Derivative Financial Instruments - CDS Notional Amounts by Credit Rating (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Credit Derivatives
Notional amount	$ 2,368	$ 2,399
Credit default contracts
Credit Derivatives
Notional amount	5	1
Fair value	0	0
Credit default contracts \| Single name \| Corporate debt
Credit Derivatives
Notional amount	5	1
Fair value	0	0
AA \| Credit default contracts
Credit Derivatives
Notional amount	0	0
AA \| Credit default contracts \| Single name \| Corporate debt
Credit Derivatives
Notional amount	0	0
A \| Credit default contracts
Credit Derivatives
Notional amount	0	0
A \| Credit default contracts \| Single name \| Corporate debt
Credit Derivatives
Notional amount	0	0
BBB \| Credit default contracts
Credit Derivatives
Notional amount	0	0
BBB \| Credit default contracts \| Single name \| Corporate debt
Credit Derivatives
Notional amount	0	0
BB and lower \| Credit default contracts
Credit Derivatives
Notional amount	5	1
BB and lower \| Credit default contracts \| Single name \| Corporate debt
Credit Derivatives
Notional amount	$ 5	$ 1

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ Details

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

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

- Definition

Fair value of credit risk derivative asset after deduction of credit risk derivative liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4K
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5708775-113959

+ Details

Name:	us-gaap_CreditRiskDerivativesAtFairValueNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_CreditDerivativesByContractTypeAxis=us-gaap_CreditDefaultSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_UnderlyingAssetClassAxis=all_SingleNameMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ExternalCreditRatingByGroupingAxis=all_InvestmentGradeCorporateDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CreditRatingStandardPoorsAxis=srt_StandardPoorsAARatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CreditRatingStandardPoorsAxis=srt_StandardPoorsARatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CreditRatingStandardPoorsAxis=srt_StandardPoorsBBBRatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CreditRatingStandardPoorsAxis=all_StandardPoorsBBAndLowerRatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: