Securities (Schedule of Credit Losses on Other-than-Temporarily Impaired Non-agency Mortgage-Backed Securities where Portion of the Unrealized Loss was Recognized in Other Comprehensive Income) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Securities
Balance at beginning of period	$ 113	$ 63	$ 130	$ 30
Credit losses on securities for which OTTI was previously recognized	2	39	5	78
Reductions for securities sold/settled during the period	(4)	(2)	(24)	(8)
Balance at end of period	$ 111	$ 100	$ 111	$ 100