Guarantees and Contingent Liabilities (Details)	9 Months Ended
Sep. 30, 2020 USD ($)
Minimum
Proceedings:
Loss contingencies, reasonably possible pretax loss exposure in excess of the amount accrued	$ 0
Maximum
Proceedings:
Loss contingencies, reasonably possible pretax loss exposure in excess of the amount accrued	$ 85,000,000

Estimate of the reasonably possible pretax loss exposure in excess of the amount accrued for the entity's lawsuits, regulatory inquiries and other legal proceedings.

No definition available.

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