Revenue - Schedule of Revenues Disaggregated By Customer Type (Details) - USD ($) $ in Millions	3 Months Ended								5 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Oct. 31, 2016
Disaggregation of Revenue [Line Items]
Revenues	$ 1,094	$ 1,075	$ 1,068	$ 793	$ 715	$ 722	$ 706	$ 676	$ 1,073	$ 4,030	$ 2,819	$ 2,732
U.S. federal government, including independent agencies
Disaggregation of Revenue [Line Items]
Revenues										3,759
Non-federal (state, local and other)
Disaggregation of Revenue [Line Items]
Revenues										271
Defense and Intelligence
Disaggregation of Revenue [Line Items]
Revenues										2,587
Defense and Intelligence | U.S. federal government, including independent agencies
Disaggregation of Revenue [Line Items]
Revenues										2,574
Defense and Intelligence | Non-federal (state, local and other)
Disaggregation of Revenue [Line Items]
Revenues										13
Civilian and Health Care
Disaggregation of Revenue [Line Items]
Revenues										1,443
Civilian and Health Care | U.S. federal government, including independent agencies
Disaggregation of Revenue [Line Items]
Revenues										1,185
Civilian and Health Care | Non-federal (state, local and other)
Disaggregation of Revenue [Line Items]
Revenues										$ 258