Accounting Standards Issued and Not Yet Implemented - Additional Information (Detail)	6 Months Ended
Jun. 24, 2016	Jun. 26, 2015
Accounting Changes and Error Corrections [Abstract]
Percentage of sales accounted for under contract accounting standards	50.00%	49.00%

Percentage of sales accounted for under contract accounting standards.

No definition available.

Name:	lll_PercentageOfSalesAccountedForUnderContractAccountingStandards
Namespace Prefix:	lll_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration