Unaudited Quarterly Financial Data - Company's Unaudited Quarterly Results of Operations (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 25, 2015	Jun. 26, 2015	Mar. 27, 2015	Dec. 31, 2014	Sep. 26, 2014	Jun. 27, 2014	Mar. 28, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Sales	$ 2,871	$ 2,564	$ 2,543	$ 2,488	$ 2,961	$ 2,653	$ 2,702	$ 2,670	$ 10,466	$ 10,986	$ 11,420
Operating income (loss)	(96)	231	153	187	294	235	217	266	475	1,012	1,117
Income (loss) from continuing operations	(56)	128	120	105	205	146	131	163	297	645	716
Net income (loss)	(162)	(296)	124	109	207	157	141	172	(225)	677	760
Net income (loss) attributable to L-3	$ (166)	$ (299)	$ 120	$ 105	$ 203	$ 154	$ 137	$ 170	$ (240)	$ 664	$ 751
Basic earnings (loss) per share from continuing operations	$ (0.76)	$ 1.56	$ 1.41	$ 1.23	$ 2.38	$ 1.68	$ 1.47	$ 1.87	$ 3.49	$ 7.40	$ 7.91
Basic earnings (loss) per share	(2.11)	(3.74)	1.46	1.28	2.41	1.81	1.59	1.97	(2.97)	7.78	8.40
Diluted earnings (loss) per share from continuing operations	(0.76)	1.54	1.39	1.20	2.34	1.65	1.42	1.80	3.44	7.20	7.76
Diluted earnings (loss) per share	$ (2.11)	$ (3.68)	$ 1.44	$ 1.25	$ 2.36	$ 1.78	$ 1.53	$ 1.90	$ (2.93)	$ 7.56	$ 8.24