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. 29, 2018	Jun. 30, 2017	Jun. 29, 2018	Jun. 30, 2017
Condensed Financial Statements, Captions [Line Items]
Total net sales	$ 2,583	$ 2,385	$ 4,954	$ 4,706
Total operating costs and expenses	(2,310)	(2,091)	(4,430)	(4,175)
Gain on sale of the Crestview Aerospace and TCS businesses	48	0	48	0
Operating income	321	294	572	531
Interest expense	(44)	(42)	(85)	(84)
Interest and other income, net	8	2	14	6
Debt retirement charge	(48)	0	(48)	0
Income from continuing operations before income taxes	237	254	453	453
Provision (benefit) for income taxes	(48)	(59)	(72)	(101)
Equity in net loss of consolidated subsidiaries	0	0	0	0
Income from continuing operations	189	195	381	352
Loss from discontinued operations, net of income taxes	190	12	206	23
Net income	379	207	587	375
Net income attributable to noncontrolling interests	(4)	(5)	(9)	(9)
Net income attributable to L3	375	202	578	366
Comprehensive income attributable to L3	306	264	555	456
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales	(95)	(101)	(192)	(177)
Total operating costs and expenses	95	101	192	177
Gain on sale of the Crestview Aerospace and TCS businesses	0		0
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 (benefit) for income taxes	0	0	0	0
Equity in net loss of consolidated subsidiaries	(221)	(191)	(411)	(336)
Income from continuing operations	(221)	(191)	(411)	(336)
Loss from discontinued operations, net of income taxes	0	0	0	0
Net income	(221)	(191)	(411)	(336)
Net income attributable to noncontrolling interests	(4)	(5)	(9)	(9)
Net income attributable to L3	(225)	(196)	(420)	(345)
Comprehensive income attributable to L3	(74)	(296)	(333)	(478)
L-3 [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales	919	894	1,726	1,744
Total operating costs and expenses	(819)	(810)	(1,541)	(1,581)
Gain on sale of the Crestview Aerospace and TCS businesses	0		0
Operating income	100	84	185	163
Interest expense	(43)	(42)	(84)	(84)
Interest and other income, net	6	2	11	5
Debt retirement charge	(48)		(48)
Income from continuing operations before income taxes	15	44	64	84
Provision (benefit) for income taxes	(4)	(10)	(10)	(19)
Equity in net loss of consolidated subsidiaries	174	156	318	278
Income from continuing operations	185	190	372	343
Loss from discontinued operations, net of income taxes	190	12	206	23
Net income	375	202	578	366
Net income attributable to noncontrolling interests	0	0	0	0
Net income attributable to L3	375	202	578	366
Comprehensive income attributable to L3	306	264	555	456
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales	1,328	1,193	2,567	2,389
Total operating costs and expenses	(1,239)	(1,049)	(2,394)	(2,145)
Gain on sale of the Crestview Aerospace and TCS businesses	48		48
Operating income	137	144	221	244
Interest expense	0	0	0	0
Interest and other income, net	1	0	1	0
Debt retirement charge	0		0
Income from continuing operations before income taxes	138	144	222	244
Provision (benefit) for income taxes	(26)	(34)	(35)	(54)
Equity in net loss of consolidated subsidiaries	47	35	93	58
Income from continuing operations	159	145	280	248
Loss from discontinued operations, net of income taxes	0	0	0	0
Net income	159	145	280	248
Net income attributable to noncontrolling interests	0	0	0	0
Net income attributable to L3	159	145	280	248
Comprehensive income attributable to L3	85	192	237	308
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales	431	399	853	750
Total operating costs and expenses	(347)	(333)	(687)	(626)
Gain on sale of the Crestview Aerospace and TCS businesses	0		0
Operating income	84	66	166	124
Interest expense	(1)	0	(1)	0
Interest and other income, net	1	0	2	1
Debt retirement charge	0		0
Income from continuing operations before income taxes	84	66	167	125
Provision (benefit) for income taxes	(18)	(15)	(27)	(28)
Equity in net loss of consolidated subsidiaries	0	0	0	0
Income from continuing operations	66	51	140	97
Loss from discontinued operations, net of income taxes	0	0	0	0
Net income	66	51	140	97
Net income attributable to noncontrolling interests	0	0	0	0
Net income attributable to L3	66	51	140	97
Comprehensive income attributable to L3	$ (11)	$ 104	$ 96	$ 170