Condensed Combining Financial Information of L3 and Its Subsidiaries- Condensed Combining Balance Sheets (Details) - USD ($) $ in Millions	Sep. 28, 2018	Jan. 01, 2018	Dec. 31, 2017	Sep. 29, 2017	Dec. 31, 2016
Current assets [Abstract]
Cash and cash equivalents	$ 507		$ 662	$ 439	$ 363
Billed receivables, net	900		723
Contracts in process	0	$ 0	1,933
Contract assets	1,707	1,349	0
Inventories	911	926	389
Prepaid expenses and other current assets	410		689
Assets held for sale	0		135
Assets of discontinued operations	0	285	306
Total current assets	4,435	4,400	4,448
Goodwill	6,834		6,615
Other assets	1,915		1,666
Investment in and amounts due from consolidated subsidiaries	0		0
Total assets	13,184	12,730	12,729
Current liabilities	2,260		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	1,893		1,869
Long-term debt	3,320		3,330
Total liabilities	7,473	7,566	7,578
L3 shareholders' equity	5,642		5,083
Noncontrolling interests	69		68
Total equity	5,711	$ 5,164	5,151	5,069	4,624
Total liabilities and equity	13,184		12,729
Eliminations [Member]
Current assets [Abstract]
Cash and cash equivalents	(23)		(71)	(18)	(107)
Billed receivables, net	0		0
Contracts in process			0
Contract assets	0
Inventories	0
Prepaid expenses and other current assets	0		0
Assets held for sale			0
Assets of discontinued operations			0
Total current assets	(23)		(71)
Goodwill	0		0
Other assets	0		0
Investment in and amounts due from consolidated subsidiaries	(12,839)		(11,972)
Total assets	(12,862)		(12,043)
Current liabilities	(23)		(71)
Liabilities held for sale			0
Liabilities of discontinued operations			0
Amounts due to consolidated subsidiaries	(444)		(391)
Other long-term liabilities	0		0
Long-term debt	0		0
Total liabilities	(467)		(462)
L3 shareholders' equity	(12,464)		(11,649)
Noncontrolling interests	69		68
Total equity	(12,395)		(11,581)
Total liabilities and equity	(12,862)		(12,043)
L-3 [Member]
Current assets [Abstract]
Cash and cash equivalents	258		432	193	262
Billed receivables, net	302		266
Contracts in process			706
Contract assets	612
Inventories	382
Prepaid expenses and other current assets	133		330
Assets held for sale			0
Assets of discontinued operations			306
Total current assets	1,687		2,040
Goodwill	2,124		2,099
Other assets	695		658
Investment in and amounts due from consolidated subsidiaries	6,144		5,662
Total assets	10,650		10,459
Current liabilities	751		811
Liabilities held for sale			0
Liabilities of discontinued operations			226
Amounts due to consolidated subsidiaries	0		0
Other long-term liabilities	937		1,009
Long-term debt	3,320		3,330
Total liabilities	5,008		5,376
L3 shareholders' equity	5,642		5,083
Noncontrolling interests	0		0
Total equity	5,642		5,083
Total liabilities and equity	10,650		10,459
Guarantor Subsidiaries [Member]
Current assets [Abstract]
Cash and cash equivalents	21		16	13	5
Billed receivables, net	322		244
Contracts in process			912
Contract assets	878
Inventories	294
Prepaid expenses and other current assets	199		235
Assets held for sale			135
Assets of discontinued operations			0
Total current assets	1,714		1,542
Goodwill	3,011		2,932
Other assets	767		687
Investment in and amounts due from consolidated subsidiaries	6,695		6,310
Total assets	12,187		11,471
Current liabilities	900		832
Liabilities held for sale			17
Liabilities of discontinued operations			0
Amounts due to consolidated subsidiaries	0		0
Other long-term liabilities	791		729
Long-term debt	0		0
Total liabilities	1,691		1,578
L3 shareholders' equity	10,496		9,893
Noncontrolling interests	0		0
Total equity	10,496		9,893
Total liabilities and equity	12,187		11,471
Non-Guarantor Subsidiaries [Member]
Current assets [Abstract]
Cash and cash equivalents	251		285	$ 251	$ 203
Billed receivables, net	276		213
Contracts in process			315
Contract assets	217
Inventories	235
Prepaid expenses and other current assets	78		124
Assets held for sale			0
Assets of discontinued operations			0
Total current assets	1,057		937
Goodwill	1,699		1,584
Other assets	453		321
Investment in and amounts due from consolidated subsidiaries	0		0
Total assets	3,209		2,842
Current liabilities	632		564
Liabilities held for sale			0
Liabilities of discontinued operations			0
Amounts due to consolidated subsidiaries	444		391
Other long-term liabilities	165		131
Long-term debt	0		0
Total liabilities	1,241		1,086
L3 shareholders' equity	1,968		1,756
Noncontrolling interests	0		0
Total equity	1,968		1,756
Total liabilities and equity	$ 3,209		$ 2,842