To Seller Percentage of claim recoveries and costs due to seller. Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Amortization expense Depreciation, Depletion and Amortization, Nonproduction Amortization of right-of-use assets Finance Lease, Right-of-Use Asset, Amortization Income from continuing operations before taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Entity Shell Company Entity Shell Company Redemption price, percentage of principal amount redeemed Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed OTHER LONG-TERM LIABILITIES Other Liabilities, Noncurrent Debt Instrument, Redemption, Period After Five Years Debt Instrument, Redemption, Period After Five Years [Member] Debt Instrument, Redemption, Period After Five Years Schedule of Long-Term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Proceeds from disposal of property and equipment Proceeds from Sale of Property, Plant, and Equipment Proceeds from borrowings under credit agreements Proceeds from Issuance of Debt Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Insurance Type and Tier Identifier [Axis] Insurance Type and Tier Identifier [Axis] Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Debt Instrument, Redemption, Period [Domain] Debt Instrument, Redemption, Period [Domain] Credit Agreement Credit Agreement [Member] Represents information pertaining to Credit Agreement. Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Operating Segments Operating Segments [Member] Gross profit (loss) Disposal Group, Including Discontinued Operation, Gross Profit (Loss) Variable Interest Entity [Table] Variable Interest Entity [Table] Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Company Selected Measure Amount Company Selected Measure Amount 2029 Lessee, Operating Lease, Liability, to be Paid, Year Three Total amounts of employer contributions paid Defined Benefit Plan, Plan Assets, Contributions by Employer Noncontrolling interests in comprehensive income of consolidated subsidiaries, net of tax Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Comprehensive income attributable to AECOM, net of tax Comprehensive Income (Loss), Net of Tax, Attributable to Parent Name Measure Name Accrued restructuring expenses Restructuring Reserve Net income attributable to AECOM from continuing operations Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent Net distributions to noncontrolling interests Payments to Noncontrolling Interests Tax benefit related to deferred tax assets resulting from legal entity restructuring Effective Income Tax Rate Reconciliation, Nondeductible Expense, Restructuring Charges, Amount Operating lease liabilities Operating Lease, Liability, Current Interest on lease liabilities Finance Lease, Interest Expense DEFERRED TAX LIABILITY-NET Deferred Income Tax Liabilities, Net Document Fiscal Period Focus Document Fiscal Period Focus Net loss attributable to AECOM from discontinued operations Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent PEP units earned (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Earned in Period, Weighted Average Grant Date Fair Value The weighted average fair value at grant date for non-vested equity-based awards earned during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). Unsecured Unsecured Debt [Member] Award Timing Method Award Timing Method [Text Block] Equity in earnings of unconsolidated joint ventures Income (Loss) from Equity Method Investments Including Discontinued Operations Income (Loss) from Equity Method Investments Including Discontinued Operations Basic continuing operations per share (in dollar per share) Income (Loss) from Continuing Operations, Per Basic Share Award Type Award Type [Axis] Foreign Currency Translation Adjustments Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Hedging Relationship [Domain] Hedging Relationship [Domain] Legal Entity [Axis] Legal Entity [Axis] TOTAL ASSETS Total assets Assets 2027 Finite-Lived Intangible Asset, Expected Amortization, Year One Trading Symbol Trading Symbol 2030 Lessee, Operating Lease, Liability, to be Paid, Year Four Vested (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Geographical [Domain] Geographical [Domain] Passed through costs included in revenue and cost of sales Passed Through Cost in Revenue and Cost The costs of subcontracts for services and other direct costs incurred by the entity on behalf of its clients. These costs are passed through to clients and included in revenue and cost of revenue. Operating Loss Carryforwards [Table] Operating Loss Carryforwards [Table] Entity Address, City or Town Entity Address, City or Town CASH FLOWS FROM OPERATING ACTIVITIES: Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Finance leases (as percent) Finance Lease, Weighted Average Discount Rate, Percent Other segment items Segment Reporting, Other Segment Item, Amount Digital assets Digital Assets [Member] Digital Assets Maturity [Axis] Maturity [Axis] Maturity Americas Americas Americas Segment [Member] This member pertains to Americas segment. Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Restricted Stock Units Restricted Stock Units (RSUs) [Member] Effect of deconsolidation of a joint venture Noncontrolling Interest, Decrease from Deconsolidation Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Total consideration Business Combination, Consideration Transferred Loss from reduction in expected future net cash proceeds Loss Contingency, Damages Awarded, Value Joint Ventures and Variable Interest Entities [Line Items] Variable Interest Entity [Line Items] 2030 Finite-Lived Intangible Asset, Expected Amortization, Year Four Entity Emerging Growth Company Entity Emerging Growth Company 2029 Long-Term Debt, Maturity, Year Three Cash dividends declared (in dollars per share) Common Stock, Dividends, Per Share, Declared 2027 Finance Lease, Liability, to be Paid, Year One Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding AECOM Capital AECOM Capital Segment [Member] Represents information pertaining to AECOM Capital (ACAP). Right-of-use assets obtained in exchange for new operating leases Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Finance leases (in years) Finance Lease, Weighted Average Remaining Lease Term Billed Billed Contracts