Joint Ventures and Variable Interest Entities (Details) (USD $)	3 Months Ended		9 Months Ended
	Jun. 30, 2013 item	Jun. 30, 2012	Jun. 30, 2013 item	Jun. 30, 2012	Sep. 30, 2012
Financial information
Number of employees in some joint ventures	0		0
Current assets	$ 3,049,684,000		$ 3,049,684,000		$ 3,147,293,000
TOTAL ASSETS	5,539,368,000		5,539,368,000		5,664,568,000
Current liabilities	1,941,556,000		1,941,556,000		2,078,402,000
TOTAL LIABILITIES	3,497,503,000		3,497,503,000		3,440,080,000
Total AECOM equity	1,985,730,000		1,985,730,000		2,169,464,000
Noncontrolling interests	56,135,000		56,135,000		55,024,000
TOTAL STOCKHOLDERS' EQUITY	2,041,865,000		2,041,865,000		2,224,488,000
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	5,539,368,000		5,539,368,000		5,664,568,000
AECOM's investment in joint ventures	83,843,000		83,843,000		91,049,000
Joint ventures summarized financial information
Total revenue	2,067,490,000	2,095,138,000	6,074,408,000	6,135,269,000
Total operating income	111,898,000	102,837,000	254,265,000	252,692,000
Summary of AECOM's equity in earnings of unconsolidated joint ventures:
Total	4,094,000	12,281,000	17,855,000	38,141,000
Consolidated joint ventures
Financial information
Current assets	201,000,000		201,000,000		243,200,000
TOTAL ASSETS	201,000,000		201,000,000		243,200,000
Current liabilities	41,600,000		41,600,000		43,100,000
TOTAL LIABILITIES	41,600,000		41,600,000		43,100,000
Total AECOM equity	115,200,000		115,200,000		145,100,000
Noncontrolling interests	44,200,000		44,200,000		55,000,000
TOTAL STOCKHOLDERS' EQUITY	159,400,000		159,400,000		200,100,000
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	201,000,000		201,000,000		243,200,000
Joint ventures summarized financial information
Total revenue			392,600,000	346,800,000
Unconsolidated joint ventures
Financial information
Current assets	565,000,000		565,000,000		598,800,000
Non-current assets	40,300,000		40,300,000		15,200,000
TOTAL ASSETS	605,300,000		605,300,000		614,000,000
Current liabilities	414,800,000		414,800,000		411,200,000
Non-current liabilities	4,300,000		4,300,000		2,700,000
TOTAL LIABILITIES	419,100,000		419,100,000		413,900,000
TOTAL STOCKHOLDERS' EQUITY	186,200,000		186,200,000		200,100,000
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	605,300,000		605,300,000		614,000,000
AECOM's investment in joint ventures	83,800,000		83,800,000		91,000,000
Joint ventures summarized financial information
Total revenue			1,504,600,000	1,478,600,000
Total operating income			49,500,000	92,700,000
Summary of AECOM's equity in earnings of unconsolidated joint ventures:
Pass through joint ventures			4,800,000	4,100,000
Other joint ventures			13,100,000	34,000,000
Total			$ 17,900,000	$ 38,100,000