Reinsurance - Narrative (Details) - USD ($) $ in Billions	Sep. 30, 2024	Dec. 31, 2023
Effects of Reinsurance [Line Items]
Ceded reserves	$ 3.5
Reinsurance recoverables	$ 42.8	$ 41.4
Investment Grade
Effects of Reinsurance [Line Items]
Reinsurance recoverable (as a percent)	82.00%	83.00%
Non-Investment Grade
Effects of Reinsurance [Line Items]
Reinsurance recoverable (as a percent)	15.00%	15.00%
Non-Investment Grade | Captive Insurers
Effects of Reinsurance [Line Items]
Reinsurance recoverable (as a percent)	81.00%	85.00%
Not Rated
Effects of Reinsurance [Line Items]
Reinsurance recoverable (as a percent)	3.00%	2.00%