Revenues (Disaggregation of revenue) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 02, 2020	Sep. 27, 2019	Oct. 02, 2020	Sep. 27, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 3,218	$ 2,777	$ 8,974	$ 8,052
United States
Disaggregation of Revenue [Line Items]
Revenues	2,959	2,556	8,266	7,416
International
Disaggregation of Revenue [Line Items]
Revenues	259	221	708	636
Cost-reimbursement and fixed-price-incentive-fee
Disaggregation of Revenue [Line Items]
Revenues	1,600	1,504	4,617	4,375
Firm-fixed-price
Disaggregation of Revenue [Line Items]
Revenues	1,223	900	3,197	2,563
Time-and-materials and fixed-price-level-of-effort
Disaggregation of Revenue [Line Items]
Revenues	395	373	1,160	1,114
DoD and U.S. Intelligence Community
Disaggregation of Revenue [Line Items]
Revenues	1,562	1,351	4,485	3,949
Other government agencies
Disaggregation of Revenue [Line Items]
Revenues	1,278	1,091	3,442	3,121
Commercial and non-U.S. customers
Disaggregation of Revenue [Line Items]
Revenues	378	335	1,047	982
Defense Solutions
Disaggregation of Revenue [Line Items]
Revenues	1,951	1,594	5,412	4,644
Defense Solutions | United States
Disaggregation of Revenue [Line Items]
Revenues	1,731	1,388	4,804	4,053
Defense Solutions | International
Disaggregation of Revenue [Line Items]
Revenues	220	206	608	591
Defense Solutions | Cost-reimbursement and fixed-price-incentive-fee
Disaggregation of Revenue [Line Items]
Revenues	1,160	1,038	3,359	3,025
Defense Solutions | Firm-fixed-price
Disaggregation of Revenue [Line Items]
Revenues	597	406	1,499	1,181
Defense Solutions | Time-and-materials and fixed-price-level-of-effort
Disaggregation of Revenue [Line Items]
Revenues	194	150	554	438
Defense Solutions | DoD and U.S. Intelligence Community
Disaggregation of Revenue [Line Items]
Revenues	1,411	1,215	4,058	3,542
Defense Solutions | Other government agencies
Disaggregation of Revenue [Line Items]
Revenues	292	177	675	487
Defense Solutions | Commercial and non-U.S. customers
Disaggregation of Revenue [Line Items]
Revenues	248	202	679	615
Civil
Disaggregation of Revenue [Line Items]
Revenues	747	678	2,118	1,954
Civil | United States
Disaggregation of Revenue [Line Items]
Revenues	708	663	2,018	1,909
Civil | International
Disaggregation of Revenue [Line Items]
Revenues	39	15	100	45
Civil | Cost-reimbursement and fixed-price-incentive-fee
Disaggregation of Revenue [Line Items]
Revenues	363	409	1,052	1,177
Civil | Firm-fixed-price
Disaggregation of Revenue [Line Items]
Revenues	278	161	740	452
Civil | Time-and-materials and fixed-price-level-of-effort
Disaggregation of Revenue [Line Items]
Revenues	106	108	326	325
Civil | DoD and U.S. Intelligence Community
Disaggregation of Revenue [Line Items]
Revenues	14	13	43	47
Civil | Other government agencies
Disaggregation of Revenue [Line Items]
Revenues	628	577	1,787	1,652
Civil | Commercial and non-U.S. customers
Disaggregation of Revenue [Line Items]
Revenues	105	88	288	255
Health
Disaggregation of Revenue [Line Items]
Revenues	520	505	1,444	1,454
Health | United States
Disaggregation of Revenue [Line Items]
Revenues	520	505	1,444	1,454
Health | International
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Health | Cost-reimbursement and fixed-price-incentive-fee
Disaggregation of Revenue [Line Items]
Revenues	77	57	206	173
Health | Firm-fixed-price
Disaggregation of Revenue [Line Items]
Revenues	348	333	958	930
Health | Time-and-materials and fixed-price-level-of-effort
Disaggregation of Revenue [Line Items]
Revenues	95	115	280	351
Health | DoD and U.S. Intelligence Community
Disaggregation of Revenue [Line Items]
Revenues	137	123	384	360
Health | Other government agencies
Disaggregation of Revenue [Line Items]
Revenues	358	337	980	982
Health | Commercial and non-U.S. customers
Disaggregation of Revenue [Line Items]
Revenues	$ 25	$ 45	$ 80	$ 112