Investments - Investment Commitments (Details) - Investments in Assets Requiring Future Purchase, Sale or Funding Commitments $ in Millions	Sep. 30, 2023 USD ($)
Investment Commitments [Abstract]
Commitments to purchase or fund investments	$ 1,600
Commitments to sell investments	$ 65

Minimum amount of other commitment in which the entity has agreed to sell investments related to various third-party limited partnerships, signed and accepted mortgage loan applications and obligations related to privately placed debt securities.

No definition available.

Name:	l_CommitmentsToSellInvestments
Namespace Prefix:	l_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant