Summary of Significant Accounting Policies - Catastrophe Exposures (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Jan. 01, 2025
Liability For Catastrophe Claims [Line Items]
Percent of catastrophic reinsurance treaty placed		100.00%
California Earthquake
Liability For Catastrophe Claims [Line Items]
Catastrophe reinsurance	$ 850
First-dollar retention	25
Outside of California Earthquake
Liability For Catastrophe Claims [Line Items]
Catastrophe reinsurance	850
First-dollar retention	50
Other Perils including Wind
Liability For Catastrophe Claims [Line Items]
Catastrophe reinsurance	750
First-dollar retention	$ 50