Reinsurance and Indemnification - Amounts Ceded to Prudential (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Contract benefits
Ceded Credit Risk [Line Items]
Reinsurance ceded amount	$ 165	$ 240	$ 179
Interest credited to contractholder funds
Ceded Credit Risk [Line Items]
Reinsurance ceded amount	20	24	25
Prudential | Premiums and contract charges | Allstate Financial
Ceded Credit Risk [Line Items]
Reinsurance ceded amount	65	72	76
Prudential | Contract benefits | Allstate Financial
Ceded Credit Risk [Line Items]
Reinsurance ceded amount	4	87	7
Prudential | Interest credited to contractholder funds | Allstate Financial
Ceded Credit Risk [Line Items]
Reinsurance ceded amount	19	20	20
Prudential | Operating costs and expenses | Allstate Financial
Ceded Credit Risk [Line Items]
Reinsurance ceded amount	$ 12	$ 14	$ 15