Revenue - Schedule of Revenues Disaggregated By Prime or Subcontractor (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
Prime contractor
Disaggregation of Revenue [Line Items]
Revenues										3,774
Subcontractor
Disaggregation of Revenue [Line Items]
Revenues										256
Defense and Intelligence
Disaggregation of Revenue [Line Items]
Revenues										2,587
Defense and Intelligence | Prime contractor
Disaggregation of Revenue [Line Items]
Revenues										2,431
Defense and Intelligence | Subcontractor
Disaggregation of Revenue [Line Items]
Revenues										156
Civilian and Health Care
Disaggregation of Revenue [Line Items]
Revenues										1,443
Civilian and Health Care | Prime contractor
Disaggregation of Revenue [Line Items]
Revenues										1,343
Civilian and Health Care | Subcontractor
Disaggregation of Revenue [Line Items]
Revenues										$ 100