Financial Information of L3 and Its Subsidiaries, Condensed Combining Statements of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities:
Net cash from operating activities from continuing operations	$ 1,042	$ 985	$ 1,022
Investing activities:
Business acquisitions, net of cash acquired	(369)	(316)	(388)
Proceeds from sale of business, net of closing date cash balances	535	18	561
Other investing activities	(257)	(155)	(183)
Net cash used in investing activities from continuing operations	(91)	(453)	(10)
Financing activities:
Proceeds from sale of senior notes	1,798	0	547
Redemption of senior notes	(1,865)	0	(856)
Common stock repurchased	(322)	(180)	(373)
Dividends paid on L3's common stock	(254)	(236)	(220)
Other financing activities	123	50	46
Net cash used in financing activities from continuing operations	(520)	(366)	(856)
Effect of foreign currency exchange rate changes on cash	(15)	20	(13)
Net increase in cash and cash equivalents of discontinued operations	(12)	113	13
Net (decrease) increase in cash	404	299	156
Cash and cash equivalents, beginning of the year	662	363	207
Cash and cash equivalents, end of the year	1,066	662	363
Parent Company [Member]
Operating activities:
Net cash from operating activities from continuing operations	555	374	440
Investing activities:
Business acquisitions, net of cash acquired	(193)	(316)	(388)
Proceeds from sale of business, net of closing date cash balances	360	17	563
Other investing activities	(119)	(92)	(63)
Net cash used in investing activities from continuing operations	48	(391)	112
Financing activities:
Proceeds from sale of senior notes	1,798		547
Redemption of senior notes	(1,865)		(856)
Common stock repurchased	(322)	(180)	(373)
Dividends paid on L3's common stock	(254)	(236)	(220)
Other financing activities	376	490	490
Net cash used in financing activities from continuing operations	(267)	74	(412)
Effect of foreign currency exchange rate changes on cash	0	0	0
Net increase in cash and cash equivalents of discontinued operations	(12)	113	13
Net (decrease) increase in cash	324	170	153
Cash and cash equivalents, beginning of the year	432	262	109
Cash and cash equivalents, end of the year	756	432	262
Guarantor Subsidiaries [Member]
Operating activities:
Net cash from operating activities from continuing operations	238	426	509
Investing activities:
Business acquisitions, net of cash acquired	0	0	0
Proceeds from sale of business, net of closing date cash balances	175	0	0
Other investing activities	(90)	(38)	(77)
Net cash used in investing activities from continuing operations	85	(38)	(77)
Financing activities:
Proceeds from sale of senior notes	0		0
Redemption of senior notes	0		0
Common stock repurchased	0	0	0
Dividends paid on L3's common stock	0	0	0
Other financing activities	(318)	(377)	(427)
Net cash used in financing activities from continuing operations	(318)	(377)	(427)
Effect of foreign currency exchange rate changes on cash	0	0	0
Net increase in cash and cash equivalents of discontinued operations	0	0	0
Net (decrease) increase in cash	5	11	5
Cash and cash equivalents, beginning of the year	16	5	0
Cash and cash equivalents, end of the year	21	16	5
Non-Guarantor Subsidiaries [Member]
Operating activities:
Net cash from operating activities from continuing operations	256	263	259
Investing activities:
Business acquisitions, net of cash acquired	(176)	0	0
Proceeds from sale of business, net of closing date cash balances	0	1	(2)
Other investing activities	(48)	(25)	(43)
Net cash used in investing activities from continuing operations	(224)	(24)	(45)
Financing activities:
Proceeds from sale of senior notes	0		0
Redemption of senior notes	0		0
Common stock repurchased	0	0	0
Dividends paid on L3's common stock	0	0	0
Other financing activities	4	(177)	(163)
Net cash used in financing activities from continuing operations	4	(177)	(163)
Effect of foreign currency exchange rate changes on cash	(15)	20	(13)
Net increase in cash and cash equivalents of discontinued operations	0	0	0
Net (decrease) increase in cash	21	82	38
Cash and cash equivalents, beginning of the year	285	203	165
Cash and cash equivalents, end of the year	306	285	203
Eliminations [Member]
Operating activities:
Net cash from operating activities from continuing operations	(7)	(78)	(186)
Investing activities:
Business acquisitions, net of cash acquired	0	0	0
Proceeds from sale of business, net of closing date cash balances	0	0	0
Other investing activities	0	0	0
Net cash used in investing activities from continuing operations	0	0	0
Financing activities:
Proceeds from sale of senior notes	0		0
Redemption of senior notes	0		0
Common stock repurchased	0	0	0
Dividends paid on L3's common stock	0	0	0
Other financing activities	61	114	146
Net cash used in financing activities from continuing operations	61	114	146
Effect of foreign currency exchange rate changes on cash	0	0	0
Net increase in cash and cash equivalents of discontinued operations	0	0	0
Net (decrease) increase in cash	54	36	(40)
Cash and cash equivalents, beginning of the year	(71)	(107)	(67)
Cash and cash equivalents, end of the year	$ (17)	$ (71)	$ (107)