Acquisitions - Pro Forma Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions		2 Months Ended	3 Months Ended								5 Months Ended		10 Months Ended	12 Months Ended
	May 31, 2018	May 31, 2018	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, 2019		Mar. 31, 2018		Oct. 31, 2016
Business Acquisition, Pro Forma Information [Abstract]
Revenue			$ 1,094	$ 1,075	$ 1,068	$ 793	$ 715	$ 722	$ 706	$ 676	$ 1,073			$ 4,030		$ 2,819		$ 2,732
Net income (loss)		$ 49	$ (19)	$ 38	$ 24	$ 29	$ 32	$ 104	$ 40	$ 32	$ 36		$ 23	$ 72		$ 208		$ 80
Earnings per common share
Basic (in dollars per share)			$ (0.12)	$ 0.23	$ 0.15	$ 0.18	$ 0.22	$ 0.73	$ 0.28	$ 0.22	$ 0.25	[1]		$ 0.44	[1]	$ 1.46	[1]	$ 0.56	[1]
Diluted (in dollars per share)			$ (0.12)	$ 0.23	$ 0.14	$ 0.17	$ 0.22	$ 0.73	$ 0.28	$ 0.22	$ 0.25	[1]		$ 0.44	[1]	$ 1.46	[1]	$ 0.56	[1]
Number of shares from distribution in a spinoff (in shares)	165,700										142,430			164,560		142,430		142,430
Weighted average common shares outstanding for diluted EPS (in shares)											142,430			164,820		142,430		142,430
Vencore and KeyPoint
Business Acquisition, Pro Forma Information [Abstract]
Revenue		244														$ 1,384
Net income (loss)		$ (57)														33
Vencore and KeyPoint
Business Acquisition, Pro Forma Information [Abstract]
Revenue													1,300
Net income (loss)													$ 185
Vencore and KeyPoint | Pro Forma Combined for the Spin-Off and Mergers
Business Acquisition, Pro Forma Information [Abstract]
Revenue														$ 4,274		4,203
Net income (loss)														$ 28		$ 128
Earnings per common share
Basic (in dollars per share)														$ 0.17		$ 0.77
Diluted (in dollars per share)														$ 0.17		$ 0.77
Vencore and KeyPoint | Effects of the Spin-Off
Business Acquisition, Pro Forma Information [Abstract]
Revenue														$ 0		$ 0
Net income (loss)														(7)		(1)
Vencore and KeyPoint | Effects of the Mergers
Business Acquisition, Pro Forma Information [Abstract]
Revenue														0		0
Net income (loss)														$ 20		$ (112)

[1] (1) Earnings per common share information for the fiscal year ended March 31, 2018, the five months ended March 31, 2017, and the fiscal year ended October 31, 2016 is computed using the 142.43 million shares of Perspecta common stock resulting from the Distribution as Perspecta did not operate as a stand-alone entity during the period, and therefore, no Perspecta common stock, stock options or other equity awards were outstanding and no dividends were declared or paid by Perspecta.