Summary of Significant Accounting Policies - Schedule of Unearned Premiums (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Deferred Policy Acquisition and Sales Inducement Costs:
Unearned premiums	$ 24,709	$ 22,299
Allstate Protection
Deferred Policy Acquisition and Sales Inducement Costs:
Unearned premiums	19,542	17,538
Protection Services
Deferred Policy Acquisition and Sales Inducement Costs:
Unearned premiums	5,150	4,745
Allstate Protection and Protection Services
Deferred Policy Acquisition and Sales Inducement Costs:
Unearned premiums	$ 24,692	$ 22,283