Reinsurance and Indemnification - Canada Catastrophe Excess of Loss Reinsurance Contract (Narrative) (Details) $ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) reinstatement	Dec. 31, 2023 CAD ($) reinstatement	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Reinsurance Retention Policy [Line Items]
Property-liability insurance premiums earned	$ 2,036		$ 1,906	$ 1,983
Catastrophe Reinsurance Program
Reinsurance Retention Policy [Line Items]
Property-liability insurance premiums earned	$ 1,020		$ 788	$ 556
Canada Catastrophe Excess of Loss | Catastrophe Reinsurance Program
Reinsurance Retention Policy [Line Items]
Limit of aggregate losses under aggregate excess agreement		$ 255
Retention amount for catastrophe reinsurance agreement contracts		$ 75
Number of reinstatements each year for each contract | reinstatement	1	1