L-3 Holdings' Earnings Per Common Share - Reconciliation of Basic and Diluted Earnings per Share (EPS) (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 26, 2015	Jun. 27, 2014	Jun. 26, 2015	Jun. 27, 2014
Reconciliation of net income:
Net income	$ 124	$ 141	$ 233	$ 313
Net income attributable to noncontrolling interests	(4)	(4)	(8)	(6)
Net income attributable to L-3 Holdings' common shareholders	$ 120	$ 137	$ 225	$ 307
Basic:
Weighted average common shares outstanding	82.1	86.1	82.2	86.1
Basic earnings per share:
Net income	$ 1.46	$ 1.59	$ 2.74	$ 3.57
Common and potential common shares:
Weighted average common shares outstanding	82.1	86.1	82.2	86.1
Assumed purchase of common shares for treasury	(2.6)	(3.3)	(2.8)	(3.4)
Assumed conversion of the CODES		1.7		1.6
Common and potential common shares	83.2	89.3	83.5	89.4
Diluted earnings per share:
Net income	$ 1.44	$ 1.53	$ 2.69	$ 3.43
Stock Options [Member]
Common and potential common shares:
Common and potential common shares	2.2	2.9	2.5	3.2
Unvested Restricted Stock Awards [Member]
Common and potential common shares:
Common and potential common shares	1.2	1.6	1.3	1.6
Performance Unit Awards [Member]
Common and potential common shares:
Common and potential common shares	0.1	0.1	0.1	0.2
Employee Stock Purchase Plan Contributions [Member]
Common and potential common shares:
Common and potential common shares	0.2	0.2	0.2	0.1