Investment Securities (Summary Of Net Gain From Sale Of Agency Securities) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Proceeds from agency MBS sold			$ 5,741	$ 44,237
Net gain (loss) on sale of MBS	$ 61	$ (39)	114	(25)
Available-for-sale Securities [Member]
Agency MBS sold, at cost	(6,123)	(4,575)	(17,146)	(22,548)
Proceeds from agency MBS sold	6,184	4,536	17,260	22,523
Net gain (loss) on sale of MBS	61	(39)	114	(25)
Gross gain on sale of MBS	62	2	122	81
Gross loss on sale of MBS	(1)	(41)	(8)	(106)
Interest Only And Principal Only Strip [Member]
Unrealized Gain (Loss) on Securities	$ (6)	$ 10	$ 5	$ 14