Condensed Combining Financial Information of L3 and Its Subsidiaries- Condensed Combining Statements of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 30, 2018	Mar. 31, 2017
Operating activities [Abstract]
Net cash from operating activities from continuing operations	$ (35)	$ 86
Investing activities [Abstract]
Business acquisitions, net of cash acquired	0	(139)
Proceeds from sale of businesses, net of closing date cash balances	0	16
Other investing activities	(83)	(35)
Net cash used in investing activities from continuing operations	(83)	(158)
Financing activities [Abstract]
Common stock repurchased	(119)	0
Dividends paid on L3's common stock	(65)	(61)
Other financing activities	38	(2)
Net cash used in financing activities from continuing operations	(146)	(63)
Effect of foreign currency exchange rate changes on cash	6	4
Net decrease in cash and cash equivalents of discontinued operations	(30)	(2)
Net decrease (increase) in cash	(288)	(133)
Cash and cash equivalents, beginning of the period	662	363
Cash and cash equivalents, end of the period	374	230
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
Proceeds from sale of businesses, net of closing date cash balances		0
Other investing activities	0	0
Net cash used in investing activities from continuing operations	0	0
Financing activities [Abstract]
Common stock repurchased	0
Dividends paid on L3's common stock	0	0
Other financing activities	58	153
Net cash used in financing activities from continuing operations	58	153
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	53	112
Cash and cash equivalents, beginning of the period	(71)	(136)
Cash and cash equivalents, end of the period	(18)	(24)
L-3 [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations	198	131
Investing activities [Abstract]
Business acquisitions, net of cash acquired		(139)
Proceeds from sale of businesses, net of closing date cash balances		15
Other investing activities	(62)	(16)
Net cash used in investing activities from continuing operations	(62)	(140)
Financing activities [Abstract]
Common stock repurchased	(119)
Dividends paid on L3's common stock	(65)	(61)
Other financing activities	(226)	(164)
Net cash used in financing activities from continuing operations	(410)	(225)
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	(274)	(234)
Cash and cash equivalents, beginning of the period	432	291
Cash and cash equivalents, end of the period	158	57
Guarantor Subsidiaries [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations	(204)	(71)
Investing activities [Abstract]
Business acquisitions, net of cash acquired		0
Proceeds from sale of businesses, net of closing date cash balances		0
Other investing activities	(17)	(16)
Net cash used in investing activities from continuing operations	(17)	(16)
Financing activities [Abstract]
Common stock repurchased	0
Dividends paid on L3's common stock	0	0
Other financing activities	256	89
Net cash used in financing activities from continuing operations	256	89
Effect of foreign currency exchange rate changes on cash	0	0
Net decrease in cash and cash equivalents of discontinued operations	(30)	(2)
Net decrease (increase) in cash	5	0
Cash and cash equivalents, beginning of the period	14	1
Cash and cash equivalents, end of the period	19	1
Non-Guarantor Subsidiaries [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations	(24)	67
Investing activities [Abstract]
Business acquisitions, net of cash acquired		0
Proceeds from sale of businesses, net of closing date cash balances		1
Other investing activities	(4)	(3)
Net cash used in investing activities from continuing operations	(4)	(2)
Financing activities [Abstract]
Common stock repurchased	0
Dividends paid on L3's common stock	0	0
Other financing activities	(50)	(80)
Net cash used in financing activities from continuing operations	(50)	(80)
Effect of foreign currency exchange rate changes on cash	6	4
Net decrease in cash and cash equivalents of discontinued operations	0	0
Net decrease (increase) in cash	(72)	(11)
Cash and cash equivalents, beginning of the period	287	207
Cash and cash equivalents, end of the period	$ 215	$ 196