v3.26.1
Segment Information - Schedule of Adjusted EBITDA to Net Income (Loss) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Jul. 03, 2026
Jun. 27, 2025
Jul. 03, 2026
Jun. 27, 2025
Segment Reporting [Line Items]        
Revenues $ 3,490 $ 3,561 $ 10,205 $ 10,468
Cost of revenues (3,130) (3,193) (9,174) (9,372)
Other segment expenses (70) (94) (203) (292)
Adjusted EBITDA attributable to Amentum Holdings, Inc. 290 274 828 804
Depreciation (7) (11) (25) (29)
Amortization of intangibles (94) (118) (282) (358)
Interest expense and other, net (62) (88) (209) (261)
Loss on extinguishment of debt (16) (3) (16) (3)
Non-controlling interests 0 (11) 0 (4)
Acquisition, transaction and integration costs (9) (32) (36) (62)
Utilization of fair market value adjustments 0 8 (1) 9
Stock-based compensation (8) (7) (23) (15)
Income before income taxes 94 12 236 81
Provision for income taxes (28) (13) (72) (59)
Net income (loss) including non-controlling interests 66 (1) 164 22
Net income (loss) attributable to non-controlling interests 0 11 0 4
Net income attributable to common shareholders 66 10 164 26
DS        
Segment Reporting [Line Items]        
Revenues 1,457 1,421 4,262 4,047
Cost of revenues (1,293) (1,245) (3,794) (3,559)
Other segment expenses (48) (62) (144) (167)
Adjusted EBITDA attributable to Amentum Holdings, Inc. 116 114 324 321
GES        
Segment Reporting [Line Items]        
Revenues 2,033 2,140 5,943 6,421
Cost of revenues (1,837) (1,948) (5,380) (5,813)
Other segment expenses (22) (32) (59) (125)
Adjusted EBITDA attributable to Amentum Holdings, Inc. $ 174 $ 160 $ 504 $ 483