Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2016		Sep. 23, 2016		Jun. 24, 2016		Mar. 25, 2016		Dec. 31, 2015		Sep. 25, 2015		Jun. 26, 2015		Mar. 27, 2015		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Unaudited Quarterly Financial Data [Abstract]
Sales	$ 2,989		$ 2,505		$ 2,664		$ 2,353		$ 2,871		$ 2,564		$ 2,543		$ 2,488		$ 10,511	$ 10,466	$ 10,986
Operating income (loss)	294		215		247		252		(96)		231		153		187		1,008	475	1,012
Income (loss) from continuing operations	192		151		151		167		(56)		128		120		105		661	297	645
Net income (loss)	192		151		151		230		(162)		(296)		124		109		724	(225)	677
Net income (loss) attributable to L3	$ 188		$ 148		$ 147		$ 227		$ (166)		$ (299)		$ 120		$ 105		$ 710	$ (240)	$ 664
Basic earnings (loss) per share from continuing operations (in dollars per share)	$ 2.43	[1]	$ 1.91	[1]	$ 1.90	[1]	$ 2.11	[1]	$ (0.76)	[1]	$ 1.56	[1]	$ 1.41	[1]	$ 1.23	[1]	$ 8.36	$ 3.49	$ 7.40
Basic earnings (loss) per share (in dollars per share)	2.43	[1]	1.91	[1]	1.90	[1]	2.92	[1]	(2.11)	[1]	(3.74)	[1]	1.46	[1]	1.28	[1]	9.17	(2.97)	7.78
Diluted earnings (loss) per share from continuing operations (in dollars per share)	2.38	[1]	1.88	[1]	1.88	[1]	2.08	[1]	(0.76)	[1]	1.54	[1]	1.39	[1]	1.20	[1]	8.21	3.44	7.20
Diluted earnings (loss) per share (in dollars per share)	$ 2.38	[1]	$ 1.88	[1]	$ 1.88	[1]	$ 2.87	[1]	$ (2.11)	[1]	$ (3.68)	[1]	$ 1.44	[1]	$ 1.25	[1]	$ 9.01	$ (2.93)	$ 7.56

[1] EPS in each quarter is computed using the weighted-average number of shares outstanding during that quarter, while EPS for the full year is computed using the weighted-average number of shares outstanding during the year. Therefore, the sum of the four quarters' EPS may not equal the full year computed EPS.