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

Fair value portion of a collateral trust account established by National Indemnity (NICO) as security for its obligations to CNA Financial Corporation (CNA).

No definition available.

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

Total consideration transferred to National Indemnity Company ("NICO") under asbestos and environmental claim (A&EP) loss portfolio transfer, including reinsurance premium paid and net book value of billed third party reinsurance receivables transferred.

No definition available.

Name:	l_ConsiderationTransferredUnderLossPortfolioTransfer
Namespace Prefix:	l_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Cumulative amounts ceded to National Indemnity Company ("NICO") under asbestos and environmental claim (A&EP) loss portfolio transfer.

No definition available.

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

Amount of asbestos and environmental ceded claim and allocated claim adjustment expense reserves under existing third party reinsurance contracts.

No definition available.

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

Aggregate limit of net asbestos and environmental claim and allocated claim adjustment expense reserves ceded to National Indemnity Company ("NICO") under a retroactive reinsurance agreement.

No definition available.

Name:	l_LiabilityForAsbestosAndEnvironmentalClaimsNetAggregateLimit
Namespace Prefix:	l_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of reinsurance premium paid to National Indemnity Company ("NICO") under asbestos and environmental claim (A&EP) loss portfolio transfer.

No definition available.

Name:	l_ReinsurancePremium
Namespace Prefix:	l_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount of retroactive benefit recognized under retroactive reinsurance accounting.

No definition available.

Name:	l_RetroactiveReinsuranceBenefitRecognized
Namespace Prefix:	l_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount of unrecognized benefit related to loss portfolio transfer to National Indemnity Company ("NICO") under retroactive reinsurance accounting.

No definition available.

Name:	l_UnrecognizedDeferredRetroactiveReinsuranceBenefit
Namespace Prefix:	l_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Carrying amount as of the balance sheet date of reserves for the costs of settling insured claims and costs incurred in the claims settlement process attributable to asbestos and environmental claims, net of estimated reinsurance recoveries.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (cc)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480081/944-40-50-3

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480081/944-40-50-3

Name:	us-gaap_LiabilityForAsbestosAndEnvironmentalClaimsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.