Reserve for Life-Contingent Contract Benefits and Contractholder Funds - Contractholder funds activity (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Contractholder funds activity
Balance, beginning of year	$ 17,692	$ 18,371	$ 19,434
Deposits	1,062	1,091	1,109
Interest credited	633	636	650
Benefits	(775)	(791)	(844)
Surrenders and partial withdrawals	(728)	(884)	(1,135)
Contract charges	(836)	(825)	(824)
Net transfers from separate accounts	5	10	6
Other adjustments	160	84	(25)
Balance, end of year	$ 17,213	$ 17,692	$ 18,371

Decrease in the liability for policyholder contract deposits resulting from benefits paid out of contract holder funds.

No definition available.

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

- Definition

An amount that an insurer deducts from a contract holder's account, as compensation for services rendered.

+ References

No definition available.

+ Details

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

- Definition

Increase in the liability for policyholder contract deposits resulting from amounts received during the period from the insured.

+ References

No definition available.

+ Details

Name:	all_DepositsToContractHolderFunds
Namespace Prefix:	all_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Increase in the liability for policyholder contract deposits resulting from interest credited during the period by the insurer to policy owner accounts.

+ References

No definition available.

+ Details

Name:	all_InterestToContractHolderFunds
Namespace Prefix:	all_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

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

- Definition

Other adjustments during the period to the liability for policyholder contract deposits, not specified elsewhere in the taxonomy.

+ References

No definition available.

+ Details

Name:	all_PolicyholderContractDepositsAdjustmentsOther
Namespace Prefix:	all_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Change in the liability for policyholder contract deposits resulting from net amounts transferred from separate accounts during the period.

+ References

No definition available.

+ Details

Name:	all_PolicyholderContractDepositsSeparateAccountsTransfersNet
Namespace Prefix:	all_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Decrease in the liability for policyholder contract deposits resulting from surrenders and partial withdrawals out of contract holder funds.

+ References

No definition available.

+ Details

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

- Definition

Amount of liability due to policyholder for deposit held under long-duration contract issued by insurance entity.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 25
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121639894&loc=d3e13193-158430

+ Details

Name:	us-gaap_PolicyholderContractDeposits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant