Acquisitions - Pro Forma Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	1 Months Ended	2 Months Ended	3 Months Ended			6 Months Ended
	Jun. 30, 2018	May 31, 2018	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Business Acquisition, Pro Forma Information [Abstract]
Revenue			$ 1,172		$ 1,068	$ 2,279	$ 1,861
Net income (loss)	$ (20)	$ 49	$ 29	$ 31	$ 24	$ 60	$ 53
Earnings per common share
Basic (in dollars per share)			$ 0.18		$ 0.15	$ 0.37	$ 0.32
Diluted (in dollars per share)			$ 0.18		$ 0.14	$ 0.37	$ 0.32
Weighted average common shares outstanding for basic EPS (in shares)			162,220		165,490	162,510	165,540
Weighted average common shares outstanding for diluted EPS (in shares)			162,900		165,790	163,090	165,820
Vencore and KeyPoint
Business Acquisition, Pro Forma Information [Abstract]
Revenue		244
Net income (loss)		$ (57)
Vencore and KeyPoint
Business Acquisition, Pro Forma Information [Abstract]
Revenue	490
Net income (loss)	$ 71
Vencore and KeyPoint | Pro Forma Combined for the Spin-Off and Mergers
Business Acquisition, Pro Forma Information [Abstract]
Revenue							$ 2,105
Net income (loss)							$ 1
Earnings per common share
Basic (in dollars per share)							$ 0.01
Diluted (in dollars per share)							$ 0.01
Vencore and KeyPoint | Effects of the Spin-Off
Business Acquisition, Pro Forma Information [Abstract]
Revenue							$ 0
Net income (loss)							(7)
Vencore and KeyPoint | Effects of the Mergers
Business Acquisition, Pro Forma Information [Abstract]
Revenue							0
Net income (loss)							$ 12