Reinsurance Reinsurance (Ceded Reinsurance Receivable Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 904	$ 758
Reinsurance Recoverables, Percentage of Total	100.00%	100.00%
Other Reinsurers [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 149	$ 115
Reinsurance Recoverables, Percentage of Total	16.40%	15.20%
AM Best, A+ Rating [Member] | Reinsurer A [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 367	$ 303
Reinsurance Recoverables, Percentage of Total	40.60%	40.00%
AM Best, A+ Rating [Member] | Reinsurer B [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 208	$ 193
Reinsurance Recoverables, Percentage of Total	23.00%	25.50%
AM Best, A+ Rating [Member] | Reinsurer D [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 53	$ 37
Reinsurance Recoverables, Percentage of Total	5.90%	4.80%
AM Best, A Rating [Member] | Reinsurer C [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 84	$ 70
Reinsurance Recoverables, Percentage of Total	9.30%	9.20%
AM Best, A++ Rating [Member] | Reinsurer E [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 43	$ 40
Reinsurance Recoverables, Percentage of Total	4.80%	5.30%