Receivable Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Significant Observable Inputs (Level 2) Fair Value, Inputs, Level 2 [Member] Less: Unamortized debt issuance costs Debt Issuance Costs, Net Tax expense related to state income taxes Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount Equity method investment Equity Method Investments Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Business Combination [Domain] Business Combination [Domain] Other Financials Information [Line Items] Other Financials Information [Line Items] 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. Non-cash loss on disposal activities Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal Operating Leases Lessee, Operating Lease, Liability, to be Paid, Fiscal Year Maturity [Abstract] Less: Amounts representing interest Finance Lease, Liability, Undiscounted Excess Amount Common stock, shares outstanding (in shares) Common Stock, Shares, Outstanding PEO PEO [Member] Schedule of Revenues Disaggregated by Revenue Sources Disaggregation of Revenue [Table Text Block] Labor-Related Costs Employee Severance [Member] Interest income Interest income Investment Income, Interest Foreign currency translation Unrealized Gain (Loss), Foreign Currency Transaction, before Tax Total net assets at fair value Fair Value, Net Asset (Liability) U.S. UNITED STATES Changes in operating assets and liabilities, net of effects of acquisitions: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Schedule of Future Amortization Expense of Intangible Assets Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Accumulated Deficits Retained Earnings [Member] Prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Units Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Effective interest rate (as percent) Debt Instrument, Interest Rate, Effective Percentage Schedule of Accrued Expenses and Other Current Liabilities Schedule of Accrued Liabilities [Table Text Block] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Restatement Determination Date Restatement Determination Date Share-Based Payment Arrangement [Abstract] Share-Based Payment Arrangement [Abstract] Income Statement [Abstract] Income Statement [Abstract] Derivative Asset Derivative Asset Income tax expense for continuing operations Income Tax Expense (Benefit) Non-Labor Facility Closing [Member] Interest rate, basis spread (as percent) Debt Instrument, Basis Spread on Variable Rate Basic discontinued operations per share (in dollar per share) Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share Accounts receivable and contract assets Increase (Decrease) in Accounts Receivable and Contract Assets The amount of increase (decrease) in accounts receivable and contract assets) Income taxes payable Taxes Payable, Current Beginning Balance Ending Balance Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Designated as Hedging Instrument Designated as Hedging Instrument [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Hedging Relationship [Axis] Hedging Relationship [Axis] Net unrealized gain (loss) on derivatives, net of tax Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax Noncash decrease in noncontrolling interest due to deconsolidation of a joint venture Disposal Groups, Including Discontinued Operations, Noncash Decrease In Noncontrolling Interest Disposal Groups, Including Discontinued Operations, Noncash Decrease In Noncontrolling Interest Diluted continuing operations per share (in dollar per share) Income (Loss) from Continuing Operations, Per Diluted Share Total AECOM Stockholders’ Equity Parent [Member] Net income Net income Net income Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Held for Sale Discontinued Operations, Held-for-Sale [Member] Notional Amount Notional value Derivative, Notional Amount Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Schedule of Debt Instrument Redemption Debt Instrument Redemption [Table Text Block] Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] City Area Code City Area Code Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] All Trading Arrangements All Trading Arrangements [Member] Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Redemption price (as percent) Debt Instrument, Redemption Price, Percentage Accrued expenses and other current liabilities Total Accrued Liabilities, Current USD USD United States of America, Dollars United States of America, Dollars Outstanding at beginning (in units) Outstanding at ending (in units) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Legal Entity of Counterparty, Type [Axis] Legal Entity of Counterparty, Type [Axis] CASH FLOWS FROM INVESTING ACTIVITIES: Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] General and administrative expenses General and Administrative Expense Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Net cash provided by operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation 2027 Senior Notes 2027 Senior Notes [Member] Represents information pertaining to 2027 Senior Notes. Accrued contract costs Accrued contract costs including professional liability accruals Accrued Contract Costs, Current Carrying value as of the balance sheet date of obligations incurred through that date and payable for obligations related to professional liability and costs for services provided by subcontractors and other non-employees. It is used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle, whichever is longer). Collections Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales Amortization of net loss (gain) Defined Benefit Plan, Amortization of Gain (Loss) Total lease cost Lease, Cost Equity Method Investment, Nonconsolidated Investee or Group of Investees Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member] Equity investment Equity Securities, FV-NI Cash Flow Hedging Cash Flow Hedging [Member] GOODWILL Goodwill, beginning balance Goodwill, ending balance Goodwill Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] Contingently liable for issuance of standby letters of credit and surety bonds Loss Contingency, Estimate of Possible Loss Schedule of Components of Lease Expenses Lease, Cost [Table Text Block] PEO Total Compensation Amount PEO Total Compensation Amount Long-Term Debt, Type [Axis] Long-Term Debt, Type [Axis] Debt Instrument, Redemption, Period Three Debt Instrument, Redemption, Period Three [Member] 2030 Finance Lease, Liability, to be Paid, Year Four 2026 (six months remaining) Finite-Lived Intangible Asset, Expected Amortization, Remainder of Fiscal Year Equity Components [Axis] Equity Components [Axis] Total Consolidated Entities [Member] Standby Letters of Credit Standby Letters of Credit [Member] Maximum project cost to pay Project Cost Liability Amount, Upper Range Limit The ceiling amount of project costs the entity is liable for. Discontinued Operations, Goodwill, and Intangible Assets Discontinued Operations, Goodwill, and Intangible Assets [Abstract] No definition available. Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Schedule of Additional Balance Sheet Information Related to Leases Assets And Liabilities, Lessee [Table Text Block] Assets And Liabilities, Lessee Number of reportable segments Number of Reportable Segments Contract with Customer, Basis of Pricing [Axis] Contract with Customer, Basis of Pricing [Axis] Thereafter Long-Term Debt, Maturity, after Year Four Long-Term Debt, Maturity, after Year Four Other Performance Measure, Amount Other Performance Measure, Amount Less: Current portion of debt and short-term borrowings Debt, Current Cash paid for debt issuance costs Payments of Debt Issuance Costs Entity Address, State or Province Entity Address, State or Province Financing cash flows from finance leases Finance Lease, Principal Payments NON - CURRENT ASSETS HELD FOR SALE Noncurrent assets held for sale Disposal Group, Including Discontinued Operation, Assets, Noncurrent Related and Nonrelated Parties [Domain] Related and Nonrelated Parties [Domain] TOTAL CURRENT LIABILITIES Current liabilities Current liabilities Liabilities, Current Other current liabilities Other Current Liabilities [Member] Long-Term Purchase Commitment, Category of Item Purchased [Domain] Long-Term Purchase Commitment, Category of Item Purchased [Domain] Derivative Instrument [Axis] Derivative Instrument [Axis] Individual: Individual [Axis] Former Affiliate and DOE Department of Energy and Amentum Environment & Energy, Inc. [Member] Represents the Department of Energy and Amentum Environment & Energy, Inc., f/k/a AECOM Energy and Construction, Inc, a former affiliate of the reporting entity. Leases Lessee, Finance Leases [Text Block] Right-of-use assets obtained in exchange for new finance leases Right-of-Use Asset Obtained in Exchange for Finance Lease Liability Entity [Domain] Entity [Domain] Net cash used in investing activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation INVESTMENTS IN UNCONSOLIDATED JOINT VENTURES AECOM’s investment in unconsolidated joint ventures Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures Revenue, performance obligation expected timing of satisfaction period Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table [Member] Document Fiscal Year Focus Document Fiscal Year Focus Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] OPERATING LEASE RIGHT-OF-USE ASSETS Operating lease assets Operating Lease, Right-of-Use Asset Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Effective tax rate (as percent) Effective Income Tax Rate Reconciliation, Percent Entity Interactive Data Current Entity Interactive Data Current Operating lease cost Operating Lease, Cost Equity Method Investment, Nonconsolidated Investee [Axis] Equity Method Investment, Nonconsolidated Investee [Axis] Recognition period of unrecognized compensation expense (in years) Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Reportable Segments Segment Reporting Disclosure [Text Block] Goodwill [Table] Goodwill [Table] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Noncash increase in noncurrent assets held for sale due to deconsolidation of a joint venture Disposal Groups, Including Discontinued Operations, Noncash Increase In Noncurrent Assets Held For Sale Discontinued Operation, Noncash Increase In Noncurrent Assets Held For Sale Current portion of long-term debt Long-Term Debt and Lease Obligation, Current Total debt Total debt Debt and Lease Obligation Increase (Decrease) in Stockholders' Equity Increase (Decrease) in Stockholders' Equity [Roll Forward] Retirement Plan Sponsor Location [Axis] Retirement Plan Sponsor Location [Axis] Finite-Lived Intangible Assets [Line Items] Finite-Lived Intangible Assets [Line Items] Department of Energy Government [Member] Schedule of Components of Net Periodic Cost for Pension Plans Schedule of Net Benefit Costs [Table Text Block] Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] Contingent Consideration Business Combination, Contingent Consideration, Liability Reclassifications out of Accumulated Other Comprehensive Loss Comprehensive Income (Loss) Note [Text Block] 2028 Finance Lease, Liability, to be Paid, Year Two Cost of revenue Disposal Group, Including Discontinued Operation, Costs of Goods Sold Amortization expense of acquired intangible assets Amortization of Intangible Assets DEFERRED TAX ASSETS—NET Deferred Income Tax Assets, Net Schedule of Accumulated Balances and Reporting Period Activities Related to Reclassifications Out of Accumulated Other Comprehensive Loss Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Depreciation and amortization Depreciation, Depletion and Amortization OTHER NON-CURRENT ASSETS Other Assets, Noncurrent Entity Central Index Key Entity Central Index Key Credit facility investment Fixed Income Investments [Member] PEO Name PEO Name Schedule of Maturities of Debt Schedule of Maturities of Long-Term Debt [Table Text Block] Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year [Member] Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Fixed-price Fixed-Price Contract [Member] Revolving Credit Facility Revolving Credit Facility [Member] Defined Benefit Plan [Table] Defined Benefit Plan [Table] Total lease liabilities Finance Lease, Liability Arrangement Duration Trading Arrangement Duration Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] FY 2025 Fourth Quarter Acquisition FY 2025 Fourth Quarter Acquisition [Member] FY 2025 Fourth Quarter Acquisition Contract liabilities Contract with Customer, Liability, Current Segments [Axis] Segments [Axis] Refinery Turnaround Project Refinery Turnaround Project Represents information pertaining to refinery