Revenues - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jul. 03, 2026	Jun. 27, 2025	Jul. 03, 2026	Jun. 27, 2025
Disaggregation of Revenue [Line Items]
Total revenues	$ 3,490	$ 3,561	$ 10,205	$ 10,468
United States
Disaggregation of Revenue [Line Items]
Total revenues	2,803	2,687	8,001	7,757
International
Disaggregation of Revenue [Line Items]
Total revenues	687	874	2,204	2,711
Prime contractor
Disaggregation of Revenue [Line Items]
Total revenues	3,244	3,197	9,291	9,339
Subcontractor
Disaggregation of Revenue [Line Items]
Total revenues	246	364	914	1,129
Cost-plus-fee
Disaggregation of Revenue [Line Items]
Total revenues	1,871	2,300	5,703	6,715
Fixed-price
Disaggregation of Revenue [Line Items]
Total revenues	1,105	817	3,015	2,455
Time-and-materials
Disaggregation of Revenue [Line Items]
Total revenues	514	444	1,487	1,298
Department of War and U.S. Intelligence Community
Disaggregation of Revenue [Line Items]
Total revenues	1,717	1,917	5,334	5,493
Other U.S. Government Agencies
Disaggregation of Revenue [Line Items]
Total revenues	1,057	997	2,811	3,003
Commercial and International
Disaggregation of Revenue [Line Items]
Total revenues	716	647	2,060	1,972
DS
Disaggregation of Revenue [Line Items]
Total revenues	1,457	1,421	4,262	4,047
DS \| United States
Disaggregation of Revenue [Line Items]
Total revenues	1,404	1,360	4,096	3,867
DS \| International
Disaggregation of Revenue [Line Items]
Total revenues	53	61	166	180
DS \| Prime contractor
Disaggregation of Revenue [Line Items]
Total revenues	1,381	1,301	4,021	3,680
DS \| Subcontractor
Disaggregation of Revenue [Line Items]
Total revenues	76	120	241	367
DS \| Cost-plus-fee
Disaggregation of Revenue [Line Items]
Total revenues	861	952	2,530	2,598
DS \| Fixed-price
Disaggregation of Revenue [Line Items]
Total revenues	424	336	1,206	1,026
DS \| Time-and-materials
Disaggregation of Revenue [Line Items]
Total revenues	172	133	526	423
DS \| Department of War and U.S. Intelligence Community
Disaggregation of Revenue [Line Items]
Total revenues	790	865	2,317	2,325
DS \| Other U.S. Government Agencies
Disaggregation of Revenue [Line Items]
Total revenues	428	401	1,249	1,222
DS \| Commercial and International
Disaggregation of Revenue [Line Items]
Total revenues	239	155	696	500
GES
Disaggregation of Revenue [Line Items]
Total revenues	2,033	2,140	5,943	6,421
GES \| United States
Disaggregation of Revenue [Line Items]
Total revenues	1,399	1,327	3,905	3,890
GES \| International
Disaggregation of Revenue [Line Items]
Total revenues	634	813	2,038	2,531
GES \| Prime contractor
Disaggregation of Revenue [Line Items]
Total revenues	1,863	1,896	5,270	5,659
GES \| Subcontractor
Disaggregation of Revenue [Line Items]
Total revenues	170	244	673	762
GES \| Cost-plus-fee
Disaggregation of Revenue [Line Items]
Total revenues	1,010	1,348	3,173	4,117
GES \| Fixed-price
Disaggregation of Revenue [Line Items]
Total revenues	681	481	1,809	1,429
GES \| Time-and-materials
Disaggregation of Revenue [Line Items]
Total revenues	342	311	961	875
GES \| Department of War and U.S. Intelligence Community
Disaggregation of Revenue [Line Items]
Total revenues	927	1,052	3,017	3,168
GES \| Other U.S. Government Agencies
Disaggregation of Revenue [Line Items]
Total revenues	629	596	1,562	1,781
GES \| Commercial and International
Disaggregation of Revenue [Line Items]
Total revenues	$ 477	$ 492	$ 1,364	$ 1,472