Derivative Financial Instruments - Derivative Netting (Details) - A+ $ in Millions	Mar. 31, 2018 USD ($) party	Dec. 31, 2017 USD ($) party
Credit Derivatives
Number of counter-parties (in Party) \| party	2	2
Notional amount	$ 54	$ 59
Credit exposure	4	3
Exposure, net of collateral	$ 0	$ 0

The amount of credit exposure by counterparties related to derivative contracts.

No definition available.

Name:	all_CounterpartyCreditExposure
Namespace Prefix:	all_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of credit exposure by counterparties net of collateral received, related to derivative contracts.

+ References

No definition available.

+ Details

Name:	all_CreditDerivativeExposureNetOfCollateral
Namespace Prefix:	all_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The notional amount of derivative contracts for which the entity has counterparty credit exposure.

+ References

No definition available.

+ Details

Name:	all_NotionalAmountOfCounterpartyCreditExposure
Namespace Prefix:	all_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The number of counterparties to which the entity has counterparty credit exposure related to derivative contracts.

+ References

No definition available.

+ Details

Name:	all_NumberOfCounterparties
Namespace Prefix:	all_
Data Type:	xbrli:integerItemType
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

- Details

Name:	us-gaap_CreditRatingStandardPoorsAxis=us-gaap_StandardPoorsAPlusRatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: