Condensed Combining Financial Information of L3 and Its Subsidiaries- Condensed Combining Statements of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2017	Jun. 24, 2016
Operating activities [Abstract]
Net cash from operating activities from continuing operations		$ 351	$ 376
Investing activities [Abstract]
Business acquisitions, net of cash acquired	$ (52)	(191)	(27)
Proceeds from sale of businesses, net of closing date cash balances		16	575
Other investing activities		(34)	(58)
Net cash (used in) from investing activities from continuing operations		(209)	490
Financing activities [Abstract]
Redemption of senior notes		0	(305)
Common stock repurchased		(26)	(276)
Dividends paid on L3's common stock		(119)	(112)
Other financing activities		15	28
Net cash used in financing activities from continuing operations		(130)	(665)
Effect of foreign currency exchange rate changes on cash		10	0
Net decrease in cash and cash equivalents of discontinued operations			(56)
Net decrease (increase) in cash		22	145
Cash and cash equivalents, beginning of the period		363	207
Cash and cash equivalents, end of the period	385	385	352
L-3 [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations		162	168
Investing activities [Abstract]
Business acquisitions, net of cash acquired		(191)	(27)
Proceeds from sale of businesses, net of closing date cash balances		15	576
Other investing activities		(33)	(11)
Net cash (used in) from investing activities from continuing operations		(209)	538
Financing activities [Abstract]
Redemption of senior notes			(305)
Common stock repurchased		(26)	(276)
Dividends paid on L3's common stock		(119)	(112)
Other financing activities		173	49
Net cash used in financing activities from continuing operations		28	(644)
Effect of foreign currency exchange rate changes on cash		0
Net decrease in cash and cash equivalents of discontinued operations			0
Net decrease (increase) in cash		(19)	62
Cash and cash equivalents, beginning of the period		291	137
Cash and cash equivalents, end of the period	272	272	199
Guarantor Subsidiaries [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations		109	206
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		11	(28)
Net cash (used in) from investing activities from continuing operations		11	(28)
Financing activities [Abstract]
Redemption of senior notes			0
Common stock repurchased		0	0
Dividends paid on L3's common stock		0	0
Other financing activities		(121)	(122)
Net cash used in financing activities from continuing operations		(121)	(122)
Effect of foreign currency exchange rate changes on cash		0
Net decrease in cash and cash equivalents of discontinued operations			(56)
Net decrease (increase) in cash		(1)	0
Cash and cash equivalents, beginning of the period		1	0
Cash and cash equivalents, end of the period	0	0	0
Non-Guarantor Subsidiaries [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations		121	79
Investing activities [Abstract]
Business acquisitions, net of cash acquired		0	0
Proceeds from sale of businesses, net of closing date cash balances		1	(1)
Other investing activities		(12)	(19)
Net cash (used in) from investing activities from continuing operations		(11)	(20)
Financing activities [Abstract]
Redemption of senior notes			0
Common stock repurchased		0	0
Dividends paid on L3's common stock		0	0
Other financing activities		(129)	(59)
Net cash used in financing activities from continuing operations		(129)	(59)
Effect of foreign currency exchange rate changes on cash		10
Net decrease in cash and cash equivalents of discontinued operations			0
Net decrease (increase) in cash		(9)	0
Cash and cash equivalents, beginning of the period		207	165
Cash and cash equivalents, end of the period	198	198	165
Eliminations [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations		(41)	(77)
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) from investing activities from continuing operations		0	0
Financing activities [Abstract]
Redemption of senior notes			0
Common stock repurchased		0	0
Dividends paid on L3's common stock		0	0
Other financing activities		92	160
Net cash used in financing activities from continuing operations		92	160
Effect of foreign currency exchange rate changes on cash		0
Net decrease in cash and cash equivalents of discontinued operations			0
Net decrease (increase) in cash		51	83
Cash and cash equivalents, beginning of the period		(136)	(95)
Cash and cash equivalents, end of the period	$ (85)	$ (85)	$ (12)