Basis of Presentation and Summary of Significant Accounting Policies (Changes in Estimates on Contracts) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jul. 01, 2022	Jul. 02, 2021	Jul. 01, 2022	Jul. 02, 2021
Accounting Policies [Abstract]
Favorable impact	$ 39	$ 37	$ 80	$ 68
Unfavorable impact	(20)	(29)	(46)	(48)
Net impact to income before income taxes	$ 19	$ 8	$ 34	$ 20
Impact on diluted EPS attributable to Leidos common stockholders (dollars per share)	$ 0.10	$ 0.04	$ 0.18	$ 0.11