Guaranteed Benefit Features (Summary Of Guaranteed Death Benefit Liabilities) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Guaranteed Benefit Features [Abstract]
Balance as of beginning-of-year	$ 110	$ 115
Changes in reserves	4	22
Benefits paid	(14)	(31)
Balance as of end-of-period	$ 100	$ 106