Refers to the debt instrument maturity date year.

No definition available.

Name:	lll_DebtInstrumentMaturityDateYear
Namespace Prefix:	lll_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Refers to the amount of additional borrowing capacity of the line of credit facility.

+ References

No definition available.

+ Details

Name:	lll_LineOfCreditFacilityAdditionalBorrowingCapacity
Namespace Prefix:	lll_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount, after accumulated amortization, of debt discount.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Period remaining on line of credit facility before it terminates, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
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-Paragraph 1
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+ Details

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

- Definition

Amount of cash outflow for payment of an obligation from a lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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Debt, Components of Debt and Reconciliation to Carrying Amount of Current and Long-Term Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Oct. 31, 2016
Components of Debt [Abstract]
Repayments under the credit facility	$ 1,328	$ 819	$ 1,194
Proceeds under the credit facility	1,328	819	$ 1,194
Available borrowings under credit facility	1,000
3.95% Senior Notes due 2016 [Member]
Components of Debt [Abstract]
Principal amount of long-term debt	200
5.20% Senior Notes due 2019 [Member]
Components of Debt [Abstract]
Unamortized discounts	(4)
4.75% Senior Notes due 2020 [Member]
Components of Debt [Abstract]
Unamortized discounts	(3)
4.95% Senior Notes due 2021 [Member]
Components of Debt [Abstract]
Unamortized discounts	(4)
3.95% Senior Notes due 2024 [Member]
Components of Debt [Abstract]
Unamortized discounts	(3)
3.85% Senior Notes due 2026 [Member]
Components of Debt [Abstract]
Unamortized discounts	$ (3)
Revolving Credit Facility [Member]
Line of Credit Facility [Abstract]
Revolving credit facility expiration period	5 years
Total aggregate borrowings under revolving credit facility				$ 1,000
Revolving credit facility expiration date	Oct. 31, 2021
Uncommitted incremental revolving facilities and additional term loan facilities				$ 600
Revolving Credit Facility [Member] \| Federal Funds Rate [Member] \| Minimum [Member]
Line of Credit Facility [Abstract]
Applicable spread on base rate	0.125%
Revolving Credit Facility [Member] \| Federal Funds Rate [Member] \| Maximum [Member]
Line of Credit Facility [Abstract]
Applicable spread on base rate	1.00%
Revolving Credit Facility [Member] \| Eurodollar [Member] \| Minimum [Member]
Line of Credit Facility [Abstract]
Applicable spread on base rate	1.125%
Revolving Credit Facility [Member] \| Eurodollar [Member] \| Maximum [Member]
Line of Credit Facility [Abstract]
Applicable spread on base rate	2.00%
L3 Technologies [Member]
Components of Debt [Abstract]
Borrowings under Revolving Credit Facility	$ 0	0
Principal amount of long-term debt	3,350	3,350
Unamortized discounts	(7)	(8)
Deferred debt issue costs	(13)	(17)
Carrying amount of long-term debt	$ 3,330	3,325
L3 Technologies [Member] \| 3.95% Senior Notes due 2016 [Member]
Components of Debt [Abstract]
Interest rate on senior notes	3.95%
L3 Technologies [Member] \| 1.50% Senior Notes due 2017 [Member]
Components of Debt [Abstract]
Interest rate on senior notes	1.50%
L3 Technologies [Member] \| 5.20% Senior Notes due 2019 [Member]
Components of Debt [Abstract]
Borrowings under Revolving Credit Facility	$ 1,000	1,000
Interest rate on senior notes	5.20%
Debt instrument maturity period	2019
L3 Technologies [Member] \| 4.75% Senior Notes due 2020 [Member]
Components of Debt [Abstract]
Borrowings under Revolving Credit Facility	$ 800	800
Interest rate on senior notes	4.75%
Debt instrument maturity period	2020
L3 Technologies [Member] \| 4.95% Senior Notes due 2021 [Member]
Components of Debt [Abstract]
Borrowings under Revolving Credit Facility	$ 650	650
Interest rate on senior notes	4.95%
Debt instrument maturity period	2021
L3 Technologies [Member] \| 3.95% Senior Notes due 2024 [Member]
Components of Debt [Abstract]
Borrowings under Revolving Credit Facility	$ 350	350
Interest rate on senior notes	3.95%
Debt instrument maturity period	2024
L3 Technologies [Member] \| 3.85% Senior Notes due 2026 [Member]
Components of Debt [Abstract]
Borrowings under Revolving Credit Facility	$ 550	550
Interest rate on senior notes	3.85%
Debt instrument maturity period	2026
L3 Technologies [Member] \| Revolving Credit Facility [Member]
Components of Debt [Abstract]
Repayments under the credit facility	$ 1,328
Proceeds under the credit facility	1,328
Available borrowings under credit facility	$ 1,000	$ 1,000