L-3 Holdings' Earnings (Loss) 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		9 Months Ended
	Sep. 25, 2015	Sep. 26, 2014	Sep. 25, 2015	Sep. 26, 2014
Reconciliation of net (loss) income:
Net (loss) income	$ (296)	$ 157	$ (63)	$ 470
Net income attributable to noncontrolling interests	(3)	(3)	(11)	(9)
Net (loss) income attributable to L-3 Holdings' common shareholders	$ (299)	$ 154	$ (74)	$ 461
Basic:
Weighted average common shares outstanding	80.0	85.1	81.5	85.7
Basic (loss) earnings per share:
Net (loss) income	$ (3.74)	$ 1.81	$ (0.91)	$ 5.38
Common and potential common shares:
Weighted average common shares outstanding	80.0	85.1	81.5	85.7
Assumed purchase of common shares for treasury		(2.9)		(3.2)
Assumed conversion of the CODES				1.1
Common and potential common shares	80.0	86.6	81.5	88.4
Diluted (loss) earnings per share:
Net (loss) income	$ (3.74)	$ 1.78	$ (0.91)	$ 5.21
Stock Options [Member]
Common and potential common shares:
Common and potential common shares		2.8		3.0
Unvested Restricted Stock Awards [Member]
Common and potential common shares:
Common and potential common shares		1.5		1.6
Performance Unit Awards [Member]
Common and potential common shares:
Common and potential common shares		0.1		0.1
Employee Stock Purchase Plan Contributions [Member]
Common and potential common shares:
Common and potential common shares				0.1