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
	Mar. 25, 2016	Mar. 27, 2015
Reconciliation of net income:
Net income	$ 230	$ 109
Net income from continuing operations attributable to noncontrolling interests	(3)	(4)
Net income (loss) attributable to L-3	227	105
Earnings attributable to L-3 Holdings' common shareholders:
Continuing operations	164	101
Discontinued operations, net of income tax	63	4
Net income attributable to L-3 Holdings' common shareholders	$ 227	$ 105
Basic:
Weighted average common shares outstanding	77.8	82.3
Basic earnings per share:
Continuing operations	$ 2.11	$ 1.23
Discontinued operations, net of income tax	0.81	0.05
Net income	$ 2.92	$ 1.28
Common and potential common shares:
Weighted average common shares outstanding	77.8	82.3
Assumed purchase of common shares for treasury	(2.1)	(3.1)
Common and potential common shares	79.0	83.8
Diluted earnings per share:
Continuing operations	$ 2.08	$ 1.20
Discontinued operations, net of income tax	0.79	0.05
Net income	$ 2.87	$ 1.25
Stock Options [Member]
Common and potential common shares:
Common and potential common shares	2.0	2.9
Unvested Restricted Stock Awards [Member]
Common and potential common shares:
Common and potential common shares	1.1	1.4
Performance Unit Awards [Member]
Common and potential common shares:
Common and potential common shares	0.1	0.2
Employee Stock Purchase Plan Contributions [Member]
Common and potential common shares:
Common and potential common shares	0.1	0.1