Reinsurance and Indemnification - Florida Hurricane Catastrophe Fund (Narrative) (Details) $ in Millions	12 Months Ended
	May 31, 2025 USD ($) numberOfHurricane	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Reinsurance Retention Policy [Line Items]
Property-liability insurance premiums earned		$ 2,260	$ 2,036	$ 1,906
Florida Hurricane Catastrophe Fund
Reinsurance Retention Policy [Line Items]
Property-liability insurance premiums earned		23	28	24
Reinsurance recoverable, qualifying losses, amount		1	(6)	$ 74
Reinsurance and indemnification recoverables, net		$ 73	$ 82
Florida Hurricane Catastrophe Fund | Forecast
Reinsurance Retention Policy [Line Items]
Percent of losses in excess of retention level to be reimbursed (as a percent)	90.00%
Retention level for losses related to hurricanes	$ 98
Number of storms | numberOfHurricane	2
Retention level for losses related to other hurricanes	$ 33
Maximum retention level for losses related to hurricanes	$ 205
Florida Hurricane Catastrophe Fund
Reinsurance Retention Policy [Line Items]
Emergency assessment maximum percentage of premiums first year (as a percent)		6.00%
Emergency assessment maximum percentage of premiums subsequent years (as a percent)		10.00%