Financial Information of L3 and Its Subsidiaries, Condensed Combining Statements of Operations (Details) - USD ($) $ in Millions		3 Months Ended												12 Months Ended
		Dec. 31, 2017	[1]	Sep. 29, 2017	[2]	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	[1]	Sep. 23, 2016	[2]	Jun. 24, 2016	Mar. 25, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Total net sales		$ 2,574		$ 2,293		$ 2,385	$ 2,321	$ 2,643		$ 2,184		$ 2,318	$ 2,065	$ 9,573	$ 9,210	$ 9,231
Total cost of sales														(8,553)	(8,253)	(8,369)
Goodwill impairment charges	[3]													0	0	(46)
(Loss) gain related to business divestitures	[4]													0	0	(31)
Operating income		263		229		292	236	282		211		220	244	1,020	957	785
Interest expense														(169)	(164)	(162)
Interest and other income, net														20	18	17
Debt retirement charge														0	(7)	(1)
Income from continuing operations before income taxes														871	804	639
Provision for income taxes														(102)	(171)	(132)
Equity in net income (loss) of consolidated subsidiaries														0	0	0
Income from continuing operations		271		146		195	157	187		149		134	163	769	633	507
(Loss) income from discontinued operations, net of income taxes														(76)	91	(732)
Net (loss) income		293		25		207	168	192		151		151	230	693	724	(225)
Net income attributable to noncontrolling interests														(16)	(14)	(15)
Net income (loss) attributable to L-3		$ 289		$ 22		$ 202	$ 164	$ 188		$ 148		$ 147	$ 227	677	710	(240)
Comprehensive (loss) income attributable to L3														712	558	(230)
L-3 Communications Corporation [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales														3,519	3,350	3,267
Total cost of sales														(3,179)	(3,069)	(3,031)
Goodwill impairment charges																0
(Loss) gain related to business divestitures																(13)
Operating income														340	281	223
Interest expense														(168)	(164)	(161)
Interest and other income, net														17	15	17
Debt retirement charge															(7)	(1)
Income from continuing operations before income taxes														189	125	78
Provision for income taxes														(22)	(26)	(16)
Equity in net income (loss) of consolidated subsidiaries														511	611	(302)
Income from continuing operations														678	710	(240)
(Loss) income from discontinued operations, net of income taxes														(1)	0	0
Net (loss) income														677	710	(240)
Net income attributable to noncontrolling interests														0	0	0
Net income (loss) attributable to L-3														677	710	(240)
Comprehensive (loss) income attributable to L3														712	558	(230)
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales														4,748	4,809	4,866
Total cost of sales														(4,350)	(4,378)	(4,441)
Goodwill impairment charges																(26)
(Loss) gain related to business divestitures																(31)
Operating income														398	431	368
Interest expense														0	0	(1)
Interest and other income, net														0	0	0
Debt retirement charge															0	0
Income from continuing operations before income taxes														398	431	367
Provision for income taxes														(47)	(92)	(76)
Equity in net income (loss) of consolidated subsidiaries														0	0	0
Income from continuing operations														351	339	291
(Loss) income from discontinued operations, net of income taxes														(75)	91	(732)
Net (loss) income														276	430	(441)
Net income attributable to noncontrolling interests														0	0	0
Net income (loss) attributable to L-3														276	430	(441)
Comprehensive (loss) income attributable to L3														278	440	(445)
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales														1,690	1,381	1,449
Total cost of sales														(1,408)	(1,136)	(1,248)
Goodwill impairment charges																(20)
(Loss) gain related to business divestitures																13
Operating income														282	245	194
Interest expense														(1)	0	0
Interest and other income, net														3	3	0
Debt retirement charge															0	0
Income from continuing operations before income taxes														284	248	194
Provision for income taxes														(33)	(53)	(40)
Equity in net income (loss) of consolidated subsidiaries														0	0	0
Income from continuing operations														251	195	154
(Loss) income from discontinued operations, net of income taxes														0	0	0
Net (loss) income														251	195	154
Net income attributable to noncontrolling interests														0	0	0
Net income (loss) attributable to L-3														251	195	154
Comprehensive (loss) income attributable to L3														378	118	43
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales														(384)	(330)	(351)
Total cost of sales														384	330	351
Goodwill impairment charges																0
(Loss) gain related to business divestitures																0
Operating income														0	0	0
Interest expense														0	0	0
Interest and other income, net														0	0	0
Debt retirement charge															0	0
Income from continuing operations before income taxes														0	0	0
Provision for income taxes														0	0	0
Equity in net income (loss) of consolidated subsidiaries														(511)	(611)	302
Income from continuing operations														(511)	(611)	302
(Loss) income from discontinued operations, net of income taxes														0	0	0
Net (loss) income														(511)	(611)	302
Net income attributable to noncontrolling interests														(16)	(14)	(15)
Net income (loss) attributable to L-3														(527)	(625)	287
Comprehensive (loss) income attributable to L3														$ (656)	$ (558)	$ 402

[1] Provision for income taxes for the fourth quarter of 2017, includes estimated tax benefits of $79 million or $0.99 per diluted share, related to the enactment of the U.S. Tax Cuts and Jobs Act (U.S. Tax Reform) in December 2017.

[2] The Company recorded a goodwill impairment charge of $187 million or $1.67 per diluted share for the Vertex Aerospace reporting unit in 2017, which is reported in discontinued operations.

[3] Represents non-cash goodwill impairment charges recorded during 2015 of $46 million related to a business retained by L3 in connection with the sale of the NSS segment.

[4] See Note 3 for information regarding the Company's business divestitures.