v3.26.1
Reportable Segments - Schedule of Financial Information Concerning the Company's Reportable Segments (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Segment Reporting [Line Items]        
Revenue $ 3,586,067 $ 4,178,440 $ 11,218,044 $ 11,964,205
Equity in earnings of joint ventures 4,512 5,290 23,461 21,707
Total        
Segment Reporting [Line Items]        
Revenue 3,586,000 4,178,400 11,218,000 11,964,200
Subcontractor and other direct costs (1,976,900) (2,240,800) (5,809,600) (6,358,200)
Employee compensation expense (1,386,900) (1,335,900) (4,070,300) (3,926,400)
Equity in earnings of joint ventures 4,600 5,300 23,500 21,700
Other segment items (242,900) (301,200) (774,700) (842,000)
Earnings before income taxes and amortization (16,100) 305,800 586,900 859,300
Operating Segments | Americas        
Segment Reporting [Line Items]        
Revenue 2,632,700 3,277,200 8,521,600 9,285,900
Subcontractor and other direct costs (1,824,300) (2,098,300) (5,404,200) (5,931,400)
Employee compensation expense (807,600) (776,400) (2,381,200) (2,252,200)
Equity in earnings of joint ventures 4,400 2,200 13,800 12,600
Other segment items (135,100) (180,300) (438,400) (484,100)
Earnings before income taxes and amortization (129,900) 224,400 311,600 630,800
Operating Segments | International        
Segment Reporting [Line Items]        
Revenue 953,100 901,100 2,696,200 2,677,900
Subcontractor and other direct costs (152,600) (142,500) (405,400) (426,800)
Employee compensation expense (579,300) (559,500) (1,689,100) (1,674,200)
Equity in earnings of joint ventures (100) 2,100 8,100 9,000
Other segment items (106,200) (118,600) (330,800) (350,500)
Earnings before income taxes and amortization 114,900 82,600 279,000 235,400
Operating Segments | AECOM Capital        
Segment Reporting [Line Items]        
Revenue 200 100 200 400
Subcontractor and other direct costs 0 0 0 0
Employee compensation expense 0 0 0 0
Equity in earnings of joint ventures 300 1,000 1,600 100
Other segment items (1,600) (2,300) (5,500) (7,400)
Earnings before income taxes and amortization $ (1,100) $ (1,200) $ (3,700) $ (6,900)