Guaranteed Benefit Features (Narrative) (Details)	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Guaranteed Benefit Features [Abstract]
Percent of permanent life insurance in force	35.00%		35.00%		33.00%
Percent of permanent life insurance sales	29.00%	30.00%	29.00%	33.00%

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:	num:percentItemType
Balance Type:	na
Period Type:	instant