v3.26.1
Revenue Recognition - Schedule of Revenues Disaggregated by Revenue Sources (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Disaggregation of Revenue [Line Items]        
Total revenue $ 3,586,067 $ 4,178,440 $ 11,218,044 $ 11,964,205
Adjusted for rounding        
Disaggregation of Revenue [Line Items]        
Total revenue 3,586,000      
Americas        
Disaggregation of Revenue [Line Items]        
Total revenue 2,632,900 3,277,200 8,521,800 9,286,200
Europe, Middle East, India, Africa        
Disaggregation of Revenue [Line Items]        
Total revenue 559,500 536,400 1,627,500 1,604,700
Asia-Australia-Pacific        
Disaggregation of Revenue [Line Items]        
Total revenue 393,600 364,800 1,068,700 1,073,300
Asia-Australia-Pacific | Adjusted for rounding        
Disaggregation of Revenue [Line Items]        
Total revenue 3,586,000      
Cost reimbursable        
Disaggregation of Revenue [Line Items]        
Total revenue 1,261,600 1,619,100 4,499,300 4,588,400
Guaranteed maximum price        
Disaggregation of Revenue [Line Items]        
Total revenue 1,311,500 1,575,800 3,825,600 4,446,800
Fixed-price        
Disaggregation of Revenue [Line Items]        
Total revenue $ 1,012,900 $ 983,500 $ 2,893,100 $ 2,929,000