Financial Information of L3 and Its Subsidiaries, Condensed Combining Statements of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities:
Net cash from operating activities from continuing operations	$ 985	$ 1,022	$ 1,035
Investing activities:
Business acquisitions, net of cash acquired	(316)	(388)	(320)
Proceeds from sale of business, net of closing date cash balances	18	561	318
Other investing activities	(155)	(183)	(188)
Net cash used in investing activities from continuing operations	(453)	(10)	(190)
Financing activities:
Proceeds from sale of senior notes	0	547	0
Redemption of senior notes	0	(856)	(297)
Common stock repurchased	(180)	(373)	(740)
Dividends paid on L3's common stock	(236)	(220)	(214)
Other financing activities	50	46	46
Net cash used in financing activities from continuing operations	(366)	(856)	(1,205)
Effect of foreign currency exchange rate changes on cash	20	(13)	(19)
Net increase in cash and cash equivalents of discontinued operations	113	13	83
Change in cash balance in assets held for sale	0	0	61
Net (decrease) increase in cash	299	156	(235)
Cash and cash equivalents, beginning of the year	363	207	442
Cash and cash equivalents, end of the year	662	363	207
L-3 Communications Corporation [Member]
Operating activities:
Net cash from operating activities from continuing operations	374	441	634
Investing activities:
Business acquisitions, net of cash acquired	(316)	(388)	(320)
Proceeds from sale of business, net of closing date cash balances	17	563	14
Other investing activities	(84)	(60)	(75)
Net cash used in investing activities from continuing operations	(383)	115	(381)
Financing activities:
Proceeds from sale of senior notes		547
Redemption of senior notes		(856)	(297)
Common stock repurchased	(180)	(373)	(740)
Dividends paid on L3's common stock	(236)	(220)	(214)
Other financing activities	565	496	781
Net cash used in financing activities from continuing operations	149	(406)	(470)
Effect of foreign currency exchange rate changes on cash	0	0	0
Net increase in cash and cash equivalents of discontinued operations	1	0	0
Change in cash balance in assets held for sale			0
Net (decrease) increase in cash	141	150	(217)
Cash and cash equivalents, beginning of the year	291	141	358
Cash and cash equivalents, end of the year	432	291	141
Guarantor Subsidiaries [Member]
Operating activities:
Net cash from operating activities from continuing operations	438	509	425
Investing activities:
Business acquisitions, net of cash acquired	0	0	0
Proceeds from sale of business, net of closing date cash balances	0	0	28
Other investing activities	(41)	(80)	(78)
Net cash used in investing activities from continuing operations	(41)	(80)	(50)
Financing activities:
Proceeds from sale of senior notes		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	(496)	(441)	(463)
Net cash used in financing activities from continuing operations	(496)	(441)	(463)
Effect of foreign currency exchange rate changes on cash	0	0	0
Net increase in cash and cash equivalents of discontinued operations	112	13	83
Change in cash balance in assets held for sale			1
Net (decrease) increase in cash	13	1	(4)
Cash and cash equivalents, beginning of the year	1	0	4
Cash and cash equivalents, end of the year	14	1	0
Non-Guarantor Subsidiaries [Member]
Operating activities:
Net cash from operating activities from continuing operations	251	258	161
Investing activities:
Business acquisitions, net of cash acquired	0	0	0
Proceeds from sale of business, net of closing date cash balances	1	(2)	276
Other investing activities	(30)	(43)	(35)
Net cash used in investing activities from continuing operations	(29)	(45)	241
Financing activities:
Proceeds from sale of senior notes		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	(162)	(158)	(420)
Net cash used in financing activities from continuing operations	(162)	(158)	(420)
Effect of foreign currency exchange rate changes on cash	20	(13)	(19)
Net increase in cash and cash equivalents of discontinued operations	0	0	0
Change in cash balance in assets held for sale			60
Net (decrease) increase in cash	80	42	23
Cash and cash equivalents, beginning of the year	207	165	142
Cash and cash equivalents, end of the year	287	207	165
Eliminations [Member]
Operating activities:
Net cash from operating activities from continuing operations	(78)	(186)	(185)
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
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	143	149	148
Net cash used in financing activities from continuing operations	143	149	148
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
Change in cash balance in assets held for sale			0
Net (decrease) increase in cash	65	(37)	(37)
Cash and cash equivalents, beginning of the year	(136)	(99)	(62)
Cash and cash equivalents, end of the year	$ (71)	$ (136)	$ (99)