Condensed Combining Financial Information of L3 and Its Subsidiaries- Condensed Combining Balance Sheets (Details) - USD ($) $ in Millions	Mar. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Current assets [Abstract]
Cash and cash equivalents	$ 374		$ 662	$ 230	$ 363
Billed receivables, net	798		723
Contract assets	1,499	$ 1,349	0
Contracts in process	0	0	1,933
Inventories	994	926	389
Prepaid expenses and other current assets	392	317	300
Prepaid expenses and other current assets			689
Assets held for sale	136		135
Assets of discontinued operations	287	285	306
Total current assets	4,480	4,400	4,448
Goodwill	6,632		6,615
Other assets	1,761		1,666
Investment in and amounts due from consolidated subsidiaries	0		0
Total assets	12,873	12,730	12,729
Current liabilities	2,162		2,136
Liabilities held for sale	19	16	17
Liabilities of discontinued operations	154	203	226
Amounts due to consolidated subsidiaries	0		0
Other long-term liabilities	1,887		1,869
Long-term debt	3,331		3,330
Total liabilities	7,553	7,566	7,578
L3 shareholders' equity	5,253		5,083
Noncontrolling interests	67		68
Total equity	5,320	$ 5,164	5,151	4,802	4,624
Total liabilities and equity	12,873		12,729
Eliminations [Member]
Current assets [Abstract]
Cash and cash equivalents	(18)		(71)	(24)	(136)
Billed receivables, net	0		0
Contract assets	0
Contracts in process			0
Inventories	0
Prepaid expenses and other current assets	0
Prepaid expenses and other current assets			0
Assets held for sale	0		0
Assets of discontinued operations	0		0
Total current assets	(18)		(71)
Goodwill	0		0
Other assets	0		0
Investment in and amounts due from consolidated subsidiaries	(10,269)		(10,859)
Total assets	(10,287)		(10,930)
Current liabilities	(18)		(71)
Liabilities held for sale	0		0
Liabilities of discontinued operations	0		0
Amounts due to consolidated subsidiaries	(395)		(348)
Other long-term liabilities	0		0
Long-term debt	0		0
Total liabilities	(413)		(419)
L3 shareholders' equity	(9,941)		(10,579)
Noncontrolling interests	67		68
Total equity	(9,874)		(10,511)
Total liabilities and equity	(10,287)		(10,930)
L-3 [Member]
Current assets [Abstract]
Cash and cash equivalents	158		432	57	291
Billed receivables, net	230		266
Contract assets	574
Contracts in process			706
Inventories	428
Prepaid expenses and other current assets	160
Prepaid expenses and other current assets			330
Assets held for sale	0		0
Assets of discontinued operations	0		0
Total current assets	1,550		1,734
Goodwill	2,269		2,269
Other assets	699		658
Investment in and amounts due from consolidated subsidiaries	5,844		5,572
Total assets	10,362		10,233
Current liabilities	796		811
Liabilities held for sale	0		0
Liabilities of discontinued operations	0		0
Amounts due to consolidated subsidiaries	0		0
Other long-term liabilities	982		1,009
Long-term debt	3,331		3,330
Total liabilities	5,109		5,150
L3 shareholders' equity	5,253		5,083
Noncontrolling interests	0		0
Total equity	5,253		5,083
Total liabilities and equity	10,362		10,233
Guarantor Subsidiaries [Member]
Current assets [Abstract]
Cash and cash equivalents	19		14	1	1
Billed receivables, net	301		232
Contract assets	740
Contracts in process			891
Inventories	348
Prepaid expenses and other current assets	160
Prepaid expenses and other current assets			231
Assets held for sale	136		118
Assets of discontinued operations	287		306
Total current assets	1,991		1,792
Goodwill	2,827		2,635
Other assets	713		556
Investment in and amounts due from consolidated subsidiaries	4,425		5,287
Total assets	9,956		10,270
Current liabilities	817		800
Liabilities held for sale	19		16
Liabilities of discontinued operations	154		226
Amounts due to consolidated subsidiaries	0		0
Other long-term liabilities	759		714
Long-term debt	0		0
Total liabilities	1,749		1,756
L3 shareholders' equity	8,207		8,514
Noncontrolling interests	0		0
Total equity	8,207		8,514
Total liabilities and equity	9,956		10,270
Non-Guarantor Subsidiaries [Member]
Current assets [Abstract]
Cash and cash equivalents	215		287	$ 196	$ 207
Billed receivables, net	267		225
Contract assets	185
Contracts in process			336
Inventories	218
Prepaid expenses and other current assets	72
Prepaid expenses and other current assets			128
Assets held for sale	0		17
Assets of discontinued operations	0		0
Total current assets	957		993
Goodwill	1,536		1,711
Other assets	349		452
Investment in and amounts due from consolidated subsidiaries	0		0
Total assets	2,842		3,156
Current liabilities	567		596
Liabilities held for sale	0		1
Liabilities of discontinued operations	0		0
Amounts due to consolidated subsidiaries	395		348
Other long-term liabilities	146		146
Long-term debt	0		0
Total liabilities	1,108		1,091
L3 shareholders' equity	1,734		2,065
Noncontrolling interests	0		0
Total equity	1,734		2,065
Total liabilities and equity	$ 2,842		$ 3,156