Securities - U.S. GSE, Agency, and Treasury Securities (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities Amortized Cost	$ 323,298	$ 353,268
Debt Securities, Fair Value	319,200	361,120
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities Amortized Cost	134,317	121,522
Debt Securities, Fair Value	131,689	123,933
Government National Mortgage Association Certificates and Obligations (GNMA) [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities Amortized Cost	114,509	124,348
Debt Securities, Fair Value	113,138	127,541
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities Amortized Cost	26,096	22,995
Debt Securities, Fair Value	$ 25,724	$ 23,502