Basis of Presentation (Details)	3 Months Ended
Dec. 31, 2012
Minimum
Length of fiscal year	364 days
Maximum
Length of fiscal year	371 days

Represents the length of fiscal year of the company in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

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