Summary of Significant Accounting Policies - Catastrophe Exposures - Additional Information (Details) - USD ($) $ in Millions		2 Months Ended
	Mar. 01, 2020	Feb. 29, 2020
Liability For Catastrophe Claims [Line Items]
First-dollar retention	$ 25	$ 25
Additional catastrophe reinsurance	100
California Earthquake
Liability For Catastrophe Claims [Line Items]
Catastrophe reinsurance	500	400
First-dollar retention		25
Non-California Earthquake
Liability For Catastrophe Claims [Line Items]
Catastrophe reinsurance	525	425
First-dollar retention		25
Other Perils
Liability For Catastrophe Claims [Line Items]
Catastrophe reinsurance	$ 375	275
First-dollar retention		$ 25