CONDENSED CONSOLIDATED STATEMENTS OF EQUITY (UNAUDITED) - USD ($) shares in Millions, $ in Millions	Total	Shares of common stock	Additional paid-in capital	Retained earnings	Accumulated other comprehensive loss	Leidos Holdings, Inc. stockholders' equity	Non-controlling interest
Beginning Balance (shares) at Dec. 29, 2017		151
Beginning Balance at Dec. 29, 2017	$ 3,383		$ 3,344	$ (7)	$ 33	$ 3,370	$ 13
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	102			102		102
Other comprehensive loss, net of taxes	14				14	14
Issuances of stock (shares)		1
Issuances of stock	5		5			5
Repurchases of stock and other	(22)		(22)			(22)
Dividends	(50)			(50)		(50)
Stock-based compensation	11		11			11
Purchase of a non-controlling interest	(10)						(10)
Ending Balance (shares) at Mar. 30, 2018		152
Ending Balance at Mar. 30, 2018	3,434		3,338	37	56	3,431	3
Beginning Balance (shares) at Dec. 29, 2017		151
Beginning Balance at Dec. 29, 2017	3,383		3,344	(7)	33	3,370	13
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	394
Other comprehensive loss, net of taxes	(29)
Ending Balance (shares) at Sep. 28, 2018		150
Ending Balance at Sep. 28, 2018	3,457		3,210	231	13	3,454	3
Beginning Balance (shares) at Mar. 30, 2018		152
Beginning Balance at Mar. 30, 2018	3,434		3,338	37	56	3,431	3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	145			144		144	1
Other comprehensive loss, net of taxes	(33)				(33)	(33)
Issuances of stock	4		4			4
Repurchases of stock and other (shares)		(2)
Repurchases of stock and other	(94)		(94)			(94)
Dividends	(48)			(48)		(48)
Stock-based compensation	12		12			12
Other	(2)						(2)
Ending Balance (shares) at Jun. 29, 2018		150
Ending Balance at Jun. 29, 2018	3,418		3,260	133	23	3,416	2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	147			147		147
Other comprehensive loss, net of taxes	(10)				(10)	(10)
Issuances of stock	7		7			7
Repurchases of stock and other (shares)		0
Repurchases of stock and other	(66)		(66)			(66)
Dividends	(49)			(49)		(49)
Stock-based compensation	10		10			10
Purchase of a non-controlling interest	(1)		(1)			(1)
Other	1						1
Ending Balance (shares) at Sep. 28, 2018		150
Ending Balance at Sep. 28, 2018	3,457		3,210	231	13	3,454	3
Beginning Balance (shares) at Dec. 28, 2018		146
Beginning Balance at Dec. 28, 2018	3,311		2,966	372	(30)	3,308	3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	189			189		189
Other comprehensive 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		2,966	372	(30)	3,308	3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	489
Other comprehensive 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 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 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