Securities (Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses and Approximate Fair Values of AFS Securities) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
AFS securities, amortized cost	$ 21,030	$ 22,168
AFS securities, gross unrealized gains	601	574
AFS securities, gross unrealized losses	457	638
AFS securities, fair value	21,174	22,104
U.S. Treasury [Member]
AFS securities, amortized cost	993	595
AFS securities, gross unrealized gains	0	0
AFS securities, gross unrealized losses	1	0
AFS securities, fair value	992	595
MBS Issued by GSE [Member]
AFS securities, amortized cost	16,952	18,397
AFS securities, gross unrealized gains	69	78
AFS securities, gross unrealized losses	408	546
AFS securities, fair value	16,613	17,929
States and Political Subdivisions [Member]
AFS securities, amortized cost	1,894	1,877
AFS securities, gross unrealized gains	119	65
AFS securities, gross unrealized losses	48	91
AFS securities, fair value	1,965	1,851
Non-Agency MBS [Member]
AFS securities, amortized cost	239	264
AFS securities, gross unrealized gains	38	27
AFS securities, gross unrealized losses	0	0
AFS securities, fair value	277	291
Other [Member]
AFS securities, amortized cost	42	46
AFS securities, gross unrealized gains	0	0
AFS securities, gross unrealized losses	0	1
AFS securities, fair value	42	45
Covered [Member]
AFS securities, amortized cost	910	989
AFS securities, gross unrealized gains	375	404
AFS securities, gross unrealized losses	0	0
AFS securities, fair value	$ 1,285	$ 1,393