Basis of Presentation and Summary of Significant Accounting Policies (Changes in Estimates on Contracts) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Apr. 01, 2022	Apr. 02, 2021
Accounting Policies [Abstract]
Favorable impact	$ 41	$ 31
Unfavorable impact	(26)	(19)
Net impact to income before income taxes	$ 15	$ 12
Impact on diluted EPS attributable to Leidos common stockholders (dollars per share)	$ 0.08	$ 0.06