Summary of Significant Accounting Policies (Changes in Estimates on Contracts) (Details) - USD ($) $ / shares in Units, $ in Millions	11 Months Ended	12 Months Ended
	Jan. 01, 2016	Dec. 29, 2017	Dec. 30, 2016
Accounting Policies [Abstract]
Net favorable impact to income from continuing operations before taxes	$ 18	$ 103	$ 37
Impact on diluted EPS from continuing operations attributable to Leidos common stockholders	$ 0.14	$ 0.41	$ 0.22