Revenues (Disaggregation of revenue) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 2,777	$ 2,575	$ 8,052	$ 7,547
United States
Disaggregation of Revenue [Line Items]
Revenues	2,556	2,339	7,416	6,856
International
Disaggregation of Revenue [Line Items]
Revenues	221	236	636	691
Cost-reimbursement and fixed-price-incentive-fee
Disaggregation of Revenue [Line Items]
Revenues	1,504	1,426	4,375	4,063
Firm-fixed-price
Disaggregation of Revenue [Line Items]
Revenues	900	767	2,563	2,305
Time-and-materials and fixed-price-level-of-effort
Disaggregation of Revenue [Line Items]
Revenues	373	382	1,114	1,179
DoD and U.S. Intelligence Community
Disaggregation of Revenue [Line Items]
Revenues	1,351	1,228	3,949	3,607
Other government agencies
Disaggregation of Revenue [Line Items]
Revenues	1,091	962	3,121	2,820
Commercial and non-U.S. customers
Disaggregation of Revenue [Line Items]
Revenues	335	385	982	1,120
Defense Solutions
Disaggregation of Revenue [Line Items]
Revenues	1,354	1,250	3,966	3,701
Revenue reclassified		9	6	34
Defense Solutions | United States
Disaggregation of Revenue [Line Items]
Revenues	1,261	1,156	3,689	3,424
Defense Solutions | International
Disaggregation of Revenue [Line Items]
Revenues	93	94	277	277
Defense Solutions | Cost-reimbursement and fixed-price-incentive-fee
Disaggregation of Revenue [Line Items]
Revenues	936	920	2,749	2,552
Defense Solutions | Firm-fixed-price
Disaggregation of Revenue [Line Items]
Revenues	299	214	870	772
Defense Solutions | Time-and-materials and fixed-price-level-of-effort
Disaggregation of Revenue [Line Items]
Revenues	119	116	347	377
Defense Solutions | DoD and U.S. Intelligence Community
Disaggregation of Revenue [Line Items]
Revenues	1,191	1,100	3,464	3,256
Defense Solutions | Other government agencies
Disaggregation of Revenue [Line Items]
Revenues	75	45	203	137
Defense Solutions | Commercial and non-U.S. customers
Disaggregation of Revenue [Line Items]
Revenues	88	105	299	308
Civil
Disaggregation of Revenue [Line Items]
Revenues	918	881	2,632	2,526
Civil | United States
Disaggregation of Revenue [Line Items]
Revenues	790	739	2,273	2,112
Civil | International
Disaggregation of Revenue [Line Items]
Revenues	128	142	359	414
Civil | Cost-reimbursement and fixed-price-incentive-fee
Disaggregation of Revenue [Line Items]
Revenues	511	464	1,453	1,377
Civil | Firm-fixed-price
Disaggregation of Revenue [Line Items]
Revenues	268	276	763	719
Civil | Time-and-materials and fixed-price-level-of-effort
Disaggregation of Revenue [Line Items]
Revenues	139	141	416	430
Civil | DoD and U.S. Intelligence Community
Disaggregation of Revenue [Line Items]
Revenues	37	40	125	89
Civil | Other government agencies
Disaggregation of Revenue [Line Items]
Revenues	679	605	1,936	1,746
Civil | Commercial and non-U.S. customers
Disaggregation of Revenue [Line Items]
Revenues	202	236	571	691
Health
Disaggregation of Revenue [Line Items]
Revenues	505	444	1,454	1,320
Health | United States
Disaggregation of Revenue [Line Items]
Revenues	505	444	1,454	1,320
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	57	42	173	134
Health | Firm-fixed-price
Disaggregation of Revenue [Line Items]
Revenues	333	277	930	814
Health | Time-and-materials and fixed-price-level-of-effort
Disaggregation of Revenue [Line Items]
Revenues	115	125	351	372
Health | DoD and U.S. Intelligence Community
Disaggregation of Revenue [Line Items]
Revenues	123	88	360	262
Health | Other government agencies
Disaggregation of Revenue [Line Items]
Revenues	337	312	982	937
Health | Commercial and non-U.S. customers
Disaggregation of Revenue [Line Items]
Revenues	$ 45	$ 44	$ 112	$ 121