Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Income Statement [Abstract]
Revenue	$ 16,139,622	$ 16,105,498	$ 14,378,461
Cost of revenue	14,922,909	15,021,157	13,432,996
Gross profit	1,216,713	1,084,341	945,465
Equity in earnings of joint ventures	27,013	2,124	(279,352)
General and administrative expenses	(157,849)	(160,105)	(153,575)
Restructuring and acquisition costs	(59,355)	(98,918)	(188,404)
Income from operations	1,026,522	827,442	324,134
Other income	10,457	17,570	8,357
Interest income	62,894	58,560	40,251
Interest expense	(184,304)	(185,420)	(159,342)
Income from continuing operations before taxes	915,569	718,152	213,400
Income tax expense for continuing operations	204,018	152,900	56,052
Net income from continuing operations	711,551	565,252	157,348
Net loss from discontinued operations	(75,364)	(104,997)	(57,207)
Net income	636,187	460,255	100,141
Net income attributable to noncontrolling interests from continuing operations	(73,287)	(59,322)	(43,262)
Net income (loss) attributable to noncontrolling interests from discontinued operations	(1,126)	1,333	(1,547)
Net income attributable to noncontrolling interests	(74,413)	(57,989)	(44,809)
Net income attributable to AECOM from continuing operations	638,264	505,930	114,086
Net loss attributable to AECOM from discontinued operations	(76,490)	(103,664)	(58,754)
Net income attributable to AECOM	$ 561,774	$ 402,266	$ 55,332
Net income (loss) attributable to AECOM per share:
Basic continuing operations per share (in dollar per share)	$ 4.82	$ 3.73	$ 0.82
Basic discontinued operations per share (in dollar per share)	(0.58)	(0.76)	(0.42)
Basic earnings per share (in dollar per share)	4.24	2.97	0.40
Diluted continuing operations per share (in dollar per share)	4.79	3.71	0.81
Diluted discontinued operations per share (in dollar per share)	(0.58)	(0.76)	(0.42)
Diluted earnings per share (in dollar per share)	$ 4.21	$ 2.95	$ 0.39
Weighted average shares outstanding:
Basic (in shares)	132,373	135,544	138,614
Diluted (in shares)	133,311	136,453	140,109