Summary of Significant Accounting Policies - Schedule of Goodwill by Reporting Unit (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Goodwill
Goodwill by reporting unit	$ 3,502	$ 3,502
Allstate Protection
Goodwill
Goodwill by reporting unit	1,563	1,563
Protection Services
Goodwill
Goodwill by reporting unit	1,494	1,494
Allstate Health and Benefits
Goodwill
Goodwill by reporting unit	$ 445	$ 445