Condensed Combining Financial Information of L3 and Its Subsidiaries- Condensed Combining Statements of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 29, 2019	Mar. 30, 2018
Operating activities [Abstract]
Net cash from operating activities from continuing operations	$ 174	$ (35)
Investing activities [Abstract]
Proceeds from sale of businesses, net of closing date cash balances	1	0
Other investing activities	(75)	(83)
Net cash used in investing activities from continuing operations	(74)	(83)
Financing activities [Abstract]
Common stock repurchased	0	(119)
Dividends paid	(70)	(65)
Other financing activities	(10)	38
Net cash used in financing activities from continuing operations	(80)	(146)
Effect of foreign currency exchange rate changes on cash	3	6
Net decrease in cash and cash equivalents of discontinued operations	19	(30)
Net (decrease) increase in cash	42	(288)
Cash and cash equivalents, beginning of the period	1,066	662
Cash and cash equivalents, end of the period	1,108	374
Eliminations [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations	0	(5)
Investing activities [Abstract]
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	0	0
Other financing activities	(59)	58
Net cash used in financing activities from continuing operations	(59)	58
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	(59)	53
Cash and cash equivalents, beginning of the period	(17)	(71)
Cash and cash equivalents, end of the period	(76)	(18)
L-3 [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations	101	198
Investing activities [Abstract]
Proceeds from sale of businesses, net of closing date cash balances	1
Other investing activities	(42)	(62)
Net cash used in investing activities from continuing operations	(41)	(62)
Financing activities [Abstract]
Common stock repurchased		(119)
Dividends paid	(70)	(65)
Other financing activities	91	(196)
Net cash used in financing activities from continuing operations	21	(380)
Effect of foreign currency exchange rate changes on cash	0	0
Net decrease in cash and cash equivalents of discontinued operations	19	(30)
Net (decrease) increase in cash	100	(274)
Cash and cash equivalents, beginning of the period	756	432
Cash and cash equivalents, end of the period	856	158
Guarantor Subsidiaries [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations	55	(204)
Investing activities [Abstract]
Proceeds from sale of businesses, net of closing date cash balances	0
Other investing activities	(19)	(17)
Net cash used in investing activities from continuing operations	(19)	(17)
Financing activities [Abstract]
Common stock repurchased		0
Dividends paid	0	0
Other financing activities	(38)	226
Net cash used in financing activities from continuing operations	(38)	226
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	(2)	5
Cash and cash equivalents, beginning of the period	21	14
Cash and cash equivalents, end of the period	19	19
Non-Guarantor Subsidiaries [Member]
Operating activities [Abstract]
Net cash from operating activities from continuing operations	18	(24)
Investing activities [Abstract]
Proceeds from sale of businesses, net of closing date cash balances	0
Other investing activities	(14)	(4)
Net cash used in investing activities from continuing operations	(14)	(4)
Financing activities [Abstract]
Common stock repurchased		0
Dividends paid	0	0
Other financing activities	(4)	(50)
Net cash used in financing activities from continuing operations	(4)	(50)
Effect of foreign currency exchange rate changes on cash	3	6
Net decrease in cash and cash equivalents of discontinued operations	0	0
Net (decrease) increase in cash	3	(72)
Cash and cash equivalents, beginning of the period	306	287
Cash and cash equivalents, end of the period	$ 309	$ 215

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Proceeds from (Payments for) Other Financing Activities, Excluding Dividends Paid and Common Stock Repurchases

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount of cash inflow (outflow) from financing activities, including discontinued operations. Financing activity cash flows include obtaining resources from owners and providing them with a return on, and a return of, their investment; borrowing money and repaying amounts borrowed, or settling the obligation; and obtaining and paying for other resources obtained from creditors on long-term credit.

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