Derivative Instruments (Effects Of Qualifying And Non-Qualifying Hedges) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Realized Gain (Loss) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total line items in which the effects of fair value or cash flow hedges are recorded	$ (2)	$ (351)
Net Investment Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total line items in which the effects of fair value or cash flow hedges are recorded	1,318	1,191
Interest rate contracts [Member] \| Realized Gain (Loss) [Member] \| Non-Qualifying Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Non-qualifying hedges gain (loss)	2,150	357
Equity market contracts [Member] \| Realized Gain (Loss) [Member] \| Non-Qualifying Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Non-qualifying hedges gain (loss)	1,070	(458)
Credit contracts [Member] \| Realized Gain (Loss) [Member] \| Non-Qualifying Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Non-qualifying hedges gain (loss)	(4)
GLB Direct And Ceded Embedded Derivative [Member] \| Realized Gain (Loss) [Member] \| Non-Qualifying Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Non-qualifying hedges gain (loss)	(7)	1
Embedded derivatives - Reinsurance related [Member] \| Realized Gain (Loss) [Member] \| Non-Qualifying Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Non-qualifying hedges gain (loss)	596	(289)
Indexed Annuity And IUL Contracts [Member] \| Realized Gain (Loss) [Member] \| Non-Qualifying Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Non-qualifying hedges gain (loss)	1,028	(239)
Fair Value Hedges [Member] \| Net Investment Income [Member] \| Qualifying Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedged items		24
Derivatives designated as hedging instruments		(24)
Fair Value Hedges [Member] \| Interest rate contracts [Member] \| Net Investment Income [Member] \| Qualifying Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedged items	127
Derivatives designated as hedging instruments	(127)
Cash Flow Hedges [Member] \| Interest rate contracts [Member] \| Net Investment Income [Member] \| Qualifying Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain or (loss) reclassified from AOCI into income		1
Cash Flow Hedges [Member] \| Foreign currency contracts [Member] \| Realized Gain (Loss) [Member] \| Qualifying Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain or (loss) reclassified from AOCI into income	1	1
Cash Flow Hedges [Member] \| Foreign currency contracts [Member] \| Net Investment Income [Member] \| Qualifying Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain or (loss) reclassified from AOCI into income	$ 11	$ 7

Amount of income (expense) line items in statement of financial position that hedges are recorded

No definition available.

Name:	cik0000726865_AmountOfIncomeExpenseLineItemsInStatementOfFinancialPositionThatHedgesAreRecorded
Namespace Prefix:	cik0000726865_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=109977999&loc=d3e76258-113986

+ Details

Name:	us-gaap_ChangeInUnrealizedGainLossOnFairValueHedgingInstruments1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement.

+ References

+ Details

Name:	us-gaap_ChangeInUnrealizedGainLossOnHedgedItemInFairValueHedge1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4D
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624177-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624171-113959

+ Details

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

- Definition

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4CC
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109998890-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624171-113959

+ Details

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

- Details

Name:	us-gaap_IncomeStatementLocationAxis=cik0000726865_RealizedGainLossMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=cik0000726865_NetInvestmentIncomeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_EquityContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CreditRiskContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cik0000726865_GuaranteedLivingBenefitsEmbeddedDerivativeReservesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cik0000726865_ReinsuranceRelatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cik0000726865_IndexedAnnuityContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_FairValueHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_CashFlowHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: