Condensed Combining Financial Information of L3 and Its Subsidiaries- Condensed Combining Statements of Cash Flows (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 29, 2018	Jun. 30, 2017
Operating activities [Abstract]
Net cash from operating activities from continuing operations	$ 178	$ 315
Investing activities [Abstract]
Business acquisitions, net of cash acquired	(69)	(191)
Proceeds from sale of businesses, net of closing date cash balances	535	16
Other investing activities	(136)	(32)
Net cash from (used in) investing activities from continuing operations	330	(207)
Financing activities [Abstract]
Proceeds from sale of senior notes	1,798	0
Repurchases and redemptions of senior notes	(1,263)	0
Common stock repurchased	(287)	(26)
Dividends paid on L3's common stock	(128)	(119)
Other financing activities	77	15
Net cash from (used in) financing activities from continuing operations	197	(130)
Effect of foreign currency exchange rate changes on cash	(8)	10
Net decrease in cash and cash equivalents of discontinued operations	7	34
Net decrease (increase) in cash	704	22
Cash and cash equivalents, beginning of the period	662	363
Cash and cash equivalents, end of the period	1,366	385
Eliminations [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations	(5)	(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 from (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	61	92
Net cash from (used in) financing activities from continuing operations	61	92
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	56	51
Cash and cash equivalents, beginning of the period	(71)	(136)
Cash and cash equivalents, end of the period	(15)	(85)
L-3 [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations	195	137
Investing activities [Abstract]
Business acquisitions, net of cash acquired	(69)	(191)
Proceeds from sale of businesses, net of closing date cash balances	360	15
Other investing activities	(79)	(33)
Net cash from (used in) investing activities from continuing operations	212	(209)
Financing activities [Abstract]
Proceeds from sale of senior notes	1,798
Repurchases and redemptions of senior notes	(1,263)
Common stock repurchased	(287)	(26)
Dividends paid on L3's common stock	(128)	(119)
Other financing activities	89	164
Net cash from (used in) financing activities from continuing operations	209	19
Effect of foreign currency exchange rate changes on cash	0	0
Net decrease in cash and cash equivalents of discontinued operations	7	34
Net decrease (increase) in cash	623	(19)
Cash and cash equivalents, beginning of the period	432	291
Cash and cash equivalents, end of the period	1,055	272
Guarantor Subsidiaries [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations	(100)	101
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	(38)	11
Net cash from (used in) investing activities from continuing operations	137	11
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	(34)	(117)
Net cash from (used in) financing activities from continuing operations	(34)	(117)
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	3	(5)
Cash and cash equivalents, beginning of the period	16	5
Cash and cash equivalents, end of the period	19	0
Non-Guarantor Subsidiaries [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations	88	118
Investing activities [Abstract]
Business acquisitions, net of cash acquired	0	0
Proceeds from sale of businesses, net of closing date cash balances	0	1
Other investing activities	(19)	(10)
Net cash from (used in) investing activities from continuing operations	(19)	(9)
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	(39)	(124)
Net cash from (used in) financing activities from continuing operations	(39)	(124)
Effect of foreign currency exchange rate changes on cash	(8)	10
Net decrease in cash and cash equivalents of discontinued operations	0	0
Net decrease (increase) in cash	22	(5)
Cash and cash equivalents, beginning of the period	285	203
Cash and cash equivalents, end of the period	$ 307	$ 198