Guaranteed Benefit Features (Summary Of Guaranteed Death Benefit Liabilities) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Guaranteed Benefit Features [Abstract]
Balance as of beginning-of-year	$ 100	$ 110
Changes in reserves	11	(5)
Benefits paid	(3)	(6)
Balance as of end-of-period	$ 108	$ 99