Summary of Significant Accounting Policies, Policyholder Dividends (Details)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Policyholder Account Balance [Abstract]
Percentage of net written premium	1.00%	1.00%	1.00%

Percentage of premiums written is the sum of premiums written by an insurance company over the course of a period of time.

No definition available.

Name:	l_PercentageOfNetWrittenPremium
Namespace Prefix:	l_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration