Contracts in Process - Additional Information (Detail)	Dec. 31, 2015
Contractors [Abstract]
Percentage of unbilled contract receivables, net billed and collected within one year	92.00%
Percentage of incurred costs billed, minimum	75.00%
Percentage of incurred costs billed, maximum	80.00%

Percentage of unbilled contract receivables billed and collected within one year.

No definition available.

Name:	lll_PercentageOfUnbilledContractReceivablesBilledAndCollectedWithinOneYear
Namespace Prefix:	lll_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant