Securities (Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses and Approximate Fair Values of AFS Securities) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
AFS securities, amortized cost	$ 20,737	$ 22,168
AFS securities, gross unrealized gains	627	574
AFS securities, gross unrealized losses	428	638
AFS securities, fair value	20,936	22,104
U.S. Treasury [Member]
AFS securities, amortized cost	1,094	595
AFS securities, gross unrealized gains	1	0
AFS securities, gross unrealized losses	0	0
AFS securities, fair value	1,095	595
MBS Issued by GSE [Member]
AFS securities, amortized cost	16,512	18,397
AFS securities, gross unrealized gains	92	78
AFS securities, gross unrealized losses	370	546
AFS securities, fair value	16,234	17,929
States and Political Subdivisions [Member]
AFS securities, amortized cost	1,899	1,877
AFS securities, gross unrealized gains	113	65
AFS securities, gross unrealized losses	58	91
AFS securities, fair value	1,954	1,851
Non-Agency MBS [Member]
AFS securities, amortized cost	247	264
AFS securities, gross unrealized gains	30	27
AFS securities, gross unrealized losses	0	0
AFS securities, fair value	277	291
Other [Member]
AFS securities, amortized cost	43	46
AFS securities, gross unrealized gains	0	0
AFS securities, gross unrealized losses	0	1
AFS securities, fair value	43	45
Covered [Member]
AFS securities, amortized cost	942	989
AFS securities, gross unrealized gains	391	404
AFS securities, gross unrealized losses	0	0
AFS securities, fair value	$ 1,333	$ 1,393