Investments, Investment Commitments (Details) - Investments in Assets Requiring Future Purchase, Sale or Funding Commitments [Member] $ in Millions	Dec. 31, 2020 USD ($)
Investment Commitments [Abstract]
Commitments to purchase or fund investments	$ 1,200
Commitments to sell investments	$ 85

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