Securities (Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses and Approximate Fair Values of HTM Securities) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
HTM securities	$ 20,432	$ 18,101
HTM securities, gross unrealized gains	111	54
HTM securities, gross unrealized losses	279	625
HTM securities, fair value	20,264	17,530
U.S. Treasury [Member]
HTM securities	1,096	392
HTM securities, gross unrealized gains	13	0
HTM securities, gross unrealized losses	0	8
HTM securities, fair value	1,109	384
GSE [Member]
HTM securities	5,604	5,603
HTM securities, gross unrealized gains	18	2
HTM securities, gross unrealized losses	203	397
HTM securities, fair value	5,419	5,208
MBS Issued by GSE [Member]
HTM securities	13,282	11,636
HTM securities, gross unrealized gains	65	38
HTM securities, gross unrealized losses	76	220
HTM securities, fair value	13,271	11,454
States and Political Subdivisions [Member]
HTM securities	33	33
HTM securities, gross unrealized gains	2	2
HTM securities, gross unrealized losses	0	0
HTM securities, fair value	35	35
Other [Member]
HTM securities	417	437
HTM securities, gross unrealized gains	13	12
HTM securities, gross unrealized losses	0	0
HTM securities, fair value	$ 430	$ 449