Condensed Combining Financial Information of L3 and Its Subsidiaries- Condensed Combining Balance Sheets (Details) - USD ($) $ in Millions	Mar. 29, 2019	Dec. 31, 2018	Mar. 30, 2018	Dec. 31, 2017
Current assets [Abstract]
Cash and cash equivalents	$ 1,108	$ 1,066	$ 374	$ 662
Billed receivables, net	804	919
Contract assets	1,735	1,590
Inventories	896	879
Prepaid expenses and other current assets	362	356
Total current assets	4,905	4,810
Goodwill	6,826	6,808
Other assets	2,532	1,900
Investment in and amounts due from consolidated subsidiaries	0	0
Total assets	14,263	13,518
Current liabilities	2,432	2,447
Amounts due to consolidated subsidiaries	0	0
Other long-term liabilities	2,391	1,843
Long-term debt	3,322	3,321
Total liabilities	8,145	7,611
L3 shareholders' equity	6,051	5,839
Noncontrolling interests	67	68
Total equity	6,118	5,907	5,320	5,151
Total liabilities and equity	14,263	13,518
Eliminations [Member]
Current assets [Abstract]
Cash and cash equivalents	(76)	(17)	(18)	(71)
Billed receivables, net	0	0
Contract assets	0	0
Inventories	0	0
Prepaid expenses and other current assets	0	0
Total current assets	(76)	(17)
Goodwill	0	0
Other assets	0	0
Investment in and amounts due from consolidated subsidiaries	(12,583)	(12,843)
Total assets	(12,659)	(12,860)
Current liabilities	(76)	(17)
Amounts due to consolidated subsidiaries	(445)	(417)
Other long-term liabilities	0	0
Long-term debt	0	0
Total liabilities	(521)	(434)
L3 shareholders' equity	(12,205)	(12,494)
Noncontrolling interests	67	68
Total equity	(12,138)	(12,426)
Total liabilities and equity	(12,659)	(12,860)
L-3 [Member]
Current assets [Abstract]
Cash and cash equivalents	856	756	158	432
Billed receivables, net	230	291
Contract assets	580	562
Inventories	369	378
Prepaid expenses and other current assets	127	127
Total current assets	2,162	2,114
Goodwill	2,124	2,124
Other assets	1,004	690
Investment in and amounts due from consolidated subsidiaries	6,049	5,931
Total assets	11,339	10,859
Current liabilities	797	821
Amounts due to consolidated subsidiaries	0	0
Other long-term liabilities	1,169	878
Long-term debt	3,322	3,321
Total liabilities	5,288	5,020
L3 shareholders' equity	6,051	5,839
Noncontrolling interests	0	0
Total equity	6,051	5,839
Total liabilities and equity	11,339	10,859
Guarantor Subsidiaries [Member]
Current assets [Abstract]
Cash and cash equivalents	19	21	19	14
Billed receivables, net	268	341
Contract assets	953	833
Inventories	268	258
Prepaid expenses and other current assets	180	166
Total current assets	1,688	1,619
Goodwill	3,007	3,009
Other assets	954	765
Investment in and amounts due from consolidated subsidiaries	6,534	6,912
Total assets	12,183	12,305
Current liabilities	1,036	955
Amounts due to consolidated subsidiaries	0	0
Other long-term liabilities	963	804
Long-term debt	0	0
Total liabilities	1,999	1,759
L3 shareholders' equity	10,184	10,546
Noncontrolling interests	0	0
Total equity	10,184	10,546
Total liabilities and equity	12,183	12,305
Non-Guarantor Subsidiaries [Member]
Current assets [Abstract]
Cash and cash equivalents	309	306	$ 215	$ 287
Billed receivables, net	306	287
Contract assets	202	195
Inventories	259	243
Prepaid expenses and other current assets	55	63
Total current assets	1,131	1,094
Goodwill	1,695	1,675
Other assets	574	445
Investment in and amounts due from consolidated subsidiaries	0	0
Total assets	3,400	3,214
Current liabilities	675	688
Amounts due to consolidated subsidiaries	445	417
Other long-term liabilities	259	161
Long-term debt	0	0
Total liabilities	1,379	1,266
L3 shareholders' equity	2,021	1,948
Noncontrolling interests	0	0
Total equity	2,021	1,948
Total liabilities and equity	$ 3,400	$ 3,214