turnaround project. Schedule of Financial Assets and Liabilities Recorded at Fair Value on a Recurring Basis Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Exercise Price Award Exercise Price Entity Filer Category Entity Filer Category Local Phone Number Local Phone Number Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Total accounts receivable—gross Accounts Receivable, before Allowance for Credit Loss, Current Tax at federal statutory rate (as percent) Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Other investing activities Payment for (Proceeds from) Other Investing Activity Share-based Payments Share-Based Payment Arrangement [Text Block] Debt instrument, floor rate (as percent) Debt Instrument, Floor Rate The floor rate of debt instrument. Guaranteed maximum price Guaranteed Maximum Price Contract [Member] Represents information pertaining to GMP which are common types of contracts for design-build and commercial and residential projects. ASSETS Assets: Assets [Abstract] Credit Facility [Axis] Credit Facility [Axis] Underlying Security Market Price Change Underlying Security Market Price Change, Percent Statement of Financial Position Location, Balance [Axis] Statement of Financial Position Location, Balance [Axis] 2029 Finite-Lived Intangible Asset, Expected Amortization, Year Three Debt Instrument [Axis] Debt Instrument [Axis] Joint Ventures and Variable Interest Entities Joint Ventures and Variable Interest Entities Disclosure [Text Block] Disclosure of the entity's joint ventures and variable interest entities (VIE), including, but not limited to the nature, purpose, size, and activities of the VIE, the carrying amount and classification of consolidated assets that are collateral for the VIE's obligations, lack of recourse if creditors (or beneficial interest holders) of a consolidated VIE have no recourse to the general credit of the primary beneficiary. An enterprise that holds a significant variable interest in a VIE but is not the primary beneficiary may disclose the nature of its involvement with the VIE and when that involvement began, the nature, purpose, size, and activities of the VIE and the enterprise's maximum exposure to loss as a result of its involvement with the VIE. Pension Benefit Obligations Retirement Benefits [Text Block] Payments for capital expenditures Capital Expenditure, Discontinued Operations Gross Amount Finite-Lived Intangible Assets, Gross Credit Facility [Domain] Credit Facility [Domain] AECOM STOCKHOLDERS’ EQUITY: Equity, Attributable to Parent [Abstract] Cash and cash equivalents Cash and Cash Equivalents, General The amount of currency on hand as well as demand deposits with banks or financial institutions, excluding cash in consolidated joint ventures. Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] Legal Entity Type of Counterparty [Domain] Legal Entity Type of Counterparty [Domain] Entity Address, Address Line One Entity Address, Address Line One Cash paid for amounts included in the measurement of lease liabilities: Cash Flow, Lessee [Abstract] No definition available. Accumulated Other Comprehensive Loss Accumulated Other Comprehensive Loss AOCI Attributable to Parent [Member] Interest rate (as percent) Debt Instrument, Interest Rate, Stated Percentage Allowance for doubtful accounts and credit losses Accounts Receivable, Allowance for Credit Loss, Current Investments [Domain] Investments [Domain] Loss from operations Disposal Group, Including Discontinued Operation, Operating Income (Loss) OPERATING LEASE LIABILITIES, NON-CURRENT Operating lease liabilities Operating Lease, Liability, Noncurrent Derivative Financial Instruments and Fair Value Measurements Derivative Instruments and Hedging Activities Disclosure [Text Block] Americas Americas [Member] Trade receivables sold with no financial and legal obligations Trade Receivables, Sold, No Financial and Legal Obligations The amount of trade receivables sold, which the entity does not retain financial and legal obligations, at reporting date. Basis of presentation Discontinued Operations, Goodwill and Intangible Assets [Line Items] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Restructuring and acquisition costs Restructuring and acquisition costs Restructuring and acquisition costs Restructuring, Settlement and Impairment Provisions Fair Value as of Grant Date Award Grant Date Fair Value Entity Registrant Name Entity Registrant Name General and administrative expenses General and Administrative Expense, Adjusted General and Administrative Expense, Adjusted Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Net periodic benefit cost (credit) Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Employee compensation expense Employee Benefits and Share-Based Compensation Deferred tax asset recognized Effective Income Tax Rate Reconciliation, Tax Contingency, Amount Granted (in units) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period Unrecognized compensation expense Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Debt Instrument, Redemption, Period Two Debt Instrument, Redemption, Period Two [Member] Type and Tier Identifier [Domain] Type and Tier Identifier [Domain] Document Quarterly Report Document Quarterly Report Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Consolidated leverage ratio Ratio of Indebtedness to Net Capital 2028 Lessee, Operating Lease, Liability, to be Paid, Year Two Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Accounting Standards Update and Change in Accounting Principle [Abstract] Accounting Standards Update and Change in Accounting Principle [Abstract] Schedule of Debt Schedule of Debt [Table Text Block] Investment Type [Axis] Investment Type [Axis] Joint Ventures and Variable Interest Entities Joint Ventures and Variable Interest Entities [Abstract] Joint Ventures and Variable Interest Entities Granted (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Interest cost on projected benefit obligation Defined Benefit Plan, Interest Cost Related and Nonrelated Parties [Axis] Related and Nonrelated Parties [Axis] Title Trading Arrangement, Individual Title Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Term Loan B Facility Term Loan B Facility [Member] Term Loan B Facility Other long-term liabilities Other Noncurrent Liabilities [Member] Schedule of Gross Amount and Accumulated Amortization of Identifiable Intangible Assets with Finite Useful Lives Schedule of Finite-Lived Intangible Assets [Table Text Block] Restatement Determination Date: Restatement Determination Date [Axis] Non-PEO NEO Non-PEO NEO [Member] Outstanding standby letters of credit Letters of Credit Outstanding, Amount Loss on disposal activities Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Contributions from noncontrolling interests Noncontrolling Interest, Increase from Subsidiary Equity Issuance Other financing activities Proceeds from (Payment for) Other Financing Activity Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Amounts reclassified from accumulated other comprehensive (loss) income Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax All Currencies [Domain] All Currencies [Domain] Name Trading Arrangement, Individual Name Minimum project cost to pay Project Cost Liability Amount, Lower Range Limit The floor amount of project costs the entity is liable for. All Award Types Award Type [Domain] 2027 Lessee, Operating Lease, Liability, to be Paid, Year One Significant claims recorded in contract assets and other non-current assets Contract Claims Recorded in Contract Assets and Other Noncurrent Assets The amounts in excess of the agreed contract price (or amounts not included in the original contract price) that the company seeks to collect from customers or others for delays, errors in specifications and designs, contract terminations, change orders in dispute or unapproved as to both scope and price or other causes of unanticipated additional costs recorded in contract assets and other non current assets. Joint ventures summarized financial information Variable Interest Entity, Measure of Activity [Abstract] Contract with Customer, Basis of Pricing [Domain] Contract with Customer, Basis of Pricing [Domain] Total lease assets Right Of Use Assets Aggregate a of lessee's right to use underlying asset under operating and finance lease. Noncontrolling interests Noncontrolling interests Equity, Attributable to Noncontrolling Interest Equity Awards Adjustments Equity Awards Adjustments [Member] Other Other Noncash Income (Expense) Cost reimbursable Cost Reimbursable Contract [Member] Represents information pertaining to two similar contract types: 1 cost-plus contracts and 2 time and materials price contracts. Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Capital commitments Long-Term Purchase Commitment, Amount Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Compensation Amount Outstanding Recovery Compensation Amount Professional Liability Accrual Professional Malpractice Liability Insurance [Member] Aggregate principal amount Debt Instrument, Face Amount Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Statement of Comprehensive Income [Abstract] Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Contract liabilities, revenue recognized Contract with Customer, Liability, Revenue Recognized Income tax benefit Discontinued Operation, Tax Effect of Discontinued Operation MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Name Awards Close in Time to MNPI Disclosures, Individual Name AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] Outstanding at beginning (in dollars per share) Outstanding at ending (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Restructuring Type [Axis] Restructuring Type [Axis] Segment, Reconciliation of Other Items from Segments to Consolidated [Line Items] Segment, Reconciliation of Other Items from Segments to Consolidated [Line Items] Gain related to contingent consideration issued Business Combination, Contingent Consideration, Change in Contingent Consideration, Liability, Increase (Decrease) Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] 2026 (six months remaining) Finance Lease, Liability, to be Paid, Remainder of Fiscal Year Credit facility investment Alternative Investment Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Make-whole payment Payment For Debt Redemption, Make-Whole Portion Payment For Debt Redemption, Make-Whole Portion Stock-based compensation APIC, Share-Based Payment Arrangement, Increase for Cost Recognition Schedule of Finance Lease, Liability, to be Paid, Maturity Finance Lease, Liability, to be Paid, Maturity [Table Text Block] Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax LONG-TERM DEBT Long-term debt Long-Term Debt and Lease Obligation 2027 Long-Term Debt, Maturity, Year One Retirement Plan Sponsor Location [Domain] Retirement Plan Sponsor Location [Domain] Financial Instruments [Domain] Financial Instruments [Domain] Contract retentions Receivables, Long-Term Contracts or Programs Cash outflow from deconsolidation of a joint venture Cash Divested from Deconsolidation Loans Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases Segments [Domain] Segments [Domain] Damages sought Loss Contingency, Damages Sought, Value Non-current assets Non-current assets Assets, Noncurrent Europe, Middle East, India, Africa EMEA [Member] PEP Units PEP Units Performance Shares [Member] Current borrowing capacity Amount available under unsecured credit facilities Line of Credit Facility, Remaining Borrowing Capacity Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Statement of Financial Position Location, Balance [Domain] Statement of Financial Position Location, Balance [Domain] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Minimum Minimum Minimum [Member] Post-Acquisition Adjustments Goodwill, Measurement Period Adjustment Company Selected Measure Name Company Selected Measure Name Senior Notes Senior Notes [Member] Other Financial Information Other Financial Information [Abstract] Other Financial Information Debt Debt Disclosure [Text Block] Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Accounts payable Accounts Payable, Current Operating cash flows from operating leases Operating Lease, Payments Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Accrued and unpaid dividend Dividends Payable All Executive Categories All Executive Categories [Member] Common stock-authorized, 300,000,000 shares of $0.01 par value as of March 31, 2026 and September 30, 2025; issued and outstanding 128,201,913 and 131,782,371 shares as of March 31, 2026 and September 30, 