Condensed Combining Financial Information of L3 and Its Subsidiaries- Condensed Combining Statements of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 29, 2017	Sep. 29, 2017	Sep. 23, 2016
Operating activities [Abstract]
Net cash from operating activities from continuing operations		$ 667	$ 586
Investing activities [Abstract]
Business acquisitions, net of cash acquired	$ (100)	(291)	(27)
Proceeds from sale of businesses, net of closing date cash balances		18	561
Other investing activities		(93)	(104)
Net cash used in from investing activities from continuing operations		(366)	430
Financing activities [Abstract]
Redemption of senior notes		0	(305)
Common stock repurchased		(91)	(326)
Dividends paid on L3's common stock		(178)	(166)
Other financing activities		30	44
Net cash used in financing activities from continuing operations		(239)	(753)
Effect of foreign currency exchange rate changes on cash		16	(3)
Net decrease in cash and cash equivalents of discontinued operations		(2)	(56)
Net decrease (increase) in cash		76	204
Cash and cash equivalents, beginning of the period		363	207
Cash and cash equivalents, end of the period	439	439	411
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		154	156
Net cash used in financing activities from continuing operations		154	156
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		113	79
Cash and cash equivalents, beginning of the period		(136)	(95)
Cash and cash equivalents, end of the period	(23)	(23)	(16)
L-3 [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations		240	203
Investing activities [Abstract]
Business acquisitions, net of cash acquired		(291)	(27)
Proceeds from sale of businesses, net of closing date cash balances		17	563
Other investing activities		(59)	(27)
Net cash used in from investing activities from continuing operations		(333)	509
Financing activities [Abstract]
Redemption of senior notes			(305)
Common stock repurchased		(91)	(326)
Dividends paid on L3's common stock		(178)	(166)
Other financing activities		270	136
Net cash used in financing activities from continuing operations		1	(661)
Effect of foreign currency exchange rate changes on cash		0	0
Net decrease in cash and cash equivalents of discontinued operations		(2)	0
Net decrease (increase) in cash		(94)	51
Cash and cash equivalents, beginning of the period		291	137
Cash and cash equivalents, end of the period	197	197	188
Guarantor Subsidiaries [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations		275	301
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		(12)	(47)
Net cash used in from investing activities from continuing operations		(12)	(47)
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		(253)	(198)
Net cash used in financing activities from continuing operations		(253)	(198)
Effect of foreign currency exchange rate changes on cash		0	0
Net decrease in cash and cash equivalents of discontinued operations		0	(56)
Net decrease (increase) in cash		10	0
Cash and cash equivalents, beginning of the period		1	0
Cash and cash equivalents, end of the period	11	11	0
Non-Guarantor Subsidiaries [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations		193	159
Investing activities [Abstract]
Business acquisitions, net of cash acquired		0	0
Proceeds from sale of businesses, net of closing date cash balances		1	(2)
Other investing activities		(22)	(30)
Net cash used in from investing activities from continuing operations		(21)	(32)
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		(141)	(50)
Net cash used in financing activities from continuing operations		(141)	(50)
Effect of foreign currency exchange rate changes on cash		16	(3)
Net decrease in cash and cash equivalents of discontinued operations		0	0
Net decrease (increase) in cash		47	74
Cash and cash equivalents, beginning of the period		207	165
Cash and cash equivalents, end of the period	$ 254	$ 254	$ 239