Reinsurance - Narrative (Details) - USD ($) $ in Billions	Sep. 30, 2025	Dec. 31, 2024
Effects of Reinsurance [Line Items]
Ceded reserves	$ 3.2
Reinsurance recoverables	$ 41.6	$ 40.5
Investment Grade
Effects of Reinsurance [Line Items]
Reinsurance recoverable (as a percent)	81.00%	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)	86.00%	81.00%
Not Rated
Effects of Reinsurance [Line Items]
Reinsurance recoverable (as a percent)	4.00%	2.00%