Commitments and Contingencies (Details) In Millions, unless otherwise specified			3 Months Ended	12 Months Ended
	Dec. 31, 2013 Standby letters of credit USD ($)	Dec. 31, 2013 Global Linguists Solutions Joint Venture USD ($)	Dec. 31, 2013 AECOM Australia item	Sep. 30, 2006 AECOM Australia AUD	Dec. 31, 2013 Hawaii Project item
Commitments and Contingencies
Contingency liability of general and professional liability insurance programs and for payment and performance guarantees	$ 294.0
Amount withheld by the U.S. government for payments due under a contract because of a dispute		19
Proceeds from initial public offering (IPO)				700
Bank loan				1,400.0
Number of initial public offering investors			770
Number of actions filed till date					0