Reinsurance - Retention limits by period of policy issuance (Details) - Allstate Financial - USD ($) $ in Millions	1 Months Ended	33 Months Ended	45 Months Ended	48 Months Ended	106 Months Ended
	Aug. 31, 1998	Dec. 31, 2017	Mar. 31, 2011	Mar. 31, 2015	Jun. 30, 2007
Reinsurance Retention Policy [Line Items]
Retention level per claim	$ 1		$ 5		$ 2
Retention level for contracts issued to individuals age 70 and over			3
Retention level for certain large contracts meeting specific criteria			$ 10		$ 5
Single life
Reinsurance Retention Policy [Line Items]
Retention level per claim		$ 2		$ 5
Retention level for contracts issued to individuals age 70 and over				3
Retention level for certain large contracts meeting specific criteria				10
Joint life
Reinsurance Retention Policy [Line Items]
Retention level per claim				8
Retention level for certain large contracts meeting specific criteria				$ 10