Revenue - Schedule of Revenues Disaggregated By Customer Type (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
U.S. federal government, including independent agencies
Disaggregation of Revenue [Line Items]
Revenues									4,225	3,759
Non-federal (state, local and other)
Disaggregation of Revenue [Line Items]
Revenues									279	271
Defense and Intelligence
Disaggregation of Revenue [Line Items]
Revenues									3,101	2,587
Defense and Intelligence | U.S. federal government, including independent agencies
Disaggregation of Revenue [Line Items]
Revenues									3,084	2,574
Defense and Intelligence | Non-federal (state, local and other)
Disaggregation of Revenue [Line Items]
Revenues									17	13
Civilian and Health Care
Disaggregation of Revenue [Line Items]
Revenues									1,403	1,443
Civilian and Health Care | U.S. federal government, including independent agencies
Disaggregation of Revenue [Line Items]
Revenues									1,141	1,185
Civilian and Health Care | Non-federal (state, local and other)
Disaggregation of Revenue [Line Items]
Revenues									$ 262	$ 258