2025, respectively Common Stock, Value, Issued Finance lease assets Finance Lease, Right-of-Use Asset, after Accumulated Amortization Goodwill [Roll Forward] Goodwill [Roll Forward] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Revenue Disposal Group, Including Discontinued Operation, Revenue Stock consideration Business Combination, Consideration Transferred, Equity Interest, Share Issued, Value Term Loan A Facility Term Loan A Facility [Member] Term Loan A Facility Diluted (in shares) Denominator for diluted earnings per share (in shares) Weighted Average Number of Shares Outstanding, Diluted COMMITMENTS AND CONTINGENCIES (Note 15) Commitments and Contingencies Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Derivative [Table] Derivative [Table] Business Combination [Axis] Business Combination [Axis] Comprehensive income, net of tax Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Entity Small Business Entity Small Business Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Non- Controlling Interests Noncontrolling Interest [Member] Thereafter Lessee, Operating Lease, Liability, to be Paid, Due after Year Four Lessee, Operating Lease, Liability, to be Paid, Due after Year Four Document Transition Report Document Transition Report Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] New Accounting Pronouncements and Changes in Accounting Accounting Standards Update and Change in Accounting Principle [Text Block] Total lease payments Finance Lease, Liability, to be Paid Underlying Securities Award Underlying Securities Amount Equity Component [Domain] Equity Component [Domain] Document Period End Date Document Period End Date PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Income Taxes Income Tax Disclosure [Text Block] Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] Hedging Designation [Axis] Hedging Designation [Axis] Estimated fair value Debt Instrument, Fair Value Disclosure Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] TOTAL STOCKHOLDERS’ EQUITY Beginning balance Ending balance Total owners’ equity Joint ventures’ equity Equity, Including Portion Attributable to Noncontrolling Interest Weighted average remaining lease term (in years): Weighted Average Remaining Lease Term [Abstract] No definition available. Document Type Document Type Significant Unobservable Inputs (Level 3) Fair Value, Inputs, Level 3 [Member] Earnings Per Share Earnings Per Share [Text Block] Name Outstanding Recovery, Individual Name Loss Contingencies [Table] Loss Contingencies [Table] Pension adjustments, net of tax Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax Additional paid-in capital Additional Paid in Capital Derivative Contract [Domain] Derivative Contract [Domain] Domestic Plan Domestic Plan [Member] Other debt Other Debt Other Debt [Member] It represents the other debt member. Proceeds from issuance of common stock Proceeds from Issuance of Common Stock Variable lease cost Variable Lease, Cost Revenue Total revenue Total revenue of consolidated joint ventures Revenue from Contract with Customer, Excluding Assessed Tax All Individuals All Individuals [Member] Long-Term Debt, Type [Domain] Long-Term Debt, Type [Domain] Payments for capital expenditures Payments to Acquire Property, Plant, and Equipment Name Forgone Recovery, Individual Name TOTAL CURRENT ASSETS Current assets Current assets Assets, Current Statistical Measurement [Axis] Statistical Measurement [Axis] Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] Disposal Group Classification [Axis] Disposal Group Classification [Axis] Commitment fee on the unused portion of leverage ratio Line of Credit Facility, Unused Capacity, Commitment Fee Percentage Fixed Rate (as percent) Fixed interest rate (as percent) Derivative, Fixed Interest Rate Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Foreign Exchange Impact Goodwill, Foreign Currency Translation, Gain (Loss) Derivative, basis spread on variable rate (as percent) Derivative, Basis Spread on Variable Rate Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Standby Letters of Credit Financial Standby Letter of Credit [Member] Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Intangible Asset, Finite-Lived [Table] Intangible Asset, Finite-Lived [Table] Loss before taxes Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax CURRENT LIABILITIES: Current: Liabilities, Current [Abstract] Geographical [Axis] Geographical [Axis] Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Discontinued Operations, Goodwill and Intangible Assets Discontinued Operations, Goodwill and Intangible Assets [Text Block] Discontinued Operations, Goodwill and Intangible Assets Quoted Prices in Active Markets for Identical Assets (Level 1) Fair Value, Inputs, Level 1 [Member] Fund outflow in other investing activities and outstanding Long-Term Line of Credit Accrued expenses and other current liabilities Increase (Decrease) in Accrued Liabilities Asia-Australia-Pacific Asia Pacific [Member] Diluted earnings per share (in dollar per share) Earnings Per Share, Diluted Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Accounts receivable—net Total accounts receivable—net Accounts Receivable, after Allowance for Credit Loss, Current Title of 12(b) Security Title of 12(b) Security Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Expected remaining scheduled annual employer contributions for the current fiscal year Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year Tax expense related to foreign residual income Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Amount Task Order, Deactivation Demolition And Removal Service Task Order, Deactivation Demolition And Removal Services, New York [Member] Represents cost-reimbursable task order with the Department of Energy (DOE) in 2007 to provide deactivation, demolition and removal services at New York Sate project site. Net income (loss) attributable to AECOM per share: Earnings Per Share [Abstract] Earnings Per Share [Abstract] Consolidation Items [Domain] Consolidation Items [Domain] Derivative Liability, Statement of Financial Position [Extensible Enumeration] Derivative Liability, Statement of Financial Position [Extensible Enumeration] Return of investment in unconsolidated joint ventures Proceeds from Equity Method Investment, Distribution, Return