Reinsurance and Indemnification - FHCF Contract (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reinsurance Retention Policy [Line Items]
Property-liability insurance premiums earned	$ 1,383	$ 1,407	$ 1,306
Florida Hurricane Catastrophe Fund
Reinsurance Retention Policy [Line Items]
Limit of aggregate losses under aggregate excess agreement	295
Retention amount for catastrophe reinsurance agreement contracts	20
Reinsurance ceded amount	118
Property-liability insurance premiums earned	9	9	10
Catastrophe Reinsurance Program
Reinsurance Retention Policy [Line Items]
Limit of aggregate losses under aggregate excess agreement	400
Retention amount for catastrophe reinsurance agreement contracts	500
Property-liability insurance premiums earned	$ 425	$ 386	$ 343