Guaranteed Benefit Features (Narrative) (Details)	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Guaranteed Benefit Features [Abstract]
Percent of permanent life insurance in force	37.00%		37.00%		37.00%
Percent of permanent life insurance sales	17.00%	32.00%	15.00%	32.00%

Universal life and variable universal life products with secondary guarantees in force as a percentage of total permanent life insurance in force.

No definition available.

Name:	cik0000726865_PercentOfPermanentLifeInsuranceInForce
Namespace Prefix:	cik0000726865_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant