Revenue - Schedule of Revenues Disaggregated By Prime or Subcontractor (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 1,099	$ 1,126	$ 1,172	$ 1,107	$ 1,094	$ 1,075	$ 1,068	$ 793	$ 4,504	$ 4,030	$ 2,819
Prime contractor
Disaggregation of Revenue [Line Items]
Revenues									4,215	3,774
Subcontractor
Disaggregation of Revenue [Line Items]
Revenues									289	256
Defense and Intelligence
Disaggregation of Revenue [Line Items]
Revenues									3,101	2,587
Defense and Intelligence | Prime contractor
Disaggregation of Revenue [Line Items]
Revenues									2,915	2,431
Defense and Intelligence | Subcontractor
Disaggregation of Revenue [Line Items]
Revenues									186	156
Civilian and Health Care
Disaggregation of Revenue [Line Items]
Revenues									1,403	1,443
Civilian and Health Care | Prime contractor
Disaggregation of Revenue [Line Items]
Revenues									1,300	1,343
Civilian and Health Care | Subcontractor
Disaggregation of Revenue [Line Items]
Revenues									$ 103	$ 100