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v3.19.1

Reinsurance - Claims expense, life contract benefits and interest credited to contractholder funds (Details) - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2019 | Mar. 31, 2018
Property and casualty insurance claims and claims expense |  |
Reductions to costs and expenses due to reinsurance ceded amounts |  |
Ceded losses incurred | $ (91) | $ (187)
Life contract benefits |  |
Reductions to costs and expenses due to reinsurance ceded amounts |  |
Ceded losses incurred | (23) | (49)
Interest credited to contractholder funds |  |
Reductions to costs and expenses due to reinsurance ceded amounts |  |
Ceded losses incurred | $ (3) | $ (4)

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- Definition Represents the amount of reinsurance ceded under various contracts. + References No definition available. + Details
Name: | all_ReinsuranceCededAmount
Namespace Prefix: | all_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- References No definition available. + Details
Name: | all_ReinsuranceClaimsBenefitsCededAbstract
Namespace Prefix: | all_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_IncomeStatementLocationAxis=all_PropertyLiabilityInsuranceClaimsAndClaimsExpenseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=all_LifeAndAnnuityContractBenefitsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=all_InterestCreditedToContractholderFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |