Summary of Segment Information (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2011	Dec. 31, 2011
Operating Statistics [Line Items]
Sales reclassified from C3ISR segment to Electronic Systems segment as a result of business unit re-alignments	$ 17	$ 55
Operating income (loss) reclassified from C3ISR segment to Electronic Systems segment as a result of business unit re-alignments	2
Assets reclassified from C3ISR segment to Electronic Systems segment as a result of business unit re-alignments			$ 124

Operating income (loss) reclassified from segment one to segment four as result of business unit re-alignments.

No definition available.

Name:	lll_OperatingIncomeLossReclassifiedFromSegmentOneToSegmentFourAsResultOfBusinessUnitRealignments
Namespace Prefix:	lll_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration