Condensed Combining Financial Information of L3 and Its Subsidiaries- Condensed Combining Statements of Operations (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 29, 2019	Mar. 30, 2018
Condensed Financial Statements, Captions [Line Items]
Total sales	$ 2,700	$ 2,371
Total operating costs and expenses	(2,389)	(2,120)
Merger, acquisition and divestiture related expenses and losses	(18)	0
Operating income	293	251
Interest expense	(37)	(41)
Interest and other income, net	4	6
Income from continuing operations before income taxes	260	216
Provision (benefit) for income taxes	(37)	(24)
Equity in net loss of consolidated subsidiaries	0	0
Income from continuing operations	223	192
Loss from discontinued operations, net of income taxes	0	16
Net income	223	208
Net income attributable to noncontrolling interests	(6)	(5)
Net income attributable to L3	217	203
Comprehensive income attributable to L3	241	249
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Total sales	(84)	(97)
Total operating costs and expenses	84	97
Merger, acquisition and divestiture related expenses and losses	0
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	(196)	(191)
Income from continuing operations		(191)
Loss from discontinued operations, net of income taxes		0
Net income	(196)	(191)
Net income attributable to noncontrolling interests	(6)	(5)
Net income attributable to L3	(202)	(196)
Comprehensive income attributable to L3	(259)	(260)
L-3 [Member]
Condensed Financial Statements, Captions [Line Items]
Total sales	904	807
Total operating costs and expenses	(785)	(722)
Merger, acquisition and divestiture related expenses and losses	(18)
Operating income	101	85
Interest expense	(37)	(41)
Interest and other income, net	3	5
Income from continuing operations before income taxes	67	49
Provision (benefit) for income taxes	(10)	(6)
Equity in net loss of consolidated subsidiaries	160	144
Income from continuing operations		187
Loss from discontinued operations, net of income taxes		16
Net income	217	203
Net income attributable to noncontrolling interests	0	0
Net income attributable to L3	217	203
Comprehensive income attributable to L3	241	249
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total sales	1,418	1,239
Total operating costs and expenses	(1,312)	(1,155)
Merger, acquisition and divestiture related expenses and losses	0
Operating income	106	84
Interest expense	0	0
Interest and other income, net	1	0
Income from continuing operations before income taxes	107	84
Provision (benefit) for income taxes	(15)	(9)
Equity in net loss of consolidated subsidiaries	36	47
Income from continuing operations		122
Loss from discontinued operations, net of income taxes		0
Net income	128	122
Net income attributable to noncontrolling interests	0	0
Net income attributable to L3	128	122
Comprehensive income attributable to L3	158	153
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total sales	462	422
Total operating costs and expenses	(376)	(340)
Merger, acquisition and divestiture related expenses and losses	0
Operating income	86	82
Interest expense	0	0
Interest and other income, net	0	1
Income from continuing operations before income taxes	86	83
Provision (benefit) for income taxes	(12)	(9)
Equity in net loss of consolidated subsidiaries	0	0
Income from continuing operations		74
Loss from discontinued operations, net of income taxes		0
Net income	74	74
Net income attributable to noncontrolling interests	0	0
Net income attributable to L3	74	74
Comprehensive income attributable to L3	$ 101	$ 107