Reinsurance and Indemnification - Florida Hurricane Catastrophe Fund (Narrative) (Details) $ in Millions	12 Months Ended
	May 31, 2024 USD ($) numberOfHurricane	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Reinsurance Retention Policy [Line Items]
Property-liability insurance premiums earned		$ 2,036	$ 1,906	$ 1,983
Florida Hurricane Catastrophe Fund
Reinsurance Retention Policy [Line Items]
Property-liability insurance premiums earned		28	24	15
Reinsurance recoverable, qualifying losses, amount		6	74	$ 13
Reinsurance and indemnification recoverables, net		$ 82	$ 96
Florida Hurricane Catastrophe Fund | Forecast
Reinsurance Retention Policy [Line Items]
Percent of losses in excess of retention level to be reimbursed	90.00%
Retention level for losses related to hurricanes	$ 152
Number of storms | numberOfHurricane	2
Retention level for losses related to other hurricanes	$ 51
Maximum Retention level for losses related to hurricanes	$ 312
Florida Hurricane Catastrophe Fund
Reinsurance Retention Policy [Line Items]
Emergency assessment maximum percentage of premiums first year		6.00%
Emergency assessment maximum percentage of premiums subsequent years		10.00%