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		9 Months Ended
	Sep. 23, 2016	Sep. 25, 2015	Sep. 23, 2016	Sep. 25, 2015
Reconciliation of net income (loss):
Net income (loss)	$ 151	$ (296)	$ 532	$ (63)
Net income from continuing operations attributable to noncontrolling interests	(3)	(3)	(10)	(11)
Net income (loss) attributable to L-3	148	(299)	522	(74)
Earnings (loss) attributable to L-3 Holdings' common shareholders:
Continuing operations	148	125	459	342
Discontinued operations, net of income tax		(424)	63	(416)
Net income (loss) attributable to L-3 Holdings' common shareholders	$ 148	$ (299)	$ 522	$ (74)
Basic:
Weighted average common shares outstanding	77.3	80.0	77.4	81.5
Basic earnings (loss) per share:
Continuing operations	$ 1.91	$ 1.56	$ 5.93	$ 4.19
Discontinued operations, net of income tax		(5.30)	0.81	(5.10)
Net income (loss)	$ 1.91	$ (3.74)	$ 6.74	$ (0.91)
Common and potential common shares:
Weighted average common shares outstanding	77.3	80.0	77.4	81.5
Assumed purchase of common shares for treasury	(2.7)	(2.5)	(2.4)	(2.7)
Common and potential common shares	78.8	81.2	78.7	82.7
Diluted earnings (loss) per share:
Continuing operations	$ 1.88	$ 1.54	$ 5.83	$ 4.14
Discontinued operations, net of income tax		(5.22)	0.80	(5.03)
Net income (loss)	$ 1.88	$ (3.68)	$ 6.63	$ (0.89)
Stock Options [Member]
Common and potential common shares:
Common and potential common shares	3.0	2.2	2.5	2.4
Unvested Restricted Stock Awards [Member]
Common and potential common shares:
Common and potential common shares	1.0	1.2	1.0	1.3
Performance Unit Awards [Member]
Common and potential common shares:
Common and potential common shares	0.1	0.1	0.1	0.1
Employee Stock Purchase Plan Contributions [Member]
Common and potential common shares:
Common and potential common shares	0.1	0.2	0.1	0.1