Commitments, Guarantees and Contingent Liabilities - California Earthquake Authority (Narrative) (Details) - California Earthquake Authority - USD ($) $ in Millions	Oct. 31, 2023	Dec. 31, 2023
Loss Contingencies
CEA capital balance	$ 6,000
Proceeds of revenue bonds	2,100
CEA existing reinsurance layer	9,300
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	$ 20,100
Share of the CEA (as a percent)		8.50%
Percentage of entity interest, expected increase		30.00%
Maximum possible assessment		$ 141