Financial Information of L3 and Its Subsidiaries, Condensed Combining Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 1,066		$ 662	$ 363	$ 207
Billed receivables, net	919		723
Contract assets	1,590	$ 1,349	0
Contracts in process	0	0	1,933
Inventories	879	926	389
Prepaid expenses and other current assets	356		300
Prepaid expenses and other current assets			689
Assets held for sale			135
Assets of discontinued operations	0	285	306	481
Total current assets	4,810	4,400	4,448
Goodwill	6,808		6,615	6,374
Other assets	1,900		1,666
Investment in and amounts due from consolidated subsidiaries	0		0
Total assets	13,518	12,730	12,729	11,865
Current liabilities	2,447		2,136
Liabilities held for sale	0	16	17
Liabilities of discontinued operations	0	203	226
Amounts due to consolidated subsidiaries	0		0
Other long-term liabilities	1,843		1,869
Long-term debt	3,321		3,330
Total liabilities	7,611	7,566	7,578
L3 shareholders' equity	5,839		5,083
Noncontrolling interests	68		68
Total equity	5,907	$ 5,164	5,151	4,624	4,429
Total liabilities and equity	13,518		12,729
Parent Company [Member]
Current assets:
Cash and cash equivalents	756		432	262	109
Billed receivables, net	291		266
Contract assets	562
Contracts in process			706
Inventories	378
Prepaid expenses and other current assets	127
Prepaid expenses and other current assets			330
Assets held for sale			0
Assets of discontinued operations			306
Total current assets	2,114		2,040
Goodwill	2,124		2,099
Other assets	690		658
Investment in and amounts due from consolidated subsidiaries	5,931		5,662
Total assets	10,859		10,459
Current liabilities	821		811
Liabilities held for sale			0
Liabilities of discontinued operations			226
Amounts due to consolidated subsidiaries	0		0
Other long-term liabilities	878		1,009
Long-term debt	3,321		3,330
Total liabilities	5,020		5,376
L3 shareholders' equity	5,839		5,083
Noncontrolling interests	0		0
Total equity	5,839		5,083
Total liabilities and equity	10,859		10,459
Guarantor Subsidiaries [Member]
Current assets:
Cash and cash equivalents	21		16	5	0
Billed receivables, net	341		244
Contract assets	833
Contracts in process			912
Inventories	258
Prepaid expenses and other current assets	166
Prepaid expenses and other current assets			235
Assets held for sale			135
Assets of discontinued operations			0
Total current assets	1,619		1,542
Goodwill	3,009		2,932
Other assets	765		687
Investment in and amounts due from consolidated subsidiaries	6,912		6,310
Total assets	12,305		11,471
Current liabilities	955		832
Liabilities held for sale			17
Liabilities of discontinued operations			0
Amounts due to consolidated subsidiaries	0		0
Other long-term liabilities	804		729
Long-term debt	0		0
Total liabilities	1,759		1,578
L3 shareholders' equity	10,546		9,893
Noncontrolling interests	0		0
Total equity	10,546		9,893
Total liabilities and equity	12,305		11,471
Non-Guarantor Subsidiaries [Member]
Current assets:
Cash and cash equivalents	306		285	203	165
Billed receivables, net	287		213
Contract assets	195
Contracts in process			315
Inventories	243
Prepaid expenses and other current assets	63
Prepaid expenses and other current assets			124
Assets held for sale			0
Assets of discontinued operations			0
Total current assets	1,094		937
Goodwill	1,675		1,584
Other assets	445		321
Investment in and amounts due from consolidated subsidiaries	0		0
Total assets	3,214		2,842
Current liabilities	688		564
Liabilities held for sale			0
Liabilities of discontinued operations			0
Amounts due to consolidated subsidiaries	417		391
Other long-term liabilities	161		131
Long-term debt	0		0
Total liabilities	1,266		1,086
L3 shareholders' equity	1,948		1,756
Noncontrolling interests	0		0
Total equity	1,948		1,756
Total liabilities and equity	3,214		2,842
Eliminations [Member]
Current assets:
Cash and cash equivalents	(17)		(71)	$ (107)	$ (67)
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
Assets of discontinued operations			0
Total current assets	(17)		(71)
Goodwill	0		0
Other assets	0		0
Investment in and amounts due from consolidated subsidiaries	(12,843)		(11,972)
Total assets	(12,860)		(12,043)
Current liabilities	(17)		(71)
Liabilities held for sale			0
Liabilities of discontinued operations			0
Amounts due to consolidated subsidiaries	(417)		(391)
Other long-term liabilities	0		0
Long-term debt	0		0
Total liabilities	(434)		(462)
L3 shareholders' equity	(12,494)		(11,649)
Noncontrolling interests	68		68
Total equity	(12,426)		(11,581)
Total liabilities and equity	$ (12,860)		$ (12,043)