XML 112 R95.htm IDEA: XBRL DOCUMENT
v3.25.3

Income Taxes - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2023
Income Tax Contingency [Line Items] |  |  |
Income (loss) from domestic operations | $ 392.7 | $ 233.0 | $ (129.2)
Income from foreign operations | 522.9 | 485.2 | 342.6
Tax benefit related to deferred tax assets resulting from legal entity restructuring | 20.1 |  |
Increase in tax benefit |  | 38.4 |
Increase in tax expense related to uncertain tax position |  | 23.0 |
Increase (decrease) in valuation allowance | (3.8) |  |
Valuation allowance | 157.1 | 160.9 |
Tax expense (benefit) related to uncertain tax positions | 46.7 | 18.6 | 9.4
Net operating loss carryforwards | 700.7 | 744.6 |
Gross deferred tax assets | 609.4 | 678.9 |
Gross tax asset exclusive of tax liabilities realizable | 452.3 |  |
Gross book-tax differences from non-U.S. subsidiaries | 1,100.0 |  |
Liability for unrecognized tax benefits, including potential interest and penalties, net of related tax benefit | 144.1 | 97.9 |
Unrecognized tax benefits | 129.6 | 81.3 | 62.1
Unrecognized tax benefits that would be included in the effective tax rate if recognized | 125.4 |  |
Accrued interest, excluding any related income tax benefits | 23.8 | 27.7 |
Accrued penalties, excluding any related income tax benefits | 3.2 | 3.5 |
Capital Loss Carryforward |  |  |
Income Tax Contingency [Line Items] |  |  |
Tax credit carryforward | 51.7 | 181.2 |
Research Tax Credit Carryforward |  |  |
Income Tax Contingency [Line Items] |  |  |
Tax credit carryforward, valuation allowance | 47.0 |  |
Research Tax Credit Carryforward | State |  |  |
Income Tax Contingency [Line Items] |  |  |
Tax credit carryforward | 30.5 |  |
Research Tax Credit Carryforward | Foreign |  |  |
Income Tax Contingency [Line Items] |  |  |
Tax credit carryforward | 0.2 |  |
Other Credits |  |  |
Income Tax Contingency [Line Items] |  |  |
Tax credit carryforward | 3.7 |  |
ACAP Investments |  |  |
Income Tax Contingency [Line Items] |  |  |
Increase (decrease) in valuation allowance |  | (21.0) |
Reduction in deferred tax assets |  | 20.2 |
Valuation allowance |  | 9.3 |
AECOM Capital Impairment Charge |  |  |
Income Tax Contingency [Line Items] |  |  |
Valuation allowance |  |  | $ 21.0
Capital Losses |  |  |
Income Tax Contingency [Line Items] |  |  |
Increase (decrease) in valuation allowance | (5.6) |  |
Foreign Net Operating Losses And Currency Translation Adjustments |  |  |
Income Tax Contingency [Line Items] |  |  |
Increase (decrease) in valuation allowance | $ 1.9 |  |
CANADA | Operating Losses and Other Deferred Tax Assets |  |  |
Income Tax Contingency [Line Items] |  |  |
Increase (decrease) in valuation allowance |  | (11.7) |
HONG KONG |  |  |
Income Tax Contingency [Line Items] |  |  |
Tax expense (benefit) related to uncertain tax positions |  | $ (6.9) |

X
- Definition Amount of decrease in the deferred tax asset due to sale of investments. + References No definition available. + Details
Name: | acm_DeferredTaxAssetReductionDueToSaleOfInvestments
Namespace Prefix: | acm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of gross book tax differences of foreign subsidiaries intended to be permanently reinvested outside the country of domicile. + References No definition available. + Details
Name: | acm_GrossBookTaxDifferencesOfForeignSubsidiaries
Namespace Prefix: | acm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of increase in income tax expense related to uncertain tax positions partially offset to the income tax benefit. + References No definition available. + Details
Name: | acm_IncomeTaxExpenseRelatedToUncertainTaxPositionsPartiallyOffsetToIncomeTaxBenefit
Namespace Prefix: | acm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of increase in income tax benefit related to state income taxes due to apportionment factor. + References No definition available. + Details
Name: | acm_IncreaseInIncomeTaxBenefitRelatedToStateIncomeTaxesDueToApportionmentFactor
Namespace Prefix: | acm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns as of the balance sheet date and potential interest and penalties, net of related tax benefit. + References No definition available. + Details
Name: | acm_UnrecognizedTaxBenefitsAndPotentialIncomeTaxPenaltiesAndInterestNetOfRelatedTaxBenefit
Namespace Prefix: | acm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-2 + Details
Name: | us-gaap_DeferredTaxAssetsGross
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-2 + Details
Name: | us-gaap_DeferredTaxAssetsNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from restructuring reserve. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-6 + Details
Name: | us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsRestructuringCharges
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-2 + Details
Name: | us-gaap_DeferredTaxAssetsValuationAllowance
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The portion of earnings or loss from continuing operations before income taxes that is attributable to domestic operations. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section S50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480738/235-10-S50-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 10A -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-10A Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(h)(1)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1 + Details
