Reinsurance and Indemnification - Wrap Fill Excess Catastrophe Reinsurance Contract (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Ceded Credit Risk [Line Items]
Limit of aggregate losses under aggregate excess agreement	$ 3,400
Wrap Fill Excess Catastrophe Reinsurance Contract
Ceded Credit Risk [Line Items]
Retention amount for catastrophe reinsurance agreement contracts	$ 200
Co-participation percentage	5.00%
Retention percentage of reinsurance limit	100.00%
Limit of aggregate losses under aggregate excess agreement	$ 1,610
Catastrophe reinsurance aggregate loss limit	3,070
Minimum | Wrap Fill Excess Catastrophe Reinsurance Contract
Ceded Credit Risk [Line Items]
Retention amount for catastrophe reinsurance agreement contracts	$ 2,750