of Capital Net loss from discontinued operations Net loss from discontinued operations Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Unconsolidated Joint Ventures Variable Interest Entity, Not Primary Beneficiary [Member] Gross profit Gross profit Gross Profit Repurchases of stock Stock Repurchased and Retired During Period, Value Contract liabilities Increase (Decrease) in Contract with Customer, Liability Segment, Reconciliation of Other Items from Segments to Consolidated [Table] Segment, Reconciliation of Other Items from Segments to Consolidated [Table] Investment commitment to fund Investment Commitment, Revolving Credit Facility Amount of investment obligation, to be paid to the borrower pursuant to revolving credit facility. Less: Amounts representing interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Expected Return (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Expected Return (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Tax Credit Carryforward [Axis] Tax Credit Carryforward [Axis] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] 2028 Finite-Lived Intangible Asset, Expected Amortization, Year Two Award Timing Disclosures [Line Items] Service costs Defined Benefit Plan, Service Cost Accrued salaries and benefits Employee-related Liabilities, Current Total lease payments Lessee, Operating Lease, Liability, to be Paid Other comprehensive (loss) income before reclassification Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Outstanding standby letters of credit Line of Credit Facility, Current Borrowing Capacity Distributions to noncontrolling interests Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Other Financials Information [Table] Other Financials Information [Table] Disclosure of information pertaining to financial information. Net income attributable to AECOM Net Income (Loss) Attributable to Parent Expiration Date Trading Arrangement Expiration Date Non-current: Liabilities, Noncurrent [Abstract] Equity Method Investment, Nonconsolidated Investee [Domain] Equity Method Investment, Nonconsolidated Investee [Domain] Other long-term liabilities Increase (Decrease) in Other Operating Liabilities Other accrued expenses Other Accrued Liabilities, Current Subcontractor and other direct costs Subcontractor and Other Direct Costs Subcontractor and Other Direct Costs Vesting period (in years) Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period Earnings before income taxes and amortization Total segment attributable earnings before taxes and amortization Earnings Before Interest Tax Depreciation And Amortization Earnings Before Interest Tax Depreciation And Amortization Schedule of Financial Information of Unconsolidated Joint Ventures Equity Method Investments [Table Text Block] PROPERTY AND EQUIPMENT—NET Property, Plant and Equipment, Net Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Payments to repurchase common stock Payments for Repurchase of Common Stock Adoption Date Trading Arrangement Adoption Date Maximum value of contingent consideration issued Business Combination, Contingent Consideration, Range of Outcomes, Maximum, Amount Base Rate Base Rate [Member] Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Total non-current lease liabilities Lease Liabilities, Noncurrent Present value of lessee's discounted obligation for lease payments from operating and finance lease, classified as non-current. Entity Current Reporting Status Entity Current Reporting Status Derivative [Line Items] Derivative [Line Items] Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Income from operations Operating Income (Loss) Consolidated Entities [Domain] Consolidated Entities [Domain] Accumulated deficits Retained Earnings (Accumulated Deficit) Financial Instrument [Axis] Financial Instrument [Axis] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Executive Category: Executive Category [Axis] Repayments of borrowings under credit agreements Repayments of Debt Finance lease liabilities Finance Lease, Liability, Current Maturity [Domain] maturity [Domain] maturity domain. Current Fiscal Year End Date Current Fiscal Year End Date Gain/(Loss) on Derivative Instruments Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table [Member] Schedule of Net Accounts Receivable Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Weighted Average Grant-Date Fair Value Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Statement [Table] Statement [Table] Other income (loss) Other income Other Nonoperating Income (Expense) Derivative Liability Derivative Liability Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract] Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract] EFFECT OF EXCHANGE RATE CHANGES ON CASH Effect of Exchange Rate on Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Including Discontinued Operation Adjustments to reconcile net income to net cash provided by operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] CASH FLOWS FROM FINANCING ACTIVITIES: Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] Net income attributable to noncontrolling interests from continuing operations Income (Loss) from Continuing Operations, Net of Tax, Attributable to Noncontrolling Interest Variable Rate [Domain] Variable Rate [Domain] Distribution of earnings from unconsolidated joint ventures Proceeds from Equity Method Investment, Distribution Finance lease liabilities Finance Lease, Liability, Noncurrent Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Weighted average discount rates: Weighted Average Discount Rates [Abstract] No definition available. Schedule of Changes in Fair Value of Level 3 Investment Assets Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Weighted average shares outstanding: Weighted Average Number of Shares Outstanding, Diluted [Abstract] All Adjustments to Compensation All Adjustments to Compensation [Member] Valuation allowance Tax Credit Carryforward, Valuation Allowance Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Amendment Flag Amendment Flag 2028 Long-Term Debt, Maturity, Year Two Leases Lessee, Operating Leases [Text Block] Termination Date Trading Arrangement Termination Date Net cash used in financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Measure: Measure [Axis] Operating leases (as percent) Operating Lease, Weighted Average Discount Rate, Percent Basic (in shares) Denominator for basic earnings per share (in shares) Weighted Average Number of Shares Outstanding, Basic Disposal Group Classification [Domain] Disposal Group Classification [Domain] Derivative Financial Instruments and Fair Value Measurements Derivative Financial Instruments and Fair Value Measurements [Abstract] Disclosure information pertaining to derivative instruments and fair value measurements. 