Condensed Combining Financial Information of L3 and Its Subsidiaries- Condensed Combining Statements of Cash Flows (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 28, 2018	Sep. 29, 2017
Operating activities [Abstract]
Net cash from operating activities from continuing operations	$ 342	$ 581
Investing activities [Abstract]
Business acquisitions, net of cash acquired	(368)	(291)
Proceeds from sale of businesses, net of closing date cash balances	535	18
Other investing activities	(193)	(91)
Net cash used in investing activities from continuing operations	(26)	(364)
Financing activities [Abstract]
Proceeds from sale of senior notes	1,798	0
Repurchases and redemptions of senior notes	(1,865)	0
Common stock repurchased	(322)	(91)
Dividends paid on L3's common stock	(191)	(178)
Other financing activities	111	30
Net cash used in financing activities from continuing operations	(469)	(239)
Effect of foreign currency exchange rate changes on cash	(9)	16
Net decrease in cash and cash equivalents of discontinued operations	7	82
Net (decrease) increase in cash	(155)	76
Cash and cash equivalents, beginning of the period	662	363
Cash and cash equivalents, end of the period	507	439
Eliminations [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations	(7)	(41)
Investing activities [Abstract]
Business acquisitions, net of cash acquired	0	0
Proceeds from sale of businesses, net of closing date cash balances	0	0
Other investing activities	0	0
Net cash used in investing activities from continuing operations	0	0
Financing activities [Abstract]
Proceeds from sale of senior notes	0
Repurchases and redemptions of senior notes	0
Common stock repurchased	0	0
Dividends paid on L3's common stock	0	0
Other financing activities	55	130
Net cash used in financing activities from continuing operations	55	130
Effect of foreign currency exchange rate changes on cash	0	0
Net decrease in cash and cash equivalents of discontinued operations	0	0
Net (decrease) increase in cash	48	89
Cash and cash equivalents, beginning of the period	(71)	(107)
Cash and cash equivalents, end of the period	(23)	(18)
L-3 [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations	248	248
Investing activities [Abstract]
Business acquisitions, net of cash acquired	(192)	(291)
Proceeds from sale of businesses, net of closing date cash balances	360	17
Other investing activities	(99)	(67)
Net cash used in investing activities from continuing operations	69	(341)
Financing activities [Abstract]
Proceeds from sale of senior notes	1,798
Repurchases and redemptions of senior notes	(1,865)
Common stock repurchased	(322)	(91)
Dividends paid on L3's common stock	(191)	(178)
Other financing activities	82	211
Net cash used in financing activities from continuing operations	(498)	(58)
Effect of foreign currency exchange rate changes on cash	0	0
Net decrease in cash and cash equivalents of discontinued operations	7	82
Net (decrease) increase in cash	(174)	(69)
Cash and cash equivalents, beginning of the period	432	262
Cash and cash equivalents, end of the period	258	193
Guarantor Subsidiaries [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations	(30)	187
Investing activities [Abstract]
Business acquisitions, net of cash acquired	0	0
Proceeds from sale of businesses, net of closing date cash balances	175	0
Other investing activities	(59)	(5)
Net cash used in investing activities from continuing operations	116	(5)
Financing activities [Abstract]
Proceeds from sale of senior notes	0
Repurchases and redemptions of senior notes	0
Common stock repurchased	0	0
Dividends paid on L3's common stock	0	0
Other financing activities	(81)	(174)
Net cash used in financing activities from continuing operations	(81)	(174)
Effect of foreign currency exchange rate changes on cash	0	0
Net decrease in cash and cash equivalents of discontinued operations	0	0
Net (decrease) increase in cash	5	8
Cash and cash equivalents, beginning of the period	16	5
Cash and cash equivalents, end of the period	21	13
Non-Guarantor Subsidiaries [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations	131	187
Investing activities [Abstract]
Business acquisitions, net of cash acquired	(176)	0
Proceeds from sale of businesses, net of closing date cash balances	0	1
Other investing activities	(35)	(19)
Net cash used in investing activities from continuing operations	(211)	(18)
Financing activities [Abstract]
Proceeds from sale of senior notes	0
Repurchases and redemptions of senior notes	0
Common stock repurchased	0	0
Dividends paid on L3's common stock	0	0
Other financing activities	55	(137)
Net cash used in financing activities from continuing operations	55	(137)
Effect of foreign currency exchange rate changes on cash	(9)	16
Net decrease in cash and cash equivalents of discontinued operations	0	0
Net (decrease) increase in cash	(34)	48
Cash and cash equivalents, beginning of the period	285	203
Cash and cash equivalents, end of the period	$ 251	$ 251