Derivative Financial Instruments and Off-balance sheet Financial Instruments - Off-balance sheet financial instruments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Commitments to invest in limited partnership interests	$ 918	$ 1,063
Private placement commitments	0	16
Other loan commitments	$ 75	$ 118

This element represents conditional commitments to purchase private placement debt and equity securities at a specified future date. The fair value of these commitments generally cannot be estimated on the date the commitment is made as the terms and conditions of the underlying private placement securities are not finalized at that point of time.

No definition available.

Name:	all_PrivatePlacementCommitments
Namespace Prefix:	all_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant