Reinsurance - Reinsurance items (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reinsurance recoverable
Interest credited to contractholder funds	$ 44	$ 40	$ 44
Prudential
Reinsurance recoverable
Premiums and contract charges	64	65	72
Contract benefits	46	(4)	87
Interest credited to contractholder funds	20	19	20
Operating costs and expenses	12	12	14
Affiliate
Reinsurance recoverable
Premiums and contract charges	44	49	51
Contract benefits	37	35	35
Interest credited to contractholder funds	18	20	20
Non-affiliate
Reinsurance recoverable
Premiums and contract charges	227	270	275
Contract benefits	139	152	214
Interest credited to contractholder funds	$ 26	$ 20	$ 24

- Definition

Premiums and contract charges related to life insurance, accident and health insurance and annuity contracts that are assumed and earned by another insurer as a result of reinsurance arrangements.

+ References

No definition available.

+ Details

Name:	all_CededLifeAndAnnuityPremiumsAndContractCharges
Namespace Prefix:	all_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount in the period for estimated recoupment of interest credited expense under annuity contracts ceded.

+ References

No definition available.

+ Details

Name:	all_ReinsuranceCededInterestCreditedToPolicyholdersAccountBalances
Namespace Prefix:	all_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount in the period for estimated recoupment of contract benefits under life insurance, accident and health insurance, and annuity contracts ceded.

+ References

No definition available.

+ Details

Name:	all_ReinsuranceCededLifeAndAnnuityContractBenefits
Namespace Prefix:	all_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount in the period for estimated recoupment of operating costs and expenses under life insurance, accident and health insurance, and annuity contracts ceded.

+ References

No definition available.

+ Details

Name:	all_ReinsuranceCededOperatingCostsAndExpenses
Namespace Prefix:	all_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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

- Details

Name:	us-gaap_CededCreditRiskAxis=all_PrudentialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_AffiliatedEntityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=all_NonAffiliatesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: