Reinsurance and Indemnification - Canada Catastrophe Excess of Loss Reinsurance Contract (Narrative) (Details) $ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) reinstatement	Dec. 31, 2024 CAD ($) reinstatement	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Reinsurance Retention Policy [Line Items]
Property-liability insurance premiums earned	$ 2,260		$ 2,036	$ 1,906
Catastrophe Reinsurance Program
Reinsurance Retention Policy [Line Items]
Property-liability insurance premiums earned	$ 1,110		$ 1,020	$ 788
Canada Catastrophe Excess of Loss | Catastrophe Reinsurance Program
Reinsurance Retention Policy [Line Items]
Limit of aggregate losses under aggregate excess agreement		$ 355
Retention amount for catastrophe reinsurance agreement contracts		$ 75
Number of reinstatements each year for each contract | reinstatement	1	1