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v3.25.3

Reinsurance and Indemnification - Additional Information (Details) - National Flood Insurance Program $ in Billions | Sep. 30, 2025 USD ($)
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Reinsurance |
Borrowing capacity is reduced | $ 1.0
Exceeded by the current program debt | $ 22.5

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- Definition Indemnification Programs, Current Program Debt + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Indemnification Programs, Maximum Borrowing Capacity + References No definition available. + Details
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Namespace Prefix: | all_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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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
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_CededCreditRiskAxis=all_NationalFloodInsuranceProgramMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |