Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Total revenues	$ 720	$ 719	$ 2,059	$ 1,952
Intersegment Sales
Disaggregation of Revenue [Line Items]
Total revenues	(7)	(4)	(15)	(18)
AST | Prime contractor
Disaggregation of Revenue [Line Items]
Total revenues	127	125	356	311
AST | Subcontractor
Disaggregation of Revenue [Line Items]
Total revenues	150	136	382	347
AST | Firm Fixed Price
Disaggregation of Revenue [Line Items]
Total revenues	241	230	633	573
AST | Flexibly Priced
Disaggregation of Revenue [Line Items]
Total revenues	36	31	105	85
AST | Intersegment Sales
Disaggregation of Revenue [Line Items]
Total revenues	2	2	5	10
AST | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenues	279	263	743	668
NC&C | Prime contractor
Disaggregation of Revenue [Line Items]
Total revenues	219	168	545	441
NC&C | Subcontractor
Disaggregation of Revenue [Line Items]
Total revenues	15	97	192	301
NC&C | Firm Fixed Price
Disaggregation of Revenue [Line Items]
Total revenues	197	226	650	658
NC&C | Flexibly Priced
Disaggregation of Revenue [Line Items]
Total revenues	37	39	87	84
NC&C | Intersegment Sales
Disaggregation of Revenue [Line Items]
Total revenues	5	2	10	7
NC&C | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenues	239	267	747	749
IMS | Prime contractor
Disaggregation of Revenue [Line Items]
Total revenues	41	69	127	195
IMS | Subcontractor
Disaggregation of Revenue [Line Items]
Total revenues	168	125	457	357
IMS | Firm Fixed Price
Disaggregation of Revenue [Line Items]
Total revenues	179	151	495	448
IMS | Flexibly Priced
Disaggregation of Revenue [Line Items]
Total revenues	30	43	89	104
IMS | Intersegment Sales
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	1
IMS | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenues	209	194	584	553
United States | AST
Disaggregation of Revenue [Line Items]
Total revenues	258	230	678	585
United States | NC&C
Disaggregation of Revenue [Line Items]
Total revenues	226	248	707	686
United States | IMS
Disaggregation of Revenue [Line Items]
Total revenues	198	188	547	532
International | AST
Disaggregation of Revenue [Line Items]
Total revenues	19	31	60	73
International | NC&C
Disaggregation of Revenue [Line Items]
Total revenues	8	17	30	56
International | IMS
Disaggregation of Revenue [Line Items]
Total revenues	$ 11	$ 6	$ 37	$ 20