Condensed Combining Financial Information of L3 and Its Subsidiaries- Condensed Combining Statements of Operations (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 24, 2016	Jun. 30, 2017	Jun. 24, 2016
Condensed Financial Statements, Captions [Line Items]
Total net sales	$ 2,732	$ 2,664	$ 5,401	$ 5,017
Total cost of sales	(2,420)	(2,417)	(4,836)	(4,518)
Operating income	312	247	565	499
Interest expense	(43)	(43)	(85)	(84)
Interest and other income, net	4	5	9	9
Debt retirement charge	0	(5)	0	(5)
Income from continuing operations before income taxes	273	204	489	419
Provision for income taxes	(66)	(53)	(114)	(101)
Equity in net income of consolidated subsidiaries	0	0	0	0
Income from continuing operations			375	318
Income from discontinued operations, net of income taxes			0	63
Net income	207	151	375	381
Net income attributable to noncontrolling interests	(5)	(4)	(9)	(7)
Net income attributable to L3	202	147	366	374
Comprehensive income attributable to L3	264	161	456	404
L-3 [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales	901	903	1,763	1,725
Total cost of sales	(811)	(803)	(1,588)	(1,542)
Operating income	90	100	175	183
Interest expense	(42)	(43)	(84)	(84)
Interest and other income, net	2	3	5	6
Debt retirement charge		(5)		(5)
Income from continuing operations before income taxes	50	55	96	100
Provision for income taxes	(12)	(14)	(22)	(24)
Equity in net income of consolidated subsidiaries	164	106	292	298
Income from continuing operations				374
Income from discontinued operations, net of income taxes				0
Net income	202	147	366	374
Net income attributable to noncontrolling interests	0	0	0	0
Net income attributable to L3	202	147	366	374
Comprehensive income attributable to L3	264	161	456	404
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales	1,512	1,374	3,019	2,559
Total cost of sales	(1,357)	(1,295)	(2,756)	(2,363)
Operating income	155	79	263	196
Interest expense	(1)	0	(1)	0
Interest and other income, net	0	0	0	0
Debt retirement charge		0		0
Income from continuing operations before income taxes	154	79	262	196
Provision for income taxes	(37)	(21)	(61)	(47)
Equity in net income of consolidated subsidiaries	0	0	0	0
Income from continuing operations				149
Income from discontinued operations, net of income taxes				63
Net income	117	58	201	212
Net income attributable to noncontrolling interests	0	0	0	0
Net income attributable to L3	117	58	201	212
Comprehensive income attributable to L3	117	61	201	223
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales	420	454	793	863
Total cost of sales	(353)	(386)	(666)	(743)
Operating income	67	68	127	120
Interest expense	0	0	0	0
Interest and other income, net	2	2	4	3
Debt retirement charge		0		0
Income from continuing operations before income taxes	69	70	131	123
Provision for income taxes	(17)	(18)	(31)	(30)
Equity in net income of consolidated subsidiaries	0	0	0	0
Income from continuing operations				93
Income from discontinued operations, net of income taxes				0
Net income	52	52	100	93
Net income attributable to noncontrolling interests	0	0	0	0
Net income attributable to L3	52	52	100	93
Comprehensive income attributable to L3	105	55	173	96
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales	(101)	(67)	(174)	(130)
Total cost of sales	101	67	174	130
Operating income	0	0	0	0
Interest expense	0	0	0	0
Interest and other income, net	0	0	0	0
Debt retirement charge		0		0
Income from continuing operations before income taxes	0	0	0	0
Provision for income taxes	0	0	0	0
Equity in net income of consolidated subsidiaries	(164)	(106)	(292)	(298)
Income from continuing operations				(298)
Income from discontinued operations, net of income taxes				0
Net income	(164)	(106)	(292)	(298)
Net income attributable to noncontrolling interests	(5)	(4)	(9)	(7)
Net income attributable to L3	(169)	(110)	(301)	(305)
Comprehensive income attributable to L3	$ (222)	$ (116)	$ (374)	$ (319)