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		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Securities
Balance at beginning of period	$ 114	$ 51	$ 129	$ 30
Credit losses on securities for which OTTI was previously recognized	2	18	3	39
Reductions for securities sold/settled during the period	(4)	(6)	(20)	(6)
Balance at end of period	$ 112	$ 63	$ 112	$ 63