Investments (Payables For Collateral On Investments) (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2023	Dec. 31, 2022
Carrying Value
Collateral payable for derivative investments	$ 4,522	$ 3,210
Securities pledged under securities lending agreements	290	298
Investments pledged for Federal Home Loan Bank of Indianapolis ('FHLBI')	2,920	3,130
Total payables for collateral on investments	7,732	6,638
Fair Value
Collateral payable for derivative investments	4,522	3,210
Securities pledged under securities lending agreements	280	287
Investments pledged for Federal Home Loan Bank of Indianapolis('FHLBI')	3,860	3,925
Total payables for collateral on investments	$ 8,662	$ 7,422
Percentage of the fair value of domestic securities obtained as collateral under securities lending agreements.	102.00%
Percentage of the fair value of foreign securities obtained as collateral under securities lending agreements.	105.00%
Maximum [Member]
Fair Value
Percentage of the fair value of FHLBI securities obtained as collateral under securities pledged for FHLBI for AFS Securities	115.00%
Percentage of the fair value of FHLBI securities obtained as collateral under securities pledged for FHLBI for mortgage loan	175.00%
Minimum [Member]
Fair Value
Percentage of the fair value of FHLBI securities obtained as collateral under securities pledged for FHLBI for AFS Securities	105.00%
Percentage of the fair value of FHLBI securities obtained as collateral under securities pledged for FHLBI for mortgage loan	155.00%

Carrying Value Of Payables For Collateral On Investments [Abstract]

No definition available.

Name:	cik0000726865_CarryingValueOfPayablesForCollateralOnInvestmentsAbstract
Namespace Prefix:	cik0000726865_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

This item represents the percentage of the fair value of AFS securities obtained as collateral pledged.

+ References

No definition available.

+ Details

Name:	cik0000726865_CollateralObtainedPercentOfFairValueOfAvailableForSaleSecurities
Namespace Prefix:	cik0000726865_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

This item represents the percentage of the fair value of Mortgage loans obtained as collateral pledged.

+ References

No definition available.

+ Details

Name:	cik0000726865_CollateralObtainedPercentOfFairValueOfMortgageLoan
Namespace Prefix:	cik0000726865_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

This item represents the percentage of the fair value of domestic securities obtained as collateral under securities lending agreements

+ References

No definition available.

+ Details

Name:	cik0000726865_CollateralObtainedPercentOfFairValueSecuritiesLendingAgreementsDomestic
Namespace Prefix:	cik0000726865_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

This item represents the percentage of the fair value of foreign securities obtained as collateral under securities lending agreements

+ References

No definition available.

+ Details

Name:	cik0000726865_CollateralObtainedPercentOfFairValueSecuritiesLendingAgreementsForeign
Namespace Prefix:	cik0000726865_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

When entering into a derivative transaction, the amount of cash received as collateral from a counterparty.

+ References

No definition available.

+ Details

Name:	cik0000726865_CollateralPayableHeldForDerivativeInvestmentsCarryingValue
Namespace Prefix:	cik0000726865_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fair value of cash received as collateral from a counterparty.

+ References

No definition available.

+ Details

Name:	cik0000726865_CollateralPayableHeldForDerivativeInvestmentsFairValue
Namespace Prefix:	cik0000726865_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair Value Of Related Investments Or Collateral [Abstract]

+ References

No definition available.

+ Details

Name:	cik0000726865_FairValueOfRelatedInvestmentsOrCollateralAbstract
Namespace Prefix:	cik0000726865_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of cash received as security in return for loaning securities to Federal Home Loan Bank of Indianapolis.

+ References

No definition available.

+ Details

Name:	cik0000726865_SecuritiesPledgedForFederalHomeLoanBankOfIndianapolisCarryingValue
Namespace Prefix:	cik0000726865_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fair value of investments loaned to Federal Home Loan Bank of Indianapolis as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	cik0000726865_SecuritiesPledgedForFederalHomeLoanBankOfIndianapolisFairValue
Namespace Prefix:	cik0000726865_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The fair value of investments loaned to another party under securities lending agreements as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	cik0000726865_SecuritiesPledgedUnderSecuritiesLendingAgreementsFairValue
Namespace Prefix:	cik0000726865_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The total fair value of investments related to payables for collateral on investments as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	cik0000726865_TotalPayablesForCollateralOnInvestmentFairValue
Namespace Prefix:	cik0000726865_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of obligation to return cash received as collateral for security loaned to another party.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-04(11))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479617/946-210-S99-1

+ Details

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

- Definition

Amount, before effects of master netting arrangements, of financial assets loaned to entities in exchange for collateral and funds outstanding borrowed in the form of a financial asset repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same financial assets at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 860
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481420/860-30-50-7

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 860
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481420/860-30-50-7

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 860
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481420/860-30-50-7

+ Details

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

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: