Summary of Significant Accounting Policies - Unearned premiums (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Deferred Policy Acquisition and Sales Inducement Costs:
Unearned premiums	$ 22,311	$ 19,844
Allstate Protection
Deferred Policy Acquisition and Sales Inducement Costs:
Unearned premiums	17,538	15,762
Protection Services
Deferred Policy Acquisition and Sales Inducement Costs:
Unearned premiums	4,745	4,054
Allstate Protection and Protection Services
Deferred Policy Acquisition and Sales Inducement Costs:
Unearned premiums	$ 22,283	$ 19,816