Derivative Financial Instruments and Off-balance sheet Financial Instruments - Off-balance sheet financial instruments (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivative Financial Instruments and Off-balance sheet Financial Instruments
Commitments to invest in limited partnership interests	$ 1,345	$ 1,400
Private placement commitments	27	13
Other loan commitments	$ 87	$ 80

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