Benefit Plans - Allstate 401(k) Savings Plan (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Retirement Benefits [Abstract]
Company's contribution to the Allstate Plan	$ 124	$ 131	$ 110
Defined contribution plan expense for eligible employees of Canadian insurance subsidiaries and Sterling	$ 14	$ 9	$ 9