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Basis of Presentation (Details)	3 Months Ended
	Dec. 31, 2012 item
Minimum
Possible number of weeks in Company's fiscal year	52
Maximum
Possible number of weeks in Company's fiscal year	53

X

- Definition

Represents the possible number of weeks in the entity's fiscal year.

+ References

No definition available.

+ Details

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