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Reinsurance and Indemnification - Aggregate Excess Catastrophe Florida and Southeast States Reinsurance Contract (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2019 USD ($)
Reinsurance Retention Policy [Line Items] |
Limit of aggregate losses under aggregate excess agreement | $ 3,400
Aggregate Excess Catastrophe Florida Reinsurance Contract |
Reinsurance Retention Policy [Line Items] |
Term of catastrophe reinsurance agreement contract | 1 year
Retention percentage of reinsurance limit | 80.00%
Limit of aggregate losses under aggregate excess agreement | $ 250

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- Definition Represents the retention percentage of annual coverage limit provided by the insurance arrangement for catastrophe claims. + References No definition available. + Details
Name: | all_CatastropheInsuranceAnnualCoverageLimitRetentionPercentage
Namespace Prefix: | all_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition The limit of aggregated losses per contract year beyond which coverage provided by an aggregate excess agreement applies. + References No definition available. + Details
Name: | all_CatastropheReinsuranceAggregateLossLimitPerContractYear
Namespace Prefix: | all_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Represents the period of catastrophe reinsurance agreement contract. + References No definition available. + Details
Name: | all_CatastropheReinsuranceAgreementContractTerm
Namespace Prefix: | all_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_ReinsuranceRetentionPolicyLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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Data Type: | na
Balance Type: |
Period Type: |