Segment Information (Details)	3 Months Ended								12 Months Ended
	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2020 USD ($) segment	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment									2
Revenue	$ 1,099,000,000	$ 1,126,000,000	$ 1,172,000,000	$ 1,107,000,000	$ 1,094,000,000	$ 1,075,000,000	$ 1,068,000,000	$ 793,000,000	$ 4,504,000,000	$ 4,030,000,000	$ 2,819,000,000
Impairment charges	$ 796,000,000	$ 0	$ 0	$ 0					796,000,000	0	0
Defense and Intelligence
Segment Reporting Information [Line Items]
Revenue									3,101,000,000	2,587,000,000
Civilian and Health Care
Segment Reporting Information [Line Items]
Revenue									1,403,000,000	1,443,000,000
Operating segments
Segment Reporting Information [Line Items]
Revenue									4,504,000,000	4,030,000,000	2,819,000,000
Segment Profit									596,000,000	527,000,000	390,000,000
Total depreciation and amortization									374,000,000	330,000,000	167,000,000
Operating segments | Series of Individually Immaterial Business Acquisitions
Segment Reporting Information [Line Items]
Total depreciation and amortization									206,000,000	165,000,000	69,000,000
Operating segments | Defense and Intelligence
Segment Reporting Information [Line Items]
Revenue									3,101,000,000	2,587,000,000	1,416,000,000
Segment Profit									444,000,000	331,000,000	168,000,000
Total depreciation and amortization									66,000,000	74,000,000	34,000,000
Operating segments | Civilian and Health Care
Segment Reporting Information [Line Items]
Revenue									1,403,000,000	1,443,000,000	1,403,000,000
Segment Profit									152,000,000	196,000,000	222,000,000
Total depreciation and amortization									102,000,000	91,000,000	64,000,000
Corporate
Segment Reporting Information [Line Items]
Impairment charges									$ 796,000,000	$ 0	$ 0