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Commitments and Contingencies - Additional Information (Detail) - CNA Financial [Member] $ in Millions | Mar. 31, 2019 USD ($)
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Commitments [Line Items] |
Aggregate amount related to indemnification agreements | $ 252
Aggregate amount related to quantifiable guarantees | 375
Potential amount of future payments under guarantees | $ 1,700

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- Definition Aggregate amount of quantifiable guarantee agreements. + References No definition available. + Details
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Namespace Prefix: | l_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Aggregate amount of quantifiable indemnification agreements. + References No definition available. + Details
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Namespace Prefix: | l_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Commitments [Line Items] + References No definition available. + Details
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Namespace Prefix: | l_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=115931803&loc=d3e12069-110248 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | dei_LegalEntityAxis=l_CnaFinancialCorporationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |