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. 28, 2012		Sep. 30, 2011		Sep. 28, 2012		Sep. 30, 2011
Earnings Per Share [Line Items]
Net income	$ 194		$ 238		$ 605		$ 691
Net income from continuing operations attributable to noncontrolling interests	(2)		(2)		(3)		(6)
Net income (loss) from discontinued operations attributable to noncontrolling interests			(1)		(4)		(3)
Net income allocable to participating securities							(2)
Net income allocable to L-3 Holdings' common shareholders	192		235		598		680
Continuing operations	193		212		570		602
Discontinued operations, net of income tax	$ (1)		$ 23		$ 28		$ 78
Weighted average common shares outstanding	96.1		103.5		97.4		106.0
Continuing operations	$ 2.01		$ 2.05		$ 5.85		$ 5.68
Discontinued operations, net of income tax	$ (0.01)		$ 0.22		$ 0.29		$ 0.74
Basic earnings per share	$ 2.00		$ 2.27		$ 6.14		$ 6.42
Assumed purchase of common shares for treasury	(3.1)		(2.7)		(2.8)		(3.1)
Assumed conversion of the CODES(1)		[1]		[1]		[1]		[1]
Common and potential common shares	97.4		104.8		98.7		107.2
Continuing operations	$ 1.98		$ 2.02		$ 5.78		$ 5.62
Discontinued operations, net of income tax	$ (0.01)		$ 0.22		$ 0.28		$ 0.72
Diluted earnings per share	$ 1.97		$ 2.24		$ 6.06		$ 6.34
Assumed exercise of stock options [Member]
Earnings Per Share [Line Items]
Common and potential common shares	2.1		1.5		1.7		2.3
Unvested restricted stock awards [Member]
Earnings Per Share [Line Items]
Common and potential common shares	2.0		2.1		2.1		1.8
Employee stock purchase plan contributions [Member]
Earnings Per Share [Line Items]
Common and potential common shares	0.3		0.4		0.3		0.1
Performance unit awards [Member]
Earnings Per Share [Line Items]
Common and potential common shares							0.1

[1] L-3 Holdings' CODES had no impact on diluted EPS for the quarterly or year-to-date periods ended September 28, 2012 or September 30, 2011 as the average market price of L-3 Holdings common stock during these periods was less than the price at which the CODES would have been convertible into L-3 Holdings common stock. As of September 28, 2012, the conversion price was $92.17.