2025 Acquisitions 2025 Acquisitions [Member] 2025 Acquisitions Number of business acquisitions Business Combination, Number of Businesses Acquired Segment Reporting [Abstract] Segment Reporting [Abstract] Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract] Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract] Cost of revenue Cost of revenue Cost of Revenue Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Debt Disclosure [Abstract] Debt Disclosure [Abstract] Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Amortization of deferred debt issuance costs Amortization of Debt Issuance Costs Entity Tax Identification Number Entity Tax Identification Number Credit facility investment including accrued interest Credit Facility Investment [Member] Credit Facility Investment Schedule of Financial Information of Consolidated Joint Ventures Schedule of Variable Interest Entities [Table Text Block] Finance lease cost: Finance Lease Costs [Abstract] No definition available. Deferred tax assets resulting from legal entity restructuring Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Restructuring Charges Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Consolidated Entities [Axis] Consolidated Entities [Axis] Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Schedule of Reconciliation of Denominators for Basic and Diluted Earnings Per Share Schedule of Weighted Average Number of Shares [Table Text Block] Common stock, shares issued (in shares) Common Stock, Shares, Issued Derivative Asset, Statement of Financial Position [Extensible Enumeration] Derivative Asset, Statement of Financial Position [Extensible Enumeration] Income taxes receivable Income Taxes Receivable, Current Operating leases (in years) Operating Lease, Weighted Average Remaining Lease Term 2030 Long-Term Debt, Maturity, Year Four Cash in consolidated joint ventures Cash in Consolidated Joint Ventures The amount of cash available for day-to-day operating needs of the consolidated joint venture. Total current lease liabilities Lease Liabilities, Current Present value of lessee's discounted obligation for lease payments from operating and finance lease, classified as current. Operating cash flows from finance leases Finance Lease, Interest Payment on Liability Dividends paid Payments of Dividends International International International Segment [Member] This member pertains to international segment. Schedule of Changes in Carrying Value of Goodwill by Reportable Segment Schedule of Goodwill [Table Text Block] Interest expense Interest expense Interest Expense, Nonoperating Trading Arrangement: Trading Arrangement [Axis] Material losses recognized in income Derivative, Excluded Component, Gain (Loss), Recognized in Earnings Total Shareholder Return Amount Total Shareholder Return Amount Commitments and Contingencies [Line Items] Loss Contingencies [Line Items] Foreign currency translation adjustments Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Insider Trading Arrangements [Line Items] Security Exchange Name Security Exchange Name Equity investment Equity Securities [Member] 2026 (six months remaining) Long-Term Debt, Maturity, Remainder of Fiscal Year Non-current liabilities Non-current liabilities Liabilities, Noncurrent Fund Investment Capital Capital Addition Purchase Commitments [Member] TOTAL LIABILITIES Total liabilities Liabilities Currency [Axis] Currency [Axis] PEP units earned (in units) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Earned in Period The number of earned during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). Maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Repurchased face amount Debt Instrument, Repurchased Face Amount Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Investment in unconsolidated joint ventures Payments to Acquire Interest in Joint Venture Thereafter Finance Lease, Liability, to be Paid, Due after Year Four Finance Lease, Liability, to be Paid, Due after Year Four Pass-through joint ventures Pass Through Joint Ventures [Member] A form of joint venture in which the joint venture itself is nothing more than the formal documents used to create it. A pass-through joint venture owns no assets other than its interest in those contracts it may have with its clients, nor does it perform any services. Instead, the joint venture subcontracts o each of its members or to third parties all services that it is required to provide to the client. Interest Earned Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings Other expense Disposal Group, Including Discontinued Operation, Other Expense PENSION BENEFIT OBLIGATIONS Liability, Defined Benefit Plan, Noncurrent Issuance of stock Stock Issued During Period, Value, New Issues Statement [Line Items] Statement [Line Items] Debt Instrument, Redemption, Period Five Debt Instrument, Redemption, Period Five [Member] Consolidation Items [Axis] Consolidation Items [Axis] Variable Rate [Axis] Variable Rate [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Total cash and cash equivalents Cash and Cash Equivalent Research Tax Credit Carryforward Research Tax Credit Carryforward [Member] Common Stock Common Stock [Member] Vested (in units) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period Tax Credit Carryforward, Name [Domain] Tax Credit Carryforward, Name [Domain] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Former Affiliate Amentum Environment & Energy, Inc.[Member] Represents Amentum Environment & Energy, Inc., f/k/a AECOM Energy and Construction, Inc. ("Former Affiliate"), Non-NEOs Non-NEOs [Member] Finance Leases Finance Lease, Liability, to be Paid, Fiscal Year Maturity [Abstract] NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation Potential common shares (in shares) Weighted Average Number of Shares Outstanding, Diluted, Adjustment