Investments - Schedule of Increase (Decrease) in Payables for Collateral on Investments (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2025	Sep. 30, 2024
Investments [Abstract]
Collateral payable for derivative investments	$ 1,674	$ 2,018
Securities pledged under securities lending agreements	15	(20)
Securities pledged under repurchase agreements	210	0
Investments pledged for FHLB	(635)	550
Total increase (decrease) in payables for collateral on investments	$ 1,264	$ 2,548

- Definition

The net change during the reporting period in the amount of cash that is received related to collateral payable held for derivative instruments.

+ References

No definition available.

+ Details

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

- Definition

Increase (Decrease) In Cash Collateral For Reverse Repurchase Agreements

+ References

No definition available.

+ Details

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Namespace Prefix:	cik0000726865_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The net change during the reporting period in the amount of cash that is received related to securities pledged under securities lending agreements.

+ References

No definition available.

+ Details

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Namespace Prefix:	cik0000726865_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The net change during the reporting period in the amount of cash that is received related to securities pledged for Federal Home Loan Bank of Indianapolis.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

The increase (decrease) during the reporting period in the amount that is received as security when loaning securities.

+ References

No definition available.

+ Details

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Namespace Prefix:	cik0000726865_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- References

No definition available.

+ Details

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