Securities (Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses and Approximate Fair Values of HTM Securities) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
HTM securities	$ 20,717	$ 18,101
HTM securities, gross unrealized gains	73	54
HTM securities, gross unrealized losses	288	625
HTM securities, fair value	20,502	17,530
U.S. Treasury [Member]
HTM securities	1,096	392
HTM securities, gross unrealized gains	8	0
HTM securities, gross unrealized losses	1	8
HTM securities, fair value	1,103	384
GSE [Member]
HTM securities	5,394	5,603
HTM securities, gross unrealized gains	11	2
HTM securities, gross unrealized losses	200	397
HTM securities, fair value	5,205	5,208
MBS Issued by GSE [Member]
HTM securities	13,587	11,636
HTM securities, gross unrealized gains	35	38
HTM securities, gross unrealized losses	87	220
HTM securities, fair value	13,535	11,454
States and Political Subdivisions [Member]
HTM securities	23	33
HTM securities, gross unrealized gains	2	2
HTM securities, gross unrealized losses	0	0
HTM securities, fair value	25	35
Other [Member]
HTM securities	617	437
HTM securities, gross unrealized gains	17	12
HTM securities, gross unrealized losses	0	0
HTM securities, fair value	$ 634	$ 449