Name: | us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The portion of earnings or loss from continuing operations before income taxes that is attributable to foreign operations, which is defined as Income or Loss generated from operations located outside the entity's country of domicile. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section S50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480738/235-10-S50-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 10A -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-10A Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(h)(1)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1 + Details
Name: | us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- 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 No definition available. + Details
Name: | us-gaap_IncomeTaxContingencyLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to increase (decrease) in income tax contingencies. Including, but not limited to, domestic tax contingency, foreign tax contingency, state and local tax contingency, and other contingencies. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 231 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482663/740-10-55-231 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 12A -Subparagraph (a)(8) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-12A Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 12 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-12 + Details
Name: | us-gaap_IncomeTaxReconciliationTaxContingencies
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-3 + Details
Name: | us-gaap_OperatingLossCarryforwards
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-3 + Details
Name: | us-gaap_TaxCreditCarryforwardAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of valuation allowance pertaining to the deferred tax asset representing potential future taxable deductions from tax credit carryforwards for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-2 + Details
Name: | us-gaap_TaxCreditCarryforwardValuationAllowance
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of unrecognized tax benefits. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 217 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482663/740-10-55-217 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 15A -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-15A Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 10B -Publisher FASB -URI https://asc.fasb.org/1943274/2147482525/740-10-45-10B + Details
Name: | us-gaap_UnrecognizedTaxBenefits
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of statutory penalties accrued for a tax position claimed or expected to be claimed by the entity, in its tax return. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 15 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-15 + Details
Name: | us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAccrued
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of interest expense accrued for an underpayment of income taxes. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 15 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-15 + Details
Name: | us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesAccrued
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 217 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482663/740-10-55-217 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 15A -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-15A + Details
Name: | us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-2 + Details
Name: | us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_TaxCreditCarryforwardAxis=us-gaap_CapitalLossCarryforwardMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_TaxCreditCarryforwardAxis=us-gaap_ResearchMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeTaxAuthorityAxis=us-gaap_StateAndLocalJurisdictionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeTaxAuthorityAxis=us-gaap_ForeignCountryMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_TaxCreditCarryforwardAxis=us-gaap_GeneralBusinessMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationAllowanceByDeferredTaxAssetAxis=acm_EquityInvestmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationAllowanceByDeferredTaxAssetAxis=acm_ImpairmentChargeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationAllowanceByDeferredTaxAssetAxis=acm_DeferredTaxAssetCapitalLossesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationAllowanceByDeferredTaxAssetAxis=acm_ForeignNetOperatingLossesAndCurrencyTranslationAdjustmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=country_CA
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationAllowanceByDeferredTaxAssetAxis=acm_OperatingLossesAndOtherDeferredTaxAssetsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=country_HK
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |