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v3.10.0.1

Condensed Consolidating Financial Information - Debt (Details) | 9 Months Ended
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Jun. 30, 2018
Condensed Consolidating Financial Information |
Ownership of directly and indirectly owned subsidiaries (as a percent) | 100.00%

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- References No definition available. + Details
Name: | acm_CondensedConsolidatingFinancialInformation
Namespace Prefix: | acm_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of subsidiary's or equity method investee's stock owned by parent immediately after all stock transactions. + References No definition available. + Details
Name: | us-gaap_SubsidiaryOrEquityMethodInvesteeCumulativePercentageOwnershipAfterAllTransactions
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration