Reinsurance and Indemnification - Amounts Ceded to Prudential (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Contract benefits
Ceded Credit Risk [Line Items]
Reinsurance ceded amount	$ 155	$ 165	$ 240
Interest credited to contractholder funds
Ceded Credit Risk [Line Items]
Reinsurance ceded amount	27	20	24
Prudential | Premiums and contract charges | Allstate Financial
Ceded Credit Risk [Line Items]
Reinsurance ceded amount	64	65	72
Prudential | Contract benefits | Allstate Financial
Ceded Credit Risk [Line Items]
Reinsurance ceded amount	46	(4)	87
Prudential | Interest credited to contractholder funds | Allstate Financial
Ceded Credit Risk [Line Items]
Reinsurance ceded amount	20	19	20
Prudential | Operating costs and expenses | Allstate Financial
Ceded Credit Risk [Line Items]
Reinsurance ceded amount	$ 12	$ 12	$ 14