Revenues (Disaggregation of revenue) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 03, 2020	Jun. 28, 2019	Jul. 03, 2020	Jun. 28, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 2,892	$ 2,716	$ 5,756	$ 5,275
United States
Disaggregation of Revenue [Line Items]
Revenues	2,648	2,502	5,307	4,859
International
Disaggregation of Revenue [Line Items]
Revenues	244	214	449	416
Cost-reimbursement and fixed-price-incentive-fee
Disaggregation of Revenue [Line Items]
Revenues	1,512	1,449	3,017	2,871
Firm-fixed-price
Disaggregation of Revenue [Line Items]
Revenues	988	888	1,974	1,663
Time-and-materials and fixed-price-level-of-effort
Disaggregation of Revenue [Line Items]
Revenues	392	379	765	741
DoD and U.S. Intelligence Community
Disaggregation of Revenue [Line Items]
Revenues	1,497	1,322	2,923	2,598
Other government agencies
Disaggregation of Revenue [Line Items]
Revenues	1,037	1,061	2,164	2,030
Commercial and non-U.S. customers
Disaggregation of Revenue [Line Items]
Revenues	358	333	669	647
Defense Solutions
Disaggregation of Revenue [Line Items]
Revenues	1,756	1,560	3,461	3,050
Defense Solutions | United States
Disaggregation of Revenue [Line Items]
Revenues	1,560	1,360	3,073	2,664
Defense Solutions | International
Disaggregation of Revenue [Line Items]
Revenues	196	200	388	386
Defense Solutions | Cost-reimbursement and fixed-price-incentive-fee
Disaggregation of Revenue [Line Items]
Revenues	1,105	1,001	2,199	1,987
Defense Solutions | Firm-fixed-price
Disaggregation of Revenue [Line Items]
Revenues	462	411	902	775
Defense Solutions | Time-and-materials and fixed-price-level-of-effort
Disaggregation of Revenue [Line Items]
Revenues	189	148	360	288
Defense Solutions | DoD and U.S. Intelligence Community
Disaggregation of Revenue [Line Items]
Revenues	1,362	1,192	2,647	2,327
Defense Solutions | Other government agencies
Disaggregation of Revenue [Line Items]
Revenues	175	154	383	310
Defense Solutions | Commercial and non-U.S. customers
Disaggregation of Revenue [Line Items]
Revenues	219	214	431	413
Civil
Disaggregation of Revenue [Line Items]
Revenues	739	661	1,371	1,276
Civil | United States
Disaggregation of Revenue [Line Items]
Revenues	691	647	1,310	1,246
Civil | International
Disaggregation of Revenue [Line Items]
Revenues	48	14	61	30
Civil | Cost-reimbursement and fixed-price-incentive-fee
Disaggregation of Revenue [Line Items]
Revenues	343	401	689	768
Civil | Firm-fixed-price
Disaggregation of Revenue [Line Items]
Revenues	289	149	462	291
Civil | Time-and-materials and fixed-price-level-of-effort
Disaggregation of Revenue [Line Items]
Revenues	107	111	220	217
Civil | DoD and U.S. Intelligence Community
Disaggregation of Revenue [Line Items]
Revenues	12	17	29	34
Civil | Other government agencies
Disaggregation of Revenue [Line Items]
Revenues	615	564	1,159	1,075
Civil | Commercial and non-U.S. customers
Disaggregation of Revenue [Line Items]
Revenues	112	80	183	167
Health
Disaggregation of Revenue [Line Items]
Revenues	397	495	924	949
Health | United States
Disaggregation of Revenue [Line Items]
Revenues	397	495	924	949
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	64	47	129	116
Health | Firm-fixed-price
Disaggregation of Revenue [Line Items]
Revenues	237	328	610	597
Health | Time-and-materials and fixed-price-level-of-effort
Disaggregation of Revenue [Line Items]
Revenues	96	120	185	236
Health | DoD and U.S. Intelligence Community
Disaggregation of Revenue [Line Items]
Revenues	123	113	247	237
Health | Other government agencies
Disaggregation of Revenue [Line Items]
Revenues	247	343	622	645
Health | Commercial and non-U.S. customers
Disaggregation of Revenue [Line Items]
Revenues	$ 27	$ 39	$ 55	$ 67