Reinsurance and Indemnification- Florida Hurricane Catastrophe Fund (“FHCF”), Insurance Linked Securities (“ILS”) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Ceded Credit Risk [Line Items]
Property-liability insurance premiums earned	$ 1,383	$ 1,407	$ 1,306
Florida Hurricane Catastrophe Fund
Ceded Credit Risk [Line Items]
Catastrophe reinsurance aggregate loss limit	633
Retention amount for catastrophe reinsurance agreement contracts	20
Limit of aggregate losses under aggregate excess agreement	295
Catastrophe reinsurance loss amount	264
Reinsurance ceded amount	118
Property-liability insurance premiums earned	9	9	10
Florida Hurricane Catastrophe Fund | Insurance Linked Securities (ILS)
Ceded Credit Risk [Line Items]
Limit of aggregate losses under aggregate excess agreement	200
Catastrophe Reinsurance Program
Ceded Credit Risk [Line Items]
Catastrophe reinsurance aggregate loss limit	4,980
Retention amount for catastrophe reinsurance agreement contracts	500
Limit of aggregate losses under aggregate excess agreement	400
Catastrophe reinsurance loss amount	2,000
Property-liability insurance premiums earned	425	$ 386	$ 343
Catastrophe Reinsurance Program | Insurance Linked Securities (ILS)
Ceded Credit Risk [Line Items]
Limit of aggregate losses under aggregate excess agreement	$ 1,530