Guarantees and Contingent Liabilities (Details)	3 Months Ended
	Mar. 31, 2025 USD ($) claim	Feb. 11, 2025 USD ($)
California FAIR Plan Association
Guarantor Obligations [Line Items]
Maximum possible assessment		$ 1,000,000,000
Insurance recoupment (as a percent)		50.00%
Personal Lines | California FAIR Plan Association
Guarantor Obligations [Line Items]
Maximum possible assessment		$ 1,000,000,000
Market share (as a percent)		4.60%
Commercial Lines | California FAIR Plan Association
Guarantor Obligations [Line Items]
Market share (as a percent)		2.00%
Holland Hewitt v. Allstate Life Insurance Company
Guarantor Obligations [Line Items]
Number of putative class actions | claim	2
Minimum
Guarantor Obligations [Line Items]
Loss contingencies, reasonably possible pretax loss exposure in excess of the amount accrued	$ 0
Maximum
Guarantor Obligations [Line Items]
Loss contingencies, reasonably possible pretax loss exposure in excess of the amount accrued	$ 70,000,000