Investment Securities (Summary Of Changes In Accumulated OCI For Available-For-Sale Security) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Unrealized Gains and (Losses), Net	$ (97)	$ 467	$ 1,038	$ (14)
Agency Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning OCI Balance	1,108	89	(27)	570
Unrealized Gains and (Losses), Net	(36)	428	1,152	(39)
Reversal of Unrealized (Gains) and Losses, Net on Realization	(61)	39	(114)	25
Ending OCI Balance	$ 1,011	$ 556	$ 1,011	$ 556