Summary of Significant Accounting Policies - Schedule of Unearned Premiums (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Deferred Policy Acquisition and Sales Inducement Costs:
Unearned premiums	$ 26,909	$ 24,709
Allstate Protection
Deferred Policy Acquisition and Sales Inducement Costs:
Unearned premiums	21,508	19,542
Protection Services
Deferred Policy Acquisition and Sales Inducement Costs:
Unearned premiums	5,385	5,150
Allstate Protection and Protection Services
Deferred Policy Acquisition and Sales Inducement Costs:
Unearned premiums	$ 26,893	$ 24,692