Securities (Gross Unrealized Losses and Fair Values of Investments by Investment Category and Length of Time) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Fair value of temporarily impaired AFS securities, less than 12 months	$ 1,977	$ 10,525
Unrealized losses on temporarily impaired AFS securities, less than 12 months	40	415
Fair value of temporarily impaired AFS securities, 12 months or more	7,519	2,376
Unrealized losses on temporarily impaired AFS securities, 12 months or more	388	223
Total fair value of temporarily impaired AFS securities	9,496	12,901
Total unrealized losses on temporarily impaired AFS securities	428	638
Fair value of temporarily impaired HTM securities, less than 12 months	5,542	14,180
Unrealized losses on temporarily impaired HTM securities, less than 12 months	69	624
Fair value of temporarily impaired HTM securities, 12 months or more	5,501	48
Unrealized losses on temporarily impaired HTM securities, 12 months or more	210	1
Total fair value of temporarily impaired HTM securities	11,043	14,228
Total unrealized losses on temporarily impaired HTM securities	279	625
U.S. Treasury [Member]
Fair value of temporarily impaired HTM securities, less than 12 months		384
Unrealized losses on temporarily impaired HTM securities, less than 12 months		8
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		384
Total unrealized losses on temporarily impaired HTM securities		8
GSE [Member]
Fair value of temporarily impaired HTM securities, less than 12 months	0	4,996
Unrealized losses on temporarily impaired HTM securities, less than 12 months	0	397
Fair value of temporarily impaired HTM securities, 12 months or more	4,788	0
Unrealized losses on temporarily impaired HTM securities, 12 months or more	203	0
Total fair value of temporarily impaired HTM securities	4,788	4,996
Total unrealized losses on temporarily impaired HTM securities	203	397
MBS Issued by GSE [Member]
Fair value of temporarily impaired AFS securities, less than 12 months	1,977	10,259
Unrealized losses on temporarily impaired AFS securities, less than 12 months	40	406
Fair value of temporarily impaired AFS securities, 12 months or more	7,023	1,935
Unrealized losses on temporarily impaired AFS securities, 12 months or more	330	140
Total fair value of temporarily impaired AFS securities	9,000	12,194
Total unrealized losses on temporarily impaired AFS securities	370	546
Fair value of temporarily impaired HTM securities, less than 12 months	5,542	8,800
Unrealized losses on temporarily impaired HTM securities, less than 12 months	69	219
Fair value of temporarily impaired HTM securities, 12 months or more	713	48
Unrealized losses on temporarily impaired HTM securities, 12 months or more	7	1
Total fair value of temporarily impaired HTM securities	6,255	8,848
Total unrealized losses on temporarily impaired HTM securities	76	220
States and Political Subdivisions [Member]
Fair value of temporarily impaired AFS securities, less than 12 months	0	232
Unrealized losses on temporarily impaired AFS securities, less than 12 months	0	8
Fair value of temporarily impaired AFS securities, 12 months or more	496	441
Unrealized losses on temporarily impaired AFS securities, 12 months or more	58	83
Total fair value of temporarily impaired AFS securities	496	673
Total unrealized losses on temporarily impaired AFS securities	58	91
Other [Member]
Fair value of temporarily impaired AFS securities, less than 12 months		34
Unrealized losses on temporarily impaired AFS securities, less than 12 months		1
Fair value of temporarily impaired AFS securities, 12 months or more		0
Unrealized losses on temporarily impaired AFS securities, 12 months or more		0
Total fair value of temporarily impaired AFS securities		34
Total unrealized losses on temporarily impaired AFS securities		$ 1