Reinsurance (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Ceded Credit Risk [Line Items]
Reinsurance Claims Recoverables	$ 262	$ 223
Claims Recoverable From Retrocessionaires Past Due	$ 16	$ 15
AM Best, A- Rating [Member]
Ceded Credit Risk [Line Items]
Ceded Credit Risk, Disclosure	“A- (excellent)”	“A- (excellent)”