Segment Information, Products and Services (Details) $ in Millions		3 Months Ended												12 Months Ended
		Dec. 31, 2017 USD ($)		Sep. 29, 2017 USD ($)	[2]	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)		Sep. 23, 2016 USD ($)	[2]	Jun. 24, 2016 USD ($)	Mar. 25, 2016 USD ($)	Dec. 31, 2017 USD ($) Segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Segment Information [Abstract]
Number of reportable segments | Segment														4
Corporate expenses														$ 32	$ 29	$ 29
Net Sales [Abstract]
Products														6,733	6,453	6,600
Services														2,840	2,757	2,631
Total net sales		$ 2,574	[1]	$ 2,293		$ 2,385	$ 2,321	$ 2,643	[1]	$ 2,184		$ 2,318	$ 2,065	9,573	9,210	9,231
Operating income [Abstract]
Operating income		263	[1]	$ 229		$ 292	$ 236	282	[1]	$ 211		$ 220	$ 244	1,020	957	785
Goodwill impairment charge	[3]													0	0	(46)
Loss related to business divestitures	[4]													0	0	(31)
Depreciation and amortization [Abstract]
Depreciation and amortization														225	198	203
Capital Expenditures [Abstract]
Capital Expenditures														224	210	195
Total Assets [Abstract]
Total Assets		12,729						11,865						12,729	11,865	12,069
Assets held for sale		135						0						135	0	0
Assets of discontinued operations		306						481						306	481	1,124
NSS Including Business Retained [Member] | Continuing Operations [Member]
Operating income [Abstract]
Goodwill impairment charge																(46)
Operating Segments [Member]
Operating income [Abstract]
Operating income														1,020	957	862
Operating Segments [Member] | Electronic Systems [Member]
Net Sales [Abstract]
Products														2,234	2,033	2,102
Services														848	812	810
Operating income [Abstract]
Operating income														403	360	337
Depreciation and amortization [Abstract]
Depreciation and amortization														79	60	59
Capital Expenditures [Abstract]
Capital Expenditures														68	76	69
Total Assets [Abstract]
Total Assets		4,796						4,369						4,796	4,369	3,968
Operating Segments [Member] | Aerospace Systems [Member]
Net Sales [Abstract]
Products														1,545	1,679	1,679
Services														1,267	1,270	1,257
Operating income [Abstract]
Operating income														210	255	193
Depreciation and amortization [Abstract]
Depreciation and amortization														51	46	43
Capital Expenditures [Abstract]
Capital Expenditures														43	50	53
Total Assets [Abstract]
Total Assets		2,014						2,084						2,014	2,084	2,190
Operating Segments [Member] | Communication Systems [Member]
Net Sales [Abstract]
Products														1,745	1,586	1,649
Services														510	488	441
Operating income [Abstract]
Operating income														212	195	190
Depreciation and amortization [Abstract]
Depreciation and amortization														49	47	50
Capital Expenditures [Abstract]
Capital Expenditures														49	37	37
Total Assets [Abstract]
Total Assets		2,063						2,031						2,063	2,031	1,984
Operating Segments [Member] | Sensor Systems [Member]
Net Sales [Abstract]
Products														1,292	1,266	1,298
Services														273	235	193
Operating income [Abstract]
Operating income														195	147	142
Depreciation and amortization [Abstract]
Depreciation and amortization														46	45	51
Capital Expenditures [Abstract]
Capital Expenditures														42	37	30
Total Assets [Abstract]
Total Assets		2,706						2,433						2,706	2,433	2,458
Corporate [Member]
Capital Expenditures [Abstract]
Capital Expenditures														22	10	6
Total Assets [Abstract]
Total Assets		$ 709						$ 467						709	467	345
Elimination of Intercompany Sales [Member]
Net Sales [Abstract]
Products														(83)	(111)	(128)
Services														$ (58)	$ (48)	$ (70)

[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.