Investment Securities (Summary Of Changes In Accumulated OCI For Available-For-Sale Security) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended							12 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Unrealized gain (loss) on available-for-sale securities, net	$ 1,190	$ 689	$ (106)	$ 216	$ 535	$ 319	$ (41)	$ 1,039	$ 1,029	$ (64)
Agency Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning OCI Balance			1,002				(28)	1,002	(28)	36
Unrealized gain (loss) on available-for-sale securities, net								2,235	1,513	29
Reversal of prior Period Unrealized (Gains) and Losses, Net on Realization								1,196	483	93
Ending OCI Balance				$ 1,002				$ 2,041	$ 1,002	$ (28)