Acquisitions (Pro Forma Information) (Details) - L3Harris Security Detection and Automation Businesses and Dynetics - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jul. 03, 2020	Jun. 28, 2019	Jul. 03, 2020	Jun. 28, 2019
Business Acquisition [Line Items]
Revenues	$ 2,984	$ 3,027	$ 6,060	$ 5,854
Net income	147	107	271	254
Net income attributable to Leidos common stockholders	$ 146	$ 105	$ 270	$ 252
Earnings per share:
Basic (in dollars per share)	$ 1.03	$ 0.73	$ 1.90	$ 1.75
Diluted (in dollars per share)	$ 1.01	$ 0.72	$ 1.88	$ 1.73