Commitments, Guarantees and Contingent Liabilities - Florida Hurricane Catastrophe Fund and California Earthquake Authority (Details) - California Earthquake Authority - USD ($) $ in Millions	Oct. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Loss Contingencies
CEA capital balance	$ 6,000
Proceeds of revenue bonds	1,100
CEA existing reinsurance layer	9,500
Policy holder surcharge	1,000
Current estimated maximum CEA assessment	1,700
CEA capital balance threshold	350
CEA capital balance to be restored	350
Projected aggregate claim paying capacity	$ 19,300
Share of the CEA (as a percent)			9.30%
Maximum possible assessment		$ 155