Reinsurance and Indemnification - Rollforward of Credit Loss Allowance for Reinsurance Recoverables (Details) $ in Millions	12 Months Ended
Dec. 31, 2020 USD ($)
Reinsurance
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	$ (74)
Property and casualty
Reinsurance
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	(60)
Increase (decrease) in the provision for credit losses	1
Write-offs	0
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	(59)
Allstate Annuities, Allstate Life and Allstate Benefits
Reinsurance
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	(3)
Increase (decrease) in the provision for credit losses	(1)
Write-offs	0
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	(15)
Allstate Annuities, Allstate Life and Allstate Benefits \| Cumulative effect of change in accounting principle
Reinsurance
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	$ (11)

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Amount of the write-down or write-off of a receivable from a reinsurer.

+ References

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- Definition

Amount of increase (decrease) in allowance for credit loss on reinsurance recoverable.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

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Amount of allowance for credit loss on reinsurance recoverable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121599878&loc=SL82895884-210446

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