Securities (Gross Unrealized Losses and Fair Values of Investments by Investment Category and Length of Time) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair value of temporarily impaired AFS securities, less than 12 months	$ 9,254	$ 2,714
Unrealized losses on temporarily impaired AFS securities, less than 12 months	356	19
Fair value of temporarily impaired AFS securities, 12 months or more	929	591
Unrealized losses on temporarily impaired AFS securities, 12 months or more	120	100
Total fair value of temporarily impaired AFS securities	10,183	3,305
Total unrealized losses on temporarily impaired AFS securities	476	119
Fair value of temporarily impaired HTM securities, less than 12 months	10,826	1,686
Unrealized losses on temporarily impaired HTM securities, less than 12 months	390	6
Fair value of temporarily impaired HTM securities, 12 months or more	10	0
Unrealized losses on temporarily impaired HTM securities, 12 months or more	0	0
Total fair value of temporarily impaired HTM securities	10,836	1,686
Total unrealized losses on temporarily impaired HTM securities	390	6
GSE Securities [Member]
Fair value of temporarily impaired HTM securities, less than 12 months	4,822	805
Unrealized losses on temporarily impaired HTM securities, less than 12 months	328	1
Fair value of temporarily impaired HTM securities, 12 months or more	0	0
Unrealized losses on temporarily impaired HTM securities, 12 months or more	0	0
Total fair value of temporarily impaired HTM securities	4,822	805
Total unrealized losses on temporarily impaired HTM securities	328	1
MBS Issued by GSE [Member]
Fair value of temporarily impaired AFS securities, less than 12 months	8,952	2,662
Unrealized losses on temporarily impaired AFS securities, less than 12 months	343	18
Fair value of temporarily impaired AFS securities, 12 months or more	436	0
Unrealized losses on temporarily impaired AFS securities, 12 months or more	26	0
Total fair value of temporarily impaired AFS securities	9,388	2,662
Total unrealized losses on temporarily impaired AFS securities	369	18
Fair value of temporarily impaired HTM securities, less than 12 months	5,984	593
Unrealized losses on temporarily impaired HTM securities, less than 12 months	61	1
Fair value of temporarily impaired HTM securities, 12 months or more	8	0
Unrealized losses on temporarily impaired HTM securities, 12 months or more	0	0
Total fair value of temporarily impaired HTM securities	5,992	593
Total unrealized losses on temporarily impaired HTM securities	61	1
States and Political Subdivisions [Member]
Fair value of temporarily impaired AFS securities, less than 12 months	256	52
Unrealized losses on temporarily impaired AFS securities, less than 12 months	13	1
Fair value of temporarily impaired AFS securities, 12 months or more	412	478
Unrealized losses on temporarily impaired AFS securities, 12 months or more	89	89
Total fair value of temporarily impaired AFS securities	668	530
Total unrealized losses on temporarily impaired AFS securities	102	90
Fair value of temporarily impaired HTM securities, less than 12 months	20	22
Unrealized losses on temporarily impaired HTM securities, less than 12 months	1	1
Fair value of temporarily impaired HTM securities, 12 months or more	2	0
Unrealized losses on temporarily impaired HTM securities, 12 months or more	0	0
Total fair value of temporarily impaired HTM securities	22	22
Total unrealized losses on temporarily impaired HTM securities	1	1
Non-Agency MBS [Member]
Fair value of temporarily impaired AFS securities, less than 12 months	46	0
Unrealized losses on temporarily impaired AFS securities, less than 12 months	0	0
Fair value of temporarily impaired AFS securities, 12 months or more	81	113
Unrealized losses on temporarily impaired AFS securities, 12 months or more	5	11
Total fair value of temporarily impaired AFS securities	127	113
Total unrealized losses on temporarily impaired AFS securities	5	11
Other Securities [Member]
Fair value of temporarily impaired HTM securities, less than 12 months		266
Unrealized losses on temporarily impaired HTM securities, less than 12 months		3
Fair value of temporarily impaired HTM securities, 12 months or more		0
Unrealized losses on temporarily impaired HTM securities, 12 months or more		0
Total fair value of temporarily impaired HTM securities		266
Total unrealized losses on temporarily impaired HTM securities		$ 3