Guaranteed Benefit Features (Summary Of Guaranteed Death Benefit Liabilities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Guaranteed Benefit Features [Abstract]
Balance as of beginning-of-year	$ 110	$ 115	$ 89
Changes in reserves	8	34	52
Benefits paid	(18)	(39)	(26)
Balance as of end-of-period	$ 100	$ 110	$ 115