This element represents loss contingency amount estimated recovery from third party

No definition available.

Name:	acm_LossContingencyAmountEstimatedRecoveryFromThirdParty
Namespace Prefix:	acm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Surety bonds issued primarily to support the Company's project execution and insurance program commitments.

+ References

No definition available.

+ Details

Name:	acm_LossContingencySuretyBondsIssued
Namespace Prefix:	acm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the estimated minimum cost to complete the project and promised amenities.

+ References

No definition available.

+ Details

Name:	acm_MinimumEstimatedCostToCompleteProjectAndPromisedAmenities
Namespace Prefix:	acm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Period the negotiated resolution agreement is effective, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	acm_NegotiatedResolutionAgreementTerm
Namespace Prefix:	acm_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of affiliates for which inspections occurred on accounts and records on those affiliates.

+ References

No definition available.

+ Details

Name:	acm_NumberOfAffiliatesForWhichInspectionsOccurredOnAccountsAndRecords
Namespace Prefix:	acm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of entities which will be required to adopt a corporate compliance program consistent with the World Bank Group's integrity compliance guidelines.

+ References

No definition available.

+ Details

Name:	acm_NumberOfEntitiesRequiredToAdoptProgram
Namespace Prefix:	acm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Period the negotiated resolution agreement is effective.

+ References

No definition available.

+ Details

Name:	acm_TermOfDebarringBiddingOnProjectsFundedByWorldBankEntityTwo
Namespace Prefix:	acm_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- 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_LossContingenciesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349

+ Details

Name:	us-gaap_LossContingencyEstimateOfPossibleLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The difference between the maximum amount of estimated loss and the amount recorded as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 05
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6395354&loc=d3e12631-108344

+ Details

Name:	us-gaap_LossContingencyRangeOfPossibleLossPortionNotAccrued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_StandbyLettersOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_SuretyBondMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=acm_DoeDeactivationDemolitionAndRemovalProjectMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=acm_DepartmentOfEnergyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=acm_WgiOhioAndDoeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=acm_WashingtonGroupInternationalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=acm_WorldBankReviewAsiaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Commitments and Contingencies (Details) $ in Millions		1 Months Ended	9 Months Ended
Commitments and Contingencies (Details) $ in Millions	Jul. 11, 2017 item	Dec. 31, 2014 USD ($)	Jun. 30, 2017 USD ($) item	Sep. 30, 2016 USD ($)
Standby letter of credit
Commitments and Contingencies
Contingency liability			$ 495.8	$ 474.5
Surety Bond
Commitments and Contingencies
Surety bonds issued			4,500.0	$ 3,300.0
DOE Deactivation, Demolition, And Removal Project \| Department of Energy \| Maximum
Commitments and Contingencies
Cost-reimbursement at risk			106.0
DOE Deactivation, Demolition, And Removal Project \| WGI Ohio and DOE \| Minimum
Commitments and Contingencies
Cost-reimbursement at risk			106.0
DOE Deactivation, Demolition, And Removal Project \| WGI Ohio and DOE \| Maximum
Commitments and Contingencies
Cost-reimbursement at risk			146.0
DOE Deactivation, Demolition, And Removal Project \| WGI Ohio
Commitments and Contingencies
Claim to DOE, including additional fees		$ 103.0
Possible costs which may exceed contracted amounts		$ 100.0
DOE Deactivation, Demolition, And Removal Project \| WGI Ohio \| Minimum
Commitments and Contingencies
Cost-reimbursement at risk			$ 146.0
World Bank Review - Asia-Pacific
Commitments and Contingencies
Number of entities inspected for compliance \| item			2
World Bank Review - Asia-Pacific \| Subsequent Event
Commitments and Contingencies
Term of debarring bidding on projects funded by World Bank, entity one	18 months
Term of debarring bidding on projects funded by World Bank, entity two	6 months
Number of entities required to adopt compliance program \| item	1