Reinsurance and Indemnification - National Flood Insurance Program (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Sep. 30, 2024
Reinsurance Retention Policy [Line Items]
Property-liability insurance premiums earned	$ 2,260	$ 2,036	$ 1,906
National Flood Insurance Program
Reinsurance Retention Policy [Line Items]
Legislation to reauthorize				$ 20,500
Reinsurance and indemnification recoverables, net	279	76
Property-liability insurance premiums earned	368	327	319
Ceded losses incurred	$ 618	$ 102	$ 435