Name:	us-gaap_BusinessAcquisitionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of consideration received or receivable for the disposal of assets and liabilities, including discontinued operation.

No definition available.

Name:	us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of revenue attributable to disposal group, including, but not limited to, discontinued operation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 5B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721673-107760

Name:	us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Gain (loss) from sale or disposal of an organization or integrated set of activities (for example, but not limited to, a partnership or corporation) engaged in providing a product or service in a commercial, industrial, or professional environment.

No definition available.

Name:	us-gaap_GainLossOnSaleOfBusiness
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 20
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=68072869&loc=d3e41242-110953

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(10))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(15))
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(8))
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Name:	us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The cash inflow associated with the amount received from the sale of a portion of the company's business, for example a segment, division, branch or other business, during the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

Name:	us-gaap_ProceedsFromDivestitureOfBusinesses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Name:	us-gaap_SalesRevenueNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=lll_CTCAviationJetServicesLimitedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=lll_L3ColemanAerospaceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=lll_DisplayProductLineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: