Revenue - Schedule of Revenues Disaggregated By Contract Type (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 1,172	$ 1,068	$ 2,279	$ 1,861
Cost-reimbursable
Disaggregation of Revenue [Line Items]
Revenues	292	251	586	381
Fixed-price
Disaggregation of Revenue [Line Items]
Revenues	662	607	1,248	1,082
Time-and-materials
Disaggregation of Revenue [Line Items]
Revenues	218	210	445	398
Defense and Intelligence
Disaggregation of Revenue [Line Items]
Revenues	777	702	1,529	1,139
Defense and Intelligence | Cost-reimbursable
Disaggregation of Revenue [Line Items]
Revenues	267	231	535	340
Defense and Intelligence | Fixed-price
Disaggregation of Revenue [Line Items]
Revenues	411	367	783	612
Defense and Intelligence | Time-and-materials
Disaggregation of Revenue [Line Items]
Revenues	99	104	211	187
Civilian and Health Care
Disaggregation of Revenue [Line Items]
Revenues	395	366	750	722
Civilian and Health Care | Cost-reimbursable
Disaggregation of Revenue [Line Items]
Revenues	25	20	51	41
Civilian and Health Care | Fixed-price
Disaggregation of Revenue [Line Items]
Revenues	251	240	465	470
Civilian and Health Care | Time-and-materials
Disaggregation of Revenue [Line Items]
Revenues	$ 119	$ 106	$ 234	$ 211