Reinsurance (Ceded Reinsurance Receivable Assets) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 950	$ 904
Reinsurance Recoverables, Percentage of Total	100.00%	100.00%
Other Reinsurers [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 178	$ 149
Reinsurance Recoverables, Percentage of Total	18.80%	16.40%
AM Best, A+ Rating [Member] | Reinsurer A [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 403	$ 367
Reinsurance Recoverables, Percentage of Total	42.40%	40.60%
AM Best, A+ Rating [Member] | Reinsurer B [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 207	$ 208
Reinsurance Recoverables, Percentage of Total	21.80%	23.00%
AM Best, A+ Rating [Member] | Reinsurer E [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 46	$ 43
Reinsurance Recoverables, Percentage of Total	4.80%	4.80%
AM Best, A Rating [Member] | Reinsurer C [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 63	$ 84
Reinsurance Recoverables, Percentage of Total	6.60%	9.30%
AM Best, A++ Rating [Member] | Reinsurer D [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 53	$ 53
Reinsurance Recoverables, Percentage of Total	5.60%	5.90%