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Reinsurance and indemnification - Rollforward of credit loss allowance for reinsurance recoverables (Details) - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2021 | Mar. 31, 2020
Property-Liability |  |
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward] |  |
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance | $ (59) | $ (60)
Increase (decrease) in the provision for credit losses | (1) | 1
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance | (60) | (59)
Allstate Health and Benefits |  |
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward] |  |
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance | (1) | (1)
Increase (decrease) in the provision for credit losses | 0 | 0
Write-offs | 0 | 0
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance | $ (1) | $ (1)

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- Definition Amount of the write-down or write-off of a receivable from a reinsurer. + 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 (d) -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447 + Details
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Period Type: | duration

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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 + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Definition 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 + Details
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- Details
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- Details
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