Financial Information of L3 and Its Subsidiaries, Condensed Combining Statements of Operations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 28, 2018	Jun. 29, 2018	Mar. 30, 2018	Dec. 31, 2017	Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Total net sales	$ 2,771	$ 2,519	$ 2,583	$ 2,371	$ 2,574	$ 2,293	$ 2,385	$ 2,321	$ 10,244	$ 9,573	$ 9,210
Total cost of sales									(9,138)	(8,542)	(8,252)
Gain on sale of the Crestview Aerospace and TCS businesses									42	0	0
Merger and acquisition related expenses									(28)	0	0
Operating Income (Loss)	276	272	321	251	268	232	294	237	1,120	1,031	958
Interest expense									(164)	(169)	(164)
Interest and other income, net									37	9	17
Debt retirement charges		21	48						(69)	0	(7)
Income from continuing operations before income taxes									924	871	804
Provision for income taxes									(103)	(102)	(171)
Equity in net income (loss) of consolidated subsidiaries									0	0	0
Income from continuing operations	232	208	189	192	271	146	195	157	821	769	633
(Loss) income from discontinued operations, net of income taxes									205	(76)	91
Net (loss) income	231	208	379	208	293	25	207	168	1,026	693	724
Net income attributable to noncontrolling interests									(21)	(16)	(14)
Net income attributable to L3	$ 225	$ 202	$ 375	$ 203	$ 289	$ 22	$ 202	$ 164	1,005	677	710
Comprehensive (loss) income attributable to L3									971	712	558
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales									3,626	3,520	3,351
Total cost of sales									(3,180)	(3,169)	(3,064)
Gain on sale of the Crestview Aerospace and TCS businesses									0
Merger and acquisition related expenses									(28)
Operating Income (Loss)									418	351	287
Interest expense									(163)	(168)	(164)
Interest and other income, net									31	6	9
Debt retirement charges									(69)		(7)
Income from continuing operations before income taxes									217	189	125
Provision for income taxes									(24)	(22)	(26)
Equity in net income (loss) of consolidated subsidiaries									607	586	520
Income from continuing operations									800	753	619
(Loss) income from discontinued operations, net of income taxes									205	(76)	91
Net (loss) income									1,005	677	710
Net income attributable to noncontrolling interests									0	0	0
Net income attributable to L3									1,005	677	710
Comprehensive (loss) income attributable to L3									971	712	558
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales									5,259	4,852	4,842
Total cost of sales									(4,943)	(4,446)	(4,406)
Gain on sale of the Crestview Aerospace and TCS businesses									42
Merger and acquisition related expenses									0
Operating Income (Loss)									358	406	436
Interest expense									0	0	0
Interest and other income, net									3	(8)	(3)
Debt retirement charges									0		0
Income from continuing operations before income taxes									361	398	433
Provision for income taxes									(40)	(47)	(92)
Equity in net income (loss) of consolidated subsidiaries									184	144	130
Income from continuing operations									505	495	471
(Loss) income from discontinued operations, net of income taxes									0	0	0
Net (loss) income									505	495	471
Net income attributable to noncontrolling interests									0	0	0
Net income attributable to L3									505	495	471
Comprehensive (loss) income attributable to L3									427	604	409
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales									1,806	1,581	1,348
Total cost of sales									(1,462)	(1,307)	(1,113)
Gain on sale of the Crestview Aerospace and TCS businesses									0
Merger and acquisition related expenses									0
Operating Income (Loss)									344	274	235
Interest expense									(1)	(1)	0
Interest and other income, net									3	11	11
Debt retirement charges									0		0
Income from continuing operations before income taxes									346	284	246
Provision for income taxes									(39)	(33)	(53)
Equity in net income (loss) of consolidated subsidiaries									0	0	0
Income from continuing operations									307	251	193
(Loss) income from discontinued operations, net of income taxes									0	0	0
Net (loss) income									307	251	193
Net income attributable to noncontrolling interests									0	0	0
Net income attributable to L3									307	251	193
Comprehensive (loss) income attributable to L3									226	378	116
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Total net sales									(447)	(380)	(331)
Total cost of sales									447	380	331
Gain on sale of the Crestview Aerospace and TCS businesses									0
Merger and acquisition related expenses									0
Operating Income (Loss)									0	0	0
Interest expense									0	0	0
Interest and other income, net									0	0	0
Debt retirement charges									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									(791)	(730)	(650)
Income from continuing operations									(791)	(730)	(650)
(Loss) income from discontinued operations, net of income taxes									0	0	0
Net (loss) income									(791)	(730)	(650)
Net income attributable to noncontrolling interests									(21)	(16)	(14)
Net income attributable to L3									(812)	(746)	(664)
Comprehensive (loss) income attributable to L3									$ (653)	$ (982)	$ (525)