Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Retained Earnings (Deficits) Cumulative effect of accounting standard adoption	Retained Earnings (Deficits)	Total AECOM Stockholders' Equity Cumulative effect of accounting standard adoption	Total AECOM Stockholders' Equity	Non-Controlling Interests	Cumulative effect of accounting standard adoption	Total
BALANCE at Sep. 30, 2018	$ 1,570	$ 3,846,392	$ (703,330)		$ 948,148		$ 4,092,780	$ 185,594		$ 4,278,374
Increase (Decrease) in Stockholders' Equity
Net income (loss)					(261,050)		(261,050)	77,060		(183,990)
Other comprehensive loss			(160,867)				(160,867)	(100)		(160,967)
Issuance of stock	44	66,517					66,561			66,561
Repurchases of stock	(39)	(23,071)			(75,098)		(98,208)			(98,208)
Stock based compensation		63,812					63,812			63,812
Other transactions with noncontrolling interests								16,208		16,208
Contributions from noncontrolling interests								5,069		5,069
Distributions to noncontrolling interests								(75,057)		(75,057)
BALANCE at Sep. 30, 2019	1,575	3,953,650	(864,197)	$ (12,452)	599,548	$ (12,452)	3,690,576	208,774	$ (12,452)	3,899,350
Increase (Decrease) in Stockholders' Equity
Net income (loss)					(186,370)		(186,370)	32,629		(153,741)
Other comprehensive loss			(54,477)				(54,477)	314		(54,163)
Issuance of stock	43	63,297					63,340			63,340
Repurchases of stock	(48)	(35,762)			(151,143)		(186,953)			(186,953)
Stock based compensation		54,229					54,229			54,229
Disposal of noncontrolling interest of business sold								(60,089)		(60,089)
Contributions from noncontrolling interests								9,917		9,917
Distributions to noncontrolling interests								(70,559)		(70,559)
BALANCE at Sep. 30, 2020	1,570	4,035,414	(918,674)	(87,787)	174,248	(87,787)	3,292,558	120,986	(87,787)	3,413,544
Increase (Decrease) in Stockholders' Equity
Net income (loss)					173,185		173,185	29,795		202,980
Other comprehensive loss			18,297				18,297	234		18,531
Issuance of stock	25	58,733					58,758			58,758
Repurchases of stock	(163)	(23,348)			(843,580)		(867,091)			(867,091)
Stock based compensation		44,742					44,742			44,742
Disposal of noncontrolling interest of business sold								(24,039)		(24,039)
Other transactions with noncontrolling interests								405		405
Contributions from noncontrolling interests								271		271
Distributions to noncontrolling interests								(10,545)		(10,545)
BALANCE at Sep. 30, 2021	$ 1,432	$ 4,115,541	$ (900,377)	$ (7,979)	$ (504,126)	$ (7,979)	$ 2,712,470	$ 117,107	$ (7,979)	$ 2,829,577