Investments (Credit Quality Indicators For Residential Mortgage Loans) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans on real estate, ACL	$ 160	$ 2
Residential [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Amortized Cost	$ 774	$ 735
Percentage of total mortgage loans on real estate	100.00%	100.00%
Mortgage loans on real estate, ACL	$ 35	$ 2
Residential [Member] \| Performing [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Amortized Cost	$ 750	$ 718
Percentage of total mortgage loans on real estate	96.90%	97.70%
Residential [Member] \| Nonperforming [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Amortized Cost	$ 24	$ 17
Percentage of total mortgage loans on real estate	3.10%	2.30%

Reflects the percentage derived from dividing mortgage loans with a specified loan-to-value ratio by total principal amount of mortgage loans.

No definition available.

+ Details

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Namespace Prefix:	cik0000726865_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919249-210447

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919249-210447

+ Details

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

- 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

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- Definition

Amount, before allowance for credit loss, of financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919230-210447

+ Details

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- Details

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- Details

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- Details

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