L-3 Holdings' Earnings Per Common Share - Reconciliation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 26, 2014	Sep. 27, 2013	Sep. 26, 2014	Sep. 27, 2013
Reconciliation of net income:
Net income	$ 157	$ 204	$ 470	$ 572
Net income attributable to noncontrolling interests	(3)	(4)	(9)	(6)
Net income attributable to L-3 Holdings' common shareholders	$ 154	$ 200	$ 461	$ 566
Basic:
Weighted average common shares outstanding	85.1	89.6	85.7	89.9
Basic earnings per share:
Net income	$ 1.81	$ 2.23	$ 5.38	$ 6.30
Common and potential common shares:
Weighted average common shares outstanding	85.1	89.6	85.7	89.9
Assumed purchase of common shares for treasury	(2.9)	(5.2)	(3.2)	(4.7)
Assumed conversion of the CODES		0.1	1.1	0.1
Common and potential common shares	86.6	91.3	88.4	91.3
Diluted earnings per share:
Net income	$ 1.78	$ 2.19	$ 5.21	$ 6.20
Stock Options [Member]
Common and potential common shares:
Common and potential common shares	2.8	4.7	3.0	3.9
Unvested Restricted Stock Awards [Member]
Common and potential common shares:
Common and potential common shares	1.5	1.8	1.6	1.8
Employee Stock Purchase Plan Contributions [Member]
Common and potential common shares:
Common and potential common shares		0.2	0.1	0.2
Performance Unit Awards [Member]
Common and potential common shares:
Common and potential common shares	0.1	0.1	0.1	0.1