Condensed Combining Financial Information of L3 and Its Subsidiaries- Condensed Combining Statements of Operations (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 30, 2018	Mar. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Total net sales	$ 2,371	$ 2,321
Total operating costs and expenses	(2,120)	(2,084)
Operating income	251	237
Interest expense	(41)	(42)
Interest and other income, net	6	4
Income from continuing operations before income taxes	216	199
Provision (benefit) for income taxes	(24)	(42)
Equity in net loss of consolidated subsidiaries	0	0
Income from continuing operations	192	157
Loss from discontinued operations, net of income taxes	16	11
Net income	208	168
Net income attributable to noncontrolling interests	(5)	(4)
Net income attributable to L3	203	164
Comprehensive income attributable to L3	249	192
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales	(97)	(78)
Total operating costs and expenses	97	78
Operating income	0	0
Interest expense	0	0
Interest and other income, net	0	0
Income from continuing operations before income taxes	0	0
Provision (benefit) for income taxes	0	0
Equity in net loss of consolidated subsidiaries	(160)	(133)
Income from continuing operations	(160)	(133)
Loss from discontinued operations, net of income taxes	0	0
Net income	(160)	(133)
Net income attributable to noncontrolling interests	(5)	(4)
Net income attributable to L3	(165)	(137)
Comprehensive income attributable to L3	(199)	(157)
L-3 [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales	807	850
Total operating costs and expenses	(722)	(772)
Operating income	85	78
Interest expense	(41)	(42)
Interest and other income, net	5	3
Income from continuing operations before income taxes	49	39
Provision (benefit) for income taxes	(6)	(8)
Equity in net loss of consolidated subsidiaries	160	133
Income from continuing operations	203	164
Loss from discontinued operations, net of income taxes	0	0
Net income	203	164
Net income attributable to noncontrolling interests	0	0
Net income attributable to L3	203	164
Comprehensive income attributable to L3	249	192
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales	1,239	1,176
Total operating costs and expenses	(1,155)	(1,077)
Operating income	84	99
Interest expense	0	0
Interest and other income, net	0	0
Income from continuing operations before income taxes	84	99
Provision (benefit) for income taxes	(9)	(21)
Equity in net loss of consolidated subsidiaries	0	0
Income from continuing operations	75	78
Loss from discontinued operations, net of income taxes	16	11
Net income	91	89
Net income attributable to noncontrolling interests	0	0
Net income attributable to L3	91	89
Comprehensive income attributable to L3	92	89
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales	422	373
Total operating costs and expenses	(340)	(313)
Operating income	82	60
Interest expense	0	0
Interest and other income, net	1	1
Income from continuing operations before income taxes	83	61
Provision (benefit) for income taxes	(9)	(13)
Equity in net loss of consolidated subsidiaries	0	0
Income from continuing operations	74	48
Loss from discontinued operations, net of income taxes	0	0
Net income	74	48
Net income attributable to noncontrolling interests	0	0
Net income attributable to L3	74	48
Comprehensive income attributable to L3	$ 107	$ 68