Summary of Significant Accounting Policies - Schedule of Goodwill by Reporting Unit (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Goodwill
Goodwill by reporting unit	$ 3,118	$ 3,245
Allstate Protection
Goodwill
Goodwill by reporting unit	1,563	1,563
Protection Services
Goodwill
Goodwill by reporting unit	1,511	1,511
Allstate Health and Benefits and Individual Health
Goodwill
Goodwill by reporting unit	$ 44	$ 171