Investments - Other-than-temporary impairment losses by asset type (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other-than-temporary impairment losses by asset type
Gross	$ (48)	$ (13)	$ (146)
Included in OCI	1	(1)	(4)
Other-than-temporary Impairment Loss, Debt Securities And Other, Portion Recognized in Earnings	47	14
Net	(47)	(14)	(150)
Net			(150)
Fixed income securities
Other-than-temporary impairment losses by asset type
Gross	(15)	(9)	(22)
Included in OCI	1	(1)	(4)
Net	(14)	(10)	(26)
Municipal
Other-than-temporary impairment losses by asset type
Gross	(2)	0	(1)
Included in OCI	2	0	(3)
Net	0	0	(4)
Corporate
Other-than-temporary impairment losses by asset type
Gross	(5)	(4)	(9)
Included in OCI	(2)	2	3
Net	(7)	(2)	(6)
ABS
Other-than-temporary impairment losses by asset type
Gross	(4)	(1)	(1)
Included in OCI	0	(2)	(2)
Net	(4)	(3)	(3)
MBS
Other-than-temporary impairment losses by asset type
Gross	(4)	(4)	(11)
Included in OCI	1	(1)	(2)
Net	(3)	(5)	(13)
Equity securities
Other-than-temporary impairment losses by asset type
Gross	0	0	(86)
Included in OCI	0	0	0
Other-than-temporary Impairment Loss, Debt Securities And Other, Portion Recognized in Earnings	0
Net		0
Net			(86)
Mortgage loans
Other-than-temporary impairment losses by asset type
Gross	0	0	(1)
Included in OCI	0	0	0
Other-than-temporary Impairment Loss, Debt Securities And Other, Portion Recognized in Earnings	0	0
Net			(1)
Limited partnership interests
Other-than-temporary impairment losses by asset type
Gross	(6)	(3)	(32)
Included in OCI	0	0	0
Other-than-temporary Impairment Loss, Debt Securities And Other, Portion Recognized in Earnings	6	3
Net			(32)
Other
Other-than-temporary impairment losses by asset type
Gross	(27)	(1)	(5)
Included in OCI	0	0	0
Other-than-temporary Impairment Loss, Debt Securities And Other, Portion Recognized in Earnings	$ 27	$ 1
Net			$ (5)

No definition available.

Name:	all_OtherThanTemporaryImpairmentLossesByAssetTypeLineItems
Namespace Prefix:	all_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Other-than-temporary Impairment Loss, Debt Securities And Other, Portion Recognized in Earnings

+ References

No definition available.

+ Details

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

- Definition

The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 8A
-URI http://asc.fasb.org/extlink&oid=118954083&loc=SL6284422-111562

+ Details

Name:	us-gaap_ImpairmentOfInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of other-than-temporary impairment (OTTI) on investment in debt security, recognized in earnings.

+ References

+ Details

Name:	us-gaap_OtherThanTemporaryImpairmentLossDebtSecuritiesPortionRecognizedInEarnings
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount before tax of other than temporary impairment loss (OTTI) on investments in available-for-sale and held-to-maturity debt securities, recognized in other comprehensive loss and attributable to parent entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=108774443&loc=SL4569643-111683

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=118930883&loc=SL7669646-108580

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=118930883&loc=d3e637-108580

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=109239629&loc=SL4573702-111684

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=118930883&loc=SL7669686-108580

+ Details

Name:	us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount after tax of other than temporary impairment (OTTI) loss on investment in available-for-sale debt security, recognized in other comprehensive loss.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=118930883&loc=SL7669646-108580

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 35
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=118985780&loc=d3e25362-111560

+ Details

Name:	us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAvailableforsaleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_FixedIncomeSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MortgagesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=srt_PartnershipInterestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_OtherThanSecuritiesInvestmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: