Document And Entity Information - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2020	Apr. 30, 2020	Sep. 30, 2019
Document Information [Abstract]
Entity Registrant Name	Perspecta Inc.
Entity Central Index Key	0001724670
Current Fiscal Year End Date	--03-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Document Type	10-K
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding (in shares)		160,584,045
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Public Float			$ 3,610