Reinsurance and Indemnification - National Flood Insurance Program (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
National Flood Insurance Program
Reinsurance Retention Policy [Line Items]
Reinsurance and indemnification recoverables, net	30	25
Property-liability insurance premiums earned	261	258	258
Reinsurance ceded amount	$ 87	$ 150	$ 118