v3.26.1
Segment Information - Schedule of Total Revenues, Segment Operating Profit and Total Asset for Reporting Segment (Details)
$ in Thousands, £ in Millions
 3 Months Ended 6 Months Ended
Jan. 02, 2026
GBP (£)
Mar. 27, 2026
USD ($)
Mar. 28, 2025
USD ($)
Mar. 27, 2026
USD ($)
Mar. 28, 2025
USD ($)
Segment Reporting Information [Line Items]          
Revenues from External Customers   $ 3,694,881 $ 2,910,415 $ 6,988,162 $ 5,843,371
Direct cost of contracts   (2,899,988) (2,172,070) (5,428,019) (4,383,759)
Selling, general and administrative expenses   (876,069) (529,697) (1,408,758) (1,042,546)
Segment Operating Profit   (81,176) 208,648 151,385 417,066
Restructuring, Transaction and Other Charges   (352,200) (23,924) (381,277) (53,856)
Amortization of Intangible Assets   (34,063) (38,040) (72,059) (76,701)
Total Other (Expense) Income, net   (49,430) (152,825) (75,769) (308,095)
(Loss) Earnings from Continuing Operations Before Taxes   (130,606) 55,823 75,616 108,971
Allocated share-based compensation expense     8,000   13,900
Restructuring and other charges   14,171 10,663 18,169 25,403
Equity method investment retained after disposal, mark-to market losses     109,500   254,700
Loss on extinguishment of debt   0 20,510 0 20,510
Equity-Based Incentive Grants          
Segment Reporting Information [Line Items]          
Allocated share-based compensation expense   214,900   237,500 13,900
Foreign Exchange Forward          
Segment Reporting Information [Line Items]          
Gain (loss) on derivatives, before taxes   (20,500)   (20,500)  
Amentum Holdings, Inc.          
Segment Reporting Information [Line Items]          
Restructuring and other charges     8,400   16,200
Amentum Holdings, Inc. | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | SpinCo Business          
Segment Reporting Information [Line Items]          
Discontinued Operation, Transition Services Agreement, Income (Expenses)     $ 10,300   $ 21,700
Joint Venture          
Segment Reporting Information [Line Items]          
Ownership percentage     50.00%   50.00%
Professional Services and Employee Seperation          
Segment Reporting Information [Line Items]          
Restructuring and other charges   7,600 $ 10,200 9,900 $ 25,100
PA Consulting Group Limited          
Segment Reporting Information [Line Items]          
Pre-tax transaction costs   120,400   122,700  
Consideration paid in cash £ 997.6     123,900  
Restructuring and other charges   6,500   8,300  
Operating Segments          
Segment Reporting Information [Line Items]          
Revenues from External Customers   3,694,881 2,910,415 6,988,162 5,843,371
Direct cost of contracts   (2,899,988) (2,172,070) (5,428,019) (4,383,759)
Selling, general and administrative expenses   (489,806) (467,733) (955,422) (911,989)
Segment Operating Profit   305,087 270,612 604,721 547,623
Infrastructure & Advanced Facilities | Operating Segments          
Segment Reporting Information [Line Items]          
Revenues from External Customers   3,336,307 2,602,753 6,275,155 5,228,961
Direct cost of contracts   (2,666,239) (1,980,582) (4,959,401) (4,000,277)
Selling, general and administrative expenses   (444,845) (418,906) (875,789) (815,145)
Segment Operating Profit   225,223 203,265 439,965 413,539
Restructuring and other charges   7,649 10,168 9,890 25,144
PA Consulting | Operating Segments          
Segment Reporting Information [Line Items]          
Revenues from External Customers   358,574 307,662 713,007 614,410
Direct cost of contracts   (233,749) (191,488) (468,618) (383,482)
Selling, general and administrative expenses   (44,961) (48,827) (79,633) (96,844)
Segment Operating Profit   79,864 67,347 164,756 134,084
Restructuring and other charges   $ 6,522 $ 495 $ 8,279 $ 259