CONDENSED CONSOLIDATED STATEMENTS OF EQUITY (UNAUDITED) - USD ($) shares in Millions, $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment	Cumulative Effect, Period of Adoption, Adjusted Balance	Shares of common stock	Additional paid-in capital	Additional paid-in capital Cumulative Effect, Period of Adoption, Adjusted Balance	Retained earnings	Retained earnings Cumulative Effect, Period of Adoption, Adjustment	Retained earnings Cumulative Effect, Period of Adoption, Adjusted Balance	Accumulated other comprehensive loss	Accumulated other comprehensive loss Cumulative Effect, Period of Adoption, Adjusted Balance	Leidos Holdings, Inc. stockholders' equity	Leidos Holdings, Inc. stockholders' equity Cumulative Effect, Period of Adoption, Adjustment	Leidos Holdings, Inc. stockholders' equity Cumulative Effect, Period of Adoption, Adjusted Balance	Non-controlling interest	Non-controlling interest Cumulative Effect, Period of Adoption, Adjusted Balance
Beginning balance (shares) at Dec. 28, 2018				146
Beginning Balance at Dec. 28, 2018	$ 3,311	$ 48	$ 3,359		$ 2,966	$ 2,966	$ 372	$ 48	$ 420	$ (30)	$ (30)	$ 3,308	$ 48	$ 3,356	$ 3	$ 3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	189						189					189
Other comprehensive income (loss), net of taxes	(5)									(5)		(5)
Issuances of stock (shares)				1
Issuances of stock	11				11							11
Repurchases of stock and other (shares)				(3)
Repurchases of stock and other	(222)				(222)							(222)
Dividends	(47)						(47)					(47)
Stock-based compensation	12				12							12
Ending balance (shares) at Mar. 29, 2019				144
Ending Balance at Mar. 29, 2019	3,297				2,767		562			(35)		3,294			3
Beginning balance (shares) at Dec. 28, 2018				146
Beginning Balance at Dec. 28, 2018	3,311	48	3,359		2,966	2,966	372	48	420	(30)	(30)	3,308	48	3,356	3	3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	489
Other comprehensive income (loss), net of taxes	(78)
Ending balance (shares) at Sep. 27, 2019				141
Ending Balance at Sep. 27, 2019	3,250				2,590		764			(108)		3,246			4
Beginning balance (shares) at Mar. 29, 2019				144
Beginning Balance at Mar. 29, 2019	3,297				2,767		562			(35)		3,294			3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	138						136					136			2
Other comprehensive income (loss), net of taxes	(38)									(38)		(38)
Issuances of stock	6				6							6
Repurchases of stock and other	(5)				(5)							(5)
Dividends	(46)						(46)					(46)
Stock-based compensation	13				13							13
Other	(3)				(1)							(1)			(2)
Ending balance (shares) at Jun. 28, 2019				144
Ending Balance at Jun. 28, 2019	3,362				2,780		652			(73)		3,359			3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	162						161					161			1
Other comprehensive income (loss), net of taxes	(35)									(35)		(35)
Repurchases of stock and other (shares)				(3)
Repurchases of stock and other	(203)				(203)							(203)
Dividends	(49)						(49)					(49)
Stock-based compensation	13				13							13
Ending balance (shares) at Sep. 27, 2019				141
Ending Balance at Sep. 27, 2019	3,250				2,590		764			(108)		3,246			4
Beginning balance (shares) at Jan. 03, 2020				141
Beginning Balance at Jan. 03, 2020	3,417	(1)	3,416		2,587	2,587	896	(1)	895	(70)	(70)	3,413	(1)	3,412	4	4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	115						115					115
Other comprehensive income (loss), net of taxes	(115)									(115)		(115)
Issuances of stock (shares)				1
Issuances of stock	9				9							9
Repurchases of stock and other	(32)				(32)							(32)
Dividends	(49)						(49)					(49)
Stock-based compensation	15				15							15
Ending balance (shares) at Apr. 03, 2020				142
Ending Balance at Apr. 03, 2020	3,359				2,579		961			(185)		3,355			4
Beginning balance (shares) at Jan. 03, 2020				141
Beginning Balance at Jan. 03, 2020	3,417	$ (1)	$ 3,416		2,587	$ 2,587	896	$ (1)	$ 895	(70)	$ (70)	3,413	$ (1)	$ 3,412	4	$ 4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	432
Other comprehensive income (loss), net of taxes	(28)
Ending balance (shares) at Oct. 02, 2020				142
Ending Balance at Oct. 02, 2020	3,715				2,624		1,180			(98)		3,706			9
Beginning balance (shares) at Apr. 03, 2020				142
Beginning Balance at Apr. 03, 2020	3,359				2,579		961			(185)		3,355			4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	154						153					153			1
Other comprehensive income (loss), net of taxes	58									58		58
Issuances of stock	8				8							8
Repurchases of stock and other	(2)				(2)							(2)
Dividends	(49)						(49)					(49)
Stock-based compensation	15				15							15
Capital contributions to non-controlling interest	4														4
Ending balance (shares) at Jul. 03, 2020				142
Ending Balance at Jul. 03, 2020	3,547				2,600		1,065			(127)		3,538			9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	163						163					163
Other comprehensive income (loss), net of taxes	29									29		29
Issuances of stock	10				10							10
Repurchases of stock and other	(1)				(1)							(1)
Dividends	(48)						(48)					(48)
Stock-based compensation	15				15							15
Ending balance (shares) at Oct. 02, 2020				142
Ending Balance at Oct. 02, 2020	$ 3,715				$ 2,624		$ 1,180			$ (98)		$ 3,706			$ 9